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Andrew Marr's History: SurvivalSaturday, 25th April 2015 10:00 - YesterdayAndrew Marr sets off on an epic journey through 70,000 years of human history, starting with our earliest beginnings... Read more: OU on the BBC: Andrew Marr's History of the World - Survival
Andrew Marr's History: SurvivalSaturday, 25th April 2015 16:00 - Yesterday
Thinking Allowed: The Ethnography Award winner 2015Monday, 27th April 2015 00:15 - BBC Four
Christopher Plummer on King LearTuesday, 28th April 2015 04:35 - Sky Arts 1
Secret History Of... Deptford High StAvailable until Friday, 22nd May 2015 03:00How did the "Oxford Street of South London" come to be one of the poorest shopping streets in modern London? Read more: The Secret History Of Our Streets - Deptford High Street
Secret History Of... Deptford High StAvailable until Friday, 22nd May 2015 03:00
Thinking Allowed: The Ethnography Award 'Shortlist' 2015Available until Friday, 15th April 2016 10:30
A History of Ideas - Descartes Cogito Ergo SumAvailable until Thursday, 14th April 2016 08:30
OU on the BBC: Andrew Marr's History of the World - SurvivalAndrew Marr sets off on an epic journey through 70,000 years of human history, starting with our... Read more: OU on the BBC: Andrew Marr's History of the World - Survival
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
Eating to win: Activity, diet and weight controlWhat should we eat before and after exercise? This free course, Eating to win: activity, diet and... Try: Eating to win: Activity, diet and weight control 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