Catch The Double Crescents This Week: Venus and the Moon

On Saturday evening, July 18, the crescent moon, moving eastward in the sky, will pass directly below the crescent planet Venus, moving westward, soon to pass below the sun.

On Saturday, July 18, the moon passes just below the planet Venus, both objects showing narrow crescents.  Credit: Starry Night software.

Both objects are being back-lit by the Sun, so that both appear in our sky as crescents. The moon is just three days past new moon, so only nine percent of its disk is lit by the sun. The remaining 91 percent is lit by sunlight reflecting off the surface of the Earth, what is called “earthshine” or “earthlight.” Sometimes this view is also called “the old moon in the new moon’s arms.”

To the naked eye, Venus appears like a brilliant pinpoint of light. Turn your binoculars on it, and that slight additional magnification will allow you to see that Venus is also a narrow crescent.

Because Venus is farther away than the moon, it is lit by the sun at a slightly different angle, so is nineteen percent illuminated, a slightly fatter crescent than the moon.

Some observers have suspected a faint glow coming from the part of Venus not in direct sunlight, a phenomenon called “the ashen light.” No one knows exactly what causes this glow, but it has been reported by many experienced astronomers. Spectroscopic observations have shown pulses in the light, so it might be due to lightning in the hot acidic atmosphere of Venus.

As mentioned above, even small binoculars provide enough magnification to turn the naked-eye pinpoint of Venus into a visible crescent. This is one of many objects in the sky which are revealed or enhanced in binoculars, which is why they are considered an essential tool for all serious skywatchers.

Binoculars for astronomy should have a front aperture of at least 50 millimeters (2 inches). This is seven times the diameter of the fully dark-adapted eye. Such a small binocular has seven times the resolution and 50 times the light-gathering power of the naked eye. 50 millimetre binoculars come in two magnifications, 7 power (7x50) and 10 power (10x50). Both are very useful for astronomy, but I prefer the 10x50 because of its slightly higher magnification and better contrast in a bright sky. I find more powerful binoculars too heavy to hold steadily for any length of time, and mounting them on a tripod defeats the ease of use.

Venus and Jupiter, Up Close and Personal

If you’ve been watching the western sky just after sunset lately, you will have noticed two bright objects, gradually drawing closer.

These are the two brightest planets, Venus and Jupiter. Venus is the brighter of the two, currently magnitude –4.6 on the upside-down brightness scale astronomers use. It will get slightly brighter over the next 10 days, reaching greatest brilliancy on July 10 at magnitude –4.7.

Jupiter is somewhat fainter at magnitude –1.8, down from a maximum of –2.6 when it was in opposition on February 6.

Although the two planets look very close in Earth’s sky, they are in fact very far apart, on opposite sides of the sun. The first graphic shows their true positions, as seen from far above the sun’s north pole. Venus is slightly nearer Earth than the sun, 0.512 astronomical units distant (47.6 million miles or 76.5 million km.) while Jupiter is 6.083 astronomical units away (565 million miles or 910 million km.) on the far side of the sun.

Seen from far above the sun’s north pole on Wednesday, July 1, Earth, Venus and Jupiter lie almost on a perfect straight line.  Credit: Starry Night software.

Viewed in a telescope, the two planets are, by coincidence, exactly the same apparent size, 32 arc seconds in diameter, about a 60th of the apparent diameter of the moon, but look very different.

Seen in the eyepiece of a telescope magnifying 65 times at sunset on July 1, Venus and Jupiter appear very close, but look very different, even though both are the same angular size. Credit: Starry Night software.

Venus, with its bright cloud cover and closeness to the sun, is a brilliant white crescent, lit from slightly behind because it is moving between us and the sun. Jupiter’s cloud tops are somewhat darker than Venus’, but it is also more than seven times farther away from the sun. As a result, despite its large size, Jupiter appears much fainter in a telescope than Venus.

Two bright planets in close proximity make a striking sight with the naked eye. In binoculars you should be able to see that Venus is a tiny crescent and Jupiter is a disk accompanied by 3 tiny moons (on July 1, Callisto will be behind Jupiter). A small telescope will make the view much clearer.

As you continue to watch these two planets over the next few weeks you will see them draw apart as both get closer to the sun, Venus passing between us and the sun on August 15, and Jupiter passing behind the sun on August 26. In another month, both will reappear in the morning sky, where they will join Mars, which passed behind the sun on June 14.

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Spot Mercury At Dawn

Mercury is always a difficult object to spot, always clinging closely to the sun’s apron strings. But you might be excused for missing its brief appearance this week in the dawn skies.

After many attempts to observe Mercury, I’ve found that the best time to spot it is about half an hour before sunrise in the morning sky, or half an hour after sunset in the evening sky. It’s always a balancing act between Mercury’s low altitude and the brightness of the background sky. I find 7x50 or 10x50 binoculars helpful in spotting Mercury, though once I’ve located Mercury in binoculars I usually have no trouble seeing it naked eye.

Unless you’re paying close attention to the sky, you’re likely to miss the current apparition of Mercury. In the northern hemisphere, Mercury can be seen half an hour before sunrise. Credit: Starry Night Software.

Because of the tilt of the ecliptic, the path the Sun and planets follow across the sky, some apparitions of Mercury are more favorable than others. Usually apparitions which are favorable for observers in the northern hemisphere are unfavorable for observers in the southern hemisphere, and vice versa.

The tilt of the ecliptic would indicate that this apparition favors southern observers, but as you can see from these two views, it really isn’t much different: catching Mercury this week will be a challenge for observers everywhere in the world.

A secondary factor affecting Mercury’s visibility is the tilt and eccentricity of its orbit. At 7 degrees, Mercury’s tilt is greater than any other planet. The eccentricity of its orbit, which measures how far it deviates from a circle, is also the greatest, more than twice as eccentric as Mars’ orbit.

The tilt this week also favors southern observers, as you can see in the charts, where Mercury’s orbit is marked in red and the ecliptic in green, but even this doesn’t help much.

The view is not much better in the southern hemisphere. Credit: Starry Night software.

If you are successful in spotting Mercury in the next few days, congratulate yourself, and let us know here!

SkyWatching: Stars Of Early Summer

Early summer is an “in-between” time in the skies. The realm of the galaxies has moved off to the west, but the summer Milky Way has not yet arrived. This is the best time of year to observe globular clusters and double stars.

The centrepiece of the early summer constellations is Boötes, the herdsman, with the bright star Arcturus at his heart. Arcturus is easy to find by following the “arc” of the Big Dipper’s handle away from the ladle: it is the only bright star in this part of the sky. Alternately, if you live in the northern hemisphere, simply look straight overhead around 11 p.m.

Just after dark on a June evening, look overhead to see the constellations of early summer: Boötes, Corona Borealis, and Serpens Caput.  Credit: Starry Night software.

Although Boötes looks like it might be pronounced like “booties,” the diaeresis (double dot) over the second “o” gives you a clue: the two “o”s are pronounced separately: Boh-OO-tes. Its stars form a distinctive kite shape, complete with tail.

Arcturus is the third brightest star in the night sky, after Sirius and Canopus. It is relatively close to us, only 37 light years distant. It is an orange giant star, slightly cooler than the sun, but quite a bit larger in diameter.

Boötes contains relatively few deep sky objects, but is rich in double and variable stars. Izar (Epsilon Boötis) is one of the finest double stars in the sky. With a separation of only 2.9 arc seconds, it requires at least 3 inches aperture, steady skies, and high magnification to see its duality; its stars are gold and greenish in colour. Alkalurops (Mu Boötis) is a much wider double at 2 arc minutes separation, but it is a challenge to see that one of its stars is itself a double.

Although not within Boötes itself, most amateur astronomers use the stars of Boötes to starhop to the Messier globular cluster Messier 3 in the dim constellation of Canes Venatici. M3 forms an almost perfect equilateral triangle with Arcturus and Rho Boötis. This is one of the finest globular clusters in the sky.

