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:

  1. The distance to the Moon
  2. The distance to the Sun
  3. Parallax distances to nearby stars
  4. The Cepheid Distance Scale
  5. 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.

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