By Alan Pickup
The fact that we have a respectable comet at last may be a case of third time lucky. After two disappointing comets this spring, Comets ATLAS and SWAN, we should be able to spot Comet NEOWISE during July as it moves through a region of sky that is circumpolar for Edinburgh, in that it is always above our horizon.
The comet, dubbed officially C/2020 F3 (NEOWISE), was discovered by NASA’s Wide-field Infrared Survey Explorer space telescope on March 27 and was watched from the southern hemisphere until it disappeared into the Sun’s glare in June. After our earlier cometary disappointments, there were fears that it, too, might fizzle out as it approached its perihelion, 44 million km from the Sun, on July 3.
Fortunately, it didn’t, and northern hemisphere observers were treated to a naked-eye object with an upwards pointing dust tail as it began to climb from the morning twilight in early July. Estimates of its overall brightness were generally in the range of magnitude zero to two.
Our chart plots its motion during July and shows the lower half of the sky between the NW and N in the middle of the night. During the period, Comet NEOWISE tracks from Auriga, across the dim constellation of Lynx and through the feet (paws?) of Ursa Major, below the Plough. Ticks along the track mark its daily position at midnight, while the magnitude values alongside the dates can be little more than a guess.
Although it is now receding from the Sun and is expected to fade, this is slightly countered by the fact that the comet is approaching the Earth and will pass 103 million km from us on July 23. Binoculars, or a low-power telescope, may give us the best views and it should be a tempting target for astrophotography.
Calculations of its orbit suggest that its previous perihelion occurred some 4,500 years ago and, given that planetary gravitational forces are giving it a slight kick this time around, it may not return to the Sun for another 6,800 years. So, catch it while you can.