As viewed edge-on, we can see all the spurs and branches off the arms of the Milky Way galaxy.

The density of the Universe is

Some large clusters of galaxies do not appear to contain enough mass to hold themselves together.

Galaxies may contain a supermassive black hole at their center but ___________ an active nucleus because of ____________ into the black hole

The first scientific attempt to map the Milky Way galaxy

The sky is flat, like a sheet of paper, and hence angular diameter is the distance measured along that flat sheet of paper.

If the change in wavelength is less than zero, then the radial velocity tells you that the star is moving _______________ you.

Which of the following is not visible during totality of a total solar eclipse?

At sunset, the ____ Moon phase will be highest above the southern horizon for an observer in the Northern Hemisphere.

The lowest of low tides occurs during neap tides.