The Evening Sky in April 2016
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The Evening Sky in April 2016
Jupiter is the 'evening star', appearing in the northeast soon after sunset. The bright real stars, Sirius and Canopus, appear soon after. Reddish Mars and off-white Saturn appear in the southeast. Mercury might be glimpsed low in the northwest twilight mid-month.
A small telescope will show the disk of Jupiter with its four bright 'Galilean' moons lined up on each side. Binoculars, held steadily, will sometimes show one or two moons looking like faint stars close to the planet. Jupiter is 700 million km away mid-month. The moon will be near Jupiter on the 18th.
Sirius is the first true star to appear at dusk, midway down the northwest sky. It is soon followed by Canopus, southwest of the zenith. Below Sirius are Rigel and Betelgeuse, the brightest stars in Orion. Between them is a line of three stars: Orion's belt. To southern hemisphere star watchers, the line of three makes the bottom of 'The Pot', now tipped on its side. Below and right of Sirius is Procyon.
Mars, looking like a bright reddish-orange star, appears in the southeast around 10 pm NZDT at the beginning of the month. To its right is Antares, similar in colour but fainter. Creamy Saturn follows Mars about 40 minutes later, rising directly below Antares. By the end of the month both planets are up around the end of twilight. The moon will appear near Mars and Saturn on the 25th.
Mars will brighten steadily through the month as we catch up on it. Its distance shrinks from 118 million km away at the beginning of April to 88 million km away at the end of the month. It remains a small object in a telescope. At mid-month a telescope needs to magnify130 times to make Mars look as big as the Moon does to the naked eye. We pass 75 million km from Mars at the end of May.
Saturn rises after 10:20 pm NZDT at the beginning of April; around 7:20 NZST by month's end. It is straight below Antares. A small telescope shows Saturn as an oval, the rings and planet blended. Larger telescopes separate the planet and rings and may show Saturn's moons looking like faint stars close to the planet. Titan, one of the biggest moons in the solar system, orbits about four ring diameters from the planet. Saturn is1400 million km away mid-month.
Mercury (not shown) might be seen setting in the bright twilight mid-month. It looks like a lone bright star on the northwest skyline. It sinks back into the twilight in May as it passes between us and the sun.
Crux, the Southern Cross, is high in the southeast. Below it, and brighter, are Beta and Alpha Centauri, often called 'The Pointers'. Alpha Centauri is the closest naked-eye star, 4.3 light years (l.y)* away. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of l.y. away. Canopus is also a very luminous distant star; 13 000 times brighter than the sun and 300 l.y. away.
The Milky Way is brightest in the southeast above Crux. The Milky Way can be traced to nearly overhead where it fades. It becomes very faint in the northwest, right of Orion. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one.
The Clouds of Magellan, LMC and SMC are midway down the southwest sky, easily seen by eye on a dark moonless night. They are two small galaxies about 160 000 and 200 000 light years away.
Low in the north is the Praesepe cluster, marking the shell of Cancer the Crab. Praesepe is also called the Beehive cluster, the reason obvious when it is viewed in binoculars. Lower and further left are Pollux and Castor, the heads of Gemini the twins, making a vertical pair of stars. Though related in myth, the Twins are quite different from each other. Pollux is an orange star 31 times brighter than the sun and 34 l.y. from us. Castor is a hot white star about 47 times the sun's brightness and 51 l.y. away.
Venus is the brilliant 'morning star, rising due east about an hour before the sun.
*A light year (l.y.) is the distance that light travels in one year: nearly 10 million million km or 1013 km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes four years to reach the nearest star, Alpha Centauri.