Month’s planets

Heading into summer affords observers the opportunity to catch the fleeting planet Mercury

Mercury is one of the Solar System’s forgotten planets. It has only been visited by a few space probes, far fewer than almost all the other worlds whirling around our Sun, and although it has a few dramatic features on its surface, it has no vast canyons like Mars or towering mountains like Venus. However, Mercury has its own attractions and claims to fame. Its best known – a huge multiringed impact feature called the Caloris basin

– is one of the largest such features in the Solar System, and it has fascinating scarps and ridges on its heat-blasted surface.

A surprising number of stargazers and amateur astronomers have never seen Mercury. Many have not even tried to look for it, believing that it is too difficult to see because of its close proximity to the Sun. And while it’s true that most of the time Mercury is lost in the Sun’s glare, when it is best placed in the sky it is quite obvious to the naked eye – and it will be well placed this month.

At the start of our observing period Mercury will be very low in the west-northwest right after sunset, too low to be seen and setting just 20 minutes after the Sun. As the days pass it will climb higher, becoming more easily visible. It will pass brighter and more obvious Venus on the evenings of 24 and 25 April – this will be a good time to look for it in binoculars, once the Sun has set, of course. By 1 May Mercury will have moved so far from the Sun that it won’t set until an hour after it. On the evening of 4 May it will move past the Pleiades star cluster – another great opportunity to see it in binoculars – and after sunset on 13 May it will be shining in the twilight close to a beautiful crescent Moon.

At the end of our observing period Mercury will be setting almost two hours after the Sun, and will be an easy naked-eye object, looking like a copper-hued star in the deepening twilight. If Mercury doesn’t jump out at you right away, don’t worry: many observers find it useful to scan the sky with their binoculars first, pinning-down its position in relation to trees or other objects on the horizon to make it easier to find when the sky is a little darker.