Overview
Whenever we look at an astronomical object—in fact, whenever we look at anything—we are detecting light that interacted with matter at a distant location and travelled to us through space over a period of time. In Module 4, you were introduced to the concept of light as electromagnetic radiation, and you learned that visible light makes up only a small part of the whole electromagnetic spectrum. Aside from the data gathered by probes we have successfully landed on, or flown through the atmospheres of distant Solar System objects (viz. the Sun, Venus, Moon, Mars, Jupiter, Titan, a few comets and asteroids), our main source of information about astronomical objects comes in the form of light that has previously interacted with them.
In this module, you’re going to find out what matter actually is—at least, according to modern physics—and you’re going to see how it was by sorting out the peculiar effects matter has on light that physicists eventually discovered what it is. The module begins with a brief sketch of the components of atoms and the ways that they are differentiated. After that, we dive into the different features of spectra and the problem of figuring out their explanation. It’s an amazing story that led to a very surprising result: quantum physics. Then, having developed a basic understanding of why any signal of light comes to have the features it does, and what it can tell us about the last bit of matter it interacted with, we’ll discuss some of the different ways this theory is applied that help us sort out the properties of distant objects we can see. In particular, we’ll end by exploring various properties of the Sun that have been deduced, particularly the source of all the light it emits.
Learning Objectives
When you have finished this module, you should be able to do the following:
- Describe the basic properties of atoms and molecules.
- Explain how radiation is produced by all objects with temperatures above absolute zero.
- Compare different types of spectra and explain how they are produced.
- Explore what can be learned from spectra of celestial objects (temperature, chemical composition, radial velocity).
- Apply theory of atoms and spectra to the Sun and analyse its physical properties such as its temperature and luminosity, and chemical composition, and explain the source of solar energy.
Key Terms and Concepts
- spectrum (absorption/emission/continuous)
- orbital
- element
- Kirchhoff’s three laws
- blackbody
- Planck’s law
- luminosity
- Stefan-Boltzmann law
- Wien’s law
- quantum mechanics
- solar constant
- nuclear fusion
- solar neutrino problem
cosmiCave.org 