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A History of Ideas - Buddhism's four Noble TruthsThursday, 2nd April 2015 12:04 - BBC Radio 4Naomi Appleton, Chancellor's fellow in Religious Studies at the University of Edinburgh, explores the Buddha's Four... Watch now: OU on the BBC: A History of Ideas - Buddhism's four Noble Truths
Joseph Fiennes on Romeo & JulietThursday, 2nd April 2015 20:00 - Sky Arts 1 HD
A History of Ideas - Ayn Rand and selfishnessFriday, 3rd April 2015 12:04 - BBC Radio 4
Thinking Allowed: Citizenship ceremonies and family tiesMonday, 6th April 2015 00:15 - BBC Radio 4
Thinking Allowed: Citizenship ceremonies and family tiesAvailable until Thursday, 31st March 2016 09:15Laurie Taylor and guests discuss studies into citizenship and the links between family ties and stories. Read more: Thinking Allowed: Citizenship ceremonies and family ties
OU on BBC: A History of Ideas - Ayn Rand and selfishnessMorality and selfishness sound like opposites - but not according to the Russian-American... Watch now: OU on BBC: A History of Ideas - Ayn Rand and selfishness
Take the photographic memory testCan you capture scenes just by looking at them? Find out with our photographic memory test. Launch now: Take the photographic memory test
The business of footballWelcome to this free new OpenLearn course produced by The Open University working in partnership... Try: The business of football now
Succeed with maths – Part 1[BETA] If you feel that maths is a mystery that you want to unravel then this short 8-week course... Try: Succeed with maths – Part 1 now
Stars can necessarily be observed only at a distance. This unit introduces the...
Stars can necessarily be observed only at a distance. This unit introduces the Hertzsprung–Russell diagram, an essential tool in understanding the nature of stars. You should have some understanding of the basic stellar properties of luminosity and temperature in order to get the most from the unit.
After studying this unit you should be able to:
- describe and comment on the main features of a Hertzsprung-Russell diagram of stars in general, and of stars in a cluster;
- outline a broad model of stellar evolution based on the observed properties of large numbers of stars, and describe how stars of different initial mass might evolve;
- describe the effects of interstellar material on starlight, and outline some of the processes by which such material might be a source of electromagnetic radiation.
- Current section: Introduction
- Learning outcomes
- 1 The Hertzsprung-Russell diagram
- 2 Observing through the interstellar medium
- 3 Summary
- 4 Questions
We can study the individual properties of individual stars, such as photospheric temperature, luminosity, radius, composition and mass. If we wish to understand more about stars and obtain some insight into their evolution, we need to look at the overall distribution of stellar properties. We would like to know the answers to such questions as ‘Can stars have any combination of these properties?’ and ‘How many stars are there of each type?’ We can potentially learn a lot more about the stars if we compare them, but what should be the basis of our comparison? We certainly want to use intrinsic properties, such as luminosity, and not properties that depend on the distance to the star, such as the flux density received on Earth. Also, as an initial step, we want to avoid properties that are well removed from what we actually observe. In this unit we look at probably the most important diagram in stellar astronomy, the Hertzsprung-Russell diagram, and how it is used to identify the main classes of stars.
This unit is an adapted extract from the course