Being the planet closest to the Sun, Mercury (the Messenger of
the gods) guards its secrets very carefully. With a mean
heliocentric distance of just 0.387 AU (about 57.8 million km)
and a orbit time of just under 88 days, it is not very easy to
observe from Earth and never appears more than 27° from the Sun
(less than the angle made by the hands of a watch at 1 o'clock).
|Mosaic of Mercury| The main problem with observing Mercury from
ground-based telescopes is that because it never strays far from
the Sun, it can only be observed during the day, when scattered
sunlight impedes clear views of the planet, or just before
sunrise and after sunset, when the light we recieve from it must
pass through 10 times as much atmospheric turbulence as when it
is directly overhead. Unfortunately this means that even the
best ground based telescopes get a worse view of it than humans
can get of the moon with the naked eye each night. This has
obviously proved an obstacle to finding out much about Mercury,
and as such, for a