Free tool
The sky on the night it happened
Pick a date, a time and a place. We draw every bright star above that horizon at that minute, with our own constellation lines and a horizon ring, the way our Night Sky plaque lays it out.
The plaque opens once our star data license for printed pieces is confirmed in writing. Leave your email and we send one note the day it opens.
Star positions: ESA/Gaia/DPAC (Gaia DR3) and the IAU Catalog of Star Names. Constellation figures: Keyedworks.
How the map is made
Each star starts as a catalog position. We step it forward to your date for the slow wobble of the Earth's axis, work out the sidereal time at your minute and longitude, and turn that into height above the horizon and compass bearing. Stars below the horizon are dropped. The rest are laid out on a flat disc with the zenith in the middle and the horizon as the ring.
Questions
How accurate is the sky?
Star positions are J2000 catalog positions moved to your date for precession, then placed for your place and minute. For the bright stars shown it is far finer than the eye can tell. Planets and the Moon are not drawn.
Which stars are shown?
Every star brighter than magnitude 4.5 above your horizon, roughly what you see from a dark back yard. Bigger dots are brighter stars, the same sizes the plaque uses.
Where do the lines come from?
The constellation figures are our own stick figures drawn between named stars. They are not copied from any planetarium program.
Why is east on the left?
It is a map of the sky seen looking up. Lie on your back with your head to the north and east is on your left hand. Every printed star map works this way.
Which time zone should I pick?
The zone of the place, not where you live now. We fill in a guess from the longitude; daylight saving is handled for the date you pick.