AOTF July 2017 Meeting
by Gerry Cassidy - 13:57 on 11 August 2017
Astronomers of the Future Club in Troon - 27th July 2017 meeting write up
Report by Alan Martin
At the Astronomers of the Future Club meeting on 27h July 2017, at the RSAS Barassie Works Club in Troon, guest speaker Prof. Alec McKinnon of Glasgow University spoke on the subject of Red & Blue stars.
Providing a highly informative and entertaining talk Prof. McKinnon started with the subject of star brightness magnitude. Contrary to intuition the lower the magnitude figure the brighter the star, with a star of magnitude 1 being twice as bright as a star of magnitude 2. The brightest star is Sirius which has a magnitude of -1.4 with the star Vega, taken as the standard from which all others are referenced, at zero. The vast majority of stars though exist in the range of magnitude 6 to 10. The stars at magnitude 6 are just visible to the naked eye with optical assistance, binoculars and telescopes required to see stars higher than this.
The magnitude of the star directly correlates to it’s temperature and distance from the observer. This gives rise to the terms Red & Blue stars. Again, counter intuitively Red stars are much cooler than the Blue, with Red stars having to be much closer or larger than it’s blue equivalent to produce the same magnitude in the night sky. Of these we are really only able to observe the giant variety of both with the naked eye. Examples of these are Betelgeuse & Rigel, probably the most famous examples of a Red and a Blue giant respectively, within the Orion constellation.
The distance from earth was originally measured using parallax effects, i.e. as the Earth orbits the sun a nearby star will appear to move against the more distant background stars. Astronomers can measure a star's position once, and then again 6 months later on the Earth’s orbit and calculate the apparent change in position and therefore it’s distance.
Prof. McKinnon then outlined the Hertzsprung-Russel diagram of which shows the distribution of stars in relation to luminosity, distance and size where the majority of stars lie on the Main Sequence band with our own Sun lying approximately half way up this. Interestingly enough the nearest stars to Earth are probably very small red & brown dwarf stars which are of such low magnitude and size they we are unable to view these using visible light.
Note, the next meeting of AOTF will be on Thursday 31st August at 7.15pm upstairs in the RSAS Barassie Works club in Shore Road, Troon, KA10 6AG when Marc Charron will speaking on the subject of Astrophotography with Camera and Tripod.
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