Now that the Moon is a waning crescent rising after midnight, observers in the British Isles can take advantage of at least three hours of darkness from 9pm BST to track down Comet Africano (C/2018 W2) at its closest and brightest as it speeds through the constellations of Pegasus, Pisces and Aquarius.
At 10:56 UT on 27 September, C/2018 W2 (Africano) passes just 0.494 astronomical units, or 74 million kilometres (46 million miles) from Earth. At this time the comet is moving against the stars of Pegasus at a rate of 3⅔ degrees per day, equivalent to the width of the full Moon every 3¼ hours.
Discovered almost simultaneously on 27 November 2018 by B. M. Africano with the Mount Lemmon 1.5-metre reflector and H. Groeller with the Catalina Sky Survey’s 0.68-metre Schmidt telescope (Africano’s report was submitted just 21 minutes earlier), C/2018 W2’s integrated magnitude is currently about +9 and may peak at about +8.5 over the coming week. Note that Comet Africano lies within a binocular field of view of outermost planet Neptune on the night of 3–4 October.
Having passed perihelion (closest point to the Sun) on 5 September, don’t miss any opportunities to view C/2018 W2 because it’s visiting the inner planets on a hyperbolic trajectory, meaning that it will never return to the Sun – unless its orbit is perturbed by the gravitational influence of a body in the outer Solar System in the distant future.
While you probably don’t relish the prospect of waking up in the small hours of most Monday mornings, you will want to set your alarm for 2am BST on Monday, 28 September for this month’s showstopper celestial event — a rare total lunar eclipse of an unusually large ‘supermoon’ visible in its entirety (weather permitting) from the British Isles!
The 12-day-old Moon lies in the same low-power binocular field as Neptune late into the evening of Thursday, 10 October 2019 when observers in the UK can find the pair highest in the southern sky against the constellation of Aquarius. The glare of the gibbous Moon will present a challenge, but well worth the attempt to find the outermost planet with modest optical aid.
Dazzling Venus and much fainter Mars have a close encounter with a young Moon in the constellation of Pisces at UK dusk on Tuesday 31 January. The trio form an equilateral triangle small enough to be encompassed by the field of view of a 7x binocular low in the west-southwest for a couple of hours from 7pm GMT.