Web PlanetariumHow the web planetarium worksUse, accuracy and sources
What this page covers: how to use the planetarium, how accurate it is, what is in English, and where the data comes from.
Open the planetarium →How to use
- Tap Place and pick a city, use your location, or type a latitude and longitude.
- Drag to look around. Pinch or scroll to zoom.
- Tap a constellation, bright star, planet or the Moon for notes.
- Open Time to move by hours, days or months, or to fast-forward.
- Tap Moon phase for the Moon’s phase, age and how much of it is lit.
Works for any place on Earth
Positions are calculated from your latitude, longitude and time, so the sky is right for any place. City times use that city’s time zone. For your location or typed coordinates, times use your device’s time zone.
Accuracy
The sky shows about 3,300 real stars down to magnitude 5.6, adjusted for precession. The Sun, Moon and five naked-eye planets come from orbital formulas, and the Moon includes parallax. Moon and planet positions are within a few arcminutes, fine for naked-eye viewing. The planet formulas are meant for 1800–2050. Atmospheric refraction, Uranus, Neptune, comets and satellites are not shown.
What is in English
Constellation names are the official IAU names. Star names follow the IAU Working Group on Star Names. Constellation myths, the constellation guide and the kids’ hiragana mode are in Japanese only for now.
Sources
- Stars: Yale Bright Star Catalogue, 5th ed. (Hoffleit & Warren, 1991), via brettonw/YaleBrightStarCatalog (MIT License)
- Planets: E. M. Standish, “Keplerian Elements for Approximate Positions of the Major Planets” (NASA JPL); brightness: Mallama & Hilton (2018)
- Moon: Paul Schlyter, “How to compute planetary positions”
- Star names: IAU WGSN, IAU Catalog of Star Names
- Sky calendar: National Astronomical Observatory of Japan (NAOJ)
Your data
Your settings and chosen place are saved only in this browser (localStorage) and are never sent anywhere. “Use my location” rounds your position to 0.1° (about 10 km) before saving. Feedback form (Google Forms, in Japanese; you can write in English). We read every message but do not reply.