Light Year Conversion
Convert light years to miles, kilometers, astronomical units, and other distance measurements
Convert Light Years
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Conversion Result
Quick Reference: 1 Light Year =
Notable Astronomical Distances
Nearest Stars
Proxima Centauri: 4.24 light years
Alpha Centauri A & B: 4.37 light years
Barnard's Star: 5.96 light years
Galactic Distances
Center of Milky Way: ~26,000 light years
Milky Way diameter: ~100,000 light years
Andromeda Galaxy: ~2.5 million light years
Observable Universe
Observable universe radius: ~46.5 billion light years
Cosmic microwave background: ~13.8 billion light years
Light Year Facts
Definition
Distance light travels in one Julian year (365.25 days)
Speed of Light
299,792,458 meters per second (exact)
Scale
9.461 trillion kilometers or 5.88 trillion miles
Travel Time
Voyager 1 would take ~73,000 years to travel 1 light year
Distance Scale Comparison
Astronomy Tips
Light year measures distance, not time
Looking at stars means seeing into the past
AU is better for solar system distances
Parsecs are preferred by professional astronomers
Understanding Light Years
What is a Light Year?
A light year is the distance that light travels in one year in a vacuum. Since light travels at a constant speed of 299,792,458 meters per second, this creates a precise and consistent unit for measuring vast astronomical distances.
Why Use Light Years?
- •Makes interstellar distances manageable
- •Relates to observable light from distant objects
- •Provides intuitive sense of cosmic scale
- •Standard unit in astronomy and astrophysics
Conversion Calculations
Light Year to Kilometers
1 ly = speed of light × seconds in a year
= 299,792,458 m/s × 31,557,600 s = 9.461 × 10¹² km
Light Year to Miles
Convert km to miles using 1 km = 0.621371 miles
= 9.461 × 10¹² km × 0.621371 = 5.88 × 10¹² miles
Note: Light year is a unit of distance, not time. The light we see from distant stars left them years ago.