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How to determine the distance from the Sun to a galaxy just by oberving the sky


This exercise enables you to determine the distance from the Sun to the Large Magellanic Cloud by studying a Cepheid and its regular variations of luminosity.

          Henrietta LeavittCepheids - discovered and studied by the American astronomer Henrietta Leavitt in 1912 - are giant yellow stars much more massive than the Sun ans hundreds or thousands times more luminous. They all possess a noteworthy disctinctive characteristic: their brightness varies periodically, to a very regular rhythm. These stars are actually like lighthouses for astrophysicists: they can indeed be observed from extremely long distances.

          As a period of variation separating two peaks of luminosity is particularly stationary and constant, these stars are more than useful in order to evaluate and work out distances between galaxies. This is what we are going to consider in this exercise.

 

  Made by Rachel Comte, thanks to an idea of Weronika Sliwa






Le Grand Nuage de Magellan         Visible to the unaided eye, the Large Magellanic Cloud is a nearby irregular dwarf galaxy which seems to be in orbit around the Milky Way. With an amount of more than 30 billion stars - among them a lot of cepheids - it is the fourth largest galaxy in the Local Group, i.e. the special group comprising more than 30 galaxies including ours.

       This exercise - thanks to 20 photographs and SalsaJ software - will enable you to determine by yourself and without any ugly mathematical formulae the distance from us to the Large Magellanic Cloud.

            To do that, you will find below a series of photographs (20) that you will have to study on SalsaJ, and a precise procedure which will give you the instructions to follow in order to do this exercise. Finally you will find an answerfile which is to be filled in as one goes along.

 Photographs (.zip)

Instructions (.pdf)

  Answerfile (.xls)