Venus and the Beehive

On the night of Wednesday July 3, the planet Venus will have an interesting encounter with a swarm of bees.


On the evening of Wednesday July 3, Venus skims just north of the Beehive star cluster. Credit: Starry Night software

Venus has only recently emerged from behind the Sun, so you may not have seen it yet as an “evening star.” Venus is of course a planet, which shines by light reflected from the sun, and not a star, a huge ball of glowing plasma in the far reaches of space. To the naked eye, stars and planets look the same, so ancient astronomers called them all “stars.”

The ancients did note that some “stars” appeared to move, so gave them a special name, “planets,” which means “wandering stars.” In particular they noticed that two especially bright planets never wandered very far from the sun. At first they thought these were two different objects, one in the morning sky, one in the evening, but at some point realized that these were really aspects of the same object, which they named “Venus.” The next step was the realization that Venus’ movements could be explained by a body revolving in a circle around the sun, peeking out first on one side, then the other.

Venus is still quite close to the sun in the sky, so you will need a low western horizon to catch a glimpse of it as it sets about an hour and a half after the sun. On Wednesday night, use your binoculars to follow it down as it gets closer to the horizon. If you’re lucky, you may catch a glimmer of hundreds of tiny stars just below it.

These stars are members of one of the closest star clusters to our sun, the Beehive Cluster in the constellation Cancer. This cluster is located 590 light years from the sun, only the Hyades and the Pleiades being closer. It contains just over a thousand stars, of which about 300 are similar to our sun. At least two of the stars in the cluster have planets, and we can only imagine how glorious the night sky must be on a planet situated in the middle of a star cluster. In fact, Isaac Asimov has written a famous science fiction story, “Nightfall,” set on such a planet.

Because it is readily visible in a dark sky with the unaided eye, the Beehive Cluster is known by different names in different cultures. Its resemblance to a swarm of bees has given it the name “the Beehive.” It has also been called “Praesepe,” Latin for “manger.” It is seen as a hay-filled manger surrounded by asses waiting to eat. The nearest stars to it are named Asellus Borealis and Asellus Australis, the Northern Ass and the Southern Ass. Astronomers know it as Messier 44, the 44th object in Charles Messier’s famous catalog.

Although the Beehive is easily visible with the naked eye in a dark sky, seeing it tonight will be a challenge. Venus is only visible close to sunset, and the sky will not be completely dark and hour and a half later when Venus sets. Besides observing from a location with a low western horizon, use binoculars to follow Venus down towards the horizon. Venus itself should be easy to see, as it’s the brightest object in the night sky after the moon, but the stars of the Beehive will be difficult without binoculars.

Your favourite space mission

One of my favourite features of Starry Night is its large database of space mission data. Sometimes I just like to position myself near Cassini spacecraft and replay its visually stunning passage through Saturn's rings. The view is breathtaking and the idea that humans have actually built a spacecraft which has done this exact thing is mind boggling.

Other times I look at the entire space mission path of Voyager missions, admiring the engineering and planning marvel that led to well used gravitational slingshots. A simple curved line becomes exciting when you put it in its proper context.

Yet, these space missions, almost entirely forgotten, still give us valuable insight about what lies in unfamiliar regions of the solar system. The latest information coming from Voyager 1, currently the furthest man-made object, presents some new questions about the edge of the solar system and the effects playing out there.

What is your favourite space mission? Do you use Starry Night to replay it? How can we make the experience more enjoyable or the information more readily available?

Cassini doing what it does best

MOOCs

I'm a big fan of Massive Open Online Courses (MOOCs). I think they'll ultimately revolutionize the way that Universities operate, and they're certainly making them rethink things already.

I've tried my hand at a few for fun, review and professional development (See: Khan Academy, Coursera and many more), but haven't tied any relating to astronomy. Have you? Have you found a good one?

What about amateur astronomy? Could it reliably be taught by video, or is there just no substitute for getting out there and doing it yourself?

Scorpius and its Stingers

Most of the constellations seem pretty much random arrangements of stars to modern eyes. Scorpius is one of the few which actually resembles its namesake, the Scorpion.

