The stars move in a predictable way, so the sky over any town on any night, past or future, can be worked out to the minute. What makes it yours is the combination: that place, that date, that time.
Finding the time of birth
The time matters, because the sky turns about fifteen degrees an hour. In England and Wales a birth certificate doesn't normally record the time, except for twins and other multiple births, so it usually comes from a parent, a baby book or the hospital record. Scottish birth certificates do record it. If nobody knows, choose a time and say so: a chart for nine in the evening is still that night's sky.
What changes from one night to the next
- The constellations: they shift with the seasons. A January birthday has Orion high in the evening; a July one has the Summer Triangle.
- The Moon: it changes phase every night and moves across the stars by about its own width every hour. The Moon on your day shows the phase on any date.
- The planets: they wander against the stars, so Jupiter or Saturn may have been bright in the south that night.
A daytime birth
If you were born in daylight, the stars were still there; you just couldn't see them against the sunlit sky. A chart for that moment shows the stars above the horizon all the same, which is a nice thing to point out on a card.
Free ways to see the night sky on the day you were born
Stellarium Web is a free planetarium in a browser: set the place and the date, and the sky turns to match. Our personalised star map does the same for one moment and lets you preview the chart free before you decide whether it's worth printing.
For other ideas built around a date, the star map gift guide covers weddings, anniversaries and first nights in a new home.
