Star map accuracy

The stars

We use a catalogue of 5,068 stars, with 673 lines for the constellations. Brighter stars are drawn larger.

Star positions slowly change as the Earth's axis wobbles. We correct each position for this movement, called precession, on the date you choose.

Your place and time

We convert your local time to universal time with the time zone of your place, including daylight saving time. Then we turn the sky to match your latitude, your longitude and that exact minute.

If a local time happens twice, when clocks go back, we use the first one. If a local time does not exist, when clocks go forward, the editor asks you to choose another time.

You can choose any date from 1900 to 2100.

The view

The map shows the whole sky that you would see when you look straight up. The point above your head is at the centre, and the circle is the horizon. Stars below the horizon are not shown.

North is at the top for places in the northern hemisphere. South is at the top for places in the southern hemisphere. East and west are as you see them when you look up, so they are the opposite of a street map.

The Moon

When you add the Moon, we calculate its position and phase for your place and time, to within a few tenths of a degree. We draw it larger than its true size so you can see the phase. It only shows when it is above the horizon.

Limits

This is a star poster, not a tool for navigation. The map does not show planets. It does not include star motion, nutation, aberration or atmospheric refraction. These effects are very small at the scale of a print.