Astronomy Observation Calculators
Explore lunar dates, compare solar-system and stellar distances, and interpret star measurements with astronomy calculators grouped by observation task.
This hub is curated around tasks, not just alphabetized links, so you can choose the right calculator before entering numbers.
AU to KM and Miles Converter
Convert astronomical units (AU) to kilometers or miles with the exact 1 AU value and clear solar-system distance examples.
Calculator groups by task
Use these groups to decide which calculator fits the question you are trying to answer.
Moon Phase Calculator & Calendar
See today's moon phase, illumination, and lunar age, plus the next full and new moon. Build a moon phase calendar for any month or date.
Orbital Period Calculator
Calculate orbital period from orbital size and central mass using the standard gravitational formula for astronomy and physics problems.
AU to KM and Miles Converter
Convert astronomical units (AU) to kilometers or miles with the exact 1 AU value and clear solar-system distance examples.
Light Year Distance Calculator
Convert between light-years, parsecs, astronomical units, and conventional measures. Calculate vast cosmic distances for astronomy research, space exploration planning, and understanding the scale of the universe.
Distance Modulus Calculator
Calculate astronomical distance modulus, distance in parsecs and light-years, apparent magnitude, or absolute magnitude from stellar brightness measurements.
Star Magnitude Calculator
Calculate star magnitude, distance modulus, and brightness ratios. Convert apparent and absolute magnitude for astronomy planning.
Stellar Temperature Calculator
Estimate stellar temperature from color or spectral class. Compare star temperature, color, and classification for astronomy calculations.
Telescope Magnification Calculator
Calculate the magnification of telescopes with different eyepieces. Determine optimal magnification for various astronomical targets, exit pupil size, field of view, and maximum usable magnification based on aperture.
Planetary Weight Calculator
Compare your Earth weight with your weight on planets, moons, and other bodies using surface gravity and simple conversion formulas.
When should I use astronomical units instead of light-years?
Astronomical units are convenient for distances within the solar system. Light-years are more practical for distances to stars and other objects beyond it.
Are apparent magnitude and absolute magnitude the same?
No. Apparent magnitude describes how bright an object appears from Earth; absolute magnitude compares intrinsic brightness at a standardized distance.
Does a Moon phase tell me the Moon's exact position?
No. Phase describes the visible fraction of the illuminated lunar disk. The Moon's position changes with time and location, so use a sky chart or ephemeris for observing coordinates.
Can telescope magnification alone predict image quality?
No. Magnification is only one factor. Aperture, optics, atmospheric conditions, target brightness, and the observer's setup also affect what can be seen.
Need a different tool?
Browse the full calculator directory or return to every topic hub.