Just to the left (east) of Boötes is a small circlet of stars forming Corona Borealis, the northern crown. Look within the circle to see if you can see R Corona Borealis, a very unusual variable star. Some have called this an “inverse nova.” Most of the time it shines steadily with a brightness of about magnitude 7, just below naked eye visibility, but easily seen in binoculars. At long and irregular intervals, instead of brightening like a nova, it dims by about 6 magnitudes. This dimming is caused by occasional expulsion of a dark obscuring cloud of dust. Currently R is entering its dark phase, but keep watching, and it should soon reappear.

These three constellations contain many interesting objects to look at with binoculars or a small telescope. Credit: Starry Night software.

Below Corona Borealis is one of the most unusual constellations, or rather “half constellations.” Serpens represents a snake cut in half, each half held in one hand of Ophiuchus. This is the front half: Serpens Caput, or the head of the serpent. The other half, located quite a ways to the east, is Serpens Cauda, the tail of the Serpent. A triangle is supposed to represent the head of the spent, but I always see this and the two stars above as a large “X.”

The brightest star in Serpens bears the ugly name Unukalhai, which is Arabic for “the serpent’s neck.” Just above Unukalhai is Delta Serpentis, a fine pair of pale yellow stars in a telescope.

But the real prize in Serpens Caput is the globular cluster Messier 5, every bit as fine as Messier 3 to the northwest. Like all globular clusters, M5 responds well to aperture and magnification. Besides resolving the cluster into myriads of tiny stars, a large telescope will reveal chains of stars and clusters within the cluster.

Spot The Asteroid Pallas In The Sky

Most of us have played video games shooting at asteroids, or watched a starship maneuvering through the Asteroid Belt on television. But have you ever seen a real asteroid in the sky? This week is an excellent opportunity to see one of the largest asteroids, Pallas, as it reaches opposition to the Sun.

The first asteroids were discovered in the early years of the 19th century. The first four asteroids, including Pallas, were discovered in a 6 year period from 1801 to 1807; a fifth asteroid was not discovered until 38 years later in 1845. This ushered in a rich period of asteroid discovery, with three dozen more discoveries in the next decade. Once photography came into play, thousands more asteroids were found.

Astronomers originally thought the first asteroids were very small planets, but once they realized how numerous they were, they created a special category called “asteroids” (because of their resemblance to stars) or “minor planets.” The vast majority of these asteroids have orbits between the orbits of Mars and Jupiter, a region of the Solar System that came to be known as the “Asteroid Belt.”

The Asteroid Belt in reality is quite different from what you see in science fiction programs. Rather than being crowded with space rocks, the Asteroid Belt is mostly empty space. Most of the time, if you were standing on one asteroid, you would need binoculars or a telescope to spot the nearest asteroid. The chances of two asteroids colliding is virtually zero.

The first asteroid discovered, Ceres, has now been reclassified as a dwarf planet, along with Pluto and Eris. At 592 miles (952 kilometres) in diameter, it is significantly larger than the remaining asteroids. Two asteroids, Pallas and Vesta, are almost identical in size, 326 miles (524 km) and 318 miles (512 km) respectively. The rest range from Hygiea (276 miles/444 km) on down through chunks of rock only 30 feet (10 meters) across. Anything smaller than that is called a “meteoroid.”

Although Pallas and Vesta are nearly identical in size, they are quite different in their composition and appearance. Pallas is a typical rocky asteroid, quite dark in surface colour, resembling a carbonaceous chondrite meteorite. Vesta, on the other hand, is highly reflective, the only asteroid sometimes visible with the naked eye.

For the rest, binoculars are needed to spot them. Asteroids, as their name implies, look exactly like faint stars. What gives them away is their rather rapid movement against the background stars.

This week Pallas reach opposition in the eastern part of Hercules, very close to the 4th magnitude star Lambda Herculis. It is motoring along from east to west at about one degree per week, so that in three weeks time it will be close to the 3rd magnitude star Sarin (Delta Herculis). Its movement from night to night, as seen in binoculars, is quite obvious.

The large asteroid Pallas will be in opposition to the Sun in Hercules on Thursday, June 11.  Credit: Starry Night software.

The path of Pallas over the next 14 days carries it parallel to the stars Lambda Hercules and Sarin. The labeled dot is Pallas’ position on June 11, and the dots to the right mark its daily travel westward. Credit: Starry Night software.

I particularly like watching asteroids when they are passing close to a bright star. In a telescope, you can see their movement over even a 15-minute period.

At opposition, Pallas will reach magnitude 9.4, making it easily visible in binoculars. It will be 2.405 astronomical units from Earth, or 224 million miles (360 million km). A tiny object, sure enough, but interesting to see with your own eyes.

Venus At Its Brightest

If you’ve been watching the sky in the early evening lately, you can’t have missed seeing the planet Venus in the west.

Credit: Starry Night software.

Venus has been travelling around its orbit towards us, appearing in evening twilight higher and higher in the sky. This week on Saturday, June 6, it reaches its greatest angular distance from the sun, 45 degrees, at what is called “greatest elongation east.” Even though we are looking at it in the western sky, it is elongated in the direction of the eastern horizon, so it is east of the sun in astronomical terminology.

As seen in a small telescope, Venus this week appears like a brilliant miniature first quarter moon. However, unlike the moon’s pock-marked surface, Venus appears perfectly smooth. That’s because we are seeing only the tops of its dense clouds, which mostly appear a featureless blank white.

Beneath those bland clouds lies one of the most bizarre of alien worlds: the greenhouse effect gone wild with a terrain of bare rock heated to a uniform world-wide temperature of  864 degrees Fahrenheit (462 degrees Celsius), where the endless clouds rain down sulfuric acid.

There are, in fact, vague shadings in the surface of Venus’ clouds. These are best seen with a deep violet filter such as the Wratten 47 available in most telescope stores. It also helps to observe Venus in a daylight sky, when much of its glare is cancelled by daylight.

Whenever Venus is close to elongation, we begin to hear many reports of UFOs in the western sky. Venus is so bright that even experienced stargazers are sometimes taken by surprise.

Over the next few weeks, Venus will begin to move closer to the sun at twilight, actually passing between Earth and sun on August 15.

Most of the planets are so small and far away that they appear as star-like dots in most binoculars. Venus is the exception to this. Study it closely with binoculars over the next few weeks, and you will see it first as a tiny half-moon, then gradually getting larger in size but with a thinner crescent shape as it draws nearer the Earth.

Because Venus’ orbit has a slightly different tilt than Earth’s orbit, Venus usually passes above or below the sun, rather than passing directly in front of it. This August it will pass just 8 degrees south of the sun.

Twice so far this century, the orbits of Earth and Venus crossed with both planets in exactly the right position, and Venus was visible in front of the sun. Unfortunately the next such transit of Venus will not occur until the year 2117. I was lucky enough to have clear skies for both the transits of Venus in 2004 and 2012, and seeing the tiny black dot of Venus through a solar filter was a highlight of my observing life.

If you'd like to follow along with NASA's New Horizons Mission to Pluto and the Kuiper Belt, please download our FREE Pluto Safari app for iOS and Android.  It is available for mobile devices. Simulate the July 14, 2015 flyby of Pluto, get regular mission news updates, and learn the history of Pluto.

Simulation Curriculum is the leader in space science curriculum solutions and the makers of Starry Night, SkySafari and Pluto Safari. Follow the mission to Pluto with us on Twitter @SkySafariAstro, Facebook and Instagram. 

Night Sky Tour: The Summer Sky

Summer is upon us and observing the summer Milky Way is one of the simple joys for night sky enthusiasts. Find out what other sights await you on a clear summer night.

The Summer Triangle

The Summer Triangle dominates the summer sky. It crosses the hazy band of the Milky Way, which is split into two near the star Deneb by a large dust cloud called the Cygnus Rift.

The Summer Triangle.

The points of the triangle are three of the brightest stars in the summer sky, each the brightest star in its own constellation. The brightest is Vega, in Lyra; second is Altair, in Aquila; and third is Deneb, in Cygnus. Even city-dwellers with glowing, light-polluted skies can find the Summer Triangle.

