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.