For observers in the Northern Hemisphere, the constellation Scorpius appears low in the southern sky on warm June evenings.   Credit: Starry Night software

As seen by observers in the Northern Hemisphere, Scorpius appears like a giant scorpion peeking over our southern horizon. With a fairly small body, marked by the red giant star Antares, the scorpion has three stars in front representing its claws, and a long curving tail behind, ending in two bright stars marking its stinger. If you live in Canada or the northern USA, part its tail will be below the horizon, but more southern observers will see the whole beast.

Antares (Alpha Scorpii) is one of the brightest stars in the sky, and one of the few with an obvious red color. This color reminded ancient observers of the red planet Mars, hence its name, which means “not Mars,” Ares being the Greek for Mars. In large amateur telescopes, this red giant is seen to have a tiny companion star. Because of the primary star’s vivid red color, the companion often appears greenish, which is an optical illusion, since there are no green stars.

Of the stars making up the Scorpion’s claws, Graffias (Beta Scorpii) and Nu Scorpii are both double stars. Both are easily split in even the smallest telescope. The stars in Graffias are relatively close, 14 arc seconds apart, while those in Nu Scorpii are much farther apart, 41 arc seconds, visible in binoculars. Both pairs are quite unequal in brightness, about 2 magnitudes difference between the two stars.

The stinger at the end of the scorpion’s tail consists of two stars, Shaula and Lesath. These appear as a double star to the naked eye, sometimes called the “Cat’s Eyes.” They point to one of the brightest and most beautiful open star clusters in the sky, Messier 7. This was first described by Claudius Ptolemy in the 2nd century AD, so sometimes is known as “Ptolemy’s Cluster.” Just above this cluster is another one, equally bright and beautiful, known as Messier 6 or the “Butterfly Cluster.” Both are visible to the naked eye, but reveal their true beauty in binoculars or a small telescope.

Just above these clusters, and just over the border in the constellation Sagittarius, is the black hole at the center of our Milky Way Galaxy. The black hole itself is of course invisible, but the area is rich in stars.

Moving back up to Antares, if you look just below it with binoculars, you will see a fuzzy patch. In a moderate sized amateur telescope this resolves into one of the finest globular clusters in the sky, known as Messier 4 or the “Cat’s Eye.” Yes, it’s confusing to have two “Cat’s Eyes” in the same constellation, but one a pair of stars and the other a globular cluster.

About half way between Antares and Graffias is another smaller globular cluster, Messier 80, also a fine sight in a telescope.

Scorpius thus offers many treats to any stargazer, whether equipped with binoculars, a telescope, or nothing but their own eyes.

Supermoon

My kids are really excited to go camping this weekend.  Not because of the birds and animals, plants and trees, the rocks, the beautiful lake, the different sounds, dad’s barbeque or the activities we have planned.  Instead they are full of anticipation for this Sunday’s “supermoon”.  

I told them about the supermoon last week while casually checking out the moon with the naked eye.  The name brought on curious looks of suspicion – is dad pulling our leg? I mean you put anything with a “super” in front of a word and kids will think its some type of character with superhuman powers.  After reassuring my 3 year old that the supermoon was indeed a “good guy”, I tried to explain that the supermoon was simply the largest full moon of the year.  

For us older folk, a supermoon is a full moon that occurs at the same time the moon is at perigee (point closest to Earth in it’s orbit).  At these times the moon can appear up to 30% brighter and 14 percent bigger to us here on Earth. Sunday’s supermoon will be the largest full moon of 2013. 

Take a moment to share the supermoon with others this Sunday and If you take any photos - cape and all  – we’d love to see them!

First Day of Summer

The summer solstice begins today (June 20) for places west of the Central Time Zone in North America and tomorrow (June 21) for places in the Eastern Time Zone.  You can use Starry Night to figure out the exact time of the solstice at your location.

Here is a question. Why isn’t the summer solstice, the longest day of the year, also the hottest day of the year?

Mercury and the Solstice

The last few weeks have provided an unusually fine opportunity for skygazers to spot the elusive planet Mercury because it has been in close proximity to brilliant Venus, and, earlier, Jupiter as well.

