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.
Neptune reaches opposition on 10 September 2019 having returned to Aquarius, the constellation in which it was discovered in 1846. We show you how to locate the outermost planet using binoculars, a task made easier this month due to Neptune’s close passage to naked-eye star phi (φ) Aquarii on 6 September.
Mercury attains a greatest easterly elongation of 19 degrees from the Sun on 1 April. This solar separation combined with a favourable inclination of the ecliptic to the western horizon an hour after sunset, means that the period 25 March to around 8 April offers the year’s best evening showing of the innermost planet for Northern Hemisphere observers.
There’s strong new evidence that an undiscovered large planet exists on the fringes of our Solar System, according to two Caltech scientists who have looked at the odd behaviour of numerous distant Kuiper Belt Objects.