Fresh off all the talk of the April 15, 2014 lunar eclipse seen in the western hemisphere comes the April 29, 2014 annular solar eclipse. What is an annular solar eclipse?
First, a solar eclipse occurs when the Moon is positioned directly in front of the Sun, casting a shadow on the Earth. The Moon is smaller than the Earth, so the Moon's shadow cast on the Earth is much smaller than the Earth's shadow cast on the Moon during a lunar eclipse. Thus solar eclipses have a very short duration and you must be at a specific location on Earth to see the eclipse.
Second, the Moon's orbit around the Earth is slightly elliptical. Thus the Moon is a bit farther away from the Earth at times. When it's a bit farther away at the same time the Moon is aligned with the Sun and the Earth, the size of the Moon in the sky is slightly smaller than the size of the Sun as seen on the sky. Thus the Moon doesn't block all of the Sun. The Moon blocks the interior disk of the Sun but not the outer ring of the Sun's disk. This is an annular eclipse.
Tomorrow, April 29, 2014 at just a couple of minutes before 6 AM EDT, an annular solar eclipse is observable from parts of Earth. If you live in Antarctica or the eastern part of Australia, you'll be in position to see this eclipse. No such luck for those elsewhere in the world.