Finding Your Way Around the Night Sky

The sky looks like chaos until you have a few fixed points to hang everything else on. The best anchor is the point the whole sky turns around — the celestial pole. Find it and you instantly know which way you're facing, roughly what your latitude is, and where to start looking for any other object. Here's how to find it from either hemisphere, and how to build on this framework. Whilst modern tracking and guidance hardware in mounts and controllers can perform the heavy lifting, it’s a good idea to have these anchors in mind whilst setting up your scope, verifying the slew of the mount, or sharing your knowledge with family and friends.

Why the pole is the place to start

Over a night, every star traces a slow circle around one point in the sky — the projection of the Earth's own rotational axis. In the northern hemisphere that point sits almost exactly where a star called Polaris happens to be, conveniently. In the southern hemisphere there's no bright star to mark it, but the spot is just as findable. Wherever you are in either hemisphere, these points stay put while everything else seemingly rotates around it, so it's the one landmark that's in the same place every clear night of the year. Check out my shot below of star trails from the Northern hemisphere, rotating around Polaris. The Eagle eyed will spot that even Polaris is rotating, and due to Earth’s axial precession, it’s not always our polar star.

See it full-size in the gallery →

Northern hemisphere: Polaris from the Plough

Start with the Plough — seven bright stars in the shape of a saucepan (bizarre I know, but it’s unmistakably kitchen utensil like), part of the larger constellation Ursa Major, the Great Bear. From the UK it never sets; it just swings around the pole, sometimes high, sometimes low, sometimes tipped on its side. Once you can pick it out, the rest is a straight line.

Look at the two stars that form the far edge of the pan, opposite the handle — Merak at the base and Dubhe at the lip. These are the Pointers. Draw a line from Merak up through Dubhe and keep going, about five times the gap between them. You'll land on Polaris — not a dazzling star, but a noticeable one in an otherwise seemingly empty patch of sky. It's the tip of the handle of the Little Dipper (Ursa Minor), which is faint and easy to lose under any light pollution, so the Pointer line is far more reliable than hunting for the shape. The mythology surrounding these two constellations is fascinating, worth taking a read some time if you are interested.

Polaris sits due north, and its height above the horizon is roughly your latitude — from my perspective in southern England, about halfway up. For a cross-check, look the same distance the other side of Polaris from the Plough and you'll find Cassiopeia, a bright W (or M) of five stars. The Plough and Cassiopeia sit on opposite sides of the pole and take turns being the high one through the night and the seasons, so whenever one is awkward to place, the other is usually obvious.

Southern hemisphere: due south from the Southern Cross

There's no southern pole star worth the name — the nearest, Sigma Octantis, is barely visible even on a good night. Instead you work out where the pole is and drop a line from it to the horizon for true south.

Find Crux, the Southern Cross: a small, compact cross of four bright stars lying in a rich stretch of the Milky Way, with a fifth fainter star off to one side. Don't confuse it with the False Cross nearby, which is larger, dimmer and more spread out — the real Crux is tighter, and it has the two brilliant Pointer stars, Alpha and Beta Centauri, close beside it.

Take the long axis of the cross — from Gacrux at the top down through Acrux at the foot — and extend it about four and a half times its own length out into the blank sky beyond. That lands you near the south celestial pole. To check it, use the Pointers: picture the line joining Alpha and Beta Centauri, then a second line rising from its midpoint at right angles. Where that second line crosses the extended axis of the Cross is the pole. Drop straight down from there to the horizon and you're facing due south.

Building outward from your anchor

Once you can find the pole and one or two bright patterns, you can hop to almost anything else by following lines between stars you already know. A few worth committing to memory:

• North: follow the curve of the Plough's handle away from the pan and you 'arc to Arcturus', a bright orange star; carry the same curve on and you 'spike to Spica'.
• North: Orion's three-star belt points down to Sirius, the brightest star in the sky, and the other way up to orange Aldebaran and the little knot of the Pleiades.
• South: the long axis of Crux and the line of the Pointers lead you into Carina and on to Canopus, the second-brightest star in the sky.

The idea is always the same — use the shapes you know as signposts to the ones you don't, a couple at a time. Once you’ve established these mental models of navigating the sky, you’ll find you’ll be able to take friends and family on a tour of the night sky and the wonders within.

A few practical things

Get somewhere as dark as you reasonably can, and give your eyes at least twenty minutes to adjust — then protect that adjustment with a dim red light rather than a white torch or a phone screen. The sky turns about fifteen degrees an hour, and any given star rises roughly four minutes earlier each night, so the patterns you see at 10pm this month are where you'd catch them at 8pm next month: the night sky is seasonal, and that's part of learning it. Don't try to take in everything at once — pick two or three patterns a session, find them again the next clear night, and they'll start to feel permanent.

If you want one physical thing to help, get a planisphere — a rotating star wheel. Dial in the date and time and it shows you exactly what's above you and where. The Philip's Planisphere for latitude 51.5°N is the standard one for the UK and northern Europe (Philip's make a 35°S version for southern skies) — it's around £12, never needs charging, and its dim card won't wreck your night vision the way a phone does. Free apps like Stellarium do the same job if you'd rather point a screen at the sky.

Between a planisphere or an app, the pole, and a handful of signpost constellations, you'll have enough to find your way around — and once the main shapes are familiar, the fainter constellations between them start filling themselves in.