WHAT'S UP

Stargazing by dark of the silvery moon

Graph showing Moon phases
Graph showing Moon phases

Things are looking dark this weekend.

The Central Arkansas Astronomical Society's stargazing calendar labels Friday and Saturday as "DSW" -- a dark sky weekend (see the link under "Events" at caasastro.org). While that sounds like it should be sad news for skywatchers, it's not ... unless what you want to look at happens to be the moon.

The calendar explains DSW as "weekends without a moon in the evening sky." Without the moon up there blaring about, other light sources could be easier to notice.

As Bruce McMath,

president of the society, puts it, the moon "hogs the sky by washing everything but the planets out. Meteors, satellites and all deep sky objects all but disappear, even many stars. Planets hold up though as they are fairly bright themselves, even though very small. So most observing amateurs do these days" is best done when there is no moon in the sky.

Where does the moon go? Unlike the sun, which always rises in the morning and sets in the evening, the moon rises and sets about 50 minutes later every day. For example, Sunday it rose about 2:59 a.m. and set about 5:11 p.m., but today it rises at 3:57 a.m. and sets at 5:57 p.m. So the moon could be "up there" in the sky in the day or the night.

But that's not the only reason for the dark sky this weekend. At 4:03 a.m. Thursday, the moon goes through its "new moon" phase.

As the National Aeronautics and Space Administration explains on its website StarChild, "we only see the moon because sunlight reflects back to us from its surface. ... If we could magically look down on our solar system, we would see that the half of the moon facing the sun is always lit. But the lit side does not always face the Earth! As the moon circles the Earth, the amount of the lit side we see changes. These changes are known as the phases of the Moon, and it repeats in a certain way over and over."

It takes the moon about 29.53 days to travel its elliptical orbit once around Earth. When the moon travels between us and the sun, the face of the moon that faces us isn't facing the sun. So it's dark, and we can't see it without special equipment.

Astronomers have chosen to mark this as the beginning of the lunar orbit -- aka the "lunar month" or "lunation" -- and so when all we see of it is just darkness, that's called the new moon.

Even though that new-moon moment of full darkness doesn't linger, it takes a few days before the relentless but gradual progress of orbit carries the moon far enough past our direct view of the sun that we are able once again see some of the moon's illuminated face.

Most of us learned these things in school ... unless we sat next to the boy who sat next to me in sixth-grade, who patiently explained that half of the moon is black, and that because the moon is a ball that rotates, the black side sometimes rolls into view.

That kid was incorrect. The moon is pretty much moon-colored all the way around.

ActiveStyle on 08/29/2016

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