Free Lookback Time Calculator
Estimate the lookback time (how far back in time you are seeing) from distance in megaparsecs, using t = d / c.
Mpc
Lookback Time
326.16 Myr
Lookback Time (Gyr)0.3262 Gyr
Lookback Time vs Distance
Lookback Time
Light travels at a finite speed, so observing a distant object means seeing it as it was in the past.
Simple Estimate
t ≈ d / c
where d is in light-years and t in years. Since 1 Mpc ≈ 3.262 Mly, the lookback time in millions of years equals the distance in Mpc × 3.262.
For very large distances, cosmological expansion makes this an underestimate of the true lookback time.
Example Calculation
A galaxy is 100 Mpc away.
- 01t ≈ 100 Mpc × 3.262 Mly/Mpc = 326.2 Mly
- 02We see this galaxy as it was 326 million years ago.
- 03In Gyr: 0.326 Gyr