Calcolatore Distanza Propria
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Proper Distance
428.0000 Mpc
Proper Distance vs Comoving Distance
Formula
Proper Distance
The proper distance is the physical distance between two objects at a particular moment in cosmic time.
Relation
d_proper = a(t) * d_comoving
At the present epoch a = 1, so proper distance equals comoving distance. In the past (a < 1) the physical distance was smaller.
Esempio Risolto
A galaxy with comoving distance 428 Mpc observed at the present epoch (a = 1).
- 01d_proper = a(t) * d_comoving
- 02d_proper = 1.0 * 428
- 03d_proper = 428 Mpc ≈ 1396 Mly
Domande Frequenti
What is the scale factor?
The scale factor a(t) describes how distances in the universe have changed over time. By convention a = 1 today; at the Big Bang a = 0.
When would I use a scale factor other than 1?
To find the physical distance at an earlier epoch. For instance, at redshift z the scale factor was a = 1 / (1 + z).
Is the proper distance directly observable?
Not directly. We infer it from redshift and a cosmological model. What we observe is the luminosity distance or angular-diameter distance.