Astronomy Calculators & Maps

Calculators and maps for the numbers behind observing: where the stars were on a date, how big things look, what your telescope can do and how long a camera exposure can run before stars trail.

Tools in this group

• Angular Size Calculator — Give any two of object size, distance and angular size and get the third, with NASA presets for the Moon, Sun and planets.
• Astrophotography Calculator — Enter your sensor, lens and target declination to get the longest untrailed exposure by the NPF, 500, 400 and 300 rules.
• Julian Date Calculator — Enter a date and time to get the Julian Date, Modified JD and Unix time, or enter a Julian Date to get the calendar date.
• Sidereal Time Calculator — Pick a place and a moment to get local and Greenwich sidereal time, plus the bright stars crossing your meridian.
• Solar System Scale Calculator — Choose the Sun's size, the Earth's size or the model's length and get every planet's model size, distance and paces.
• Solar System Simulator — Pick a date or press Play and watch the planets move around the Sun where they really are.
• Star Map Generator — Pick a place, date and time and get an accurate chart of that sky, ready to download or print.
• Telescope Magnification Calculator — Enter your telescope and eyepiece to get magnification, exit pupil and true field, and see which eyepieces suit your scope.