The Evening Sky in May 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 May 2017
Two bright planets and the brightest stars share the evening sky this May. Soon after sunset golden Jupiter appears in the northeast. Beside Jupiter is Spica, the brightest star in Virgo. Below Jupiter, near the horizon, is orange Arcturus, the brightest star in the northern sky. As the sky darkens Sirius, the brightest of all the stars, appears midway down the northwest sky. Canopus, second brightest, is southwest of overhead. Midway up the southeast sky are 'The Pointers', Beta and Alpha Centauri. Well below them is the hook-shaped pattern of Scorpius with orange Antares marking the Scorpion's body. Below Antares, and brighter, is Saturn, rising in the southeast.
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 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.
Antares is a red-giant star like Betelgeuse: around 20 times the mass of the sun but wider than Earth's orbit. It is 600 light years away and 19 000 times brighter than the sun. Arcturus 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. When low in the sky Arcturus often twinkles red and green as the air breaks up its orange light.
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.
At the beginning of May Jupiter sets due west around 5 a.m., reducing to around 3 a.m. by month's end. Jupiter is 700 million km away. It is always worth a look in a telescope. Its four big moons look like faint stars near the planet. One or two can be seen in binoculars if you can hold them steadily enough. All four are easily seen in any telescope magnifying 20x or more. The Moon will be near Jupiter on the 7th and 8th. Saturn is a great sight in any telescope with its rings near maximum tilt. It is 1,370 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. The Moon will be near Saturn on the 13th.
Brilliant Venus (not shown on the chart) appears in the eastern morning sky, rising before 4 a.m. So around 4 a.m., for at least the first half of the month, Venus is rising in the east as Jupiter sets in the west. Venus is 67 million km away at the beginning of the month. It appears as a crescent in a telescope. The Moon is near Venus on the 23rd. About 90 minutes before sunrise Mercury rises in the empty sky below and right of Venus. Mercury looks like a medium brightness star at the beginning of May but brightens steadily through the month.
*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.