نجوم و کیهان‌شناسی

If the plane of the Moon’s orbit was the same as that of the Earth’s orbit around

the Sun, we would get eclipses of the Sun at new moon and eclipses of the Moon

at full moon. Due to the fact that the Moon’s orbit is inclined by about 5°, the

Moon often passes above or below the Sun–Earth line, and eclipses happen less

often. It might be thought that the Moon would totally disappear during a lunar

eclipse, but light that is scattered through the Earth’s atmosphere falls on the

Moon so it can still be seen – though far less bright. If we observed the Earth

from the Moon during a lunar eclipse we would see that it would have a red limb

as the molecules in the Earth’s atmosphere scatters blue light more than red

(which also explains why the Sun appears red at sunset). The Moon thus takes on

a reddish hue at totality with the brightness and colour very dependant on the

amount of dust in the Earth’s atmosphere. Following a major volcanic eruption,

so little light reaches the Moon it can appear a very dull dark grey but conversely,

when the atmosphere is relatively free of dust, it can appear a beautiful orange

red (Figure).