Hubble's Law states that the galaxy's recession speed = H o * distance, where H o is known as the Hubble constant and is a measure of the slope of the line through the distance versus recession velocity data. Where v is the galaxy's velocity (in km/sec), d is the distance to the galaxy (in megaparsecs 1 Mpc = 1 million parsecs), and H o proportionality constant, called 'The Hubble constant'. Hubble concluded that the fainter and smaller the galaxy, the more distant it is, and the faster it is moving away from us, or that the recessional velocity of a galaxy is proportional to its distance from us: the distance of the galaxies, he found a surprising relation: more distant galaxies are moving faster away from us. The Hubble Distance - Redshift Relationship The speed of light, c, has a constant value of 300,000 km/sec.Īnd the is moving away from us with a velocity, v = c * z = 300,000 km/sec * 0.01275 = 3826 km/sec

For example:Ībsorption lines of hydrogen, normally measured to be at 4861Å and 6563Å, are measured in the spectrum of a particular galaxy to be at 4923Å and 6647Å. One can use the measured wavelengths of known spectral lines to determine the velocity of a galaxy. In the data collected by Hubble, the characteristic absorption and emission line features in the spectrum due to hydrogen, calcium and other elements which appear at longer (redder) wavelengths than in a terrestrial laboratory. Wavelengths of optical light are usually measured in either Angstroms (1 Å = 10 -10 m) or nanometers (1 nm = 10 -9 m). It is common to use 'delta_lambda' to represent the observed wavelength minus the rest wavelength. Where 'lambda_0' is the rest wavelength of the radiation, and is 'lambda_v' is the observed wavelength which has been shifted due to the radial motion between the object and the observer. The radiation coming from a moving object is shifted in wavelength: The change in wavelength of the spectral features is due to the Doppler effect, the change in wavelength that results when a given object and an observer are in motion either toward or away from each other. Redshift is a term used to describe situations when an astronomical object is observed to being moving away from the observer, such that emission or absorption features in the object's spectum are observed to have shifted toward longer (red) wavelengths. In 1929 Hubble published his findings, detailing revealed that the fainter and smaller a galaxy appeared, the higher was its redshift. Hubble compared recession velocities of galaxies measured from their spectra to their apparent brightness estimated from photographic plates. Utilizing the 100-inch telescope at California's Mount Wilson Observatory (at the time the world's largest telescope) Hubble obtained spectra and measurements of the distance to a few dozen galaxies, leading to the discovery that the Universe is expanding.

Measuring the Distance to Nearby Galaxies Hubble's Distance - Redshift RelationĮdwin Hubble, redshifted spectra, and distances to galaxiesĭuring the 1920's, Edwin Powell Hubble demonstrated that the small hazy patches of light which were then known as 'spiral nebulae' are actually entire galaxies containing hundreds of billions of stars.

Observed redshift equation