Andromeda by numbers
Distance, width, stars and speed, with the sources side by side.
How this site works. Every fact is in our own words and linked to its source, beside it. Where good sources disagree, we show each version in a “Sources differ” box.
How far away?
How far is Andromeda? Sources differ
- NASA gives its distance as 2.5 million light-years. NASA, M31
- Britannica says about 2,480,000 light-years from Earth. Britannica
- The Royal Observatory’s ‘closest galaxy’ page says about 2 million light-years. Royal Observatory, closest
2.5 and 2.48 million light-years are the same figure rounded differently; the Royal Observatory’s page uses a rounder number still.
How wide?
How wide is Andromeda? Sources differ
- Royal Observatory: about 152,000 light-years wide. Royal Observatory
- Britannica: approximately 200,000 light-years across. Britannica
- NASA: some 220,000 light-years across. NASA, how big
A galaxy has no hard edge, so the width depends on where you decide it stops.
How big in the sky?
How big does it look? Sources differ
- It is so close that it looks six times as wide as the full Moon in the sky. NASA, M31
- NASA’s 2025 satellite story says it appears to the naked eye roughly the size of the full Moon. NASA, 2025
- EarthSky says it stretches about 3 degrees by 1 degree, twice as wide as the full Moon. EarthSky
The difference is how much of the faint outer glow you count. Long-exposure photos show far more than your eyes do.
How many stars?
ESA/Hubble says the whole galaxy contains over one thousand billion stars: more than a trillion. ESA/Hubble, 2015
How fast is it coming?
Andromeda is getting about 110 km (70 miles) closer to us every second. Royal Observatory
NASA put its approach at about 250,000 miles per hour, fast enough to get from here to the Moon in an hour. NASA, 2012
That speed was measured with the Doppler effect: Andromeda’s motion towards us squashes the waves of its starlight. NASA, 2012
Our view, with our own arithmetic: at 110 km a second, it would take Andromeda about 2,700 years to close the gap by a single light-year. There is no need to tidy up yet.
Next: Hubble and VAR! →