Astronomy

Planet weights, light-travel time, telescope and orbital calculators.

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Find your weight on other planets and the Moon.

Calculate how long light takes to travel a distance.

Calculate telescope magnification from focal lengths.

Calculate a telescope’s focal ratio (f-number).

Find the maximum useful magnification of a telescope.

Calculate orbital period from semi-major axis (Kepler’s third law).

Calculate a star’s distance from its parallax.

Estimate recession velocity from redshift.

Calculate the angular size of an object.

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

Find the moon phase for any date.

Calculate the surface gravity of a body.