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June 27, 2022

Backyard Astronomy: The Moon

By Cheryl Haimann

The Moon is in a class by itself. Even if you can't recognize another feature in the night sky, you can recognize the moon. A two-year old can recognize the moon. It can be seen from any place on earth, and it is as easily visible in the daytime as at night. It is probably second only to love for inspiring poetry, songs, art, folklore, dreams, and even worship. Its influence on earth can be seen and felt daily in the changing tides. The Moon was one of the first objects Galileo saw in his telescope. It is the only celestial object humans have visited, and the quest for that achievement (forty years ago this year) was responsible for many of the scientific developments of the last half of the twentieth century.

So why do astronomers hate the moon?

Okay, they don't really hate it. But sometimes the Moon annoys them for the same reason everyone else loves it--it's big and bright. When the Moon is full, or close to it, its light washes out all but the brightest objects near it. The irony is that the moon is not really that bright. The Moon's light is reflected sunlight, but its dusty surface only reflects about 12 percent of the light that hits it. You can safely look at the Moon any time, even with binoculars or a telescope. At worst, you may end up with a little temporary "flashbulb eye".

One way you can prevent that is to observe the moon at dusk or dawn. When it is not completely dark, the difference in brightness the Moon and the surrounding sky is not so severe, and viewing is easier on the eyes.

The Moon is quite forgiving of low tech astronomy. Many features are visible to the naked eye, most notably the dark areas known as maria, or seas. Binoculars will give you a view of the lunar surface that would have thrilled Galileo, with craters and mountains evident.

If you have binoculars or a telescope, be sure to look at features along the terminator, the dividing line between dark and light. The angle of the sun on those areas (essentially the Moon's dusk or dawn) brings out the details of the features more dramatically than when they are facing the sun directly.

In fact, this changing light is one of the things that makes lunar observing so enjoyable. Not only are different features visible every day, but the same feature may look different from one day to the next as it moves into or out of the Sun's light.

If you really want to be like Galileo, try sketching your observations over several nights. This can be as simple as drawing the shape and location of the Moon at the same time every night. You can also draw maps of the features you see, again, noting how they may look different from one night to the next.

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Cool Thing of the Week: Lunation at APOD

APOD has an animation showing lunation, or a complete lunar cycle. This animation shows that, while the same side of the Moon always faces earth, a slight wobble means that we are able to see slightly more than half of the lunar surface during the course of its cycle.

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Article © Cheryl Haimann. All rights reserved.
Published on 2009-02-16
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