There’s a fine astro-photo opportunity on the night of 16/17 February when a first-quarter Moon passes under a degree south of Messier 45, the marvellous Pleiades open cluster in Taurus. As twilight fades, from about 6pm GMT, Taurus’ most westerly extremities, which includes the Pleiades, are very well-placed due south some 60° high. At this time the first-quarter Moon lies around 1.7° to the south-west of Alcyone (eta Tau, magnitude +2.8). Between 7pm and 1am GMT watch as the Moon approaches from the west, coming closest at about 9pm.
The marvellous Pleiades
The Pleiades open cluster, designated Messier 45, in Taurus is as good as it gets for night-sky eye candy. There are only a handful of deep-sky objects that come close to its fame and sheer majesty. For newbie and experienced observers alike, its impact is not limited in any way: it is easily visible to the naked-eye in most skies and looks superb through a pair of binoculars or a small telescope, while owners of larger telescopes can explore in detail the wispy blue nebulosity that blankets its bright stars and imagers can capture the full depth of its grandeur.
Counting Pleiades
How many individual stars within the cluster can you see without optical help? There are in fact ten Pleiads (as individual stars here are often termed) that shine brighter than sixth-magnitude. The five brightest Pleiades — Alcyone (eta [η] Tauri, the brightest Pleiad, Atlas, Electra, Maia, and Merope — range from magnitude +2.9 to +4.2 and should be immediately apparent, but most people report six or seven.
The cluster is traditionally known as the Seven Sisters, a reference to ancient Greek mythology, but as many as 14 to 18 Pleiads have been claimed by eagle-eyed individuals!
A binocular field of view easily encompasses M45, which, spanning two degrees across or four full moon-widths, is larger in angular extent than many expect. The wonderful view reveals some of the hundreds of fainter stars scattered around the brighter cluster members, including the aforementioned principal stars.
Beautiful blue nebulosity
Images of the Pleiades shows it’s substantially swathed in picturesque, wispy-blue nebulosity that’s courtesy of the blue-white light of Messier 45’s young stars being beautifully reflected and scattered by a huge, random dust cloud that the cluster is presently travelling through.
The brightest part of this nebulosity surrounds magnitude +4.1 Merope, the bright star at the southern corner of the ‘Plough’. Designated NGC 1435, a 250mm (ten-inch) telescope is a safe bet to pick it up under typical UK sky conditions.
