A Map of the Night Sky

Posted by on May 19, 2011

Have you ever wanted to be able to look at the sky and know right away what it is you’re looking at? If you’ve spent 5 minutes with me outdoors at nighttime you may have seen me point out over two dozen bright stars in the sky. You’d be surprised to know how easy this is to accomplish. I don’t memorize a map of the stars, instead, I’ve learned what the relative positions of stars are. During the winter, I use Orion, and in the summer, I use something else. That is what we’re here for today.

If you wait ’til nighttime, you can look into the sky and see one of the most recognizable constellations in the sky: Ursa Major, otherwise known as the Big Dipper.

The Big Dipper is special, everyone knows what it is, and it is a roadmap for the rest of the sky. If you know a few points on the map, you can point out several other constellations as you become more familiar with the spring-summer night sky.

A simplified roadmap to the late spring/early summer sky

The Big Dipper has a long handle, a top and a bottom to the pot, and two sides: one towards the handle and one away. Let’s learn some of these rules and then use the two images below to help you find these stars, that way you don’t have to go outside and get used to night vision or stand in the bitter cold. Use the drawing on top to get a quick familiarization, then find Ursa Major in the next three drawings for an accurate depiction of the night sky. Now let’s try some quick and simple exercises. (hint: the first star in the Big Dipper is named Alkhaid. This will assist you in finding it. If the black screenshots are too small, there’s one with a green border at the bottom that should assist you).

  • If you follow the arc handle starting from the pot and going away, you end up in Arcturus. It is commonly known as “Follow the arc to Arcturus”. It is the major star in the Bootes constellation.
  • If you keep going along that Arc, you’ll come against another bright star: Spica, the brightest star in the Virgo constellation.
  • Follow the star connecting the handle to the pot, and go down from there to the bottom star in the handle-side of the pot, and you eventually make it to Regulus, the brightest star in the Leo constellation.
  • With the handle-to-pot star, and going to the opposite star in the pot, you go straight to Pollux: one of the two (and the brighter of) the Gemini Twins. The other is Castor.
  • A very important one: follow the two pot stars, opposite the handle, going “up” the pot: this goes straight to Polaris, the famous North Star. It’s not super bright, but it’s bright enough, and it’s also the first star in the Little Dipper. I like to remember this as “The Pot Always Spills North” (I made that up, which is why it’s kind of a lame mnemonic)
  • If the first star in the Big Dipper handle is a certain distance away from the Gemini Twins, at the exact “opposite” side of the Twins is Betelgeuse: Orion’s Shoulder. This is a red supergiant that is ready to supernova in the “near” future – you and I may have been dead for hundreds of thousands of years before this happens, but when it does, it’ll outshine the moon for a few days.

See what other patterns you can discern, and make your own rules. Go out one night and see if you can spot just one of these. If you do this occasionally, before long, you’ll know all of the brightest stars in the sky.

A screenshot of the Stellarium software, free for download from http://stellarium.org! My apologies if it's all too small, it was a challenge to fit all of this in here :)

Same Stellarium screenshot, this time with constellation lines

Again the same screenshot, but this time it's got art.

A slightly more technical shot of the night sky around these times



  • Rune

    What stars were most important for the sailors to navigate? Did it change depending on what hemisphere they were in?

  • Anonymous

    In the northern hemisphere, sailors would use Polaris, not only is it bright and easy to find due to its succint location at the beginning of the Little Dipper and pointed to by the Big Dipper, its location in the sky changes less than one degree throughout the year.

    The Southern Cross, known as the Crux, is not nearly as bright and doesn’t actually have a pole star. A distance is marked between the stars, and multiplied by 4.5 times, and that points to close to the southern celestial pole.

    See this image to see how good Polaris is at marking north: http://upload.wikimedia.org/wikipedia/commons/c/c6/Star_Trail_above_Beccles_-_geograph.org.uk_-_1855505.jpg