IC 4584

IC 4584 is a spiral galaxy in the constellation Triangulum Australe about 172 million ly from Earth. It spans roughly 98,000 ly, about the width of our Milky Way. The light reaching us tonight left it about 172 million years ago.

Because its light is 172 million ly from home, you are seeing IC 4584 as it looked roughly 172 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).