SpectroscopyA Tool of Astronomers

Definitions

• Spectroscopy- the study of the light from an object.

• Spectrometer- an instrument which spreads out light making a spectra.

• Spectra- range of electromagnetic energy separated by wavelength.

Astronomers use spectroscopy because it allows them to determine the makeup of stars… without having to be present to take samples.

Studying an objects spectra can tell scientists the composition of an object, its temperature, its density and its motion.

Two modern applications of spectroscopy in space…

Mars Exploration MissionThe Mars Exploration Rovers were launched with the goal of searching for and analyzing rock and soils on Mars. They utilized several spectrometers to analyze samples.

Mini-TES: miniature thermal emission spectrometer (examine rock, soil & atmosphere)

MB: Mossbauer Spectrometer (examine mineralogy of rocks & soils)

APXS: Alpha Particle X-ray Spectrometer (analyze elements in rocks & soils)

Cassini-Hyugen’s MissionMission: to gather information on Titan (Saturn’s moon).

VIMS: Visual and Infrared Mapping Spectrometer (gather data about surface, rings & atmosphere of Titan and Saturn).

CIRS: Composite Infrared Spectrometer (searches for heat and by that gather information on the object’s composition.

2 Basic Types of Spectra

• Continuous- energy of all wavelengths

• Discrete- energy at a particular wavelength– Emission or bright lines– Absorption or dark lines

Continuous Spectrum

• Also called thermal or blackbody spectra

• Spectra of stars, planets, moons

• Depends on temperature

Ex: sunlight passing through a prism

Hotter objects

Shift toward this end

Cooler objects

Shift toward this end

Shorter wavelength

Longer wavelength

Continuous Spectrum continued

Discrete Spectrum Absorption

Hot object

Cool, thin gas

Spectra

Absorptionspectrum

Ex: stars, planets w/ atmospheres, & galaxies

Each element has a unique signature of absorption lines. That pattern helps scientists identify the element(s).

Discreet spectrum-

Emission

Cold, empty space

Spectra

Emissionspectrum

Thin,hotgas

Again, the pattern of the lines determines the identity of the element.

Ex: comets, nebula & certain stars

Motion of Objects in Space

Blue shift shows object ismoving toward the observer.

This shows the normal position or no motion.

This shows a red shift meaning that the object is moving away from the observer.

Compare the dark lines in the middle spectra to the dark lines in the other two spectra.

Spectroscopy Lab

Determining the Spectraof Certain Elements

What type of spectrais shown here?

•Continuous•Absorption•Emission

What type of spectrais shown here?

•Continuous•Absorption•Emission

Why does this picture represent just the continuous spectrum of light?

Light is just one portion of the electromagnetic spectrum.

Name 5 other parts of the EM spectrum.

Acknowledgements

• www.ipac.caltech.edu/Outreach/Edu/Spectra/spec.html• www.astronomynotes.com/lights4.htm• http://saturn.jpl.nasa.gov/spacecraft/instruments-cassini-cirs.cfm• http://pmo-sun.uoregon.edu/~astrosites.html• http://marsrovers.nasa.gov/overview

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