About SkyCalc HTML

A single-file, dependency-free browser port of the classic skycalc.c astronomical calculator — no server, no build step, no external libraries. Open the file and go.

Original program

skycalc.c was written by John Thorstensen, Department of Physics & Astronomy, Dartmouth College, and has been widely used at observatories for decades. Every astronomical algorithm in this web app is a faithful port of that C code, validated number-for-number against the compiled binary.

This browser port

HTML/JavaScript version by Karl Glazebrook (Swinburne University of Technology), developed collaboratively with Claude (Anthropic). Released under the MIT License.

Source, tests, and version history:
github.com/karlglazebrook/Skycalc-HTML-Javascript