Using the Big Dipper as the guide to the other stars and constellations, imagine a line extending 75 degrees of sky from the two bowl stars closest to the handle, to a point in the middle of the Summer Triangle. Stretch out your arm out at full length and measure about three spread hands from little finger to thumb. Each hand covers about 25 degrees of sky.

The Harp of the Gods

Vega is the brightest star in the triangle and is almost directly overhead in the summer. Contrary to what you might have seen in the movie Contact, no signs of an extraterrestrial civilization have been detected around this hot star—at least not yet.

Lyra, the Harp.

The name Vega comes from the Arabic word meaning swooping eagle or vulture. Vega is the luminary of Lyra, the Harp, a small but prominent constellation that is home to the Ring Nebula and the star Epsilon Lyrae. In mythology, Orpheus led Eurydice back from the underworld by charming the guards of the underworld with the music of his harp.

M57, the Ring Nebula.

The Ring Nebula is a luminous shell of gas that was ejected from an old star. It resembles a smoke ring or doughnut. Epsilon Lyrae appears to the naked eye as a double star, but through a small telescope you can see that the two individual stars are themselves double! Epsilon Lyrae is popularly known as the "double double."

Vega is a hydrogen-burning dwarf star, 54 times as luminous and 1.5 times as massive as the sun. It's relatively close to us, 25 light-years away.

The Eagle of Zeus

Once you have found Vega, look down to the south-southeast and you will see Altair in the constellation Aquila (the Eagle).

Aquila, the Eagle.

Altair spins at an amazing 750,000 kilometers (470,000 miles) per hour. This rotation has stretched Altair into an egg shape, wider than it is tall.

Altair is one of our nearest neighbors, 16 light-years away.

The Northern Cross

The most prominent constellation that forms part of the Summer Triangle is Cygnus. The main stars in Cygnus create a pattern in the sky known as the Northern Cross, with Deneb at the top. 

Cygnus, the Swan.

Cygnus is in an area of the Milky Way that contains many objects easily seen with an amateur telescope, including a beautiful red and blue double star at the base of the cross, Albireo.

The Strong Man of the Heavens

Imagine drawing a line from Phecda, the star on the bottom of the bowl of the Big Dipper closest to the handle, and continuing through Mizar, the star at the bend of the handle. It will pass by the constellation Hercules. Using Mizar as your starting point, stretch your arm out at full length and measure about two spread hands from little finger to thumb.

Hercules, the Hero.

Hercules is an ancient and faint constellation devoid of bright stars, such as those forming the Summer Triangle. Four of its main stars form a trapezoidal asterism called "the Keystone." On one side of the Keystone is a beautiful globular cluster—a stellar ball containing several hundred thousand stars. 

The Hercules Cluster (M13).

The Hercules cluster—also named Messier 13 or simply M13—is one of the sky's most beautiful sights and the finest globular cluster in the Northern Hemisphere. It is visible with the unaided eye by observers far removed from a city's glow. In binoculars, M13 looks like a fuzzy star; it's one of the more spectacular objects in the sky when seen through a telescope.

Edmond Halley, better known for predicting the return of the comet that still bears his name, discovered the Hercules Cluster.

M13 was selected as a target for one of the first radio messages broadcast to extraterrestrials from the Arecibo Observatory in Puerto Rico. If alien civilizations exist in the Great Hercules Cluster, we won't receive their reply for 50,000 years, because M13 is 25,000 light-years from Earth.

The Summer Milky Way

Summer nights offer the best time to explore our own Milky Way, a ribbon of pale light, formed by the combined light of billions of stars, that in summer stretches across the entire sky from northeast to southwest.

The Summer MilkyWay.

As summer comes on, the view gets exciting. We are treated to glowing clouds of dust, dark rifts, and star clusters as we look at our galaxy edge-on. Think of it as a flattened pancake of stars, seen on its edge.

The Milky Way is one of the most remarkable naked-eye sights in good dark skies far removed from the bright glows of civilization. You should be able to see the Cygnus Rift, a dark lane in the Milky Way between the constellations Cygnus and Scutum. The Cygnus Rift is not a hole in the Milky Way but rather a cloud of dust that obscures the view of distant stars.

Scanning with binoculars unveils the misty band of the Milky Way and reveals a sparkling river of thousands of stars. The most interesting regions stretch from the Summer Triangle toward the south-southeastern horizon.

If you'd like to follow along with NASA's New Horizons Mission to Pluto and the Kuiper Belt, please download our FREE Pluto Safari app for iOS and Android.  It is available for mobile devices. Simulate the July 14, 2015 flyby of Pluto, get regular mission news updates, and learn the history of Pluto.

Simulation Curriculum is the leader in space science curriculum solutions and the makers of Starry Night, SkySafari and Pluto Safari. Follow the mission to Pluto with us on Twitter @SkySafariAstro, Facebook and Instagram. 

Sky Events For June 2015

Moon Phases

Full Moon

Tuesday, June 2, 12:19 p.m. EDT

The Full Moon of June is known as the “Mead Moon,” “Strawberry Moon,”  “Rose Moon,” or “Thunder Moon.” It rises around sunset and sets around sunrise; this is the only night in the month when the Moon is in the sky all night long. The rest of the month, the Moon spends at least some time in the daytime sky.

Last Quarter Moon

Tuesday, June 9, 11:42 a.m. EDT

The Last Quarter Moon rises around 1:15 a.m. and sets around 1:15 p.m. It is most easily seen just after sunrise in the southern sky.

New Moon

Tuesday, June 16, 10:05 a.m. EDT

The Moon is not visible on the date of New Moon because it is too close to the Sun, but can be seen low in the East as a narrow crescent a morning or two before, just before sunrise. It is visible low in the West an evening or two after New Moon.

First Quarter Moon

Wednesday, June 24, 5:03 a.m. EDT

The First Quarter Moon rises around 12:30 p.m. and sets around 1:15 a.m. It dominates the evening sky.

Observing Highlights

Double shadow transit on Jupiter

Thursday, June 4, 12:58–2:13 a.m. EDT

The shadows of Io and Ganymede will simultaneously fall on the face of of Jupiter.

Venus at greatest elongation east

Saturday, June 6, evening twilight

Venus reaches its greatest eastward distance from the sun, its orbit shown in white here. It is closing in on Jupiter.

Pallas at opposition

Thursday, June 11, 9 p.m. EDT

Pallas, the second largest asteroid, will be in opposition to the Sun. At magnitude 9.4, it will be located just south of Lambda Hercules, below the “keystone” of Hercules.

Uranus and the Moon

Thursday/Friday, June 11/12

The Moon will be close to Uranus just before sunrise. In southern Australia and the South Pacific Ocean, the Moon will actually occult Uranus, as seen here from Melbourne, Australia.

Mercury and the Moon

Monday, June 15, sunrise

As seen here from Sri Lanka, the Moon will occult the planet Mercury. Other parts of the world will see the thin crescent of Mercury very close to the thin crescent of the moon just before sunrise.

Aldebaran and the Moon

Monday, June 15, sunrise

As seen here from eastern North America, the Moon will occult the bright red giant star Aldebaran.

Solstice

Sunday, June 21, 12:38 p.m. EDT

The sun reaches its most northern point, marking the middle of the astronomical summer season in the Northern Hemisphere, and winter in the Southern Hemisphere. The actual seasons tend to lag behind the astronomical seasons by about 6 weeks.

Mercury at greatest elongation west

Wednesday, June 24, dawn

Mercury will be at its farthest from the sun, and close to the red giant star Aldebaran.

Venus and Jupiter within 0.3 degrees

Tuesday, June 30, dusk

Venus and Jupiter will pass really close to each other, appearing within the same telescope field. Both will be 32 arc seconds in diameter, but Jupiter is much further away from both the Earth and the sun, so will be much fainter than Venus.

Planets

 Mercury is well placed in the eastern sky at dawn. It is better placed for observers in the Southern Hemisphere.

Venus shines high in the western sky after sunset, reaching its greatest elongation from the sun on June 6.

