WHEN: Throughout May, as described
Comet 21P/Giacobini-Zinner is currently a rather faint object tracking through the summer constellations of May’s early morning sky. It passes Earth by just 0.39 AU next month but despite this is only expected to
reach 11th magnitude. Things should improve later in the year when 21P may become bright enough to be seen with the naked-eye and, more importantly for the UK, will be well-positioned in the sky.
Back to this month and the comet starts its apparent journey against the background stars in the constellation of Sagitta, the Arrow. It should be around mag. +14.4 at this time so rather faint for visual detection but certainly a target for photography. It’s conveniently located close to the mag. +4.4 star Alpha (_) Sagittae at 01:00 BST (00:00 UT) on 1 May.
Next 21P tracks through to Vulpecula passing between the mag. +7.9 open cluster NGC 6830 and mag. +7.4 planetary nebula M27 – the Dumbbell Nebula – on the night of 10/11 May. It remains relatively close to M27 on 11/12 May providing a reasonably good photographic opportunity to catch comet and nebula together in the same shot, despite the comet’s dim 14th magnitude status.
Now the comet tracks north through Vulpecula and into Cygnus. It ends the month at mag. +12.8 lying 5° westnorthwest of the vast supernova complex known as the Veil Nebula.
This area of sky is rich in background stars thanks to the Milky Way. If you continue to follow 21P as it tracks up across Cygnus’s eastern wing, its most exciting encounter will come at the end of June when it skirts the eastern edge of NGC 7000, the North America Nebula.
Path of comet 21P/Giacobini-Zinner through May. Positions correct for 01:00 BST on dates shown