NGC 3991 NED01

NGC 3991 NED01 is an irregular galaxy in the constellation Ursa Major about 148 million ly from Earth. It spans roughly 50,000 ly, about 50% of our Milky Way's width. The light reaching us tonight left it about 148 million years ago.

Because its light is 148 million ly from home, you are seeing NGC 3991 NED01 as it looked roughly 148 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). Distance computed by gravityfinder from redshift via Hubble's law (H0 = 70 km/s/Mpc).