Mars is too close to the Sun to be visible. It will be in conjunction with the sun on June 14.

Jupiter is low in the western evening sky all month, closing in on Venus.

Saturn is just past opposition and shining brightly in Libra all night.

Uranus is in the eastern morning sky in Pisces.

Neptune rises after midnight in the constellation Aquarius.

If you'd like to follow along with NASA's New Horizons Mission to Pluto and the Kuiper Belt, please download our FREE Pluto Safari app.  It is available for mobile devices. Simulate the July 14, 2015 flyby of Pluto, get regular mission news updates, and learn the history of Pluto.

Simulation Curriculum is the leader in space science curriculum solutions and the makers of Starry Night, SkySafari and Pluto Safari. Follow the mission to Pluto with us on Twitter @SkySafariAstro, Facebook and Instagram. 

Where's Pluto? How to See it Through A Telescope

With NASA’s New Horizons probe zeroing in on Pluto, due to pass it on July 14, attention of astronomers all over the world is focusing in on Pluto.

Let’s leave aside the question of whether Pluto is the smallest planet of the Sun or the largest of the Kuiper Belt Objects, and agree that it is an interesting and mysterious member of the solar family.

Many amateur astronomers are interested in seeing Pluto with their own telescopes, and this is what we will discuss here. Pluto is at present around 14th magnitude, requiring a telescope with at least 8 inches (200mm) aperture to be seen. The good news is that it is traveling in front of a rich part of the Milky Way, so there will be plenty of guide-posts among the stars to help you find it. The bad news is that it is easily lost amongst those stars, because it will look no different from a 14th magnitude star.

With Starry Night, I have plotted a series of charts zooming in on this tiny target. The first chart is what you will see with naked eye and binoculars at 3 a.m. this week: the familiar “teapot” of Sagittarius. Use Ascella and Nunki in the “handle” of the teapot to locate the two 4th magnitude stars Omicron and Xi2 in your telescope.

With naked eye and binoculars, locate Pluto in relation to the well-known “teapot” asterism of Sagittarius. It is close to the stars Chi2 and Omicron Sagittarii, just north of the “handle” of the teapot.  Credit: Starry Night software.

Switch to a low power eyepiece to see the view in the second chart. To give you some idea of scale, this chart shows the position of the New Horizons probe, although it is too faint to be visible in even the most powerful telescopes on Earth.

With a low power eyepiece in your telescope, zero in on Xi2 and Omicron Sagittarii. Credit: Starry Night software.

Notice the wide triangle of 9th magnitude stars just below Pluto’s location which points to it. The left two stars of the triangle point to a wide pair of stars at about 10th magnitude, and these will serve as a reference to locate Pluto’s position in the third chart.

This chart shows the position of Pluto for the next eight nights, as seen in a high-power eyepiece. The left-most dot, labeled “Pluto,” is its position tonight at 3 a.m., the rightmost dot, its position on June 4. Remember that the date changes at midnight. Credit: Starry Night software.

The brown dots in this chart show Pluto’s position at 3 a.m. EDT on the nights of (from left to right) May 28 through June 4. These dates are for the second half of the night (after midnight), when the date has changed to the next day’s date.

Pluto will resemble a tiny star, and the only way to make sure you are looking at the right star is to make a careful plot of the stars in the field. Comparing positions the next night will tell you for sure which “star” is Pluto: It’s the one that has moved.

So, to positively identify Pluto, is essential to observe it on at least two successive nights.

Because of the great interest in Pluto with the impending fly-by of New Horizons, Simulation Curriculum has released a free app for iOS and Android called Pluto Safari. This will be updated with new information as the fly-by approaches.

If you'd like to follow along with NASA's New Horizons Mission to Pluto and the Kuiper Belt, please download our FREE Pluto Safari app.  It is available for mobile devices. Simulate the July 14, 2015 flyby of Pluto, get regular mission news updates, and learn the history of Pluto.

Simulation Curriculum is the leader in space science curriculum solutions and the makers of Starry Night, SkySafari and Pluto Safari. Follow the mission to Pluto with us on Twitter @SkySafariAstro, Facebook and Instagram. 

Night Sky Tour: The Spring Sky

The spring is a wonderful time to observe. Learn what to look for in the spring night sky tour.

Your Celestial Guidepost

The Big Dipper is a great starting point to learn your way around the night sky; in spring it's conveniently overhead. The Big Dipper itself is not an official constellation but part of a larger constellation called Ursa Major (the Great Bear). Ancient cultures saw the Big Dipper's star pattern as a bear with a long tail. 

The orientation of the Big Dipper from mid-northern latitudes one hour after sunset.

The name originates from the dipper-shaped pattern formed by the seven main stars of the constellation, although observers with keen vision will see that Mizar, the second star from the end of the dipper's handle is, in fact, a double-star. Binoculars make it easier to split the pair.

The stars of the Big Dipper serve as a handy guide to other stars and constellations. The two stars that form the front part of the dipper's bowl point straight to Polaris, the North Star, and because Polaris marks the location of the celestial north pole, the other stars in the sky seem to turn counterclockwise around it. Find Polaris and you know which way is north!

The Little Dipper and Polaris as seen from mid-northern latitudes one hour after sunset.

Polaris itself marks the end of the handle of another dipper—the Little Dipper in Ursa Minor (the Little Bear). Wrapping around Polaris is the constellation Draco. The stars that form this constellation are associated with dragons in the mythologies of many different cultures. 

Earth's north pole has wandered over the millennia and so has pointed to different stars in different eras. Right now it points to Polaris, but one of Draco's stars, Thuban, was the North Star when the pyramids were built.

Arc to Arcturus...

The handle of the Big Dipper points to two of spring's brightest stars—Arcturus and Spica.

The Little Dipper and the star Arcturus as seen from mid-northern latitudes one hour after sunset.

Arcturus is the Alpha (meaning the brightest) star of the constellation Bootes (the Herdsman). Follow the arc of the handle of the Big Dipper until you come to a bright orange star. This is Arcturus, forming the point of a pattern of stars resembling a kite. 

Arcturus is a giant star, twice as massive and 215 times as bright as the sun. It takes 37 years for the light of Arcturus to reach us, so when we gaze at it, we're seeing the star as it looked 37 years ago.

Ancient astromers had measured the position of Arcturus for nearly 2,000 years, which gave Edmond Halley enough data, in 1718, to discover that it was slowly moving against the background stars of its constellation. Before this discovery of proper motion, the stars were thought to be permanently fixed in the sky. Today we know that all stars move, but Arcturus moves much faster than most—about the width of the full moon every 800 years.

...and Speed on to Spica

If you keep following the arc of the handle of the Big Dipper past Arcturus, you'll encounter another bright star, Spica. Keep them straight by remembering this phrase: "Arc to Arcturus and speed on to Spica."

Polaris to Arcturus and on to Spica as seen from mid-northern latitudes one hour after sunset.

Spica resides in the constellation Virgo (the Virgin), a large zodiacal constellation that over time has represented almost every major female deity.

The Prominent Constellation of Spring

The most prominent constellation in the cool evenings of spring is Leo (the Lion).

Leo as seen from mid-northern latitudes one hour after sunset.

To find Polaris, you used the front of the bowl. To find Leo, you need to draw a line through the stars at the back of the bowl—away from Polaris. Stretch out your arm to its full length and measure about three fist-widths from Phecda—the star at the bottom of the bowl. This should put you at a point within the constellation of Leo.

Leo is a constellation of the Zodiac whose main stars have been included in many different mythologies. Stars depicting the mane and head of Leo form a pattern of stars resembling a sickle or a backward question-mark.The brightest star in Leo is Regulus, marking the end of the handle of the sickle or the dot in the question-mark. Regulus, Arcturus, and Spica are the three brightest stars of spring.

The Leonids meteor shower radiates from this constellation around mid-November.

A Beehive of Stars

To the side of Leo is the fainter constellation of Cancer (the Crab).

The Beehive Cluster in Cancer as seen from mid-northern latitudes one hour after sunset.

