Edwin Powell Hubble (1889-1953), the man who discovered the expansion of the Universe, was a lawyer. He earned his law degree from Oxford University in 1913, and then moved to Louisville in Kentucky, where he practiced for about a year. He got bored with the profession though, which at that time and in that place wasn't as lucrative as it is today, and enrolled in a PhD program in Astronomy at the University of Chicago. Three years later, in 1917, he delivered his dissertation on ``Photographic Investigations of Faint Nebulae''.
Over the years that followed Hubble determined that the ``faint nebulae'' in question were large extragalactic clusters of stars, not unlike our own cluster, which today we call the Milky Way, or the Galaxy. Although he wasn't able to measure distances to other galaxies with great accuracy, he nevertheless observed that the farther away a galaxy, the larger its redshift.
The redshift of those far away galaxies was not accompanied by spectral distortions, so it could not be explained by dust absorption. There was only one explanation: the Doppler shift, which implied that the far away galaxies were moving away from us at great speeds. The farther the galaxy, the greater its escape velocity.
In this section we shall apply Fortran, the Hierarchical Data Format (HDF) libraries, and Gnuplot to analyse this phenomenon. We shall use fitting formulae, derived while playing with the Playsome Threesome (cf. Section 2.1.8), to evaluate slopes, offsets, and uncertaines thereof, associated with data collected by Sandage and Tamman.
While working with the HDF libraries you will learn how to write and read HDF files, and how to annotate HDF data with informative labels.
This section contributes to points 1a, 1b, 3, 5a, 5b, 5e, and 5g of the Syllabus (cf. Section 1.1).