The period-luminosity relationship of Cepheid variables can be used if the Cepheid can be resolved in the galaxy. However, the brightest Cepheids have magnitudes of approximately -5 at maximum and since we are limited to an apparent magnitude of about 23 with a 200 inch telescope, we can use Cepheids to a maximum distance of only about 4 megaparsecs. Only galaxies in and very close to our own local group are within 4 megaparsecs. We can also use the maximum magnitude of nova or supernova to estimate galactic distances. However, these events do not occur frequently and hence are not available for systematic and intensive study.
Some galaxies contain emission nebula that are brighter than the brightest stars in the galaxy.
However, the method used here can give only rough distances since it requires knowledge of the luminosity of the nebula, and this is frequently uncertain. Similarly, estimates have been made by observing the brightest stars in globular clusters or galaxies and assuming that they are comparable in magnitude to stars in nearby galaxies of a similar type. However, these values are also uncertain. Several methods of distance determination are summarized in Table 1. In 1929 astronomer Edwin Hubble found a correlation between the red shift or velocity of recession of galaxies and their distances in that the velocity is directly proportional to the distance.