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Wastemen: The Home FrontSaturday, 23rd May 2015 02:55 - BBC TwoIn the first of the series, Christmas is coming. And the most magical time of the year brings with it enormous... Read more: Wastemen: The Home Front
Thinking Allowed: Poverty in Britain and unemployment as a choiceMonday, 25th May 2015 00:15 - BBC Radio 4
OU on the BBC: Inside The Medieval Mind - SexMonday, 25th May 2015 20:00 - BBC Four
OU on the BBC: Inside The Medieval Mind - SexTuesday, 26th May 2015 02:00 - BBC Four
Inside The Medieval Mind: KnowledgeAvailable until Saturday, 20th June 2015 00:00Explore the way medieval eyes saw the world – a place of mystery, enchantment, culminating in birth of the modern... Read more: OU on the BBC: Inside The Medieval Mind - Knowledge
Thinking Allowed: Poverty in Britain and unemployment as a choiceAvailable until Friday, 20th May 2016 12:00
Inside The Medieval Mind: KnowledgeAvailable until Saturday, 20th June 2015 00:00
Secret History Of... Portland RoadAvailable until Friday, 19th June 2015 02:20
Thinking Allowed: Happiness industry and wellness syndromeLaurie Taylor and guests discuss why policy makers are focused on measuring happiness in this... Read more: Thinking Allowed: Happiness industry and wellness syndrome
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
Introduction to bookkeeping and accountingLearn about the essential numerical skills required for accounting and bookkeeping. This free... Try: Introduction to bookkeeping and accounting 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