Sun & Stars

Part 1

There are four chapters in part 1:

Chapter One - Seeing the Sun.

Describes the photosphere, chromosphere and corona of the Sun. Covers the features visible on the Sun's surface, the Sun's inner and outer atmosphere, line spectra (absorption and emission), continuous spectra - Wien's displacement law. The image at the top left of this page is of the Sun, showing prominences, filaments and coronal holes, courtesy of NASA.

Comments:

I found this chapter very straightforward. There is a lot of descriptive material about the Sun and more information can be found on the WWW. Maths-wise, the main equation you'll come across is Wien's displacement law. The course CD-ROM has a useful interactive section covering basic background science, such as energy levels in the atom and the periodic table. This helps if your knowledge is rusty.

Useful links:

• Sacramento Peak solar observatory. Images and current data from the Sun.

• Spaceweather.com. News and information about the Sun-Earth environment.

• Physics 2000 Uses Java applets to illustrate basic principles of physics. In particular, the electomagnetic spectrum and the quantum atom are covered, as well as the periodic table, atom energy levels, isotopes and radioactivity.

• The origin & nature of light. Concepts covered: atoms, electromagnetic spectrum, light as a wave and a particle, continuous spectra, Doppler shift.

• Light and Spectroscopy help. What are those squiggly lines? The purpose of this site is to make the concepts of light and astronomical spectroscopy understandable. Discusses a wide range of issues relating to spectroscopy.

Chapter Two - The Working Sun.

Describes the internal structure and composition of the Sun. Covers the energy source of the Sun - the ppI chain, and how energy reaches its surface. Discusses evidence for theories of the solar interior based on solar oscillations and neutrino observations. Solar activity is covered: sunspots, active regions, solar flares, coronal mass ejections, magnetic reconnection, the solar cycle. Finally the effects of the Sun in space are mentioned, mainly the solar wind and its interaction with Earth's atmosphere.

Comments:

This chapter is longer than the first, but is very interesting with a lot of material on the Sun's interior: its composition, the main energy source of the Sun, and solar activity. Again, there's very little maths here to worry about.

Useful links:

• Helioseismology. The global oscillation network group page.

• Sudbury neutrino observatory. Lots of links and information about the solar neutrino problem.

• Magnetism on the Sun. Explaining magnetic reconnection on the Sun.

• NASA's site on exploring the magnetosphere. A comprehensive guide to all aspects of the Sun's magnetosphere. Covers many aspects of the Sun's features and the historical background to many discoveries.

Chapter Three - Measuring Stars.

The attention of the book turns to the stars and how they move relative to Earth. The Doppler shift is covered. Methods for measuring the distance to stars are discussed. Binary and multiple star systems are introduced. The size, temperature and colour of stars is covered, introducing the Harvard spectral class system. Luminosity is defined and its relation to a star's radius and temperature is described. Absolute and apparent visual magnitudes are introduced. The power of spectroscopy in determining luminosities, radii and distances is covered, especially with respect to variable stars. The composition of stars is discussed, as is measuring stellar masses. The chapter finishes by describing how to find stellar radii from eclipsing binary stars.

Comments:

This is where if you are a bit shaky with maths that you may have some difficulties. There is no calculus, but there are a lot of equations that you need to be able to manipulate to get various quantities. If you've only done S194 previously to this course, without any other maths, then you will find this is a big jump. However, if you've successfully completed MST121 then you should be OK. For those of you desperate to know exactly what is entailed, this is a list of learning outcomes for Ch.3 given on the course website:

• Perform calculations involving proper motion, transverse velocity and radial velocity.
• Outline how to obtain stellar distances by the methods of trigonometric parallax and spectroscopic parallax; calculate stellar distances using these two methods.
• Describe how to obtain stellar radii from stellar angular diameters and distances, and from stellar luminosity and photospheric temperatures; calculate stellar radii using these two methods.
• Outline how to obtain photospheric temperatures from flux density ratios, and from spectral classes; obtain estimates of temperature using the latter method.
• Outline how to obtain stellar luminosities from stellar radii and temperatures, and from various spectral lines in stellar spectra; calculate stellar luminosities using the former method.
• Describe how magnitudes can be used to define stellar brightness; perform calculations using magnitudes.
• Describe the basic properties of binary stars, variable stars and star clusters and be aware of their value in determination of basic stellar properties.
• Outline how stellar compositions are obtained from spectral line studies and describe in broad terms the composition of stars.
• Outline how stellar masses may be obtained for binary systems; calculate stellar masses using these methods.

Useful links:

• Star Clusters. Has links to the Messier catalog of star clusters with detailed information about each cluster.

Chapter Four - Comparing Stars.

This chapter covers the overall distribution of stellar properties. The Hertzsprung-Russell diagram is introduced showing how luminosity and temperature (or visual magnitude and colour) are related. The main classes of stars are described: main sequence, red giants, supergiants, white dwarfs. The next section focusses on how we can explain the distribution of stars on the H-R diagram. Stellar masses in relation to stellar evolution is discussed, as are star clusters and their evolution. Finally, observing through the interstellar medium is described. The effects of interstellar gas and interstellar dust are discussed and how we can use stars to probe the interstellar medium.

Comments:

The Hertzsprung-Russell diagram is introduced, and gets a lot more airplay as the course goes on. This chapter is mainly descriptive, no difficult concepts as far as I could see. There are many resources on the H-R diagram on the WWW, so I've only mentioned a couple.

• The Hertzsprung-Russell diagram. Shows some interesting H-R diagrams of various clusters. Also shows the luminosity classes.

• An introduction to the H-R diagram. An article discussing various aspects of the diagram, mentioning some of the more advanced topics.