The Night Sky in April
Jupiter dominates the night sky to the south around midnight. Its brilliant dot appears close to Spica, the brightest star in Virgo. The only thing to outshine Jupiter at night currently is the Moon and on the evening of April 10, Jupiter will appear just below the full Moon’s disc. Later in the month, a 14 per cent lit waning crescent Moon can be seen rising in morning twilight close to Venus. Look for them toward the east on April 23 from 5am BST. Venus is the brightest planet of all and now appears in the morning sky following solar conjunction last month.
The night sky at this time of year is a rather gentle affair. The brash winter stars have drifted out of view, their summer equivalents slipping on stage in the early hours. The main part of the night is dominated, if that’s the correct term, by the subtle constellations of spring. Several key patterns here are useful for navigational ‘star-hopping’.
The easiest place to start is the Plough, located virtually overhead. Its seven middle-bright stars form a distinctive pattern representing an old manual plough, complete with blade and handle. The Plough is sometimes referred to by its contemporary alter-ego, the Saucepan, making it easier to describe for a modern audience. In mythology the pattern represents the backside and tail of the Great Bear, Ursa Major.
The Saucepan’s curving handle arcs from the pan to arrive at the bright, orange-giant star, Arcturus. Follow the arc and you’ll eventually arrive at the contrasting whitecoloured star Spica, the brightest visual neighbour of Jupiter.
If you regard the Saucepan’s handle as part of a circle, the circle’s centre is marked by Cor Caroli, the alpha star of Canes Venatici, the Hunting Dogs, which comprises just two stars, Cor Caroli and Chara. So basically, just a line. Despite this basic structure, Canes Venatici is rich in deep sky treasures. Just inside its northern boundary, not far from the star Alkaid at the end of the Saucepan’s handle, is the beautiful whirlpool galaxy M51, visible through binoculars as a smudge. It is a face-on spiral galaxy presented so we see its bright star-forming arms like a cosmic catherine wheel.
Through telescopes a second galaxy smudge, NGC 5195, can be seen nestling against M51. Entwined by gravitational forces with the whirlpool, tidal interactions between both galaxies have stretched a bridge of stars between them. This is all happening some 37 million light years away.
Roughly midway between M51 and Cor Caroli lies M63, the Sunflower Galaxy. This is another spiral showing a tightly wound, flocculent pattern reminiscent of the seeds at the centre of a sunflower.
The imaginary line between Cor Caroli and Chara is a useful guide. Head north from its mid-point by a distance one-third its length, to locate M94, another face-on spiral galaxy visible with binoculars. Draw the line from Cor Caroli to Chara, turn 90 degrees heading north and move one line length in this direction to locate a star on the edge of naked-eye visibility. This is Y Canum Venaticorum, or La Superba. Binoculars or a telescope show it to have a superb red colour. Its informal title arises more from the appearance of its unusual carbonrich spectrum than its colour.
Finally, at the mid-point of the imaginary line between Cor Caroli and Arcturus, lies the impressive globular cluster M3. On the edge of naked eye visibility, this magnificent object is estimated to contain up to half a million stars.