In the heavens above us, two objects have always commanded humankind’s attention. The ever-constant
sun and the more mysterious moon. Each day the sun rises in the East and every evening it
sets in the West, remaining dependably consistent and unchanging. The moon, however, seems to
us more changeable and elusive as each month it performs its slow dance from new moon to full moon
and back again. Its ever-changing face has inspired myths and legends for thousands of years.
Let’s learn a little more about our nearest cosmic neighbor.
Although the distance changes slightly during its orbit, on average the moon is 384,400 km from the
earth. To give you an idea of how far this is, the same distance would allow you to travel
all the way around the earth almost 10 times! Because the atmosphere surrounding the moon is so
thin, the temperature on the moon’s surface can fluctuate wildly, from more than 250 degrees F
in the sun, to less than minus 250 degrees F, in the dark! In comparison the coldest temperature
ever recorded on Earth was minus 128 degrees F. Have you ever seen old videos of astronauts
jumping and bounding across the surface of the moon? They can do this because the moon has much
weaker gravity than the Earth, making objects weigh significantly less. In fact, a 200 lb man
here on earth would only weigh 33 lbs on the moon. If you ever stood on the moon you might
weigh less than a small dog does here on Earth! Perhaps you already know that the moon affects
our oceans here on Earth; creating high tides and low tides. This happens because of the
gravitational pull of the moon on the Earth. Interestingly, this affects not only the oceans;
in a smaller way it also affects lakes, the atmosphere, and even the rocks in our planet.
This gravitational pull has two fascinating consequences. The tidal
effect it creates is actually slowing the rotation of the Earth slightly,
lengthening our day by 2.3 milliseconds every 100 years. And,
during this process, the energy the Earth loses is transferred to the moon, which causes it to
move a little farther from our planet. Each year the moon travels about 3.8 cm away from the earth.
Like the Earth, the moon spins on its axis while it completes its orbit. Unlike the Earth,
its rotation and orbit both take the same amount of time: approximately 27 days. Meaning it takes
the same amount of time for the moon to spin around once as it does to orbit the earth once.
This is called a synchronous orbit and because of this the same side of the moon is always
facing the earth. Every time you see the moon in the sky, you are seeing the same side. Humankind
had never viewed the other side of the moon until 1959 when a space probe took pictures
of it for the first time. Because we can not see it, the far side is often referred to as the “dark
side of the moon” even though it receives just as much sunlight as the side that we can see.
Perhaps the most fascinating phenomenon happens during lunar and solar eclipses.
These events occur when the earth, sun, and moon are all in a straight line.
A lunar eclipse occurs when the earth lines up between the moon and the sun,
causing the earth’s shadow to fall across the moon. This can only occur during a full moon.
A solar eclipse can happen when the moon lines up directly between the Earth and the sun,
causing the moon’s shadow to fall on the Earth. This can only occur during a new moon.
It is a misconception that total eclipses are extremely rare, in fact they can happen
every year and a half, visible from somewhere on the Earth. However, they don’t often occur
repeatedly in a single location. The average length of time for a total solar eclipse to
occur in the same place is around 400 years! Although we have discovered many of the
moon’s secrets, our beautiful nighttime companion remains mysterious in many ways.
While scientists and astronomers continue to explore and study the moon,
we continue to admire its beauty and grace as it dances across the night skies above us.