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Astronomical distances
Beginner
Light-years, parsecs and astronomical units.
1 AU = 1.5×10¹¹ m; 1 light-year = 9.46×10¹⁵ m; 1 parsec = 3.26 ly. Nearest star Proxima Centauri: 4.24 ly.
Milky Way diameter ~100,000 ly.
Distances are time-delayed.
In more detail
Astronomical distances are measured using parallax, standard candles and redshifts. The nearest stars are a few light-years away, and galaxies are billions of light-years distant.
Real-world uses
- Distance measurements map the scale of the universe.
- Astronomers use them to calibrate the expansion rate.
- Astronomers use light-years and parsecs to describe the vast distances between stars and galaxies.
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Frequently asked questions
What is a light-year?
The distance light travels in one year, about 9.46 trillion kilometres.
How far is the nearest star?
Proxima Centauri, about 4.2 light-years away.
What is a parsec?
About 3.26 light-years, the distance at which one astronomical unit subtends an angle of one arcsecond.
Related topics in Particle Physics & Cosmology
Fate of the universe · Exoplanets · Habitable zone · Parallax and standard candles · Multiverse ideas