Comet 2020 F8 (SWAN) is now on show across the UK after rocketing northwards during April and earlier this month. Initially, it was hoped that the comet would reach a peak brightness of around magnitude +3, but this now looks optimistic as SWAN has stopped brightening and currently shines at around magnitude +5.8. This theoretically puts it comfortably in range of a pair of 10 x 50 binoculars, but the comet is immersed in the unwelcome glare of twilit skies soon after sunset and in the pre-dawn, especially so the further north you are in the UK. You’ll also need to find a decent observing horizon with views from the north-west around to the north-east.
The comet was discovered on by Michael Mattiazzo of Swan Hill, Victoria, Australia, in images taken on 25 March by the Solar Wind ANisotropies (SWAN) camera on board ESA and NASA’s SOHO spacecraft. It’s been present in Southern Hemisphere skies for some time, with astrophotographers producing some cracking images that show it sporting a superbly structured tail over five degrees in length. The most up to date light-curve indicates that the comet appears to have peaked in visual brightness at around magnitude +4.6 at the end of April and into early May, although CCD observations have the comet about a magnitude fainter at this time.
Comet 2020 F8 (SWAN) has already made its closest approach to Earth, when it passed about 85.6 million kilometres (0.575 astronomical units, AU, or 53.4 million miles) from us on 12 May. At the time, the comet was placed among the stars of Pisces but it subsequently moved quickly across Triangulum to enter Perseus on 18 May.
This evening (19 May), comet SWAN will be located under half a degree east of magnitude +4.7 star pi (π) Persei, which itself is just over two degrees south-west of Algol (beta [β] Persei, the famous eclipsing binary variable star). Visit the Minor Planet Center to generate the comet’s RA and Dec. for any time and date from your location. Visual observations have the comet currently shining at around magnitude +5.8 and it seems to be fading. Given a transparent sky, it should be visible through a pair of binoculars or a small telescope. Perihelion passage (i.e. closest approach to the Sun), at a distance of 64 million kilometres (0.43AU, or 40 million miles) from the Sun, occurs on 27 May.
Presently, the comet is circumpolar from the UK and is visible after sunset above the north-north-western horizon and in the pre-dawn north-north-eastern sky. It’s slightly better placed in the pre-dawn. At the beginning of nautical twilight (when the Sun is between 6 and 12 degrees below the horizon) tomorrow morning (20 May), at around 3.18am BST (02:18 UT) from London, SWAN lies about 10 degrees up, as opposed to barely four degrees at the end of nautical twilight at 10.35pm BST (21.35 UT).
The comet continues to head north through Perseus (reaching its most northerly point on 28 May), pulling it further out of the twilight mire. By 28 May, from London, SWAN sits about 10.5 degrees, and almost 13 degrees up, respectively, at 10.53pm BST (21.53 UT) and 3am BST (02.00 UT), the end and beginning of nautical twilight.
From northern England and especially Scotland, the bright twilit sky will significantly hamper observations. From Edinburgh, there is a short window this month where some degree of astronomical twilight persists (when the Sun is between 12 and 18 degrees below the horizon), so perhaps the best strategy will be to observe SWAN when the sky is at its darkest. Tonight, the sky is darkest at around 1.10am BST (12.10UT), when the comet sits around six degrees above the north to north-north-eastern horizon. Through to the end of May the comet’s position steadily improves, so that by the end of May it lies almost due north at an altitude of 12 degrees at around 1am BST. Thankfully, the Moon is new on 22 May and won’t start to interfere with evening observations until June.
By the start of June, SWAN is heading southwards and has moved into Auriga to lie just over a degree south-west of brilliant Capella (alpha [α] Aurigae). As June progresses, SWAN moves south-eastwards through Auriga, advantageously maintaining a presence in the post-sunset sky.