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By Drew Farwell
It captured the imagination of mankind from the very beginning. Its light illuminated the darkness and eased our most primitive fears. On its surface our ancestors saw the faces of men, women and even animals. As our intellect evolved, the dream of a man in the moon gave way to more complex ideas. We watched in amazement as the moon went through its phases. It seemed bound to the Earth, and we to it. In the 5th century B.C. the ancient Greek philosopher Anaxagoras reasoned that both the Sun and the Moon were large spherical stones, and that the light of the moon was merely the light it reflected from the burning stone Sun.In the 2nd century B.C., Seleucus postulated (correctly) that the Moon’s mere presence regulated the tides of the oceans.
It is the Moon’s close proximity to Earth that allows us to study it with ground based telescopes in far greater detail than any other body in the solar system, including the gas giants like Jupiter (which is a staggering 300 times more massive than Earth, but resides as far as 576,682,809 miles away). Galileo and his telescope witnessed with amazing detail the enormous craters, mountains, valleys and plains that litter the lunar surface.
Just how bright is it? Well, to be sure it is the brightest object in the night sky. It takes up one half of one degree of the entire night sky with an apparent magnitude of approximately -12.74 when full. The Moon seems at times so bright and so close that we could almost touch it. In fact, we have.
At a mere 238,900 miles from Earth, the Moon is the only celestial body within the reach of manned space exploration today. It is the only celestial body aside from the Earth that mankind has ever set foot on. From a terrestrial point of view, 238,900 miles is a very large distance. The Earth has a circumference of 24,901 miles. This means that you would have to circle the Earth almost 10 times (at the equator) to equal a one way trip to the moon. It would be a daunting task for any who would try to attempt it. In cosmological terms though, often measured in light years (a light year is the distance light travels in a year - light travels at a fixed velocity of 186,000 miles per second, roughly 6 trillion miles per year) 238,900 miles seems far less daunting. In 1969 we left our footprints on the Moon and forever changed the course of human history.
Today, the moon remains a popular target for astronomers across the world. With the utilization of a moon filter, almost every type of amateur telescope from refractors and reflector to binoculars and catadioptric scopes can be used to observe and even photograph the moon. Do not overestimate the importance of a moon filter for lunar viewing. It is important that you realize that you are compressing the inches of light gathered by the aperture of your telescope down to your 7mm pupil. This can be almost blinding and will impair your vision during your viewing session long after you look away from the eyepiece. Additionally, having a filter will allow you see greater detail on the lunar surface in the form of increased contrast.
So here’s an idea of what you can expect to see when you find yourself at the eyepiece of a telescope that is focused on the moon.
To bring out the most detail, focus on the area where the light and shadow meet. This area is called the terminator and it will provide you the most detail for your observation. Due to this fact, the best lunar observation can be done closest to the Moon’s quarter phases when the terminator splits the moon into two equal halves.
The moon is one of the absolute best targets for astronomy outreach. It shows well even in less than ideal viewing and the amount of detail that can be shown during good seeing will take even the most hardened skeptic’s breath away. It is available year round, its phases illustrate fundamental cosmological concepts and it has fascinated mankind since the beginning of time.
The next time you look into the clear night sky, won’t you make your destination Luna?