How is the number 400 significant to Bailey’s beads?

looney_tunes

"Near the beginning and end of total solar eclipse, the thin slice of the Sun visible appears broken up into beads of light. These lights are called Baily's Beads after the British astronomer Francis Baily who discovered them. They occur because the edge of the Moon is not smooth but jagged with mountain peaks. ... It is one of the most remarkable coincidences of nature that the Sun lies approximately 400 times as far away from Earth as does the Moon, and the Sun is also approximately 400 times as large in diameter as the Moon. As a result, as seen from Earth, the Sun and the Moon appear to be nearly the same apparent size." http://www.crystalinks.com/eclipse.html Sep 07 09, 3:00 AM

edmund80

Correct. Since they both appear about the same size, the moon neither overwhelmingly obscures (no Bailey's beads) nor appears too small for the sun, (which in that case would form a bright ring around the moon). "The moon's diameter is about 400 times smaller than that of the sun, but it is also about 400 times closer. As a result, both the moon and the sun appear about the same size in the sky. Consequently, when the moon goes in front of the sun, it blocks that everyday sun, cutting the sunlight reaching us on Earth. If the Earth, moon, and sun are perfectly aligned, when the moon completely blocks the sun we have a total solar eclipse....Just before the moon entirely covers the sun, the sky darkens so much that the reddish solar chromosphere and the pearly white solar corona become visible. Since the moon's edge is irregular, a few beads of bright sunlight come through the valleys between the mountains on the moon, and are called Baily's beads. The last Baily's bead seems so bright compared with anything else in the sky that it is known as the diamond ring effect. The Baily's beads last less than a minute and the diamond ring effect lasts only a few seconds." http://knol.google.com/k/jay-m-pasachoff/eclipse/IDZ0Z-SC/wTLUGw# Sep 07 09, 10:40 AM