Pluto reaches opposition on 17 July 2021 and while technically within the boundary of the faint star-rich constellation of Sagittarius, the Archer, it’s located east of the Milky Way’s core region in a relatively barren area of sky just over 3˚ to the west of the mag. +8.6 globular cluster M75.
This makes a good challenge, to see if you can find and photograph Pluto in the night sky.
How to find Pluto
M75 is in a good position to be a starting point for finding Pluto. Consult our guide to the Messier Catalogue for RA and dec information.
Locate the cluster, then identify the stars to the west and southwest we’ve marked in our wide-field chart (above) as A, B and C. These are not too faint and shouldn’t pose any real issues.
Once you’ve located C, switch to the narrow-field chart (below). This chart is presented upside down to give you a telescopic view.
It shows stars down to mag. +14.0, which is likely to be below your telescope’s visual range unless you have really dark skies and a large scope over 375mm.
Although there have been claims of visual sightings of Pluto with smaller scopes, its low UK altitude probably means a camera setup is best for most people.
Take your time and attempt to identify the field stars shown in the narrow-field chart. The key here is to identify patterns that will make subsequent identification easier.
We’ve started you off with some distinctive ones you may find useful. The key star is mag. +7.8 D because it unlocks that large pattern near to the track of Pluto. If you can identify that pattern, Pluto should be relatively easy to find.
To image Pluto you’ll need a tracking mount with a relatively accurate drive and good polar alignment.
Dark frames – exposures of the same length as regular imaging shots, but with the lens cap on – are highly recommended.
Subtracting these from your regular ‘light’ frames will help remove noise (unwanted artefacts) that could be mistaken for Pluto.
If you’re planning to use a standard photographic lens, we’d recommend one with at least a 200mm focal length to provide sufficient image scale.
Take photos over the course of several nights, align them and flick between them. Do you see anything faint moving between frames? If so, you might just have caught yourself a dwarf planet.
Pete Lawrence is an experienced astrophotographer and a presenter on The Sky at Night.
This guide originally appeared in the July 2021 issue of BBC Sky at Night Magazine.