Why can't Venus or Mercury cause a solar eclipse?
Venus and Mercury are far away so they only appear as a point of light
in the sky which isn't big enough to cover up the whole sun. Venus and
Mercury do go in front of the sun sometimes, and astronomers call these
transits, and observe them as well, although they just look like a dot
going across the sun, instead of a disk like the moon.
Can an asteroid cause an eclipse?
Asteroids are also too small and too far away to cover up the whole sun,
but they can transit the sun as well.
Why is it that you can only see the corona during an eclipse?
The corona is very faint and wispy, about a million times fainter than
the surface of the sun, so we can't see it normally because the rest of
the sun washes it out. It's the same reason you can't see stars during
the daytime - they're just too faint compared to the light of the sun,
but they're always there, just like the corona is always there, even though we can't always see it.
Did anyone see the Hale-Bopp comet during the eclipse?
I don't think so. Hale-Bopp is very faint right now and the sky doesn't
get very dark during an eclipse, so it's still better for astronomers to
look for it at night.
How long does it take for a comet to pass Earth, go around the Sun, and pass Earth again?
Some comets come back after only a few years, like comet Encke, while
others like comet Halley or Hale-Bopp take much longer. How far away they
go from the sun determines when they will come back. Some comets never
return - they just keep heading out into space!
Sincerely,
Steve Martin
Instructor, Dept. of Astronomy
Williams College
