This broad field of barchan sand dunes – dunes with crescent shapes – in the Olympia Undae region near Mars’ northern polar cap was imaged by NASA’s Mars Odyssey orbiter. The image, showing a small segment of the dune field, was taken during summer when the surface was free of frost. The dunes cover an area of some 470,000 square kilometres (181,000 square miles), larger than the U.S. state of California, and surround about a quarter of the northern polar cap. It is the most expansive continuous field of dunes on Mars.
See the Moon meet the Red Planet on the UK night of 23 August
Mars may be almost four weeks past opposition, but it’s still an imposing sight low in the southern sky around local midnight. But if you are in any doubt about identifying the Red Planet, the waxing gibbous Moon acts as a convenient celestial guide late into the UK night of Thursday, 23 August. See both the Moon and the Red Planet in the same field of view of low-power binoculars.
View the longest total lunar eclipse of the 21st century on 27 July
Friday, 27 July sees the second total lunar eclipse of 2018, which also happens to be the longest of the 21st century. Observers in Antarctica, Australasia, Russia, Asia, Africa, Scandanavia, Europe, Central and Eastern South America will see the event. The Moon rises at mid-eclipse as seen from the British Isles, some 6 degrees north of Mars at opposition.