This graphic shows the appearance of the sky to the east-southeast at midnight for the beginning of May as seen from the heart of the British Isles. Arcturus, the brightest star in the northern celestial hemisphere, lies in the south almost 60 degrees, or three spans of an outstretched hand at arm’s length, from Vega in the east. Between and below these readily identifiable stars lie Rasalhague in the constellation of Ophiuchus and Rasalgethi in Hercules — two stars that will fit within a low-power binocular field of view. Rasalhague and Rasalgethi form an equilateral triangle with Comet 252P/LINEAR. See the detailed finder chart for this region below. AN graphic by Ade Ashford.On the afternoon of 21 March, Comet 252P/LINEAR brushed by Earth just 14 lunar distances away. In the intervening 5½ weeks the comet’s rapid ascent into northern skies has slowed owing to its increasing separation from our planet and as its motion describes a graceful clockwise loop through northern Ophiuchus. On 10 May, 252P reaches a peak northerly declination of +9.1 degrees whereupon it starts to head south, still following an almost circular arc, crossing the constellation border into Hercules on 26 May.
Now that this fascinating comet is visible from the UK low in the east before midnight, make the most of any clear skies you may have over the coming week to view 252P/LINEAR in a moonless sky before it fades below the range of binoculars and small telescopes. A periodic comet with a 5⅓-year orbit, 252P is currently about a quarter of an astronomical unit (~23 million miles) from Earth, but it can still be seen as a diffuse circular glow with minimal optical aid if you can find an observing location that is devoid of streetlights and other sources of artificial illumination.This detailed finder chart shows the nightly position of comet 252P/LINEAR at 12am BST over the coming week. It is a 4x enlargement of the wide-field view above and shows stars down to approximately magnitude +9. Rasalhague (α Ophiuchi) and Rasalgethi (α Herculis) lie 5¼ degrees apart. The red circle is five degrees in diameter, or the field of view of a typical 10×50 binocular. Click the graphic for a greyscale version of this finder chart suitable for printing and use outside. AN graphic by Ade Ashford.In the telescope, 252P presents a diffuse round coma about two-thirds of a degree across (somewhat larger than the full Moon in angular size) with virtually no tail. It’s still relatively bright, with an integrated magnitude of around +6.5, but fading. Astroimagers will readily capture its greenish-blue colour due to diatomic carbon (C2) molecules fluorescing in the sunlight.This daily topocentric ephemeris of 252P/LINEAR is computed for 12am BST on the dates shown for the centre of the British Isles. Observers in the UK with computerised GoTo mounts or digital settings circles can therefore enter the J2000.0 epoch coordinates directly. The stated integrated magnitudes are conservative estimates. Computing credit: JPL’s HORIZONS system.
Inside the magazine
Find out all you need to know about observing Comet 252P/LINEAR and the other solar system bodies currently in the night sky in the May 2016 edition of Astronomy Now.
Based on computer simulations, astrophysicists at the University of Bern conclude that comet 67P/Churyumov–Gerasimenko did not obtain its duck-like form during the formation of our solar system 4.5 billion years ago. Although it does contain primordial material, they are able to show that the comet in its present form is hardly more than a billion years old.
Rosetta mission scientist Matt Taylor says the science team is jubilant after the Philae lander captured the historic, first close up images of the surface of a comet and began returning data from its science instruments.
Barnard’s Star is a familiar name in both the history of astronomy and popular culture, but did you realise that it’s the closest stellar body to the Sun that you can see from the British Isles and similar latitudes? We tell you some fascinating facts about this famous runaway star and show you how to locate it.
