Calcolatore Tempo di Retrospezione
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Lookback Time
326.16 Myr
Lookback Time vs Distance
Formula
## 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.
Esempio Risolto
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
Domande Frequenti
Is lookback time the same as distance?
Not exactly. For nearby objects t ≈ d/c works well, but at cosmological distances the expansion of space means the object is now farther than its lookback distance.
What is the maximum lookback time?
About 13.8 billion years, corresponding to the age of the universe. The cosmic microwave background represents a lookback of 13.787 Gyr.
Why does this matter?
Telescopes are time machines. Looking at distant objects reveals conditions in the younger universe.