Comet 19P/Borrelly will make a good target from the Northern Hemisphere
Comet 19P/Borrelly is potentially visible using binoculars and should be a great target for small telescopes. It joins comet C/2019 L3 ATLAS in January’s night sky to produce a great cometary feast.
The comet is currently moving northeast and brightening as it goes. Starting the month in Cetus, not far from mag. +2.0 Deneb Kaitos (Beta (β) Ceti), the comet remains inside the Cetus boundary for much of the month, managing to slip into Pisces at the end of January. On the evening of 1 January, 19P sits 5˚ west of Deneb Kaitos, visible after evening twilight has subsided and true darkness has descended, just after 18:00 UT. This places the comet slightly to the west of south, around 19˚ up as seen from the centre of the UK.
By the month’s end, 19P is predicted to have brightened to mag. +8.9 and, located 3˚ southwest of mag. +4.9 Mu (μ) Piscium on the evening of the 31st, its altitude will have improved too, the comet appearing about 34˚ up as true darkness arrives. This is despite the region of sky containing Borrelly having naturally drifted further west of south as darkness falls.
We know about the comet thanks to a visit by the Deep Space 1 probe in 2001. Its nucleus is 8km x 4km x 4km and it follows an elliptical orbit, which takes it out as far as 5.83 AU from the Sun and in as close as 1.35 AU, the distance the comet will be from the Sun at perihelion on 1 February. It takes Borrelly 6.8 years to make one orbit. Its closest approach to Earth is 55 million km.