Astronomy tools & calculators

Hand-coded, run in your browser, no sign-up. Numbers worth checking against.

Convert light-years to kilometers, AU and parsecs in one step.

How long does light take to reach you from the Sun, the Moon, or any distance?

Precise solar event times for any date and location — civil, nautical and astronomical twilight.

Calculate the true field of view from telescope focal length and eyepiece specs.

Magnification from telescope focal length divided by eyepiece focal length.

Dawes and Rayleigh limits in arcseconds for any telescope aperture.

Convert between kilometers, AU, light-years and parsecs.

See how the logarithmic magnitude scale changes apparent brightness.

Compute the event horizon size for any mass — from a star to a supermassive black hole.

How fast you must move to escape any planet, moon or star's gravity.

The 9-class system that tells you what you can actually see at the eyepiece from any location.