Why do astronomers study stellar spectra

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. Search for:. Astronomy and Philanthropy 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.

Key concepts and summary 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. Licenses and Attributions.

Spectroscopy lets scientists identify silicon dust in the clouds of gas giant planets like HD b located light-years away. As a fan of StarStuff , I often hear scientists talking about using 'spectroscopy' to study distant stars. Just recently, astronomers discovered a distant solar system, light years away with up to seven planets orbiting a Sun-like star called HD Like the very first exoplanet Pegusus discovered in , this new system was found using the science of spectroscopy.

In fact, most of the roughly planets so far found orbiting other stars, were detected by the same method. Spectroscopy — the use of light from a distant object to work out the object is made of — could be the single-most powerful tool astronomers use, says Professor Fred Watson from the Australian Astronomical Observatory.

From this you can work out all sorts of things," says Watson. When heated or when electrically charged, certain chemicals emit radiation at very specific colours or wavelengths called emission lines.

There are also absorption lines that appear as dark marks dividing the spectrum at specific wavelengths. Absorption lines are created when light from something hot like a star passes through a cooler gas, cancelling out the emission lines the chemicals in the gas would normally create. When you look at the spectrum of a star, for example, you can see absorption lines because the star's outer atmosphere is cooler than the central part, explains Watson.

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.

Three types of spectra: continuous, emission line and absorption. Each element in the periodic table can appear in gaseous form and will produce a series of bright lines unique to that element. Hydrogen will not look like helium which will not look like carbon which will not look like iron Thus, astronomers can identify what kinds of stuff are in stars from the lines they find in the star's spectrum.

This type of study is called spectroscopy. The science of spectroscopy is quite sophisticated. From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star.

The spectral line also can tell us about any magnetic field of the star. The width of the line can tell us how fast the material is moving. When Newton described the laws of refraction and dispersion in optics, and observed the solar spectrum, all he could see was a continuous band of colors. With this device, Wollaston saw that the colors were not spread out uniformly, but instead, some ranges of color were missing, appearing as dark bands in the solar spectrum.

He mistakenly attributed these lines to natural boundaries between the colors. In , German physicist Joseph Fraunhofer , upon a more careful examination of the solar spectrum, found about such dark lines missing colors , which led scientists to rule out the boundary hypothesis Figure 3. Figure 3. They did this by passing their light through various apparently transparent substances—usually containers with just a bit of thin gas in them.

These gases turned out not to be transparent at all colors: they were quite opaque at a few sharply defined wavelengths. Something in each gas had to be absorbing just a few colors of light and no others. All gases did this, but each different element absorbed a different set of colors and thus showed different dark lines.

If the gas in a container consisted of two elements, then light passing through it was missing the colors showing dark lines for both of the elements.

This discovery was one of the most important steps forward in the history of astronomy. What would happen if there were no continuous spectrum for our gases to remove light from? What if, instead, we heated the same thin gases until they were hot enough to glow with their own light? When the gases were heated, a spectrometer revealed no continuous spectrum, but several separate bright lines. That is, these hot gases emitted light only at certain specific wavelengths or colors.

When the gas was pure hydrogen, it would emit one pattern of colors; when it was pure sodium, it would emit a different pattern. A mixture of hydrogen and sodium emitted both sets of spectral lines. The colors the gases emitted when they were heated were the very same colors as those they had absorbed when a continuous source of light was behind them. From such experiments, scientists began to see that different substances showed distinctive spectral signatures by which their presence could be detected Figure 4.

Just as your signature allows the bank to identify you, the unique pattern of colors for each type of atom its spectrum can help us identify which element or elements are in a gas. Figure 4. Continuous Spectrum and Line Spectra from Different Elements: Each type of glowing gas each element produces its own unique pattern of lines, so the composition of a gas can be identified by its spectrum. The spectra of sodium, hydrogen, calcium, and mercury gases are shown here. In these experiments, then, there were three different types of spectra.

A continuous spectrum formed when a solid or very dense gas gives off radiation is an array of all wavelengths or colors of the rainbow. A continuous spectrum can serve as a backdrop from which the atoms of much less dense gas can absorb light.