Star date: 01:23:99
Moon Gazing
The Moon is Earth's constant companion
in its journey around the Sun. Songs have been written about it, lovers
have gazed upon it's surface and 12 people have walked across its barren
surface. It is also nearly always the first object a beginning amateur
astronomer turns their sights towards.
This week it is nicely placed in the sky, and is at a
favorable phase to aid viewing. The Moon is going to be exibiting a waxing
gibbous phase on the night Tuesday,
January 26th. The word gibbous
means that three quarters of the Moon will be visible. Waxing denotes that
more of the Moon will be visible on the next night. Whenever the Moon is
in the waxing half of its orbit, the "right" hand side of the
Moon is visible, and there will be more of the Moon visible the next night.
When the Moon is in the waning half of it's orbit, there
is less of it visible each night, and we see the "left" hand
side of Earth's sole companion. More of the Moon will be visible each night
this week, but there is a price to pay. The craters will become harder
to see as the night progresses. This is due to the fact that as the Moon
approaches a full phase, the shadows created inside the craters become
smaller and smaller. Thus, they become harder and harder to see.
The Moon is about 3475 km (2170 miles) across. It also
orbits the Earth at a mean distance of 384,400 km (240,250 miles). This
means that the Moon appears to be about 1/2 of a degree across as seen
from the Earth. This is also about the same angular size as the Sun as
seen from Earth.
The Sun is much larger than the Moon, but the Moon is
much closer. When speaking of astronomy, many people tend to speak of one
object orbiting around another object. This, however, is more of a convienence
than an accurate statement. In fact, any two objects orbit around each
other, centered around an imaginary spot known as the barycenter. If the
two objects are the same mass, then the barycenter is right in the middle
between them. If one object is twice as heavy as another, the barycenter
is 2/3 of the way towards the more massive member. This is the same as
two children on a seesaw. If one child is twice as heavy as another, then
that child would need to sit half way towards the center of the seesaw
in order to make the seesaw work well.
At one time, the Moon was closer to the
Earth than it is now, and eclipses must have been much more common. In
the future, the Moon will be further away from the Earth than it is today,
and eclipses will become less common. This is due to the fact that the
tides on the Earth (and the tides of the Moons solid surface!) produce
heat. The energy for this heat has to come from somewhere, and that somewhere
is the energy in the orbit of the Moon.
One day, in about 10,000 years (and it will be a gradual
process), there will be no more solar eclipses. Solar eclipses being the
type of eclipse where the Moon blocks out the Sun. The other type of eclipse
(where the Moon often turns red as it hides in the shadow of the Earth)
is known as a lunar eclipse.
In all the centuries of debate, there has never been a
definite answer found for the question of how the Moon formed. It is possible
that the Moon formed when a young proto-Earth was struck by a large object,
possibly carving out a good size gouge in the Earth, perhaps the Pacific
Ocean. Another school of thought has the Moon forming at the same time
as the Earth from the same gaseous nebula. The problem with this idea is
that the Moon seems to be made of materials which are in many ways similar
to the materials in the crust of the Earth, but far different from the
materials which compose the core of the Earth. If the Moon formed at the
same time as the Earth, it seems likely that it would have the same composition
as the Earth, and this does not appear to be the case. However it formed,
it is always a treat to view, and is a lovely sight any night.
Clear skies, and good viewing.
"Understanding is joyous" - Carl Sagan
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