NGC 4038

Antennae Galaxies is a barred spiral galaxy in the constellation Corvus about 78 million ly from Earth. It spans roughly 120,000 ly, about the width of our Milky Way. It is receding from us at about 1,663 km/s.

Because its light is 78 million ly from home, you are seeing Antennae Galaxies as it looked roughly 78 million years ago. The photons left before that much of history had passed, and are only now reaching us. This distance is estimated from the galaxy's redshift, so the lookback time is approximate.

Source: structural data (position, morphology, brightness, redshift) from OpenNGC (CC BY-SA). Recession velocity from RC3 (de Vaucouleurs et al. 1991, via NASA/HEASARC, public domain). Distance computed by gravityfinder from redshift via Hubble's law (H0 = 70 km/s/Mpc).