Free interactive tools to explore the cosmos. Convert units used in astronomy, calculate distances between celestial bodies, and discover what you can see in the night sky from your location.
Convert between astronomical units, light-years, parsecs, kilometers, and more. Also supports temperature (Celsius, Fahrenheit, Kelvin) and mass (Earth masses, Jupiter masses, Solar masses) conversions.
Calculate the distance between any two bodies in our solar system. See results in multiple units and discover how long it would take to travel at different speeds — from walking to the speed of light.
Find out which planets, stars, and celestial objects are visible from your location tonight. Includes current moon phase, sunrise and sunset times, and tips for stargazing.
Space is unimaginably vast. The distances between objects in our solar system — and beyond — are so enormous that everyday units like kilometers become impractical. That is why astronomers developed specialized units: the Astronomical Unit (AU), defined as the average distance between Earth and the Sun (about 149.6 million km), is used for distances within our solar system.
For interstellar distances, the light-year (the distance light travels in one year — about 9.46 trillion km) and the parsec(about 3.26 light-years, derived from parallax measurements) are the standard units. Our nearest star system, Alpha Centauri, is 4.37 light-years or 1.34 parsecs away.
Temperature in space is measured in Kelvin, which starts at absolute zero (-273.15°C) — the theoretical point where all molecular motion stops. The cosmic microwave background radiation has a temperature of about 2.7 K, while the surface of the Sun reaches approximately 5,778 K.
An Astronomical Unit is the average distance between the Earth and the Sun, approximately 149,597,870.7 kilometers (92,955,807.3 miles). It is the standard unit for measuring distances within our solar system. For example, Mars is about 1.52 AU from the Sun, and Jupiter is about 5.20 AU.
A light-year is approximately 9.461 trillion kilometers (5.879 trillion miles). It is the distance that light, traveling at 299,792 km/s, covers in one year. The Milky Way galaxy is about 100,000 light-years across.
The travel time to Mars depends on the relative positions of Earth and Mars in their orbits. At their closest approach (about 55 million km), a spacecraft traveling at 58,000 km/h (like New Horizons) would take roughly 39 days. In practice, missions like Perseverance took about 7 months using a Hohmann transfer orbit, which is the most fuel-efficient route.