21.   Astronomers use Hubble telescope to find oldest, most distant galaxy.

22.   Astronomers use the brightness of Cepheids observed in far-off galaxies and compare them with Cepheids in a galaxy known as the Large Magellanic Cloud.

23.   Astronomers used the quasar as a light bulb to see whether anything was blocking its ultraviolet light.

24.   By looking at the very faintest and oldest white dwarfs possible, astronomers can use this cooling rate to estimate the age of the universe.

25.   The astronomers are using large telescopes at observatories in both the northern and southern hemisphere to probe the entire sky visible from Earth.