On the evening of Thursday June 20, Mercury reaches its maximum elongation east of the sun, placing it directly below brilliant Venus in the evening twilight sky.  Credit: Starry Night software

This opportunity is now coming to a close as Mercury passes its maximum elongation from the sun on Thursday June 20 and begins its rapid drop towards the horizon, passing between us and the sun on July 9. For the next few nights, Mercury will be a tiny speck just below Venus. It is closest on June 20, slightly less than two degrees away, but will also be very close one night earlier or later.

The best time to see Mercury is about half an hour after local sunset. Any earlier, and it will be lost in the sky’s glare; much later and it will be too low to make out. It is most easily spotted with binoculars, but once you’ve located it, it should be relatively easy to see naked eye.

This week also marks the solstice, on Friday June 21 at 1:04 a.m. EDT. The sun reaches its most northern declination, marking the middle of summer in the northern hemisphere and the middle of winter in the southern hemisphere.

Because the sun is as far north as it can get, it is above the horizon in the northern hemisphere as long as is possible. Also, at local noon, it is as high in the sky as it can get. These two factors bring the maximum solar heating possible.

In the southern hemisphere, the opposite is true. The day is as short as it can get, and the sun is low in the northern sky, giving little warmth.

If June 21 is the “midsummer” or “midwinter” day, why is it that we always think of the seasons as beginning on this day? It’s because it takes time for the sun to have its effect, causing the seasons to lag behind the sun, so that the hottest days of summer (or the coldest days of winter) are usually a month or two after the solstice.

The solstices have always been important dates for humans. Most calendars mark the beginning of the year close to the winter solstice. Determining the exact date of the solstice was important to fix the calendar, and structures like Stonehenge in England were built to make accurate measurements of the sun’s rising and setting points.

Windowed or Fullscreen?

As a developer, I find myself with multiple applications, windows and tabs open on multiple monitors at any given moment. My workflow is that of a typical developer, I think, but probably not that of a typical Starry Night user.

When working on, or simply using Starry Night, I often find myself wondering whether people make use of fullscreen mode, and whether we could provide them a better experience by improving it.

It's not a (typical) productivity application, but neither does it demands the users constant focus, as a game would.

With the emergence of tablets as the dominant (or at the very least, growth) platform, users might expect a more robust full-screen mode.

How do you use Starry Night? Windowed? Fullscreen? If so, when and why?

Sometimes you've got stuff to do, but other times it's just nice to block out everything else, and stare at the sky

Seeing the Southern Cross from Tulum

I had an amazingly satisfying SN related experience recently: I was down in Tulum Mexico. My friend had, for reasons that I still do not understand, brought his laptop to this totally off the grid palapa / hut on the beach.  

We fired up Starry Night and were able to verify that what I was seeing low on the southern horizon was actually the Southern Cross! It was my first time ever seeing this super-cool asterism.

And I was able to see both the cross and Polaris at the same time, which freaked me out - I would think you couldn't do that. But I guess the Southern Cross is not really at the South Pole -- it circles it widely enough that we could see it even though we were still at 20 degrees north.  As Starry Night showed us quite clearly.

Anyway, it turned out to be very cool to have a planetarium program at the beach, and now I am thinking about which small scope might make sense to bring next time.

Awesome.

A Perfect Trifecta

On Monday evening, June 17, the moon will be 9 days old and just to the right of Spica. On Tuesday evening, it will have moved to a position between the two, as shown in the graphic. By Wednesday night it will be off to Saturn’s left, 11 days old.

Saturn and Spica have been making an attractive pair in the evening sky. On Tuesday June 18 they will be joined by the waxing gibbous moon, making an astronomical trifecta.  Starry Night software

To skywatchers without a telescope, watching the moon move past Spica and Saturn over three successive nights will bring a vivid demonstration of how rapidly our moon circles the Earth.

If you own a telescope, there is much to be revealed. On the moon, the rising sun illuminates the craters Plato (in the north), Copernicus (in the center), and Tycho and Clavius (in the south). Clavius is one of the largest craters on the surface of the moon, and it’s always a challenge to observers to see how many craterlets they can count within its walls.

Moving your telescope onto Saturn, you are always guaranteed a treat with its tiny perfect rings. But if you look on Tuesday night, look beyond the rings to Saturn’s moons, several of which are readily visible in small telescopes

Saturn’s brightest moon Titan, the only moon in the solar system large enough to have a  substantial atmosphere, can be seen in any telescope. On Tuesday night it will be at its maximum elongation eastward from the planet. Between Titan and the rings look for Tethys, visible in a 90mm telescope. South of Saturn is Rhea, its second brightest moon. Dione is immediately north of Saturn.

