The Astrophysics Spectator

November 10, 2004

One of the greatest challenges in astronomy is the determination of the distances to objects outside of our Solar System. Within the Galaxy, the best method for determining the distance to an object is the measurement of a parallax. Outside of the Galaxy, the distance to a galaxy can be measured by observing Cepheid variables, type 1a supernovae, and the cosmological redshift. All four of these methods are discussed in background pages added with this issue of The Astrophysics Spectator.

The commentary for this week is on Pythagoras and the distance of modern astrophysics from this philosopher.

Commentary

Pythagoras. Numerology is the central fire of the Pythagorean universe, and mathematics is the Sun of modern science. The ancient mysticism of our forefathers is now alien to us, despite its role in the development of modern science. (continue)

More commentaries.

New Background

Galactic Distances. Distances within the Solar System are known to extremely high accuracy through measurements of the light travel time from Earth to artificial satellites. Because we know the size of Earth's orbit to high accuracy, we can determine the distance to a nearby star to high accuracy by measuring its parallax. (continue)

Extragalactic Distances. To determine a distance to a galaxy, we need to use a standard candle, which is an object of a known luminosity. The best standard candle in astronomy is the Cepheid variable, a star with a luminosity that is dependent only on the star's pulsation period. A second standard candle, the type 1a supernova, has become a key tool for studying the expansion of the universe. The most convenient distance measure for the most distant galaxies is the cosmological redshift, which can be obtained for any galaxy. These three measures are the primary tools for studying the structure of the universe. (continue)