What is the cosmic distance ladder?

The cosmic distance ladder is a series of methods used to measure distances in the universe.

The cosmic distance ladder is a set of techniques used by astronomers to determine the distances to objects in the universe. It is called a "ladder" because each method builds upon the previous one, allowing astronomers to measure distances to increasingly distant objects. The first rung of the ladder is parallax, which is the apparent shift in the position of a nearby star when viewed from different points in Earth's orbit. By measuring the angle of this shift, astronomers can calculate the distance to the star.

The next rung of the ladder is the use of standard candles, which are objects with a known luminosity. By measuring the apparent brightness of a standard candle, astronomers can calculate its distance. Examples of standard candles include Cepheid variables, which are pulsating stars with a known period-luminosity relationship, and Type Ia supernovae, which have a consistent peak brightness.

The final rung of the ladder is the use of cosmological redshift, which is the stretching of light waves as the universe expands. By measuring the redshift of distant galaxies, astronomers can determine their distance and calculate the expansion rate of the universe.

The cosmic distance ladder is an important tool in astronomy, as it allows astronomers to measure the size and age of the universe, as well as the distances to objects such as stars, galaxies, and quasars. However, each method has its own limitations and uncertainties, and astronomers must carefully analyse their data to ensure accurate measurements.