Astrophotography
Mars and Venus in conjunction
THE INNER PLANETS Mercury, Venus and Mars are relatively fast movers against the fixed backdrop of the night sky. Unlike the more distant members of the Solar System, these rocky worlds tend to have more frequent encounters with other objects. When two objects appear close together in the sky, this is known as a conjunction. This month we have a meeting between Venus, Mars and – for two nights – a crescent Moon, providing a perfect opportunity to photograph something rather special.
Watching two or more bodies apparently come together in the night sky can be mesmerising. Venus and Mars will be best seen low in the west-southwest from 19-23 February, and they are a distinctively mismatched pairing: Venus is around mag. –4.0 at the time of closest approach, while Mars is a far more modest mag. +1.3. This means that Venus will be 132 times brighter than Mars.
Photographing the pair against a darkening twilight sky will produce a shot with two star-like dots. This can be done quite simply, using a camera and a lens with a focal length of at least 100mm attached to a fixed tripod. Use a remote shutter release to take shots without wobbling the camera, a mid-to high-ISO and a relatively short exposure.
It pays to be creative with your composition. Placing a foreground object in the view can help to make the final result more interesting to the viewer. This doesn’t need to be complicated, and something like a tree silhouetted against a not-quite-dark twilight sky can look amazing. Similarly, if you’re located in a town or city, a shot with everything lit and carrying on as usual below the celestial meeting above can add dynamism. The trick is to avoid having something too bright in the foreground that will simply overexpose the shot.
Another option is to stop down the camera lens. Internally, this is performed by aperture blades reducing the size of the hole that lets light through to the sensor. The construction of the blades means that typically, the hole isn’t perfectly circular but rather made up of very short straight edges designed to emulate a perfect circle. Through a stopped down lens, a longer exposure on a bright light source such as Venus can show a very pleasing and attractive starburst diffraction pattern.
Here, stopping down the lens will reduce the amount of light that enters the camera. Consequently, to get a decent result the exposure time has to be increased. This is where a driven equatorial mount comes in handy, because a fixed tripod will result in trailing.
If a fixed tripod mount is all that’s available to you, another interesting technique is to stop down the camera and set it at a low sensitivity. Using a lockable remote shutter to take a long exposure of the planets setting will render them as trails heading towards the horizon. If you simply want a static dots-in-the-sky type shot, our natural photo enhancer – the Moon – will be on hand to help out. On 20 and 21 February, the lovely sight of a thin waxing lunar crescent showing earthshine will provide a superb addition to the scene.