The Night Sky in April
The brilliant planet Venus is now clearly visible low in the western part of the sky approximately 45 minutes after sunset. Look out for a pairing between Venus and a thin waxing crescent Moon on April 17. From April 22 to 26, Venus appears south of the Pleiades, or Seven Sisters, open cluster. If you locate the planet an hour after sunset between these dates, stay with it as the sky darkens. The dimmer Pleiades should then pop into view towards the right of the planet as seen from the UK.
Mars and Saturn can be seen together in the early hours. Both planets are located just north of a pattern of stars known unofficially as the Teapot asterism, part of Sagittarius, early in the month.
On the nights of April 21/22 and 22/23, keep a look out for Lyrid meteors. Although the rates from this shower aren’t spectacularly high, the shower’s radiant – the area of sky where the shower meteors appear to emanate from – is optimally positioned from the UK. A Lyrid meteor will appear to come from west of the bright star Vega in the constellation of Lyra the Lyre.
The April night sky is “dominated” by the stars of spring. These lack the vibrancy of those visible during winter and summer because we’re looking into deep space in a direction perpendicular to the plane of our Milky Way galaxy.
The two largest constellations are visible around 1am BST. These are Hydra and Virgo. Hydra the Water Snake, is the largest by area occupying 1,303 square degrees, or around one thirty second of the entire area of the sky. It does this in a very linear fashion, snaking across the sky for around 100 degrees. If you’re unfamiliar with the degree measurement scale, your hand at arm’s length provides a reference. Outstretched, the distance between the tip of your thumb and little finger is about 25 degrees, so Hydra is four times this. Despite Hydra’s size, it contains only one middle bright star. This is known as Alpha Hydrae or Alphardor “solitary one”. The rest of the pattern consists of dim stars forming the rather indistinct body and head of the water snake.
Virgo the Virgin is the second largest constellation by area containing 1,294 square degrees. Although just 9 square degrees smaller than Hydra, Virgo is far more distinctive. Follow the arc of the familiar Plough’s and you’ll eventually arrive at the orange coloured star Arcturus, the brightest star in Bootes the Herdsman. Keep the arc going and you will arrive at the pure white star Spica, the brightest in Virgo. Move your gaze between Arcturus and Spica and, although subtle, the colour difference is most obvious.
Spica sits at the bottom of Virgo. To the northwest is a large semicircular bowl of stars. Spica and the bowl pattern resemble a capital Y. North of this is the faint but curious smattering of stars that forms part of the constellation of Coma Berenices, or Queen Berenices’s Hair. The faint stars here belong to an open cluster known as Melotte 111 and appear to shimmer from a dark sky location.
The region between Melotte
111, the Bowl of Virgo and the star Denebola, which marks the end of Leo the Lion’s tail, is known as the “Realm of Galaxies”, a window into the Virgo and neighbouring Coma Superclusters. The Virgo Supercluster contains some real monsters. One of the largest being Messier 87, a giant elliptical galaxy estimated to contain a trillion stars with a mass equivalence of 2,600 billion Suns; approximately twice the mass of the Milky Way galaxy.