In his second lecture Malcolm Longair explains the science of stars.

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This was recorded on 2 Dec 1990.
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From the 1990 programme notes:
Most of the visible light in the Universe is starlight. We now understand in some detail how it is that stars like the Sun function. The source of energy in their interiors is nuclear energy powered by nuclear reactions which convert hydrogen into helium. A remarkable recent advance has been the ability of astronomers to probe the interior of the Sun in two different ways. First, they can study minute particles called neutrinos which are produced in enormous quantities in the nuclear reactions which power the Sun. These have now been detected but in somewhat smaller numbers than expected - this is very worrisome. Second, they can probe the internal structure by studying the Sun's own oscillations which have provided an entirely new way of probing into the internal density and temperature of the Sun.
Star formation is one of the most important aspects of stellar evolution but also among the most poorly understood. Fortunately, we can now probe deep inside the regions where stars are forming by using infrared cameras which see through the obscuring dust. These observations give us important clues about the three big problems in understanding the formation of stars. First, how can a collapsing cloud lose energy sufficiently rapidly to enable it to form; second, how can it get rid of its rotation; third, how can it get rid of magnetic fields. We will show how answers to these problems are being suggested by new observations of the behaviour of the youngest stars we know of deep inside dusty giant molecular clouds.
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About the 1990 CHRISTMAS LECTURES
The astronomical sciences have developed out of all recognition over the last 40 years. Up till about 1950, astronomy meant optical astronomy, but now it could mean radio astronomy, X-ray astronomy, infrared and ultraviolet astronomy, γ-ray astronomy and even more exotic ways of looking at the Universe through neutrino astronomy. Each of these disciplines has contributed essential new facts about the origin and evolution of different classes of object in the Universe. The aim of these lectures is to put all this new knowledge into a coherent picture of our present understanding of the origin and evolution of the Universe.
To solve the problems of the origins of astronomical systems, we must call upon an enormous range of physical tools to understand what it is we have to explain. We need to introduce many ideas from simple physics in order to define precisely the astrophysical problems which have to be solved. We will introduce these ideas as the lectures develop – we will need ideas like Newton’s law of gravity, the conservation of angular momentum, Einstein’s mass-energy relation E = mc2, simple ideas about black holes, nuclear reactions in stars and so on. We will introduce much of the essential physics through demonstrations, models and analogies. By the end of the lectures, we will not have answered the question of the origins of all the contents of the Universe but we will have gained an understanding of what the key questions are which still need to be addressed.
Find out more about the CHRISTMAS LECTURES here: https://www.rigb.org/christmas-lectures
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