M44, the Beehive Cluster.

Inside the boundaries of Cancer is a group of stars neatly tucked together into a beehive shape. The Beehive Cluster (also known as Messier 44) was first described by Galileo, but it has been known since antiquity. 

The beehive is easily visible to the unaided eye as a faint round patch of light. Through binoculars, it resembles a swarm of bees.

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SkyWatching: Shadow Play on Jupiter

Jupiter’s rapidly moving moons constantly surprise us with their dance around the giant planet. There will be two spectacular shadow plays this week.

Jupiter’s moons are very small, even in a large telescope, but their shadows are slightly larger, and can often be seen crossing Jupiter’s face with a good amateur telescope. I’ve seen the shadows with telescopes as small as 90mm aperture, but a telescope with 6-inch or larger aperture will show them much more clearly. Steady atmospheric seeing is also essential.

If you live on the eastern seaboard, look for Jupiter just after sunset on Wednesday, May 20 around 8:10 p.m. EDT. The first thing you will notice is that only two of Jupiter’s usual four moons are visible. That’s because two of the Moons, Io and Callisto, are in front of Jupiter’s disk, and are said to be “in transit.” You probably won’t see Io, because its color and brightness blend in so well with the cloud tops behind it. You may be able to see Callisto because its dark surface stands out against Jupiter’s bright clouds. I usually see it as a tiny greyish spot. Look more closely, and you’ll see two small dark shadows on Jupiter’s face. One of these is Io’s shadow, but the other is not the shadow of Callisto. Instead it is the shadow of Ganymede, off to Jupiter’s right. That’s because of the angle at which the sun is illuminating the tableau. 

On Wednesday night, May 20, the shadows of Jupiter’s moons Ganymede and Io will cross Jupiter’s face. This shows the shadows at 8:10 p.m. EDT, just after Io’s shadow has started across, and just before Ganymede’s shadow leaves.  Credit: Starry Night software.

Take another look later in the evening, around 9:55 p.m., and you’ll see that Ganymede’s shadow has left the disk and that Io’s shadow is about to be hidden behind Callisto. This will be the first time I have ever seen a moon’s shadow eclipsed by another moon. 

Nearly two hours later at 9:55 p.m., Ganymede’s shadow has left, and Io’s shadow is about to be eclipsed by the moon Callisto. The Great Red Spot is well placed close to Jupiter’s central meridian. Credit: Starry Night software.

Also keep a lookout for the Great Red Spot, though it is not nearly as “great” nor as “red” as it once was. It’s more usually seen as a light notch in the North edge of Jupiter’s South Equatorial Belt. At moments of steady seeing, its salmon pink color may appear briefly.

A week later on May 27, the situation nearly repeats itself, but is about two hours later, making it more easily seen across the whole of North America. Ganymede’s shadow starts across Jupiter’s face at 8:58 p.m. EDT. Io’s shadow follows at 10:01 p.m., and both shadows are present until Io’s shadow leaves at 12:18 a.m., followed by Ganymede’s at 12:34 a.m. 

Exactly a week later, on Wednesday, May 27 at 10:05 p.m., the pattern repeats, except that the shadows are closer together and Callisto is no longer in front of Jupiter. Credit: Starry Night software.

Notice that at around 11:48 p.m., Io’s faster moving shadow actually passes Ganymede’s, and the two shadows merge.

At 11:48 p.m., Io’s faster moving shadow catches up with Ganymede’s, and the two shadows merge. Again, the Great Red Spot is well placed. Credit: Starry Night software.

Once again, the Great Red Spot should be in evidence.

If you live west of the Eastern time zone, be sure to subtract the appropriate corrections from the times given above: 1 hour for CDT, 2 hours for MDT, and 3 hours for PDT.

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Observing Saturn

On Friday, May 22, at 10 p.m. EDT, Saturn will be in opposition to the sun. This means that it will be directly opposite the sun in our sky. It will rise as the sun sets in the evening, shine brightly all night long, and set as the sun rises at dawn.

On May 22, Saturn reaches opposition with the Sun. It will be right on the border between Libra and Scorpius, just above the three stars which form the Scorpion’s claws. Credit: Starry Night software.

If you just look at the sky on a single night, everything seems quite static. But if you watch Saturn over a period of a few weeks and note its position against the background stars, you will see that it is in constant motion.

Currently Saturn is moving with what is called “retrograde motion,” from left to right against the background stars. This is actually an optical illusion caused by the Earth’s much more rapid movement around the sun. Once the Earth is well past Saturn in early August, Saturn will appear to reverse directions and begin moving in its true direction, from right to left.

This retrograde motion puzzled early skywatchers, who though the planets must go around it tiny circles called epicycles. This was because they incorrectly believed that the Earth was fixed in space and everything revolved around it, the “geocentric theory.” Once Copernicus made clear that the sun, not the Earth, was the center of the Solar System, the geometry of the planets’ motion became much simpler.

Saturn, like all the planets, is much smaller in angular size than most people realize. I once tried an experiment to see how much magnification was needed to see Saturn’s rings. With a binocular magnifying 10 times, Saturn looked just like a bright star. With a 15x binocular, I could just see a hint that Saturn was oval rather than round. It took a telescope magnifying 25 times to see Saturn’s true shape, though even then no detail was visible. I generally use magnifications of 150 to 250 times to see the details of Saturn and its ring system.

Saturn really has multiple rings, of which the brightest are the outer A ring and the inner B ring. The A ring is noticeably darker than the B ring, and the two are separated by the dark Cassini Division, named after 17th century Italian astronomer Giovanni Domenico Cassini, who was the first to observe it in 1675. Cassini also discovered four of Saturn’s five brightest moons.

The Cassini Division separates the A and B rings.

Titan, the largest and brightest of Saturn’s moons was discovered in 1655 by Dutch astronomer Christiaan Huygens. It is visible in even the smallest telescopes. It is the second largest moon in the Solar System (after Jupiter's moon Ganymede), the only moon to have a dense atmosphere, and the only moon other than our own to have been landed on by a spacecraft.

Huygens was also the first person to deduce that Saturn’s rings were flat circular objects in the plane of Saturn’s equator. Further study has shown that they are made up of thousands of tiny fragments of rock and ice. I once watched a star pass behind these rings, and the star continued to be visible, since there is more empty space that rock and ice in the rings, making them translucent.

Saturn’s smaller moons are worth looking for if you have a good telescope. The brighter ones are visible in a 90mm telescope. Because they are in constant motion around Saturn, you need a planetarium program like Starry Night to identify which ones are visible on a given night. Most of the bright moons move in the same plane as the rings, so appear to trace ovals around the planet.

In a telescope at about 150 power, Saturn is small but beautiful in its perfection, the jewel of the Solar System. Look around the planet for its brightest moons. Credit: Starry Night software.

Iapetus is a particularly interesting moon. Its orbit lies outside those of the other bright moons, and is tilted at an angle of 15 degrees compared to the other moons and the rings. Like all major moons in the Solar System, Iapetus always keeps one face permanently turned towards its planet. The side of Iapetus which leads it around in its orbit has encountered a large amount of debris, painting that face of the moon dark black. When that blackened side of Iapetus is facing Earth, at the moon’s greatest elongation east, it is almost two magnitudes fainter than when the trailing side of Iapetus is facing us, at greatest western elongation.

Right now Iapetus is close to its western elongation, so is at its brightest, magnitude 10.1. By greatest elongation east on June 27, it will be at its faintest, magnitude 11.9.

The globe of Saturn itself is rather bland when compared to its more active neighbor Jupiter. It shows a system of darker belts and brighter zones, but their contrast is muted compared to Jupiter. From time to time bright spots have been observed in Saturn’s cloud tops, but they have short lives compared to cloud features on Jupiter. In large telescopes, the polar regions of Saturn take on an olive green color.

It is interesting to observe the pattern of shadows on Saturn. The rings cast shadows on the globe of the planet, and the planet in turn casts its shadow on the rings. I have observed these shadows in a telescope as small as 90mm aperture under steady seeing conditions.

