One of the most difficult problems in astronomy is measuring the

vast interstellar distances between us and

everything else in
the

Universe. Over the centuries, astronomers have developed a

bootstrapping series of methods, each applicable to more distant
objects, and each dependent on the previous methods. The series of
methods is known collectively as the "cosmic distance scale ladder".
Here are some of the most important

rungs on the CDS ladder:

- The distance to the Moon
- The distance to the Sun
- Parallax distances to nearby
stars
- The Cepheid Distance Scale
- Hubble's Law: the redshift-distance relation.

There are other important distance methods involving eclipsing binaries,
Type Ia supernovae (and other standard candles), moving star clusters, and other beasts.