The Evening Sky in May 2016
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 May 2016
Three bright planets and the brightest stars share the evening sky this May. Soon after sunset golden Jupiter appears in the north and orange Mars in the east. As the sky darkens Saturn appears below Mars and Sirius, the brightest star, appears northwest of the zenith. Canopus, the second brightest star, is southwest of overhead. Midway up the southeast sky are 'The Pointers', Beta and Alpha Centauri. Soon after dusk Arcturus appears in the northeast, often twinkling red and green as the air breaks up its orange light.
Below Sirius are bluish Rigel and reddish 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. Sirius, 'the Dog Star', marks the head of Canis Major the big dog, now head down tail up in the west.
Crux, the Southern Cross, is southeast of the zenith, to the right of 'The Pointers'. Alpha Centauri, the brighter Pointer, is the closest naked-eye star, 4.3 light years* away. Beta Centauri, like most of the stars in Crux, is a very luminous blue-giant star hundreds of light years away. Canopus is also very luminous and distant: 13 000 times brighter than the sun and 300 light years away.
Orange Antares, right of Mars, marks the body of Scorpius, the Scorpion. Antares means 'rival to Mars' in Greek for the planet and star are often similar in colour and brightness (but not now). Antares is a red-giant like Betelgeuse; 600 light years away and 19 000 times brighter than the sun.
Arcturus, in the northeast, is the brightest red star in the sky but, at 37 light years, is much closer than Antares. It is about 120 times brighter than the sun.
The Milky Way is brightest in the southeast toward Scorpius and Sagittarius. In a dark sky it can be traced up the sky past the Pointers and Crux, fading toward Sirius. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. The thick hub of the galaxy, 30 000 light years away, is in Sagittarius. The nearby outer edge is by Orion where the Milky Way is faintest. A scan along the Milky Way with binoculars shows many clusters of stars and some glowing gas clouds, particularly in the Carina region and in Scorpius.
The Clouds of Magellan, LMC and SMC, are midway down the southern sky, easily seen by eye on a dark moonless night. They are small galaxies. The Large Magellanic Cloud is 160 000 light years away and is about 5% the mass of our Milky Way galaxy. The Small Cloud is around 200 000 light years away and 3% the mass of our galaxy. That's still many billions of stars in each.
Mars is closest to Earth at the end of May. It will then be 75 million km away. It is a small planet, half the diameter of Earth, so never looks big in a telescope. At this approach one needs to magnify Mars 100 times to make it appear as big as the full Moon does to the naked eye. We catch up on Mars and pass it by every 26 months. At the next pass or 'opposition' in 2018 Mars will be 58 million km away and appear 1/3rd bigger than now.
At the beginning of May Jupiter sets around 2 a.m., reducing to around midnight by month's end. Jupiter is 750 million km away. It is always worth a look in a telescope. Its four big 'Galilean' moons look like faint stars near the planet. One or two can be seen in binoculars. All four are easily seen in any telescope magnifying 20x or more. Sometimes one or more of the moons will be invisible as they pass in front of, or behind, Jupiter. The Moon will be near Jupiter on the 15th.
Saturn is a great sight in any telescope with its rings now near maximum tilt. It is 1360 million km away. Titan, its biggest moon, orbits four ring diameters from the planet. Three or four smaller moons can be seen in larger telescopes closer to Saturn.
*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 for the sun's light to reach the nearest star, Alpha Centauri.