During the early twentieth century, astronomers discovered that galaxies are rushing away from us at huge speeds. The Sombrero galaxy, for instance, was found to be moving away from the Earth at about 1000 km/s. These speeds can be found very accurately from the doppler red shift of spectral lines.
Hubble concluded that the speed of a galaxy is proportional to its distance – that is, that if one galaxy is three times further from us than another, then it will be moving away at a speed which is three times greater than the other. This result was a huge step forward for astronomers. It implied that in the beginning, the Universe was very much more dense than it is now, and that since the Big Bang all the matter in the Universe has been flying apart. http://www.aps.org/ publications/apsnews/200801/physicshistory.cfm
Using a subset of Edwin Hubble’s original data from the 1920’s, you will plot a graph by hand of velocity against distance and draw a straight line (by eye) to the points which “best fits” the data. Should the line should go through the origin? The slope of the line represents velocity/distance, and is known as the Hubble constant Ho. Use your value of Ho to deduce the age of the Universe.
As you prepare this assignment for submission. NOTE:
Marks will be deduced for incomplete and poorly presented work. Steps in the calculations need to be described or explained as required, terms in the equations defined. The graph (by hand) needs to be properly titled and axes labeled, i.e., “V versus D” is not a title, a title should be at least a complete sentence which describes what is being shown.
An estimate for the age of the Universe, 1/Ho is being derived by a “best fit line” through a set of data points. Ho is the Hubble Constant in Hubbles, Law: V = Ho*D.
V is the recessional velocity and D is the distance to far away galaxies. Note that nearby galaxies, our local group, are not necessarily moving away from us but are in mutual gravitation orbits.
Also keep in mind, that the data being plotted is from the 1920’s — Hubble’s original data. The age estimate derived has been vastly refined over the decades through more data, but primarily from a better understanding of stellar properties and assumptions made in distance estimates — Hubble’s distance estimates were flawed resulting in considerable activity in the scientific community — both Astronomy and Earth Science.
