The Evening Sky in April 2017
Download a PDF containing this chart, additional charts for specific areas of the sky and descriptions of interesting objects visible at this time of year.
The Evening Sky in April 2017
Jupiter is the 'evening star', appearing in the east soon after sunset. It crosses the sky through the night being due north around midnight and setting due west at dawn. Saturn rises in the southeast around 11 pm NZDT at the beginning of the month. It looks like a cream-coloured star, the brightest in that region but much fainter than Jupiter. It rises earlier through the month. By the end of April it is up soon after 8 pm NZST.
A small telescope will show the disk of Jupiter with its four bright 'Galilean' moons lined up on each side. Binoculars, held steady, will sometimes show one or two moons looking like faint stars close to the planet. Jupiter is 670 million km away mid-month. Jupiter is the biggest planet by far. Its mass is more than all the other planets combined. It rotates quickly, once in 10 hours. This stretches it out at the equator, giving it the oval shape. It circles the sun in 12 years so it shifts roughly one zodiacal constellation eastward each year. The Moon is left of Jupiter on the 10th.
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 is1430 million km away mid-month. The moon is left of Saturn on the 16th.
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.
Low in the northern sky is a fuzzy patch of light, 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. Praespe is 600 l.y away. Its stars are 600 million years old. The biggest and brightest stars in the original cluster have long ago burnt out so only the medium-brightness stars remain. This gives the cluster its uniform appearance in contrast to the much younger Pleiades/Matariki/Subaru cluster which still has several prominent stars.
Lower and further left are Pollux and Castor, the heads of Gemini the twins, making a vertical pair. 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.
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.
The brilliant planet Venus, not shown, moves quickly up the dawn sky after passing between Earth and Sun. It rises 70 minutes before the Sun on the 1st and three hours before the Sun by the 30th. It looks like a small crescent moon in a telescope. Venus is 52 million km away mid-month. At the end of the month Mercury begins a dawn sky appearance, below and right of Venus but much fainter.
*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.