Spectroscopy

How Light Tells us about the Universe

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Unit 4: Cosmology

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Definitions

• Spectroscopy - the study of the light from an object
• Spectrometer - an instrument which spreads out light making a spectra
• Spectrum - range of electromagnetic energy separated by wavelength

Astronomers use spectroscopy because it allows them to analyze the universe from a distance

Studying an object’s spectrum can tell scientists the composition of an object, its temperature, its density and its motion

3 Types of Spectra

• Continuous – energy of all wavelengths
• Absorption – dark lines showing how gas is absorbed
• Emission – light lines showing how light shines

Continuous Spectrum

• From objects that give off heat
• stars, planets, moons
• Depends on temperature
• Ex: sunlight passing through a prism

Hotter objects

Cooler objects

Shorter wavelength

Longer wavelength

Continuous Spectrum

Discrete Spectrum �Absorption

Black body

(hot object)

Cool, thin gas

(like our atmosphere)

Spectra

Absorption

spectrum

Ex: stars, planets w/ atmospheres, & galaxies

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

Discrete Spectrum�Emission

Cold, empty space

Spectra

Emission

spectrum

Thin,hot

gas

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

Ex: comets, nebula,

& certain stars

What type of spectra�is shown here?

1. Continuous
2. Absorption
3. Emission

What type of spectra�is shown here?

1. Continuous
2. Absorption
3. Emission

What type of spectra�is shown here?

1. Continuous
2. Absorption
3. Emission

How astronomers use spectroscopy…

118 Known Elements

Emission Spectra

Absorption Spectra

Using Emission and Absorption Spectra

Hydrogen

When the lines MATCH then we know what the star is made of.

This star has hydrogen!

Mars Exploration Mission

The 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 Mission

Mission: 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.

It works for other disciples, as well – like gemology!

Spectra can also be expressed as a graph…

…and is used by forensic scientists to identify different drugs