BBC Sky at Night Magazine

…but will C/2019 Y4 Atlas shine brighter?



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.

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Comet C/2019 Y4 moves down from Camelopard­alis to Perseus
▲ Comet C/2019 Y4 moves down from Camelopard­alis to Perseus

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