Page 77 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

WHAT TO SEE

EARTHSHINE

The Sun is the main object that lights
BY DAY BY NIGHT the Moon, but Earth also has an
effect. Our planet is over 3.5 times the
diameter of the Moon, so we refl ect
more light onto its surface than the
Moon gives us when it is full. This is
called earthshine and it can be seen
as a faint glow on the unlit part of the
Moon when it is a thin crescent (before
and after a new Moon).

Contrary to popular myth, The full Moon refl ects the Sun’s
the Moon does come out during light and has no illumination
the day of its own

gets fi ltered through Earth’s the Moon is not full, as its light
atmosphere. All the particles washes out most nearby stars.
that make this up scatter the The passing of the Moon in
blue light, which leaves mostly front of the star or planet,
red light to reach us when blocking it, is known as an
we’re watching the spectacle occultation and these are listed
on the ground. in the handbook of the British
Astronomical Association. If
A MOVING MOON you’ve never seen a star being
As for the Moon’s own travels, blinked out by the Moon, then
try and fi nd a star very close to you have an assignment – go
its left side. An hour later the out and see one! Even better is a
Moon will have passed over the planet: Venus or Saturn are my
star, which should now be sitting favourites. Saturn is especially
to the Moon’s right. The Moon good: with a scope you can
may not completely cover the watch as the rings are slowly
star, sometimes the star will just covered by the Moon, dipping
graze its top or bottom. You’ll in and out of the lunar valleys
have more success seeing this if before fi nally disappearing.

First
OF THE MOON Waxing quater Waxing
gibbous crescent
identical phase, for example half Moon to half Moon). Phase of the
The Sun is always shining on one half of the Moon Moon visible
from Earth
– how much of the lighted side we see depends on
where the Moon is in orbit around Earth. The new
Moon happens when the Moon sits between us and
the Sun, and so the far side is lit (this is also the only Earth
time a solar eclipse can occur).
As the Moon moves around Earth and each day Full New Sun
passes, we see more and more of its lighted side, Moon Moon
a waxing (growing) evening crescent fi rst, then half
Moon, waxing gibbous and fi nally full Moon. At this The Moon’s
point, the Moon sits on completely the opposite side of path around
the Earth
the sky to the Sun. Now everything reverses and the Waning Waning
waning (shrinking) phases go through gibbous, half gibbous Third crescent
and waning morning crescent, fi nally back to new. quater

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