the catalogue

the hyg database is a free, open star catalogue. the name stitches its three sources together: hipparcos, yale bright star, gliese. it was assembled by david nash at astronexus.com and released under cc by-sa, so anyone can use it. star focus does.

every row is one real star. position in 3d (right ascension, declination, and distance from earth in light years). apparent and absolute magnitude, meaning how bright the star looks from here and how bright it actually is. spectral type, the temperature class from hottest blue to coolest red: o, b, a, f, g, k, m. luminosity class, which is also how astronomers categorise stellar size, from supergiant down to dwarf. proper motion across the sky. and a name, if humans have ever given it one.

the distance numbers are the hard part. you cannot just measure how far a star is. you measure how much it appears to shift against more distant stars as the earth moves around the sun, half a year later. that shift is parallax. the hipparcos satellite did this from orbit between 1989 and 1993, mapping over a hundred thousand stars to a precision earth-based telescopes had never reached. the yale bright star catalogue contributed the traditional naked-eye stars. gliese contributed the close-to-the-sun ones. hyg merges, deduplicates, and tidies all three into a single table.

in star focus, every row in our trimmed cut is a real destination. routes are picked by session length. five minutes is a hop. twenty-five minutes crosses real distance. two hours is a chunk of the local arm. pro unlocks chart course if you want to pick yourself. mostly you should let the catalogue surprise you.