On the night of Tuesday June 18, Saturn’s moons are particularly well placed.  Credit: Starry Night software.

The special treat tonight is located a bit further north of Saturn beyond Dione: its most unusual moon Iapetus. As you can see in the graphic, the inner moons all move in orbits in the same plane as the rings, right above Saturn’s equator. Iapetus moves in a completely different orbit, tilted strongly with respect to Saturn’s equator. This often takes Iapetus far from Saturn, but tonight it is passing just north of Saturn, and so is much closer and easier to spot than usual. Iapetus is a bit fainter than the other moons, so may require a 150mm telescope.

Look beyond the moon and Saturn for other telescopic treats in Virgo, such as the close double star Porrima (Gamma Virginis) to Spica’s right. The countless galaxies in Virgo will have to wait a week until the moon gets out of this part of the sky.

Mercury at the Max

This week continues to be an excellent opportunity to observe the elusive planet Mercury.  Why is Mercury so hard to observe? After all, it is one of the brightest objects in the sky?

On Wednesday June 12, Mercury will be at its maximum elongation from the Sun. A crescent Moon and brilliant Venus will frame it, making it particularly easy to see.  Credit: Starry Night software.

The problem with Mercury is that it never gets very far from the sun. It is the closest planet to the sun, and rarely strays very far away, so most of the time its tiny speck of light is lost in the scattered light surrounding the sun.

Astronomers eagerly await the date when Mercury is at its farthest from the sun, called “greatest elongation.” During the current apparition of Mercury, greatest elongation occurs on Wednesday June 12. On that date, Mercury will be 24 degrees away from the sun.

There is an added difficulty with the current apparition of Mercury for observers in the northern hemisphere. The current angle of the ecliptic, the path of the sun and planets in the sky, puts it very close to the horizon, so that planets like Mercury and Venus, both currently to the east of the sun, never get very high above the horizon.

The good news is that Venus has recently emerged from behind the sun, and now provides a brilliant beacon pointing the way to Mercury.

The trick for finding Mercury is first to find Venus. At a location with a low western horizon, you should be able to spot Venus a few minutes after the sun sets, around 9 p.m. in most locations. Look for Venus slightly north of due west, low on the horizon. Mercury will be just above and to the left of Venus if you’re in the northern hemisphere. I find binoculars very helpful for spotting Mercury, the 7x50 and 10x50 size being especially useful. Focus the binoculars on Venus, then scan above and to its left for Mercury. Don’t wait too late, as Mercury and Venus set quite quickly after the sun.

On Monday June 10, the thin crescent moon will join Mercury and Venus, and the three will form interesting patterns for the next few nights.

In the southern hemisphere, look for Mercury above and to the right of Venus. Because of the angle of the ecliptic, the planets will be much higher in the twilight sky than in the northern hemisphere.

Some of you may be wondering why, if Mercury is the closest planet to the sun, it currently appears farther from the sun in the sky. That’s because of the positions of Mercury and Venus in their respective orbits. On June 12 Mercury is at its maximum elongation from the sun, 24 degrees, while Venus is still far away on the far side of the sun. It won’t reach its maximum elongation from the sun, 47 degrees, until November 1, by which time Mercury will be on the other side of the sun, in the morning sky.

Ophiuchus and his Snake

Although it is one of the largest constellations in the sky, Ophiuchus, the Serpent Bearer, is one of the least well known. Although large in area and prominent in the summer sky, it contains no bright stars, so is rarely seen.

Ophiuchus is a little known but important constellation, which graces our evening skies this month. Credit: Starry Night software.

Ophiuchus is surrounded by brighter, more famous constellations. Boötes is to his right, the Summer Triangle is to his left, Hercules is above his head, and Scorpius is at his feet. For simplicity I’ll describe the view from the Northern Hemisphere. Observers in the Southern Hemisphere will need to make the usual corrections. Like Orion, Ophiuchus is an equal opportunity constellation: on the celestial equator, he is equally visible everywhere in the world.

