Elliptical galaxies contain more gas, dust, and young stars than do Sa galaxies.

Soon after discovery, it was observed that quasars had a starlike appearance which was blurred by Earth’s atmospheric “seeing”. Despite the blurring, it was realized that the intense energy-emitting regions of quasars must be small because they

Isotropic is the same as homogeneous.

For a galaxy to be active, the supermassive black hole needs to have matter flow into it.

Old stars are poor in heavy elements because there were very few previous generations of stars before the old stars formed.

The units of proper motion are km/s because proper motion is the motion of stars across the sky.

Almost every celestial object we see in the sky on a dark, clear night is within the Milky Way galaxy.

The night sky is dark because the Universe is not infinitely old.

Space-time will be flat if

The radio radiation emitted by a radio lobe is mainly synchrotron radiation.