Looking up, one sketch at a time.

I started Horizon mostly as a supporting toolkit for Astronomický kurz 2026/27(opens in a new tab) (1st year, in person), which I'm taking at Planetum.

I may add more simulations as the course goes on, if time allows.

I'm not a professional physicist or astronomer. I build the simulations with care and draw on published work, but they are meant mostly for exploration and the joy of discovery: illustrative aids, not an authoritative scientific source. Please take them with a grain of salt.

Simplified

Models keep what matters for the idea and leave out the rest.

Approximate

Values and scales are close, but not always exact.

Tuned for speed

Some physics is simplified further so the scenes run smoothly in a browser.

For teaching, study, or anything that depends on exact values, please check primary sources.

Horizon is open source under the MIT licence: the code is on GitHub(opens in a new tab). Spotted a mistake? Issues and fixes are welcome.

I'm grateful to everyone who made the course possible.

• Planetum, organiser
• Jakub Rozehnal, teacher
• Petr Kulhánek, teacher
• The team around them, behind the scenes