Comet 2020 F3 (NEOWISE): a naked-eye comet visible in the pre-dawn sky

Comet 2020 F3 (NEOWISE): a naked-eye comet visible in the pre-dawn sky
By Mark Armstrong

Comet 2020 F3 (NEOWISE) is looking great in the pre-dawn sky at the moment, shining at around magnitude +1 and sporting nice tail of around a degree in length. Gerald Rhemann shot this striking image of the comet on the morning of 6 July at 01:12 UT from Jauerling, Lower Austria. He used a 200mm ASA Astrograph, at f/2.9, and a ASI ZWO 6200 camera for this LRGB image (five seconds for each RGB and three, five-sec exposure for luminance).

Comet 2020 F3 (NEOWISE) is putting on a fine showing in the pre-dawn sky northern sky after emerging intact from perihelion (closest point to the Sun), which occurred on 3 July when the comet passed 0.29 astronomical unit, or 43 million kilometres from the Sun. It was discovered by NASA’s Near Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft on March 27.

The flood of images taken post-perihelion show a healthy-looking comet punching through the strong twilit sky and sporting a tail about a degree long. Presently shining around magnitude +1, reports have it as a reasonably easy object to spot with the naked eye in a haze-free pre-dawn sky.

Look to the north-eastern horizon in the early hours to spot comet 2020 F3 (NEOWISE). This is the view at 3.30am BST from London (around 80 minutes before sunrise) when the comet lies in Aurigae, below brilliant Capella and second-magnitude Menkalinan (alpha and beta Aurigae) at about an altitude 8–9 degrees. All AN graphic by Greg Smye-Rumsby.In the small hours of 8 July, comet 2020 F3 (NEOWISE) is circumpolar (never-setting) across the length and breadth of UK. It’s visible for a while shortly after sunset too, but for the next few days your best chance of seeing or imaging it is to have to get up early to catch it in the pre-dawn sky. You’ll need to find an outlook with an unobstructed horizon from due north around to the north-east (the comet’s azimuth is between about 27 and 32 degrees).

By mid-month, comet 2020 F3 (NEOWISE) is reasonably placed in the north-north-western early-evening sky. This is the view from London at the end of nautical twilight at 11pm BST from London, when the comet lies in Lynx at about an altitude of 14 degrees.

By the beginning of nautical twilight (when the Sun lies between 12 and 6 degrees below the horizon), which occurs at 2.45am and 3am BST (01:45 and 02:00 UT) from Manchester and London (in Scotland, nautical twilight persists throughout the night), respectively, NEOWISE lies about six degrees above the north-north-eastern horizon. It’s located among the stars of Auriga, just under four degrees south-east of magnitude +2.6 theta Aurigae. Brilliant Capella, lying at just under 20 degrees altitude is a good guide for locating the comet. Look directly south towards the horizon to find theta (θ) Aurigae, and then to the left (east). Try sweeping with a pair of binoculars to find it and then see if you can see it without optical aid.

Owing to its diffuse nature, like a planetary nebula or galaxy, NEOWISE won’t be as easy to spot as the point-source brightness of a star of similar magnitude.

As dawn approaches, the comet climbs away from the horizon to lie about 12 degrees up by the beginning of civil twilight (when the Sun lies between 6 and 0 degrees below the horizon), which takes place shortly after 4am (03:00 UT) from London and Manchester, and around 3.40am BST (02:40 UT) from Edinburgh.

Follow the comet through the rest of July as it powers its way north-eastwards across Auriga and Lynx into Ursa Major. On 23 July it passes closest to the Earth at a distance of 0.69 astronomical units or 103 million kilometres.

As the month progresses, comet 2020 F3 (NEOWISE) improves in visibility across the UK, increasing in elevation as it moves north-eastwards through Auriga. Hopefully, it will hold steady in brightness, but there’s no knowing exactly how it will behave as it pulls away from the Sun. NEOWISE then becomes better placed in the early-evening sky; by 10 July at the end of civil twilight, it sits about nine to eleven degrees above the north-north-west horizon (at an azimuth of between 332 and 340 degrees).

By mid-month, comet 2020 F3 (NEOWISE) has moved into neighbouring Lynx and will have improved significantly in early-evening visibility, lying not far short of 20 degrees altitude in the north-north-western sky at the end of civil twilight (at about 10pm, 10.20pm and 10.40pm BST (21:00, 21:20 and 21:40 UT) from London, Manchester and Edinburgh, respectively. The comet has picked up speed in its motion across the sky as it heads towards closest approach to Earth, which occurs on 23 July when NEOWISE passes us at a distance of 0.69 astronomical unit or 103 million kilometres.

Although comet 2020 F3 (NEOWISE) can’t be ranked along the great comets of the past (yet…!), such as Hale-Bopp or 2006 P1 (McNaught), it’s one to enjoy as the first naked-eye comet of 2020 and an anecdote to the earlier naked-eye disappointments of comets 2019 Y4 (ATLAS) and 2020 F8 (SWAN).

This is Comet C/2020 F3 (NEOWISE) taken from Brancaster beach in Norfolk, UK, in the early hours of 6 July 2020. Both images were taken with a Canon6D camera, using a 100mm lens (wide shot) for a six-sec exposure and a 200m lens (closeup) for a four-second exposure. Images: Jamie Cooper.

July 7, 2020 at 11:09PM
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