How do you read a star map, and why does it look back to front?

A star map (or star chart) shows the stars as dots, with bigger dots for brighter stars. To use one, pick the chart for your month and hemisphere, face a direction, and turn the chart so that direction’s label is at the bottom. The part of the chart just above the edge is the sky just above your horizon. The thing that confuses everyone at first: east and west look swapped, because the chart is meant to be held up against the sky, not laid on a table.

Three kinds of star map

All-sky monthly chart. A circle: the edge is the horizon, the centre is the point straight overhead (the zenith). It is drawn for one latitude and a set evening time. Skymaps.com’s free Evening Sky Map is this type, with a separate edition for each hemisphere.

Planisphere. A rotating disc of stars under a window. You turn it to the date and hour, and the window shows what is above the horizon. We have a whole planisphere guide.

Constellation or atlas chart. One part of the sky on a grid of right ascension (hours) and declination (degrees), like the IAU’s charts of the 88 constellations. These don’t care about time or place. They tell you where a star is among its neighbours.

How to read it, step by step

1. Check the hemisphere and latitude. A chart made for 40° north will be off in Sydney and a little off in Singapore.
2. Check the time. Monthly charts are usually drawn for mid-evening. An hour later, everything has moved about 15 degrees to the west.
3. Face a direction and turn the chart. Facing south? Hold the chart so “S” is at the bottom. The stars printed near the bottom edge are low in the south; the ones near the centre are high overhead.
4. Find one bright anchor. Start with something hard to miss, such as Orion’s belt in winter or the Big Dipper in the north, and hop from there.
5. Scale it. A fist at arm’s length covers about 10 degrees. Charts are much smaller than the sky, so patterns look bigger outside than you expect.

What the dots and lines mean

Dot size is magnitude: the smaller the number, the brighter the star. Sirius is about -1.5; the faintest stars you see from a dark site are around magnitude 6. From a city you will see only the larger dots, so don’t worry if half the chart is missing (city stargazing).

The lines joining stars are drawn by people, not by the IAU. The IAU fixes constellation boundaries; the stick figures differ between books and apps. Planets are usually missing from fixed charts because they move; monthly charts print them for that month.

“Star map by date”: what those posters show

Many searches for “star map” are for custom posters that show the sky over a place on a wedding day or birthday. These are computed views of the same sky, drawn for one moment and one location. If you buy one, check that it states the time and the place, because the sky turns about 15 degrees an hour.

Paper chart or phone?

A paper chart doesn’t need a battery and shows the whole sky at once. A phone app knows your location and the time. I build Sky Map, so weigh my opinion: its AR view labels stars, planets and constellations over the camera, and it shows altitude and azimuth for each object (altitude and azimuth explained). Many people use both: a printed monthly chart to plan, the phone to confirm.

Next steps: how to find constellations and the list of all 88 constellations.

Sources: Skymaps.com, The Evening Sky Map (free monthly chart); IAU: The Constellations (88 constellation charts with Sky & Telescope, boundaries). Checked 31 October 2026.