- Current section: Introduction
- Learning outcomes
- 1 The Hertzsprung-Russell diagram
- 2 Observing through the interstellar medium
- 3 Summary
- 4 Questions
from The Open University
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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.
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