How can spectroscopy be used to identify elements in stars

Spectroscopy can be very useful in helping scientists understand how an object like a black hole, neutron star, or active galaxy produces light, how fast it is moving, and what elements it is composed of. Spectra can be produced for any energy of light, from low-energy radio waves to very high-energy gamma rays.

Each spectrum holds a wide variety of information. For instance, there are many different mechanisms by which an object, like a star, can produce light. Each of these mechanisms has a characteristic spectrum. White light what we call visible or optical light can be split up into its constituent colors easily and with a familiar result: the rainbow. All we have to do is use a slit to focus a narrow beam of the light at a prism.

This setup is actually a basic spectrometer. The resultant rainbow is really a continuous spectrum that shows us the different energies of light from red to blue present in visible light.

But the electromagnetic spectrum encompasses more than just optical light. It covers all energies of light, extending from low-energy radio waves, to microwaves, to infrared, to optical light, to ultraviolet, to very high-energy X-rays and gamma rays.

But when an atom has a different number of protons and electrons it becomes a different element. Because each element has a different number of protons in the nucleus, the energy level of each element is unique.

Scientists can use this information in two main ways. First, when a substance gets extra energy -- such as when you put salt in a flame -- the elements in the substance will often get rid of that energy by emitting light, called an emission spectrum.

Second, when light travels through a gas, for example, the gas can absorb some of that light -- that's an absorption spectrum. In emission spectra, bright lines will show up corresponding to the difference between energy levels of the elements, where in an absorption spectrum, the lines will be dark.

By looking at the pattern of lines, scientists can figure out the energy levels of the elements in the sample. Since every element has unique energy levels, the spectra can help identify elements in a sample.

First published in , Richard Gaughan has contributed to publications such as "Photonics Spectra," "The Scientist" and other magazines. How to Use The Periodic Table. What Are the 4 Atomic Models? Snapshot : Curiosity sees glowing clouds on Mars. What echoing radio waves taught us about Venus. InSight tracks down the origin of two big marsquakes. Blast from the past: Rare meteorite recovered in the U. Cosmos: Origin and Fate of the Universe. Astronomy's Moon Globe.

Galaxies by David Eicher. Astronomy Puzzles. Jon Lomberg Milky Way Posters. Astronomy for Kids. Sign up. Table of Contents Subscribe Digital Editons. A chronicle of the first steps on the Moon , and what it took to get there. The Magazine News Observing. Photos Videos Blogs Community Shop. If a star is rotating rapidly, there will be a greater spread of Doppler shifts and all its spectral lines should be quite broad. In fact, astronomers call this effect line broadening , and the amount of broadening can tell us the speed at which the star rotates Figure 6.

A rotating star will show broader spectral lines than a nonrotating star. Measurements of the widths of spectral lines show that many stars rotate faster than the Sun, some with periods of less than a day! An example of this is the star Vega , which rotates once every The Sun, with its rotation period of about a month, rotates rather slowly.

Studies have shown that stars decrease their rotational speed as they age. Young stars rotate very quickly, with rotational periods of days or less.

Very old stars can have rotation periods of several months. Figure 7: Comparison of Rotating Stars. This illustration compares the more rapidly rotating star Altair to the slower rotating Sun.

As you can see, spectroscopy is an extremely powerful technique that helps us learn all kinds of information about stars that we simply could not gather any other way. We will see in later chapters that these same techniques can also teach us about galaxies, which are the most distant objects that can we observe. Without spectroscopy, we would know next to nothing about the universe beyond the solar system.

Throughout the history of astronomy, contributions from wealthy patrons of the science have made an enormous difference in building new instruments and carrying out long-term research projects. She was the widow of Henry Draper, a physician who was one of the most accomplished amateur astronomers of the nineteenth century and the first person to successfully photograph the spectrum of a star. Anna Draper gave several hundred thousand dollars to Harvard Observatory.

Atop the foundation rose a inch refractor, which for many years was the main instrument at the Lick Observatory near San Jose. Figure 8: Henry Draper — and James Lick — After his death, his widow funded further astronomy work in his name. The Lick telescope remained the largest in the world until , when George Ellery Hale persuaded railroad millionaire Charles Yerkes to finance the construction of a inch telescope near Chicago. Now, if any of you become millionaires or billionaires, and astronomy has sparked your interest, do keep an astronomical instrument or project in mind as you plan your estate.

But frankly, private philanthropy could not possibly support the full enterprise of scientific research in astronomy. Much of our exploration of the universe is financed by federal agencies such as the National Science Foundation and NASA in the United States, and by similar government agencies in the other countries. In this way, all of us, through a very small share of our tax dollars, are philanthropists for astronomy. Spectra of stars of the same temperature but different atmospheric pressures have subtle differences, so spectra can be used to determine whether a star has a large radius and low atmospheric pressure a giant star or a small radius and high atmospheric pressure.

Stellar spectra can also be used to determine the chemical composition of stars; hydrogen and helium make up most of the mass of all stars. Measurements of line shifts produced by the Doppler effect indicate the radial velocity of a star.

Broadening of spectral lines by the Doppler effect is a measure of rotational velocity. Skip to main content. Analyzing Starlight.