ASTRONOMY: There is always the moon …



Over the past month, amateur visual and photographic astronomy has been difficult. During the day, you may have noticed that, even on the clearest days, the sky was often not the blue you would expect, but blue mixed with brown – smoke! The fires in California and Oregon generated so much smoke that even here in Arkansas, seeing objects in the night sky, as well as trying to photograph them, was very difficult.

But – there is always the moon. As I write these lines towards the end of September, it is a clear night and the night of the full moon for this month. It is easy to observe even in bad weather and can be very dramatic even with a small telescope.

An ongoing debate among astronomers is the question of why the moon is so large compared to the Earth. If you look at the sizes of other moons in the solar system and compare these sizes to their primaries, such as Jupiter, Saturn, Uranus, and Neptune, you can easily notice that the moons of these planets are tiny compared to the sizes of the planets. around which they revolve. One prominent theory is that in Earth’s past, Earth was struck by an object the size of today’s Mars. The remaining debris from this collision is believed to have melted into our moon. Interesting …

Scientists believe that there were two very different eras in the geology of the moon. At one time, the moon was very heavily cratered. The moon probably acted as a sort of shield, preventing early Earth from being as cratered with craters as the moon was. Earth had a share of meteor craters, but the combination of weathering, water flow, and tectonic activity buried many craters on Earth that we could see today.

At another time in the history of the moon, there was great volcanism and lava flow. On a full moon night, we can see, with the naked eye, places where the moon appears quite white and other, darker areas, where the moon is dark gray. If one looked at the moon even through a small telescope, one would see that some of these darker areas are indeed dark – in some places almost black. These dark areas were considered by the Romans to be seas, but they are relatively smooth areas of lava flows or lava beds. Some of them were cratered by meteors that fell after the great period of volcanism and lava flow, but these dark areas are usually much smoother than the cratered areas.

I selected a photo that I took that hopefully shows both types of lunar terrain. Part of the photo shows a place on the moon where there are a lot of craters, and in the lower right of the image the dark lava, mostly basalt, has long since cooled down into a relatively smooth plain . The very large crater pictured is Clavius, one of the largest craters, measuring around 144 miles in diameter. If you look at it through a telescope, you can see crater upon crater – a story of massive bombardment carved into the surface of the moon.

Jupiter and Saturn are still high in the southern sky at night. Looking south around 9 p.m. or after, Jupiter will be the brightest object there, unless the moon is shining. Saturn will be much darker but quite visible “in front of” Jupiter as the Earth rotates and night progresses.

In October, we can have the clearest and most transparent skies all year round. This, of course, except rain, clouds, snow or smoke! Sometimes we even have so much dust in the air that it’s not worth trying to observe.

Nonetheless, go out and watch. As my father used to say, “You can’t catch fish if you don’t have a line in the water.” See what you can catch!

David Cater is a former faculty member at JBU. Email him at [email protected] The opinions expressed are those of the author.


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