Ophiuchus made the news a couple of years ago when astrologers finally acknowledged his existence. Although astronomers, the scientists of the sky, have known about Ophiuchus for thousands of years, and that he literally sticks his foot into the zodiac, he has never figured among the astrologers’ twelve signs of the zodiac. Astrologers promptly made up a new set of imaginary qualities of “Ophiuchans,” which of course are just as fanciful (and imaginary) as their other inventions.

If you look at the picture of Ophiuchus, you will see that he is apparently wrestling with a very large snake. This is represented by two constellations on either side of him, Serpens Caput (head of the snake) on the right and Serpens Cauda (tail of the snake) on the left. Although Serpens consists of two distinct areas of sky with Ophiuchus in between, it only counts as one of the eighty-eight constellations.

This association with a snake links Ophiuchus to Asclepius, the ancient Roman healer, it is said, who observed one snake bringing medicine to another snake. These snakes survive as the two snakes encircling the staff of Asclepius, symbol of medicine.

Ophiuchus is a constellation worth getting to know because it is full of interesting objects. In particular, because of its location just off the Milky Way, it contains a wealth of globular clusters, the ancient clusters of stars which orbit the center of the Milky Way Galaxy. In fact, there are no fewer than seven Messier globulars in Ophiuchus; only Sagittarius contains this many Messier globulars.

The finest of these globular clusters is Messier 12, sometimes known as the Gumball Cluster. This is easily spotted in a dark sky with binoculars, as there is nothing else like it in the open empty area in the middle of Ophiuchus, except for its nearby twin, Messier 10. Look for two faint fuzzy patches. In a medium sized amateur telescope, both these cluster resolve easily into thousands of stars.

Ophiuchus’ snake also has its share of deep sky objects. Serpens Caput features Messier 5, one of the finest globular clusters in the sky, while Serpens Cauda contains the Eagle Nebula, Messier 16, famed for the Hubble Space Telescope’s iconic “Pillars of Creation” image.

There is one very special star in Ophiuchus. This was discovered by American astronomer E. E. Barnard in 1916 when he found it to be the fastest moving star in the sky. It still holds that record to this day. It moves only about 10 arc seconds a year, about half the diameter of the planet Saturn, but that’s more than any other star in the sky.

Barnard’s Star moves that quickly because it is very near to the Sun, in fact, after the three stars of the Alpha Centauri system it is the nearest star to the Sun, only six light years away. Unfortunately, Barnard’s Star, as it came to be known, is a very dim red dwarf star, and so needs a telescope to be seen.

In a telescope, Barnard’s Star is a very ordinary looking reddish 9th magnitude star. But if you plot its position relative to nearby stars, and then go back in 10 years time, you will find that it has moved slightly. Even in photographs taken a year apart, it has moved noticeably.

So, on one of these fine summer evenings, have a look at Ophiuchus, with his beautiful globular clusters and his fast moving star.

Dancing Planets

Take a look at the western sky just after sunset this week, and you’ll see an amazing sight: three bright planets in close formation.


Just after sunset on Sunday May 26 the three brightest planets, Venus, Jupiter, and Mercury, will form a perfect tiny triangle in the western sky. Credit: Starry Night software.

The giant planet Jupiter is moving behind the sun, so is dropping rapidly in the western sky. Mercury and Venus, much closer to Earth, are just emerging from behind the sun, moving in the opposite direction from Jupiter. The three meet this week.

Find yourself a location with a very low western horizon. Go there just after sunset. A small 7x50 or 10x50 binocular will help, but don’t point it in the direction of the sun until it is well below the horizon.

Venus is the brightest of the three, and so should be the first that you see, just above and to the left of the point where the sun has just set.

Astronomers use an upside down scale to measure brightness. The brightest stars are magnitude 1; the faintest the human eye can see are magnitude 6. Really bright objects, like these planets, end up with negative brightness. Tonight Venus will be magnitude –4.

Once you’ve spotted Venus, look for Jupiter nearby. Jupiter will be two magnitudes fainter than Venus, magnitude –2, still extremely bright.

Finally, try to spot the third planet, Mercury, slightly fainter than Jupiter at magnitude –1. Tonight (May 22) and tomorrow night it will be just to the right of Venus, moving upward and to the left more rapidly than Venus.

