Accuracy you can check yourself
"Astronomically accurate" is an easy claim and a rare practice. Here is exactly what we compute, from which data, and how to verify it without trusting us.
- 8,920 stars from a named catalog
- Every star to visual magnitude 6.5 — the naked-eye limit under a perfect dark sky — from the HYG database (Hipparcos + Yale Bright Star + Gliese), sized by true brightness. We name our catalog; ask other sites for theirs.
- Your exact minute, not just your date
- The sky rotates 15° every hour. We convert your local wall-clock time — with the correct historical time zone and DST rules — and compute sidereal time for your longitude. A 9:00 PM sky and a midnight sky are visibly different maps.
- The moon, with its real phase
- Full, crescent, or new — the moon appears where it stood, lit as it was lit, computed from the same ephemerides (Astronomy Engine) used by professional tools. The five naked-eye planets are placed too.
- Correct east/west orientation
- A star map shows the sky you look up at, so east belongs on the left — mirrored from a ground map. Some well-known products ship mirror-imaged skies; ours is covered by an automated test on every release.
Verify it in five minutes
- Install Stellarium (free, open source) or open stellarium-web.org.
- Set your map's location, date, and time.
- Look straight up (zenith view) and compare: bright stars, moon phase and position, planets.
- They should match. If you ever find a mismatch, email us — we'll fix it and refund you.