Whenever I observe Saturn in a telescope, I always take a few minutes to just sit back and admire its sheer beauty. Saturn was one of the first objects I looked at when I got my first telescope as a teenager, and I still recall the wonder I felt at witnessing this beauty for the first time with my own eyes: “It really has rings!”

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Double Stars around Boötes

On a May evening many years ago, I made my first exploration of the night sky. The only star pattern I could recognize was the Big Dipper, but with a star chart in a book, I used that to discover the bright star Arcturus in the constellation Boötes.

The curve of the Big Dipper's handle leads to Arcturus, the brightest star in the kite-shaped constellation of Boötes. Surrounding Boötes is an amazing variety of double stars. Credit: Starry Night software.

The trick to learning the constellations is to begin with the stars you know, and use them to identify their neighbors. This same technique, known as "starhopping" is the key to discovering all the wonders hidden amongst the stars.

Start, as I did, with the Big Dipper, high overhead as the sky gets dark at this time of year. The stars that form the Dipper’s handle fall in a gentle arc, and if you project that arc away from the Dipper’s bowl, you come to a bright star. This is Arcturus, the third brightest star in the night sky, and the brightest star in the northern sky. Only Sirius and Canopus, far to the south, are brighter.

Arcturus is bright in our sky for two reasons, first because it is relatively close to us, 38 light years away, and secondly because it is inherently a bright star, much brighter than our Sun. Though larger and brighter, it is a slightly cooler star than our Sun, so appears orange to our eyes.

Although Boötes is supposed to be a ploughman in mythology, its pattern of stars most resembles a kite, with Arcturus marking the bottom of the kite where the tail attaches. Notice the little dots over the second “o” in Boötes: this indicates that the two "o"s are supposed to be pronounced separately, as "bow-oo’-tees," not "boo’-tees."

Once you have identified Boötes, you can use its stars to identify a number of constellations surrounding it. Between it and the Big Dipper are two small constellations, Canes Venatici (the hunting dogs) and Coma Berenices (Bernice's hair). To Boötes left (towards the eastern horizon) is the distinctive keystone of Hercules. Between Hercules and Boötes is Corona Borealis (the northern crown) with Serpens Caput, the head of the serpent, poking up from the south.

Although most stars appear to our unaided eyes as single points of light, anyone with access to binoculars or a telescope soon discovers that nearly half the stars in the sky are either double or multiple stars. Some of these are just accidents of perspective, one star happening to appear in the same line of sight as another, but many are true binary stars: two stars in orbit around each other, similar to the stars which shine on the fictional planet Tatooine in Star Wars.

Every star labeled on this map of Hercules, Boötes, and Ursa Major is a double star, worth exploring with a small telescope. Some, like Mizar in the Dipper’s handle, can be split with the naked eye. A closer look with a telescope shows that this is really a triple star. Others require binoculars or a small telescope. Some of the finest are Cor Caroli in Canes Venatici, Izar (Epsilon) in Boötes, Delta Serpentis, and Rho Herculis.

One of the joys of double star observing is the colour contrasts in some pairs. Others are striking for matching colours and brightness. My favorites are stars of very unequal brightness, which look almost like stars with accompanying planets.

Also marked on this chart are three of the finest deep sky objects: the globular clusters Messier 13 in Hercules and Messier 3 in Canes Venatici, and the Whirlpool Galaxy, Messier 51, tucked just under the end of the Big Dipper’s handle. You will probably need to travel to a dark sky site to spot this galaxy. A six-inch or larger telescope will begin to reveal its spiral arms, including the one that stretches out to its satellite galaxy, NGC 5195.

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Asterisms and Constellations

On a recent warm and humid summer night, sky transparency was very poor. Only the brighter stars punched through the water-laden atmosphere but three stars were very prominent. They formed a triangular pattern aptly called the Summer Triangle.

The Summer Triangle begins to rise in the Spring.  As seen from mid-northern latitudes in mid-May near midnight.

The Summer Triangle is an example of an asterism: a group of stars that form a recognizable pattern or shape. The Big Dipper, the Little Dipper and the Great Square of Pegasus are other examples of asterisms.

Asterisms are often confused with constellations and indeed, in ancient times, constellations were mythological figures, animals or objects that were seen in groupings of stars.

The Big Dipper asterism as seen from mid-northern latitudes in mid-May at 10:00 p.m.

Almost everyone in North America is familiar with the Big Dipper which is part of the figure of the Big Bear, or the constellation of Ursa Major.

The Big Dipper asterism belongs to the constellation Ursa Major (Great Bear).

The modern constellation of Ursa Major includes all stars within an area defined by the International Astronomical Union in 1930. So the star 24 Ursae Majoris "belongs" to the constellation Ursa Major even though it is not part of the figure of the bear.

Modern constellation boundaries

Some asterisms such as the Big Dipper, the Sickle of Leo, the teapot of Sagittarius and the Great Square of Pegasus have been known for a long time. All are best appreciated when viewed without optical aid because of their large angular size.

But over the years, people using binoculars and telescopes have come across other striking asterisms and some of these have become well known to amateur astronomers.

Here are some examples.

The Diamond Ring

A tight group of 7th and 8th magnitude stars with Polaris as the "solitaire". Best seen with binoculars in a dark sky or a small telescope with a low power eyepiece showing about a 1° field.

The Coathanger
RA = 19h 25m, Dec = 20° 04'

A group of fifth and sixth magnitude stars in Vulpecula appearing like an upside down coathanger to northern hemisphere observers. Use binoculars for best views.

ET Cluster
RA = 1h 19 m, Dec = 58° 17.5'

This open cluster, also known as NGC 457, is located in Cassiopeia. With a bit of imagination you can make out the figure of ET. (Hint: the two bright stars are ET's eyes). Because of its small size, a telescope is needed to make out this asterism.

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Virgo and Her Treasures

Although Virgo is the second largest constellation in the sky (after Hydra), it is poorly known to casual skywatchers. That’s because it contains only one first magnitude star, Spica, and its other stars do not form an easily recognizable pattern like the Big Dipper or Orion.


Virgo is the second largest constellation by area, and is well placed just after dark for exploration. Credit: Starry Night software.

Most of the stars which form the pattern of Virgo are third or fourth magnitude, so are hard to see unless you have dark country skies. City dwellers will need binoculars to see them. Starting from bright Spica there is a chain of four stars to its right, with Porrima (Gamma Virginis) in the middle the brightest. Two stars extend northwards from Porrima, ending with Vindemiatrix.

 Porrima is one of the finest double stars in the sky, but has been hard to split in recent years because the apparent distance between its two components had been closing. It is once again opening up, and its separation of slightly more than 2 arc seconds makes it easy to split in all but the smallest telescopes.

 There are two other double stars in neighboring constellations worth a look: Algorab in Corvus and Zubenelgenubi in Libra, which can be split in binoculars.

If Virgo has few bright stars it makes up for it by containing more galaxies than any other constellation in the sky. It is most famous for containing the Virgo Galaxy Cluster, the nearest galaxy cluster to our own Local Group. Located 60 million light years distant, this is the richest cluster of galaxies in the sky.

The Virgo Galaxy Cluster is an easy starhop from Vindemiatrix. Credit: Starry Night software.

You can locate the Virgo Cluster by sweeping first westward from Spica to Porrima, and then northward to Vindemiatrix. Five degrees west of Vindemiatrix is Rho Virginis at the center of a distinctive Y-shaped group of stars. The Y points upwards to the galaxy cluster. The problem with the Virgo Cluster is not spotting the galaxies, but trying identify which is which. This chart <> will help you to follow the starhop and identify the galaxies. The secret to observing galaxies is to view them from a location with dark skies on a moonless night.

Charles Messier in the Eighteenth Century observed and catalogued eight galaxies in this cluster, plus six more just across the border in Coma Berenices. Two more Messier galaxies are outliers from the main Virgo Group, Messier 49 and Messier 61.

