On May 20 or May 21, the Sun is going to turn into a ring of fire. There will be an annular solar eclipse visible from eastern Asia, the Pacific and North America. On May 21 residents of Tokyo will see a “black hole” in the centre of the Sun as the Moon passes over the face of the Sun but does not completely cover it up. A ring of the Sun will still shine around the edge of the Moon. The path of the eclipse will move across the Pacific to North America, crossing the International Date Line as it does – so this eclipse starts May 21, but finishes May 20! Areas out of the direct line of sight of the annular eclipse will see a partial eclipse. Many viewers from western North America will see a partially eclipsed Sun at sunset on May 20– it should be a great photo opportunity!
Annular Eclipse credit: NASA
Annular eclipses occur when the Moon is at its most distant from the earth in its orbit – and so is marginally too small to completely cover the disc of the Sun – in this case up to 94% of the Sun will be covered. This is still blindingly bright, so safety first, do not look directly at the eclipse. Use some sort of projection technique or solar filter to view the eclipse. From Ireland this eclipse will not be visible at all. If you want to see any live images that might be broadcast it gets underway shortly after 11 pm May 20 and is all over by 3am May 21.
Eclipses of the Sun are awe-inspiring phenomena. In many early cultures they were believed to be bad omens. The word eclipse comes from the Greek, from “ekleipein” – to fail to appear. A fragment of a lost poem by Archilochus, a Greek poet and soldier who lived in the seventh century BC seems to clearly describe a total solar eclipse:
Nothing there is beyond hope,
Nothing that can be sworn impossible,
Nothing wonderful, since Zeus,
Father of the Olympians,
Made night from mid-day,
Hiding the light of the shining Sun,
And sore fear came upon men.
And eclipses have played their part in modern literature too – in Mark Twain’s A Connecticut Yankee in King Arthurs Court, the Yankee hero Hank avoids being burnt at the stake by recalling a solar eclipse that happened 528. Unfortunately in the film version, the eclipse is utterly inaccurate – with a black disk over the sun, yet the sky remains blue! Instead, during an annular eclipse, grass and skin turn to silver, the landscape becomes platinum and the sky shades to navy blue. I hope the North Americans get some good pictures!
UPDATE: view some great photos at this Flickr site
This episode of “What is the Stars?” was first broadcast during the week of May 14, 2012. Listen live on RTÉ’s lyricfm on Mondays and Fridays at 22:45. 
