Incredible is Everywhere

This was the view outside my tutorial room yesterday.  That's the Christ Church Quadrangle.  I was there for a meeting with Leo Huckvale and we had our first real session - an introduction to Astronomy and Cosmology.  Leo doesn't work at Christ Church and neither does Christopher Taylor (they are the two professors teaching my "History and Practice of Observational Astronomy" tutorial).  But Mr. Taylor's wife, Dr. Rowena Archer, she teaches Medieval History at Christ Church and kindly allowed us the use of her office.

The session went really well.  We covered the notable achievements of Hipparchos, Ptolemy, Brahe & Kepler.  Apparently Brahe was such a genius the King of Denmark gave him an island and enough funds to build a castle observatory there.  The castle still stands on the island of Hven (Ven in Swedish).

We spent the bulk of our time discussing stellar magnitudes, which are of paramount concern.  When we gaze at the heavens, some stars appear much brighter than others.  The Greek astronomer Hipparchos created the first catalogue of stars and grouped them according to brightness as seen with the unaided eye.  This was done sometime between 130 and 160 BC.  These stars (the 251 of them that Hipparchos studied) were separated into six groups - the brightest being termed 1st magnitude and the dimmest 6th magnitude.  This system is still used today, although our method for measuring brightness has become more exact.  Hipparchos' estimations of the differences between magnitudes has been verified as almost right on.  He identified a logarithmic relationship between each step up in magnitude.  Since a 1st magnitude star is about 100 times brighter than a 6th, the scale is like the Richter Scale which measures earthquake severity.  So each step up into a new whole number means exponentially more ground shaking, or in this case, stellar brightness.  

But hold on you are saying, just because one star looks brighter than another that doesn't necessarily mean its got a greater magnitude.  A star that appears bright to us could be either a faint star that is close to the Sun or a ridiculously luminous one really far away.  So this system is really about apparent magnitudes.  But with the aid of geometry and calculus we have learned to determine just how far away each star is and thus its actual magnitude.  In fact this system of magnitudes, once aided by the right math, was the source of the first understanding of cosmic distances.


I'm really into this stuff.  Can't wait to learn the math and stand on the shoulders of giants.