Moon tour

Our destination this month is the star of one of the most famous sci-fi films ever made…

Destination Harpalus this month as you look upon a feature that's also a film star

This crater was the uncredited star of a film that was released 18 years before 2001: A Space Odyssey and stunned audiences with its realistic depiction of space exploration – Destination Moon.

Of course, many lunar features and landmarks have been featured in science-fiction films and TV shows over the years. Some of the very first science-fiction films were silent movies that showed people visiting the Moon in glorified artillery shells fired from huge cannons, to meet either bizarrelooking aliens or dancing girls.

In the aforementioned classic 2001, astronauts excavated an enigmatic alien monolith from deep beneath the crater Clavius. In Star Trek: First Contact the USS Enterprise’s timetravelling First Officer Riker waxes lyrical to warp drive inventor Zefram Cochrane about gazing up at the terraformed Moon in his century and seeing the lights of cities shining there, and Lake Armstrong too. The Moon has even been visited by Spongebob Squarepants!

But in 1950 the film Destination Moon was the first to attempt to show the Moon, and the view from it, realistically, by featuring the stunning artwork and models of artist Chesley Bonestell. Many consider Bonestell to be the original – and still the best – ‘space artist’. Although his lunar landscapes were much more dramatic and jagged than the ones the Apollo astronauts would gaze out on and explore decades later, they were still far more realistic than anything painted or shown on screen before.

When Destination Moon came out, 19 years before Apollo landed on the Moon for real, it took audiences on a thrilling mission to a real crater you can find for yourself on the Moon this month: Harpalus.

Sitting almost in the centre of Mare Frigoris or ‘The Sea of Cold’, a long, narrow stain just above the beautiful crescent-shaped Sinus Iridum in the far northerly reaches of the Moon, Harpalus is a physically small crater. Just 40 kilometres (25 miles) across and 3 kilometres (1.8 miles) deep, it is less than a third as wide as Copernicus and just one eighth the size of Clavius. Visually it is an unremarkable feature, not helped by the fact that its close proximity to the lunar north pole means that our view of it from here on Earth is greatly foreshortened, so it usually looks like more of an oval than a circular feature. However, sometimes the Moon’s libration – the axial wobble it has which causes it to occasionally but regularly tilt features around its limb towards us and then away from us again, meaning we can sometimes see a little way ‘around the edge’ of the Moon – sometimes causes Harpalus to be tipped towards us, allowing us a much better view. This month Harpalus will be well placed for observation.

Photos taken from directly above by orbiting probes show Harpalus is roughly circular, with shallow, terraced walls, a trio of low mountains rising up from its hummocky floor and a system of rays spreading away from it. In this way it looks rather like a smaller version of the ‘celebrity’ crater Copernicus. If you look at Harpalus through a small telescope around 30 and 31 August, when it is at its best, you will be able to see right into it and will be able to make out details on its walls and floor, including a small crater there.

So when can you see this crater at its best this month?

At the start of this issue’s observing period Harpalus cannot be seen; it is fully hidden in shadow. You’ll have to wait until the evening of 22 August to see it emerging from the darkness, as the terminator passes over it and allows the Sun to shine on its raised rim again.

By the evening of 23 August the crater will be in full sunlight and very easy to see in a small telescope. It should even be visible – just – through a good pair of binoculars.

The crater will remain fully illuminated until 4 September, when the terminator will return and begin to sweep back over it again, cutting off the sunlight. By the evening of 5 September Harpalus will be out of our view once more.