As the days lengthen and the nights shorten there is still plenty to see in this month’s night sky. The winter constellations will gradually disappear beyond the western horizon as the spring constellations of Leo and Virgo dominate our southern sky. Also, after a gap of a few months, shooting stars return in the form of the Lyrids meteor shower, which peaks on the night of 21-22 April.
This month, the sun sets around 8:30 pm and the stars and the constellations start to become visible from about 10:00 pm onwards. So, once it is getting dark, look directly above your head and you’ll see the Plough, which is an asterism that is familiar to a lot of people. This makes it an excellent starting point from which to navigate your way around the southern night sky.
If you trace a line from the Plough down to the southern horizon, you will find Regulus, the brightest star in the constellation of Leo (The Lion) about halfway down. This star is at the bottom of a backwards question-mark which is made up of a total of 6 stars and called The Sickle. This asterism is the back of The Lion’s head and the six stars in it are Epsilon Leonis, Mu Leonis, Zeta Leonis, Gamma Leonis, Eta Leonis, and Alpha Leonis. Follow a line left and slightly up from Regulus and you’ll come to Denebola. This forms the bright tip of The Lion’s tail and its name comes from the Arabic for lion’s tail.
Up from and to the right of Regulus, you will find Castor and Pollux, the two stars which mark the heads of the Twins, Gemini. The bodies of the Twins are the two lines of stars which extend towards Orion (The Hunter), which will be low on the horizon out to the west and will be best found by identifying Betelgeuse, the bright red star which forms the Hunter’s left shoulder at the top of the constellation.
Below and to the left of Leo is the constellation of Virgo (The Virgin), with its brightest star Spica sitting down towards the horizon. In some cultures, Virgo is the "Wheat-Bearing Maiden" or the "Daughter of the Harvest” and is depicted holding several spears of wheat in each hand and Spica is one of the ears of grain hanging from her left hand. If you can’t find Spica, try going back up to the Plough and follow the curve of its handle down through the very bright star, Arcturus and then further on down to Spica, which will be low in the sky.
Below Virgo, you will see the small constellation of Corvus (The Crow), which ranks 70th in size among the 88 constellations in the night sky. The four brightest stars in this constellation form a square asterism known as the Sail, or the Spica’s Spanker, because two of the stars point the way to Spica. It is an ancient constellation that has been known since the time of the Babylonians. They saw it as a raven, and it was sacred to Adad, the god of rain and storm. To the ancient Greeks, it was a crow sent by Apollo to fetch water. The raven wasted his time eating figs. After returning late, Apollo punished him by throwing him into the heavens. He was also condemned to endure eternal thirst. This is why the crow caws instead of singing like other birds.
If you are at a location with little or no light pollution, you may be able to pick out Hydra (The Water Snake), which wriggles along the southern horizon and is the largest constellation in the night sky. Most of its stars are faint, but Alphard, its brightest star, is quite easy to find if you look below and to the right of Leo’s brightest star, Regulus (See above). Alphard is from the Arabic for "the solitary one" as there are no other bright stars near it. You might also be able to pick out the head of the Water Snake. It is an almost square set of four stars about halfway between Regulus and Procyon, the brightest star in Canis Minor, which sits below Castor and Pollux.
This month’s full Moon is on 16 April, becoming 100% full at 7:55 pm. This means that it will appear full on the nights of 15-16 April, 16-17 April, and 17-18 April. It will rise in the east at about 7:00 pm on the 15 April, at about 8:30 pm on the 16 April (traversing the sky next to Spica) and at about 10:00 pm on 17 April. It is often called the Pink Moon because of the pink flowers – phlox – that bloom in early spring in North America. In other cultures, it is called the sprouting grass moon, the egg moon, and the fish moon.
The last quarter Moon is on 23 April and on the following nights from 24 to 27 April it passes below the planets of Saturn, Mars, Venus and Jupiter over on the eastern horizon at dawn. You’ll need a very clear horizon to see the Moon and a pair of a binoculars or a telescope to make out the planets more clearly in the twilight glow.
There is another new Moon (no moon) on 30 April.
This month there are no bright planets in the night sky at all this month and they are pretty difficult to see in the morning as well., with the exception of Uranus which, at a magnitude of +5.8 will be very difficult to see. Saturn, Mars, Venus and Jupiter are all in a line, rising just before the Sun over in the east at around 5:00 am. Saturn and Mars are furthest from the rising Sun, so you might be able to spot them, but the others are closer to the Sun and will most likely be lost in the twilight glow.
However, later in the month, Mercury will be in the evening sky and on 29 April it will be at its furthest from the Sun, making it the best time look for this typically difficult to find planet. Look over in the west from about 45 minutes after sunset and you may be able to spot it low down on the horizon before it sets at around 10:30 pm.
After several months without any major meteor showers, we have the Lyrid meteor shower this month. It starts on 15 April and reaches its peak on the night of 21-22 April, when its dust particles that originate from the comet Thatcher hit our atmosphere are expected to produce around 15-20 meteors per hour. However, a good number of meteors can usually be seen on the night before and the night after the peak. This year, the peak happens close to a last-quarter Moon that doesn’t rise until about 3:30 am, making it great for spotting any shooting stars because the sky will remain dark pretty much all night.
The meteors will appear to emanate from the constellation of Lyra (The Lyre) at a radiant point near Vega, the constellation’s brightest star and the fifth brightest star in the night sky. You will find Vega over in the north-eastern night sky from 10:00 pm, although you don’t need to look there to see meteors as they’ll appear across the whole night sky. Start looking for them from about 10:00 pm as that is when the radiant point is above the horizon and bear in mind that the higher the radiant point gets in the night sky, the greater the number of meteors you should see.