The final Messier galaxy in Virgo is one of the brightest galaxies in the sky and lies slightly nearer than the rest of the Virgo galaxies, 50 million light years distant. This is the famous Sombrero Galaxy, number 104 in Messier’s catalog. It can most easily be found by following a starhop which starts at Gienah, the upper right star in Corvus. In binoculars you can see a long chain of stars extending northeastward from Gienah, ending in a small triangle followed by a group of stars shaped like an arrow. The arrow points right at the Sombrero Galaxy.


This starhop from Gienah in Corvus will lead you directly to the Sombrero Galaxy, Messier 104. Credit: Starry Night software.

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The Lure of Variable Stars

I’m a sucker for action. I love change. My favorite planet is Jupiter because of its rapid rotation, ever-changing moons, and volatile cloud features. I love watching Near Earth Asteroids and comets as they move across star fields. Recently I’ve become addicted to watching solar flares and prominences in rapid action with my solar telescope. But most of all, I love to observe variable stars.

All stars vary in brightness to some degree. Even our Sun, which seems so stable, changes its brightness as more or less of its surface is obscured by sunspots. But there are stars in the sky that undergo vast changes in brightness and color. Many are highly unpredictable in their behavior, and need years of study to uncover the mechanisms that drive them.

The Variable Zoo

The most famous are the novas and supernovas which suddenly shoot up from obscurity to prominence. Supernovas are relatively rare in our neighborhood. The last one was over 400 years ago in 1604. Novas are more common, several being observable in any given year.

Some stars appear to vary for purely mechanical reasons. These are called eclipsing binaries: two stars in a close orbit where one star eclipses the other, as regular as clockwork. Algol in the constellation of Perseus is a famous example of an eclipsing binary.

Other stars expand and contract slowly because of processes going on within them. The most common of these “pulsating variables” are long period variable stars like Mira in the constellation Cetus. Mira is larger in diameter than the orbit of Mars, and changes size, brightness, and color over a period of just under a year. It ranges over nearly six magnitudes in brightness, meaning that at its brightest, it is a hundred times brighter than when it’s at its dimmest. Another group of pulsating variables is called the Cepheids, named after the star Delta Cephei. These have much shorter periods than the Miras, ranging from 1 to 70 days, and their period is closely tied to their luminosity, which has led to their use as measuring sticks to determine the distance of globular clusters and galaxies.

Another group of variable stars is called “cataclysmic variables.” These include novas, supernovas, and the so-called “dwarf novas.” These last are the stars that interest me the most because they show the most action. My favorite is SS Cygni (TCY 3196-723-1), located close to the open cluster Messier 39. This star normally sits around twelfth magnitude, just visible in a small telescope, but every few weeks it shoots up unpredictably to about eighth magnitude. If you’re lucky enough to catch it in outburst, you can actually see it get visibly brighter. Stars like SS Cygni are actually close double stars consisting of a red dwarf and a white dwarf. The white dwarf is surrounded by a disk of gas stolen from the red dwarf which is drawn down into the white dwarf where it ignites, causing the sudden outburst in brightness.

 

Observing Variable Stars

Professional astronomers realized over a century ago that there were more variable stars in need of study than they could handle, so they enlisted the aid of amateur astronomers to monitor the brightness of a number of stars well suited to amateur observation: stars which changed in magnitude over a wide range and which took a long period to complete their cycle of brightness. For many years this work required no more than a telescope and a good set of charts, and such simple visual observations are still useful today, although nowadays amateurs have access to photoelectric photometers and CCD cameras which are capable of studying just about any star. The American Association of Variable Star Observers acts as a central clearing house for all sorts of amateur variable star observations, providing instruction, charts, and other support, and giving amateurs a simple online system for recording their observations.

Why observe variable stars? Mainly because it’s fun! You never know from night to night what you are going to find…remember what I said about action? No special equipment is needed other than a set of star charts which plot the variable star and give the brightness of non-variable stars around it, which are used to estimate the brightness of the variable.

If you are a deep sky observer, you already have one of essential skills of a variable star observer: you know how to locate objects in the sky. It doesn’t matter how you do it. I used traditional starhopping for several years, but now I use my Orion SkyQuest XT6’s IntelliScope setting circles to locate my variables. Once you’ve located the variable, you estimate its brightness as compared to other stars on the chart, and record the time of the observation. With a little practice you can make estimates to within a tenth of a magnitude. You can then log onto the AAVSO’s web site and enter your observation. Within ten minutes it will be moved into their database of over ten million observations, and you can see your observation on a light curve along with those of hundreds of other observers around the world. What could be neater?!

Unlike most of the observations amateur astronomers make, variable star observations have a serious side. By making a numerical estimate of the brightness of a star at a particular point in time, you are logging a piece of scientific data. The AAVSO maintains records online of every observation submitted to them over the past hundred years, keeping the records available to researchers around the world.

On a typical night, I’ll observe about a dozen stars from “my” list of about sixty stars visible at different times of year.

I keep finder charts along with the AAVSO charts in plastic sleeves in a loose-leaf binder, so that everything I need is close at hand. Since you never know ahead of time how bright a variable is going to be, you need to have a complete set of charts for each star; these can be downloaded from the AAVSO web site:

The biggest challenge in finding a variable star is that you’re looking for something that may be quite bright, or may be below the magnitude limit of your telescope, totally invisible to you. So what you look for is the star field, the pattern of stars surrounding the variable. Once you’ve found the field, you then check to see how bright the variable is. You then consult your AAVSO charts to see which stars are closest in brightness to the variable. Comparison stars on the charts are marked with their brightness to the nearest tenth of a magnitude. Because a decimal point might be confused with a faint star, they are left out, so that a 9.7 magnitude star is marked “97” and a 11.4 is marked “114” on the chart. You try to find a couple of stars, one slightly brighter than the variable, one slightly fainter, and then estimate where the variable falls between them.

Equipment for variable star observing

For visual observing as I have described above, the equipment needs are very simple. There are many variable stars within range of a pair of small binoculars, and some that can be observed with the naked eye alone. On the other hand, access to a large telescope lets you follow stars that become very faint at minimum.

I have found it advantageous to use eyepieces with a wide field of view, since they show me more of the sky at any given magnification, and let me see more comparison stars without having to move the telescope about.

My current strategy is to survey “my” variables using my Celestron 6" SCT telescope. I’ve programmed the controller with the coordinates of my variables, so I can quickly move through the list. Any variables which are currently too faint to be observable with the 6”, I revisit the next night with my larger 11” Dobsonian.

Where to start?

If you’re still not sure whether variable star observing is for you, I’d recommend reading Starlight Nights by Leslie Peltier (Sky Publishing). Peltier was the finest variable star observer of the 20th century, and his book is an entertaining introduction to a wonderful man and his love of the stars. It’s probably my very favorite astronomy book.

The AAVSO web site includes everything you need to get started. It has a complete observing manual, a list of good stars to start on, and all the charts you will need, all free of charge. Visit http://www.aavso.org

I’d recommend starting on stars that are easy to find and visible all year round, such as these stars in and around the Big Dipper:

A final warning though: variable star observing is highly addictive. Variable star observers probably spend more time at the eyepiece than any other amateur astronomers because, unlike deep sky or planetary observing, they are not dependent on dark skies or steady seeing. For years I carried out regular variable star observing every clear night from the middle of a large city, even when the Moon was full. The only thing that can stop you is clouds!

If you'd like to follow along with NASA's New Horizons Mission to Pluto and the Kuiper Belt, please download our FREE Pluto Safari app.  It is available for iOS and Android mobile devices. Simulate the July 14, 2015 flyby of Pluto, get regular mission news updates, and learn the history of Pluto.

Simulation Curriculum is the leader in space science curriculum solutions and the makers of Starry Night, SkySafari and Pluto Safari. Follow the mission to Pluto with us on Twitter @SkySafariAstro, Facebook and Instagram. ​

Saturn Through the Ages

On May 23rd, Saturn will reach opposition — the closest it will be to Earth in 2015.

Saturn, the original Load of the Rings.

