moon tour

As 2019 begins we pay our respects to ‘The Monarch of The Moon’

Copernicus is perhaps the most famous lunar crater, with beautiful impact rays to view

If you’ve ever seen a TV documentary about the Moon you’ll have seen a space boffin enthusiastically hurling a stone into a tray full of flour to demonstrate how impact craters are formed. Of all the hundreds of thousands of craters on the Moon, one looks exactly like the feature these dramatic demonstrations produces – a deep, sharp-edged pit, like a skull’s eye socket, surrounded by rays of debris.

Copernicus looks exactly like a lunar crater should: a great hole in the Moon with a dark, shadowed floor; a high, sky-scratching rim and lots of bright rays of dust and pulverised rock splashing away from it. Its nickname, The Monarch of the Moon, is entirely justified – no other crater comes close to it for sheer ‘wow’ factor when seen through a telescope eyepiece. That’s why Moon observers go back to it again and again and again, staring down into it every chance they get.

Copernicus is young in lunar terms. It was formed between 800 million and 1 billion years ago when the most advanced forms of life on Earth were essentially clumps of scum floating about in the oceans. One day the Moon was struck by a large asteroid, and the enormous explosion caused by the impact blasted a huge hole out of the area of the Moon we now know as Oceanus Procellarum, or the Ocean of Storms. The gaping pit left behind was almost four kilometres (2.5 miles) deep and more than 93 kilometres

(58 miles) wide. But the impact didn’t just blast out a hole; it sent enormous amounts of debris spraying out across the lunar landscape. Some of it fell back down to the Moon, leaving bright rays of ejecta on the landscape. The longest of these debris rays stretches for over 800 kilometres (50 miles) and can even be seen with the naked eye when the Moon is full, looking like white chalk lines drawn on the Moon’s darker face.

Seen through a telescope, or from an orbiting probe, Copernicus is roughly hexagonal in shape. Its walls are steep and terraced on all sides, giving the strong impression of a flight of stairs descending to its floor. High magnification shows where a wide shelf of rock has dropped down on the western side and also hints at landslides in several places. The northern part of the crater’s floor is quite flat, but the southern half is hummocky and hilly, pocked here and there with many smaller, much younger craterlets. In the centre of the crater a trio of mountains protrude from the lava plain, the tallest one, close to the western wall, has a peak which rises above the crater’s floor.

In November 1969 the Apollo 12 Lunar Module Intrepid set down on a landing site around 350 kilometres (217 miles) south of the huge crater. So precise was Intrepid’s landing that its crew, Pete Conrad and Alan Bean, were able to walk to the Surveyor 3 probe. After carefully removing pieces of the probe to be studied back on Earth, they collected samples of rock, some of which might have showered from the sky after the formation of Copernicus almost a billion years earlier.

So, how and when can you see this celebrity crater during this month?

At the start of our observing period Copernicus is hidden from view, deep in lunar night. You’ll have to wait until the evening of 14 January for your first sighting of it as it emerges from the darkness with the approach of the terminator, the line between night and day. As lunar dawn breaks over Copernicus’ eastern horizon it will come fully into view the next evening, the 15th, and from then until the 28th will be available for your attention with binoculars or a telescope. When the Moon is full on 21 January the crater’s system of rays will appear at their most dramatic and obvious. By the 29th Copernicus will be hard to see as the terminator sweeps towards it, and it will vanish from our view on the 30th, swallowed up by the bitter lunar night once more when the Moon will be a waning crescent glowing in the east before dawn.