Try to catch these three every night for the next week, and you’ll see them appear to circle around. On Sunday night, May 26, they will form a perfect equilateral triangle, two degrees on a side.

Mercury continues to rise and Jupiter continues to set so that by the middle of next week they will appear in a straight line with Mercury highest and Jupiter lowest, brilliant Venus in the middle.

We don’t often get to see three planets in such close proximity and see how rapidly they appear to move.

The Mountains of the Moon

When you look at the moon through binoculars or a small telescope, the first thing you notice is that the moon is divided into two distinct forms of terrain: large dark flat plains and bright mountainous highlands. Both of these are pockmarked by an enormous number of craters of all sizes.

The northern half of the moon exhibits many mountain ranges and a few isolated peaks. Credit: Starry Night software.

Early observers of the moon assumed that the large flat plains were seas, not knowing that liquid water was not available on the dry airless surface of the moon, and so named them “maria,”the Latin for “seas,”singular “mare.”“Mare”is pronounced “mah-ray,”not like a female horse. They named the lunar highlands for the mountains of Earth, not knowing that the mountains of the moon were formed by a totally different process from the mountains of Earth.

On Earth, mountains are formed by two different processes. Most mountains, and mountain ranges, are formed by tectonic action: the plates that make up the surface of the Earth bump into each other causing mountains to rise up. Other mountains on Earth are caused by volcanic action: hot magma welling up from the depths of the Earth to deposit itself on the surface as volcanoes.

The moon has neither tectonic plates nor volcanic action. Virtually all of its mountains are the result of impacts by asteroids in the distant past. Early in the moon’s history, there were many gigantic asteroids in the solar system. When these impacted the moon and planets, they formed craters far larger than the ones we see today, forming the lunar maria and leaving their rims to form lunar mountain ranges. The enormous heat generated by these impacts melted the surface material of the moon and caused it to flow, swamping some craters and mountains, which stand out now as ruins on the surface of the maria.

This chart shows some of the mountain features visible this week at the current phase of the moon, around first quarter. Several prominent craters are marked to help you get your bearings: Aristoteles, Plato, Archimedes, and Copernicus.

The mountain ranges and individual mountains are labeled with their Latin names, “montes” for mountain ranges and “mons” for individual mountains. Far over to the east are the Taurus Mountains (Montes Taurus), the landing place of the last of the manned lunar explorers, Apollo 17.

Two major mountain ranges divide the Mare Serenitatis from the Mare Imbrium: the Montes Caucasus to the north and the Montes Apenninus to the south. Where these two meet is the prominent mountain Mons Hadley, named for British optician and instrument maker John Hadley (1682–1743). This is where Apollo 15 landed in July 1971. The lunar Alps, the Montes Alpes, sweep off to the northwest, enclosing the perfect oval crater Plato.

On the barren floor of the Mare Imbrium are two of the most impressive single mountain peaks on the surface of the moon, Mons Piton and Mons Pico.

The Mons Piton has a base 16 miles (25 km.) in diameter and towers 7,380 feet (2,250 m.) over the surrounding plain. The Mons Pico is even more impressive, with a base measuring 9 x 16 miles (15 x 25 km.) and a height of 7,870 feet (2,400 m.) Both these are named after mountains on the island of Tenerife in the Canary Islands.

Although these mountains look impressive under the low light of a rising sun, they really are quite gentle when compared to the mountains of Earth. If you look again in a day or two, they will be practically invisible except for their whiter color.

Enjoy your lunar mountain climbing expedition.

Ring of Fire Eclipse

On May 9 and 10 there will be an annular eclipse of the sun by the moon, visible only in some of the most remote parts of the world: western and northern Australia, Papua New Guinea, the Solomon Islands, and a few remote Pacific atolls.

The annular eclipse of the Sun by the Moon, as it will appear from Cooktown, Queensland, Australia on the morning of May 10 at 8:49 a.m. Credit: Starry Night software.

What is an annular eclipse?

The orbit of the Earth around the sun is an ellipse, not a circle. Similarly, the orbit of the moon around the Earth is also an ellipse. This means that sometimes the Earth is closer to the sun (called perihelion) than at others (called aphelion), and sometimes the moon is closer to the Earth (called perigee), sometimes farther away (called apogee).

