about
About Byulgil
Byulgil is a stargazing web app that computes the night sky as it actually appears from your location — anywhere in the world — in real time. Use your current location (GPS) or choose a major city such as Seoul, Tokyo, New York, or Sydney, and compare how the sky changes between the northern and southern hemispheres. The constellations on screen aren’t imagined: they are the real positions of stars standing in that part of the sky at this very moment.
How does it work?
Every star is stored in J2000.0 equatorial coordinates (Right Ascension · Declination), which barely change over the ages. From your observing time and location (latitude/longitude), the app computes the local sidereal time and converts those coordinates into horizontal coordinates (Azimuth · Altitude) — the direction a star sits in the sky right now. It recomputes every second, so the stars rise in the east and drift west just like the real sky.
AR mode
On mobile devices, an AR mode uses the orientation sensor and compass. Point your phone at the sky and the constellations in that direction overlay the screen. It corrects for magnetic declination (about 8° west in Korea) so it aligns to true north rather than magnetic north.
What’s inside
Byulgil features many constellations and all nine worlds of the Solar System, each paired with the science modern astronomy has uncovered and the myths behind their names and stars. You can also inspect each star’s name, magnitude, and coordinates.
A note
Byulgil is made for education and enjoyment. Star positions are based on real astronomical computation, but some fine corrections (atmospheric refraction, precession, and so on) are simplified, so it isn’t intended for precise observation or navigation.
Constellations featured