The Role of Spectroscopy in Astronomy

Spectroscopy is the study of the relationship between light (electromagnetic radiation) and physical matter. In astronomy, this can be highly useful. The role of spectroscopy in astronomy is to analyze the light received from distant planets and interstellar phenomena and, based on that light, estimate what chemicals are present at the source, and in what proportions.

– Spectroscopy –

Spectroscopy is the means chemists and physicists use to study the relationship between electromagnetic radiation – including the small portion of the electromagnetic spectrum that comprises visible light – and physical matter, i.e. chemical elements and compounds. More specifically, it is a technique used to identify what chemicals are present in a sample.

In general, then, the role of spectroscopy is to help an observer identify what chemicals are present, and in what amounts. This can be highly useful in a number of important and common applications. Basic spectroscopy experiments are often introduced to senior high school students in chemistry, and certainly to college and university students taking introductory chemistry labs. Beyond that, one common case where spectroscopy becomes important is in analysis of magnetic resonance imaging (MRI), a common if highly expensive medical technology.

– Spectroscopy in Space –

The role of spectroscopy in astronomy is, functionally, no different than the role of spectroscopy on the ground. The main difference in astronomy is that it is a tool used to measure very large objects, very far away, rather than relatively small and confined samples in the laboratory.

There are several basic applications for spectroscopy. One of the most important is identifying star types. All stars vary in terms of their size and brightness, but also in terms of their makeup. Because all stars consist mostly of hydrogen and helium, astronomers have a special shorthand, “metallicity,” which refers not to all metals according to the chemical definition of the term, but all chemicals on the periodic table that are not helium or hydrogen. Based on existing models of stellar evolution, astronomers using spectroscopic data can now analyze a given star and estimate its metal content, its age, and even its life expectancy (how fast it will run out of hydrogen fuel and either collapse or explode).

Similar spectroscopic analysis can, of course, be applied to all other space objects as well. Closer to home, the role of spectroscopy in astronomy is to identify the composition of the atmospheres of distant planets, like Uranus and Neptune. Much farther away, the role of spectroscopy is to identify the general composition of entire galaxies, like Andromeda.

– The Red Shift –

In the last forty years, one of the most important and groundbreaking contributions of spectroscopy in astronomy, however, has been its role in detecting and analyzing the so-called “red shift” in starlight. The redshift is exactly analogous to the Doppler effect on sound: when something is travelling away from the listener at high speeds, sounds it emits (like an engine in a fast-moving car, for example) become lower, more drawn-out, and trail away, whereas sounds coming from a fast-approaching object or car reach the listener faster, therefore sounding higher.

Light travels at extremely rapid speeds, but when astronomers study massive interstellar objects travelling at the enormous speeds which characterize all celestial objects, light starts to display similar properties. Most galaxies in the universe are actually travelling away from ours at very high speed, which means the wavelengths of the light that reach us stretch out: in other words, they look redder than they should. (By contrast, the few objects which are speeding toward us, like Andromeda, behave in the opposite manner, and look bluer than they actually should.)

The redshift is very useful in determining just how far an object is from us, and how old it is. Originally, the discovery that galaxies were moving away from each other confirmed the theory of the Big Bang: the theory that they all started in a very close, central location and have since been speeding apart, blown apart by some vast universal force. More recently, the same data has been used to support the theory of dark matter, a dense and difficult-to-understand concept in advanced theoretical physics.