Saturn can be viewed in the morning sky until May 23, when it moves into the evening sky. From November to the end of the year it will be behind the Sun.

Looking south-east on May 23, 2015 at 11:00 p.m. from mid-northern latitudes.

The rings are now widely open, making them easy to see in any telescope magnifying more than about 30x. Saturn’s largest moon Titan is readily visible in a small telescope, and several more moons may be seen in larger telescopes. At opposition, the planet’s equatorial angular diameter will be 19 arc seconds, its rings being 42 arc seconds across.

As you peer through your eyepiece and ponder the ringed planet with the benefit of our modern understanding of science, consider how perplexing Saturn must have been to ancient people whose instruments and grasp of nature were at their infancy.

Eyepiece view (10 arc minutes) of Saturn on May 23, 2015.  The planet’s equatorial angular diameter will be 19 arc seconds, its rings being 42 arc seconds across.

In our feature article below, “Saturn Through the Ages” — a departure from our usual technical take on the universe — we will be returning to times past to explore a piece of the puzzle that highlights our search for knowledge and meaning.

Saturn Through the Ages  

Throughout human history, we have looked to the light of the heavens to illuminate our role on Earth. Next time you are star gazing, consider all of the people throughout time and across the world who have reflected upon the same celestial bodies, conducting their nightly dance across our sky.

Our study of the celestial sphere has brought us understanding of physical and mathematical principles, models for society and perhaps fundamentally, a comforting sense of order. It is the human imagination however, and our quest to find a meaning behind this order, that led us to create a screenplay of the night sky. For millennia we have told our own tale through the guise of a heavenly cast of characters. Because celestial mythology is common throughout many cultures, these stories reveal our discoveries of the human condition.

In the upcoming month, many of us will be gazing at the planet Saturn in the northeastern sky. Perhaps due to a planet’s slow trek through our heavens, the stories we've told about Saturn often involve the passage of time and inevitable fate. We've expressed through Saturn both our appreciation for life and our fear of time's cruel and inescapable quality.

In ancient Mesopotamia, they prayed to Saturn as the Lord of Death, appealing to him thus:

“O Lord Saturn
whose name is august
whose power is widespread
whose spirit is sublime
O Lord Saturn
the cold, the dry, the dark, the harmful…
crafty sire who knowest all wiles
who are deceitful, sage and understanding
who causest prosperity and ruin
happy or unhappy is he whom thou makest such.”

In ancient Rome, Saturn was an agricultural god, a harvest deity. Controlling our fate through the success of our crop, he was celebrated in times of bounty and appealed to when times were hard. The Golden Age of Saturn, an ideal era of equality and abundance, was memorialized during the mid-winter festival of Saturnalia. A time of feasts and gifts from which we can trace rituals of modern day Christmas. During the celebration, a man chosen to represent the god was attentively fêted, only to be sacrificed on the final day of the festival. Try as we have to sway him however, we are all equally powerless before the forces personified by Saturn. 

In Hindu mythology, Saturn appears as the god Sani, holder of the secrets of fate. One could predict the future through use of a Saturn diagram, which represents the planet’s path through our skies. This god is so malevolent that a single glance from the evil-eyed deity burned off the head of the infant Ganesa, god of good fortune and prosperity. Associated with childhood disease, Sani demonstrates that not even a god’s luck can stand against the inevitability that Saturn represents.

Though we may wish it otherwise, nothing in our human existence remains static; nothing escapes the passage of time. Falcon-headed Horus, Saturnine god of the ancient Egyptians, succeeded his father Osiris when he was dethroned, marking the beginning of a new regime. As all change implies death of the old, we tell our tales of Saturn to reconcile ourselves to the necessity of welcoming the new. 

Cronos, Saturn-god of ancient Greece, whose name may originally have referred to his universal governance (from the verb kreno), became known as Father Time. Cronos not only overthrew and replaced his father, but consumed each of his own children at birth, much as time itself consumes all that it creates. Demonstrating the universality of this principle, Cronos himself was ultimately dethroned by his offspring, making way for a new era.

Through our creation of Saturn mythology, we attempt to explain our relationship to fate, time and death. Our ability to perceive these issues is fundamental to our very humanity. When next gazing at Saturn in the night sky, perhaps you will see not only a wonder of the cosmos, but also the history of humanity’s struggle to find meaning therein.

If you'd like to follow along with NASA's New Horizons Mission to Pluto and the Kuiper Belt, please download our FREE Pluto Safari app.  It is available for iOS and Android mobile devices. Simulate the July 14, 2015 flyby of Pluto, get regular mission news updates, and learn the history of Pluto.

Simulation Curriculum is the leader in space science curriculum solutions and the makers of Starry Night, SkySafari and Pluto Safari. Follow the mission to Pluto with us on Twitter @SkySafariAstro, Facebook and Instagram. 

Sky Events For May 2015

Moon Phases

Full Moon

Sunday, May 3, 11:42 p.m. EDT

The Full Moon of May is known as the “Milk Moon,” “Flower Moon,”  or “Corn Planting Moon.” It rises around sunset and sets around sunrise; this is the only night in the month when the Moon is in the sky all night long. The rest of the month, the Moon spends at least some time in the daytime sky.

Last Quarter Moon

Monday, May 11, 6:36 a.m. EDT

The Last Quarter Moon rises around 2 a.m. and sets around 1 p.m. It is most easily seen just after sunrise in the southern sky.

New Moon

Sunday, May 18, 12:13 a.m. EDT

The Moon is not visible on the date of New Moon because it is too close to the Sun, but can be seen low in the East as a narrow crescent a morning or two before, just before sunrise. It is visible low in the West an evening or two after New Moon.

First Quarter Moon

Monday, May 25, 1:19 p.m. EDT

The First Quarter Moon rises around 1 p.m. and sets around 2:15 a.m. It dominates the evening sky.

Observing Highlights

Mercury at greatest elongation

Thursday, May 7, evening twilight

This is the best evening apparition of Mercury this year for observers in the northern hemisphere. Use Venus to help you locate it. Mercury is most easily located by sweeping with binoculars, but once you’ve located it, you should be able to see it with your unaided eyes

Uranus and the Moon

Friday, May 15, dawn

The Moon will pass just south of the Uranus just before sunrise.

Double shadow transit on Jupiter

Wednesday, May 20, 8:06–8:35 p.m. EDT

The shadows of Io and Ganymede will be on opposite limbs of Jupiter, while the moons Io and Callisto will be central on the disk.

Saturn at opposition

Friday, May 22, 10 p.m. EDT

Saturn will be in opposition to the Sun.

Note how most of Saturn’s moons are in the same plane as the rings, except for Iapetus, whose orbit is tilted 8.3 degrees. At opposition, Iapetus is close to maximum elongation towards the west, while Tycho is close to maximum elongation towards the east.

Double shadow transit on Jupiter

Wednesday, May 27, 10:01 p.m.–12:18 a.m. EDT

The shadow of Io chases the shadow of Ganymede across the face of Jupiter, catching up with it and passing it at 11:48 p.m. EDT. The Great Red Spot will also cross Jupiter’s disk during this period.

Planets

 Mercury is well placed for northern hemisphere observers in the evening twilight sky for the first three weeks of May.

Venus shines high in the western sky after sunset.

Mars moves from Aries to Taurus on May 3, too close to the Sun to be visible.

Jupiter is well placed in the evening sky all month.

Saturn is just north of Scorpius’ “claws.” At opposition on May 22, it is visible all night.

Uranus rises just before the Sun in Pisces.

Neptune is in the eastern morning sky in the constellation Aquarius.

If you'd like to follow along with NASA's New Horizons Mission to Pluto and the Kuiper Belt, please download our FREE Pluto Safari app.  It is available for iOS and Android mobile devices. Simulate the July 14, 2015 flyby of Pluto, get regular mission news updates, and learn the history of Pluto.

Simulation Curriculum is the leader in space science curriculum solutions and the makers of Starry Night, SkySafari and Pluto Safari. Follow the mission to Pluto with us on Twitter @SkySafariAstro, Facebook and Instagram.