Observing the Moon

Mike Swanson

The first object most of us saw through a telescope was the Moon.  The Moon is by far the largest object in the night sky and provides a great amount of detail with even modest optical aid.  The view changes from one hour to the next as the Moon slowly rotates and the line between light and dark - the terminator - crawls across the surface.  You can easily find enjoyment several nights each month by visiting the Moon.  In fact, the word month derives from the same root as moon and our measurement of a month is based upon the 29-day journey of the Moon around the Earth.

It is a common misconception that the best time to view the Moon is when it is full, but actually that is the least favorable phase.  The greatest detail is found along the terminator - the surface features extend long shadows as the Sun rises or sets upon them.  The landscape of the Moon offers craters, valleys, mountains and plains.  Literally thousands of features can be discerned in the eyepiece of a telescope.  You will likely find greater enjoyment if you can put names to those features.  For that, you will need a lunar map or atlas.  Orion Telescope (www.telescope.com) and Sky and Telescope (www.SkyandTelescope.com) are good places to go shopping.  You might also want to try the Virtual Moon Atlas (http://astrosurf.com/avl/UK_index.html) - a free lunar map program for Windows computers.

If you have even a modest pair of binoculars, take them out for a look.  You will need something to steady them upon - perhaps a pole or a swivel-head mop handle.  If you have a telescope, try all your eyepieces to see what features are visible at different magnifications.  With a telescope you can also make use a lunar filter; in fact, you will probably find it is absolutely necessary.  The filter reduces the amount of light that exits the eyepiece to a comfortable level that will allow you to concentrate on seeing more details.  Without a filter you will likely find the Moon so bright as to be painful.

When viewing the Moon, watch for smaller craters inside of larger craters.  Also, many larger craters have small peaks in them.  Some craters have lines of debris streaking away, evidence of the impacts that created them.  Watch for mountain ranges and other linear features.  Many of the longer features have terraced faces visible in moderately sized telescopes.  If you have an artistic talent, try sketching the features that you see.  Otherwise, keep track of your discoveries, entering them by name in your logbook.

Copyright 2002-2006,
Ryukyu Astronomy Club

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