Welcome to the Night Sky Map for May! This month, learn about asterisms, which are unofficial star patterns contained in constellations. They’re an easy—and entertaining—way to observe the night sky.
Just click here or on the image below to open the printable map—then bring outside!
All About Asterisms
An asterism is an easily recognized star pattern that lies within a constellation. Unlike constellations, asterisms are entirely “unofficial.” There is no international organization or governing body that assigns names to asterisms. Their names have come into popular usage because they are a convenience—an easy way to navigate the sky. If you wish, feel free to identify and name your own asterisms. Who knows? Your names might catch on!
For a fine example of an asterism, look near the center of this month’s star map for the Keystone, a compact pattern of four stars that lies within the constellation Hercules, the Hero. Hercules is a sprawling constellation, the fifth largest in the sky, but the distinctive shape of the Keystone really stands out.
Above and to the right of the Keystone is the constellation Corona Borealis, the Northern Crown. In my opinion, this semicircle of stars looks far more like a tiara than a crown, so The Tiara it is, at least for me.
Higher in the sky lies Boötes, the Herdsman, whose main stars form an asterism known as The Kite. It’s a sloppy-looking kite, to be sure, but the shape is certainly suggestive of one—enough so that it can help you to get your bearings and find Boötes. The bright star Arcturus anchors the tail of The Kite.
The Little Dipper
Off to the left, look for the Little Dipper asterism, part of the constellation Ursa Minor, the Lesser Bear. At the end of the dipper’s handle is Polaris, the North Star. From brightly lit suburbs, you’ll see only Polaris and the brighter stars of the dipper’s bowl. Leave town to see the whole dipper.
The Dragon’s Head
Between the Little Dipper and The Kite slithers the body of Draco, the Dragon, which culminates in the Dragon’s Head, a four-sided asterism that shows up well when viewed from a dark location.
Below the Dragon’s Head, look for two very bright stars that point the way to a great pair of asterisms, one small and the other quite large.
Vega & the Parallelogram
The star Vega in the small constellation Lyra, the Lyre, achieved notoriety as home to the fictional aliens who sent a message to Earth in the 1997 Jodie Foster film Contact. Beneath Vega is a small but beautifully symmetrical asterism, the Parallelogram. Its exquisite and geometrically perfect shape is a wonder.
Deneb & the Northern Cross
To the lower left is the bright star Deneb, marking the tip of the Northern Cross, which lies on its side at this time of year. Deneb and the Northern Cross are part of the large constellation Cygnus, the Swan. The name “Deneb” is derived from the Arabic word for “tail,” and indeed Deneb sits at the tail of the Swan.
The left side of our sky map features The House, an asterism within the constellation Cepheus, the King. Yes, it’s a lopsided house, but no more lopsided than the ones we all drew as children.
Altair & the Summer Triangle
We’ve already mentioned that Vega and Deneb can help you to find two lovely asterisms. These two stars, plus brilliant Altair, comprise the three corners of the large asterism known as the Summer Triangle, marked in purple on our Sky Map below. The Summer Triangle will be prominent in the sky from now well into autumn.
With that, we’ll leave you to explore and enjoy the May night sky!
Sky map produced using Chris Marriott’s Skymap Pro
Note: How to Read the Sky Map
Our monthly sky map does not show the entire sky which would be almost impossible. Instead, the map focuses on a particular region of the sky each month where something interesting is happening. The legend on the map always tells you which direction you should facing, based on midnight viewing. For example, if the map legend says “Looking Southeast,” you should face southeast when using the map.
The map is accurate for any location at a so-called “mid northern” latitude. That includes anywhere in the 48 U.S. states, southern Canada, central and southern Europe, central Asia, and Japan. If you are located substantially north of these areas, objects on our map will appear lower in your sky, and some objects near the horizon will not be visible at all. If you are substantially south of these areas, everything on our map will appear higher in your sky.
The items labeled in green on the sky map are known as asterisms. These are distinctive star patterns that lie within constellations. When getting your bearings under the stars, it’s often easiest to spot an asterism and use it as a guide to finding the parent constellation.
The numbers along the white “Your Horizon” curve at the bottom of the map are compass points, shown on degrees. As you turn your head from side to side, you will be looking in the compass direction indicated by those numbers. The horizon line is curved in order to preserve the geometry of objects in the sky. If we made the horizon line straight, the geometry of objects in the sky would be distorted.