PROJECT 3 Track a ‘wandering star’
Capture the planet’s meandering path across the sky
If you’re looking for a planetary imaging project that isn’t adversely affected by the low altitude of your target then why not try capturing a planet’s apparent motion against a dark, star-filled sky over the course of a few days or weeks. Jupiter, Saturn and Mars are perhaps the best targets for this as they move across the sky much more quickly than distant Uranus and Neptune.
Essentially what you need to do is record an image each night showing the planet – obviously – but crucially all the shots need to be centred on the same patch of starry sky every night. This is because later you’re going to composite together all the shots you get so that the only thing that ‘moves’ between them should be the planet.
For this to work you need to have a setup that can record the planet, and the stars around it, well enough that you can easily overlay and align the resultant images. In principle, you can achieve this with a DSLR and a fast lens on a static tripod, though you may find it easier – if you have the kit available – to mount a camera and lens (or wide-field telescope) on a tracking mount and capture longer exposures.
If you decide to use a longer focal-length lens or scope for this, the nightly change in position of the planet will be more obvious. But be aware that you might only record the planet at a handful of locations before it moves out of the fixed field of view. You may, therefore, find it best to use a lens of, say, 50-100mm focal length.
Once you’ve got at least several nights’ worth of shots, bring them into a layers-based image editor and load them as separate layers within one image file. It’s likely you’ll need to tweak each layer’s position and orientation so the star fields are aligned. Once they are, set each layer’s ‘blend mode’ to ‘lighten’, whereby the planet should appear in multiple places across the frame – its wandering across the sky revealed.
The retrograde motion of Mars can be shown in a montage of several images