Spectral AnalysisSpectral Analysis

Gleaming Information From Gleaming Information From The StarsThe Stars

Somethings wrong?Somethings wrong?

But How do we know?But How do we know?

We’ve been there!We’ve been there!

But what about outer space?But what about outer space?

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

Spectral AnalysisSpectral AnalysisAstronomers can analyse electromagnetic radiation received Astronomers can analyse electromagnetic radiation received from space to obtain information about distant objectsfrom 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 SpectraEmission Spectra

A light bulb emits radiation of all wavelengths A light bulb emits radiation of all wavelengths (mostly in the visible range) (mostly in the visible range)

Viewed through a spectroscope, the spectrum Viewed through a spectroscope, the spectrum of the light from the bulb would show the of the light from the bulb would show the familiar rainbow of colors, from red to violet in familiar rainbow of colors, from red to violet in a a continuous spectrumcontinuous spectrum..

Spectral LinesSpectral Lines

Light produced by Light produced by excited hydrogen gas excited hydrogen gas does does notnot consist of all consist of all possible colors but possible colors but instead includes only instead includes only a few narrow, well-a few narrow, well-defined defined emission emission lineslines..

Spectral Lines of Other ElementsSpectral Lines of Other ElementsSimilar experiments on many different Similar experiments on many different gases show that sometimes the pattern of gases show that sometimes the pattern of lines is fairly simple, sometimes it is very lines is fairly simple, sometimes it is very complex but always it is complex but always it is uniqueunique to that to that element. element.

Spectral lines provided a one-of-a-kind "fingerprint" of the substance under investigation.

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

Analysing the Spectra from StarsAnalysing the Spectra from Stars

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

Stellar SpectraStellar SpectraThis image shows This image shows spectra from spectra from several different several different types of stars.types of stars.

The image can be The image can be in black and white in black and white because it is the because it is the relative position of relative position of the lines that the lines that identify the identify the elements present.elements present.

Learning From AfarLearning From Afar

Virtually all we know about planets, stars, and Virtually all we know about planets, stars, and galaxies is gleaned from studies of the light we galaxies is gleaned from studies of the light we receive from them.receive from them.After using the spectroscopes you should be After using the spectroscopes you should be able to identify:able to identify:– The difference between Continuous and Emission The difference between Continuous and Emission

SpectraSpectra– Spectral lines from excited gases using reference Spectral lines from excited gases using reference

books and tablesbooks and tables– The chemical composition of several ‘cosmic bodies’ The chemical composition of several ‘cosmic bodies’

from their emission spectrafrom their emission spectra