What Is a Light-Year?
A light-year is a measure of distance, not time — and a very large one.
A light-year is the distance light travels in a vacuum in one year: about 9.46 trillion kilometers (5.88 trillion miles). The “year” names the travel time, but the unit itself is a length — like “man-hours” describe work, not people.
How fast is light?
- 1 second
- 299,792 km — 7.5 times around Earth
- 8 min 20 s
- Sunlight reaches Earth
- 4.24 years
- From Proxima Centauri, our nearest star
- 1 light-year
- ≈ 9.46 trillion km
Why we use light-years
For stars, kilometers become an unreadable string of zeros. Light-years keep cosmic numbers graspable — and carry a romantic bonus: the light you see left the star N years ago, so looking at stars is looking back in time.
How far away is your star
The stars in our catalog mostly sit between tens and hundreds of light-years. Regulus in Leo, for example, is 79.3 light-years away — what you see of it today left 79.3 years ago. Every star page shows the real distance.
FAQ
What is the difference between a light-year and a year?
A year measures time; a light-year measures distance — how far light travels in one year.