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Astronomical Distance Converter

Cosmic Distances: Convert between astronomical units (AU), light years, parsecs, and other cosmic distance measurements.
Light Year
ly

Distance light travels in one year: 9.461 × 10¹² km. Used for stellar distances.

Parsec
pc

Distance at which 1 AU subtends 1 arcsecond. 1 pc = 3.26 ly. Professional astronomy unit.

Astronomical Unit
AU

Average Earth-Sun distance: 149.6 million km. Solar system scale reference.

Megaparsec
Mpc

Million parsecs. Used for galactic and cosmological distances. 1 Mpc = 3.26 million ly.

Cosmic Distance Scale

Observable Universe: The farthest we can see is about 46.5 billion light years due to cosmic expansion.
Earth-Moon
384,400 km

Average distance to Moon. 1.28 light seconds. Closest celestial body.

Earth-Sun
1 AU

149.6 million km. 8.3 light minutes. Defines astronomical unit.

Solar System Edge
~100 AU

Kuiper Belt extends to ~50 AU, Oort Cloud to ~100,000 AU.

Nearest Star
4.24 ly

Proxima Centauri. 1.3 parsecs. Closest star to our solar system.

Milky Way Diameter
~100,000 ly

Our galaxy spans about 30 kpc. Contains 100-400 billion stars.

Andromeda Galaxy
2.5 million ly

Nearest major galaxy. 0.77 Mpc. Approaching for future collision.

Local Group
~10 Mpc

Galaxy group containing Milky Way, Andromeda, and ~80 other galaxies.

Observable Universe
46.5 billion ly

Comoving distance to cosmic horizon. 14.3 Gpc diameter sphere.

Famous Space Objects

Alpha Centauri
4.37 ly

Nearest star system. Triple star system with potentially habitable exoplanet.

Sirius
8.6 ly

Brightest star in night sky. Binary system with white dwarf companion.

Vega
25 ly

Former and future pole star. Standard reference for magnitude scale.

Pleiades Cluster
444 ly

Seven Sisters star cluster. Young hot blue stars in Taurus constellation.

Betelgeuse
700 ly

Red supergiant in Orion. Potential supernova candidate.

Galactic Center
26,000 ly

Sagittarius A* supermassive black hole. 8 kpc from solar system.

Large Magellanic Cloud
160,000 ly

Satellite galaxy of Milky Way. Southern hemisphere observation.

Hubble Deep Field
~13 billion ly

Most distant galaxies observed. Near the cosmic horizon.

Parallax & Distance Measurement

Parallax Method: Most direct way to measure stellar distances. 1 arcsecond parallax = 1 parsec distance.
Parallax Formula
d = 1/p

Distance in parsecs = 1 / parallax in arcseconds. Foundation of cosmic distance ladder.

Ground-based Limit
~100 pc

Atmospheric seeing limits ground telescopes to ~0.01" parallax precision.

Hipparcos Mission
~500 pc

ESA satellite measured parallaxes to 0.002" precision. 118,000 stars.

Gaia Mission
~30,000 pc

Current ESA mission. Microarcsecond precision for 1 billion stars.

Astronomical Calculators

Parallax to Distance

Light Travel Time

Angular Size

Redshift Distance