On Sunday May 20 (May 21st across the date line in Asia) the moon will blot out 94 percent of our star’s early evening light in an annular solar eclipse event that should leave a dazzling ring of fire in the sky. The eclipse will not be total because the moon will be at its farthest point from Earth in its elliptical orbit and will therefore appear slightly smaller than the disk of the sun.
This annular eclipse will still be pretty spectacular, making the sun appear as a bright ring, or annulus, surrounding the outline of the Moon.
Experts caution not to look at the eclipse directly, even though it might appear as though the sun is almost entirely obscured. "The ring of sunlight during annularity is blindingly bright," Fred Espenak, an eclipse expert at NASA's Goddard Space Flight Center, said in a written statement. "Even though most of the sun's disk will be covered, you still need to use a solar filter or some type of projection technique [to watch the eclipse]. A No. 14 welder's glass is a good choice. There are also many commercially available solar filters."
The eclipse will be visible all across the Pacific and the Western U.S. and will begin at 5:30 PM Pacific Time. The ring of fire is expected to last four and a half minutes.
Solar eclipses occur on Earth as a result of the moon passing directly in front of the sun, whereby the moon partially or fully blocks the sun. In a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses only part of the Sun is obscured.
If the Moon were to be in a perfectly circular orbit close enough to the Earth and in the same orbital plane as the Earth is to the sun, there would be total solar eclipses every single month. But the moon’s orbit around the earth is elliptical and angled at 5 degrees to the Earth’s orbit around the sun, so its shadow at new moon (when the moon is fully round) often misses the Earth. the orbital planes cross each year at a line of nodes resulting in at least two, and up to five, solar eclipses occurring each year; no more than two of which can be total eclipses.