We are fortunate to live in a time when the sun and the moon are very close to the same apparent size in our sky. This is an illusion of perspective: the moon is small (2,159 miles/3,475 km.) and close by (238,855 miles/ km.) while the sun is large (865,278 miles/1,392,530 km.) and far away (92,955,808 miles/149,597,872 km.)

Notice that the sun is about 400 times larger than the moon in diameter. It is also about 389 times farther away, pretty close to 400. This explains why the two appear to be almost the same size in the sky. But “almost” is not exact, which explains why there are different kinds of eclipses.

Distances in the sky are measured in angles, 360 degrees making up a full circle. Both the sun and the moon appear to be just slightly more than half a degree in diameter. Degrees are divided into 60 arc minutes, and the exact size of the sun varies from 33 arc minutes when it is closest to the Earth on January 2, to 31 arc minutes when it is farthest from the Earth on July 5. On May 10 it will be 32 arc minutes in diameter.

Over the course of a month, the moon’s size also varies. On April 27 it was at its closest to Earth and appeared to be 33 arc minutes in diameter. If an eclipse had occurred on that day, the moon would have covered the sun completely, and we would have had a total eclipse. On May 10 the moon will appear to be 30 arc minutes in diameter, since it is only a few days away from its farthest from the Earth on May 13. A 30 arc minute moon doesn’t quite cover a 32 arc minute sun, so the sun peeks out as a ring all around the moon. “Annular” is Latin for “ring,” so this is called an “annular eclipse.”

Astronomers tend not to get as excited over an annular eclipse than a total eclipse. Because the moon doesn’t cover the sun completely, you don’t see the prominences and corona which are the most exciting part of a total eclipse. Thus I was quite surprised by the annular eclipse I observed from Toronto exactly 19 years ago on 1994 May 10. Having observed a total eclipse in the past, I wasn’t expecting much from this annular eclipse, yet I found it to be a very powerful emotional experience. Even though 5 percent of the sun was still peeking around the moon, it had the same ominous feel as a total eclipse, much more so that the several partial eclipses I’ve witnessed. Seeing the “ring of fire” around the moon is far more impressive than seeing only part of the sun covered.

Where to see it?

Unfortunately, very few people will get to see this annular eclipse, as its path travels over some of the most remote and unpopulated parts of the Earth.

The eclipse begins at sunrise over the wilderness of Western Australia. It then sweeps over equally empty Northern Territory and on to northern Queensland, far to the north of Cairns where many people witnessed last years total eclipse. Only a few roads intersect the eclipse path. The eclipse path crosses the Coral Sea and touches the eastern end of Papua New Guinea, then crosses through the middle of the Solomon Islands. From there the path neatly avoids just about every island in the south Pacific except for Tarawa and Fanning Islands, both part of the Republic of Kiribati, formerly known as the Gilbert Islands.

Although few people will see the complete annular eclipse, a much larger number will see it as a partial eclipse. This includes all of Australia, Papua New Guinea and the Hawaiian Islands, much of Indonesia, the Philippines, and New Zealand. Unfortunately the partial eclipse just misses being visible in North America, except just at sunset at the southern tip of Baja California. In Honolulu, maximum eclipse will be at 3:48 p.m. on May 9, when 32 percent of the sun will be hidden by the moon.

How to observe it?

For most people who may see this eclipse, it will be a partial eclipse, which is the most dangerous kind of eclipse, because people will be tempted to take quick glimpses of it without proper protection. DON’T DO IT! Looking directly at the sun is always dangerous and can cause permanent damage to your eyes.

There are two safe ways to view a partial (or annular) eclipse. The first is with an approved solar filter. These can be purchased from telescope stores. The only safe equivalent is a #14 welder’s glass. This is denser that the #12 widely available, and usually can only be found in dealers specializing in welding supplies.

The other safe viewing method is to use a large cardboard box to make a pinhole camera. Make a pinhole in one end of the box to act as the lens, and a large hole in the bottom of the box to stick your head through to view the image of the sun. Natural pinhole cameras often are formed by chinks in window blinds or gaps between leaves of trees. So don’t look at the sun, but put your back to it and look instead at the ground in front of you.