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THE NIGHT SKY FOR APRIL 2015

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during April 2015.

Orion is sinking in the west as darkness falls, followed by Gemini and its bright stars Castor and Pollux. Further towards the south is the faint constellation of Cancer. It contains the Beehive Cluster, an open star cluster visible in binoculars, and currently plays host to the planet Jupiter as well. Leo is due south in the evening, with its bright star Regulus. Nearby, in Virgo and Coma Bernices, is an area called the Realm of the Galaxies. In this region, an 8" telescope can pick out a number of galaxies that are part of the Virgo Cluster, the largest cluster of galaxies in our local universe and itself part of a much bigger supercluster. Higher up is Bootes, with its bright star Arcturus, and overhead is Ursa Major. Later in the night, Lyra and its bright star Vega rise in the north-east.

The Planets

  • Jupiter, two months past opposition (when it was opposite the Sun in the sky), is still high in the south-west in the evening. During April, it dims from magnitude -2.3 to -2.1 and shrinks from 41.5 to 38" across. As it switches from westward (retrograde) to eastward motion this month, it remains in Cancer and moves very little relative to the stars. A small telescope can reveal the equatorial bands, Great Red Spot (at certain times) and Galilean moons.
  • Saturn rises in the evening, a little earlier each night, and lies close to the left-hand star of the fan of Scorpius. It brightens from magnitude +0.3 to +0.1 and grows from 17.8 to 18.4" in diameter during the month. It reaches 22 degrees' elevation when due south in the early hours of the morning, and the ring system is inclined at 25 degrees to our line of sight.
  • Mercury reaches superior conjunction (behind the Sun in the sky) on the 10th, and remains invisible until around the 19th, when it appears low in the west-north-west about 45 minutes after sunset. Shining at magnitude -1.4, it climbs higher each evening on its way to eastern elongation (its furthest from the Sun in the sky) on the 7th of May.
  • Mars, ever-present in the evening sky for many months, is finally disappearing into the Sun's glare. Lying close to Mercury from around the 19th to 24th, it has an angular size of 4" and so reveals no surface details to us here on Earth.
  • Venus blazes at magnitude -4, rising higher in the evening western sky as the month progresses. It moves from Aries into Taurus on the 7th, aproaching the Pleiades Cluster around the 13th. Its angular size increases from 14 to 16" during April, as its phase wanes from 78 to 68 percent.

Highlights

Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during April 2015

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Compiled by Ian Morison