Moonwatch - crater Copernicus
Image Credit:
NASA/GSFC/Arizona State University Type:Crater
Size: 90km (56 miles)
Age: Less than 1 billion years
Location: Latitude 9.7ºN, longitude 20ºW
Recommended equipment: 4-inch telescope
My choice this month is one of the most important and striking craters on the whole of the Moon: Copernicus, in the Oceanus Procellarum, slightly northwest of centre. It is easy to identify whenever it is sunlit, and it is at the heart of one of the two main ray-centres (see Glossary, page 105). Crater Tycho, in the southern uplands, is the other. Under high lighting, the Tycho and Copernicus rays are so dominant that they make other features difficult to locate.
Crater Copernicus is named after the great Polish scholar who showed that the Earth moves round the Sun, rather than being the centre of the Universe – but there is a story here, not without its amusing side. The main craters were named in 1651 by the Jesuit astronomer Giovanni Riccioli, who drew the first really useful telescopic map of the Moon. Not unnaturally he named prominent features after himself and his pupil Grimaldi, but he was no supporter of Copernicus, and continued to believe the old Ptolemaic geocentric theory of a stationary, motionless Earth. To show his contempt, he “flung Copernicus into the Ocean of Storms”. His plan misfired; the crater he chose is magnificent, and is often referred to as ‘the Monarch of the Moon’.
"Copernicus is bright because it is so young; it has not been darkened by the solar wind and micrometeorite bombardment."
Because Copernicus is not far from the centre of the lunar disc it is not appreciably foreshortened, and is on view for a good part of every lunation. It is 90km (56 miles) in diameter with high, beautifully terraced walls. There is no single central mountain, but there are several peaks and groups of hills near the middle of the floor, which is otherwise fairly level and has not been flooded with lava. It is fascinating to watch the progress of sunrise or sunset over the crater and the surrounding area; the whole scene changes dramatically over a very short period of time.
The rays extend for at least 805km (500 miles) across the surrounding plain, and they overlap rays coming from other craters, notably Kepler, so that they must be younger. Copernicus post-dates the Late Heavy Bombardment, and may well be less than a thousand million years old. The rays differ from those of the other major centre, Tycho, because Tycho’s rays are long, linear and regularly arranged, while those from Copernicus are less regular and give the impression of being tangential to the crater. There are small secondary craters, and the whole area is hilly.
Copernicus is bright because on the lunar timescale it is so young; it has not been darkened by the effects of the solar wind and micrometeorite bombardment. The rays are surface deposits, and do not show up until the Sun is well above their horizon.
Copernicus dominates the whole of this part of the Moon, but there are other notable features too. Well to the northeast of Copernicus, not far from the end of the Apennines, lies the 61km (38-mile) diameter Crater Eratosthenes, which is very like a slightly smaller edition of Copernicus, apart from the fact that it has no comparable ray system. Southwest of Eratosthenes we find Crater Stadius, which must have once been a grand formation, but has been so overwhelmed by lava that it has been reduced to the status of a ghost. The walls are traceable under suitable lighting conditions, but nowhere rise to more than a few tens of feet.
In 1966, when mapping the Moon from spacecraft had only just begun, an oblique view of Copernicus was shown in an image obtained by NASA’s Lunar Orbiter 2. It was widely acclaimed, and became known as ‘the Picture of the Century’. It is still well worth looking at, and it is easy to see why this crater deserves its nickname – the Monarch of the Moon.
This article appeared in the June 2010 issue of Sky at Night Magazine
Like this article? Why not:
