BBC Sky at Night Magazine
…but will C/2019 Y4 Atlas shine brighter?
BEST TIME TO SEE: End of May
Comet C/2019 Y4 Atlas was the last comet discovery of 2019. It was discovered by the Asteroid Terrestrial-Impact Last Alert System (Atlas) on 28 December 2019 when it appeared at magnitude +19.6. In January this year, Y4 Atlas underwent an outburst, brightening by 100 times to 12th magnitude. This month, there’s a possibility that it’ll become bright enough to be seen with the naked eye although, as is fairly typical with comets, this will occur as it’s approaching perihelion and badly positioned in the sky.
Y4 Altas has an orbit not dissimilar to that of the Great comet of 1844 (C/1844 Y1). From the UK it’ll be best placed in the middle of May, passing closest to Earth on 23 May by a distance of 117 million km. If it follows its current brightness trend, it should appear around seventh magnitude on 1 May, approaching fourth magnitude mid-month. Throughout this period the comet will head south from Camelopardalis into Perseus, placing it in a low northern part of the sky for UK viewing. At 01:00 BST (00:00 UT) on 15 May it lies close to Mu (m), Lambda (l) and b Persei. Despite being low, the comet will be circumpolar for most of May, giving an opportunity to track it from evening into the morning. As ever with comets, their brightness can go down or occasionally up relative to predictions.