Spectral Analysis Gleaming Information From The Stars

Somethings wrong? But How do we know? We’ve been there! But what about outer space?

Visible Spectrum While passing through a prism, white light splits into its component colors, spanning red to violet in the visible part of the electromagnetic spectrum.

Spectral Analysis Astronomers can analyse electromagnetic radiation received from space to obtain information about distant objects Radiation is analysed with an instrument known as a spectroscope (or spectrometer) consisting of a telescope (to capture the radiation), a dispersing device (to spread it out into a spectrum-usually a prism or diffraction grating), and a detector.

Emission Spectra A light bulb emits radiation of all wavelengths (mostly in the visible range) Viewed through a spectroscope, the spectrum of the light from the bulb would show the familiar rainbow of colors, from red to violet in a continuous spectrum.

Spectral Lines Light produced by excited hydrogen gas does not consist of all possible colors but instead includes only a few narrow, well- defined emission lines.

Spectral Lines of Other Elements Similar experiments on many different gases show that sometimes the pattern of lines is fairly simple, sometimes it is very complex but always it is unique to that element. Spectral lines provided a one- of-a-kind "fingerprint" of the substance under investigation.

ASTRONOMICAL APPLICATIONS Once astronomers knew that spectral lines were indicators of chemical composition, they set about identifying the observed lines in the solar spectrum (The spectrum given out by the sun). Almost all the lines in light from extraterrestrial sources were attributed to known elements, however, some new lines also appeared in the solar spectrum. Almost all the lines in light from extraterrestrial sources were attributed to known elements, however, some new lines also appeared in the solar spectrum. In 1868, astronomers realised that those lines must correspond to a previously unknown element. It was given the name helium, after the Greek word helios, meaning "Sun." Only in 1895, almost three decades after its detection in sunlight, was helium discovered on Earth.

Analysing the Spectra from Stars By analysing the spectra of a star or nebula, it will show many superimposed lines from the different atoms that make up the star or nebula’s composition. This picture shows the actual spectrum observed from the hot gases in the Omega nebula

Stellar Spectra This image shows spectra from several different types of stars. The image can be in black and white because it is the relative position of the lines that identify the elements present.

Learning From Afar Virtually all we know about planets, stars, and galaxies is gleaned from studies of the light we receive from them. After using the spectroscopes you should be able to identify: –The difference between Continuous and Emission Spectra –Spectral lines from excited gases using reference books and tables –The chemical composition of several ‘cosmic bodies’ from their emission spectra