The #10 sight on our “Bucket List” for backyard stargazer was the dazzling globular cluster Omega Centauri, which hovers high overhead in the southern night sky this time of year.
Today, we move on to sight #9, one of the most moving and dynamic scenes you’ll ever see in a small telescope: the sun slowly rising over one of the Moon’s most spectacular craters.
And you can see it from anywhere on Earth once you know how, when, and where to look.
First, a little orientation…
Look at the Moon any night during the two weeks between its new and full phase. You’ll see a bright area and a dark area. An astronaut standing on the bright part of the Moon would enjoy lunar daytime. On the dark area, he would experience night. And along the boundary between the two, which is called the terminator, he would see the sun just rising over the lunar horizon.
Because of the sun’s low angle at lunar sunrise, our astronaut would see even the lowliest stump of a hillock casts a long, exaggerated shadow across the Moon’s surface. And we get the same view from Earth. Which is why the terminator almost always offers the most vivid viewing of the Moon’s mountains and ridges and craters. Even a small ridge a few hundred meters high, which would be invisible from Earth most telescopes, casts a shadow many kilometers long… big enough to glimpse in a small scope. And the bigger the hill, the bigger the shadow.
Of course, some lunar surface features cast more dramatic shadows than others.
Where the terminator crosses the dark, flat lunar seas (or maria), you see no shadows at all… just a bright side and a dark side. Not particularly exciting.
But when the sun rises over a lunar mountain range or walled crater, it casts an immense shadow. And it often illuminates higher elevations first, setting them apart from unlit lower-lying regions. You might, for example, see an illuminated mountain peak standing out like a candle flame from the lower-lying regions along the terminator. Very striking.
Perhaps no other lunar feature comes close to capturing the drama of a lunar sunrise than the immense crater Copernicus. A fairly young crater at just 800 million year old, Copernicus spans some 100 km just north of the lunar equator and south of the Mare Imbrium (see image below). The crater has tall, terraced side walls and a cluster of peaks near its center. So there are many hilly features which cast long shadows when the crater lies along the terminator.
The Moon as it looks nine days after “new” phase and five days before full, showing the crater Copernicus near the terminator.
Copernicus graces the terminator about nine days after new moon each month, and about five days before full moon. So it’s well placed for viewing in the evening… you don’t need to stay up late. And if the timing’s right, you can watch sunlight fan out over Copernicus during the course of an evening. It’s a stirring sight to see the crater’s walls and central peaks catch the sun’s first rays, followed by the low-lying crater floor.
And while you can certainly see the crater in binoculars, a telescope gives you a much better view. Since the Moon is bright, you can use high magnification if you have steady air. Try different eyepieces and magnifications to see what gives you the best view. The image at the top of the page gives you an idea of what you can see at 200-300x.
Like all lunar features, if you miss this sight one month, just wait 29 days to see it again.
Only 24 humans– all Apollo astronauts– have witnessed sunrise on the Moon close up. It will be a long time before anyone returns to the Moon. But with a small scope, from your backyard or balcony, you too can see a magnificent sunrise over the craters and mountains of the Earth’s nearest neighbor.
A grand sight for all of us to see, surely, before we “kick the bucket.”