1. Spectroscopy Lecture

2. Standards
Explain how objects in the universe emit different electromagnetic radiation and how this information is used
Describe how waves are used for practical purposes (e.g., Doppler effect)
Understand how knowledge about the universe comes from evidence collected from advanced technology (e.g., telescopes)

3. Spectroscopy
How do we know what objects out in space are made out of without directly examining them?
Spectroscopy – is the way in which astronomers can determine the chemical composition of objects such as stars and planets
This is done by observing the object’s spectrum (plural, spectra)

4. Spectroscopy
Spectroscopy is the study of how atoms absorb and emit electromagnetic radiation
This happens when electrons move to different energy levels within an atom.

5. Spectroscopy
Absorption – an electron gains energy from an incoming photon and it jumps to a higher energy level.
Emission – occurs when the electron returns to a lower energy level and gives off (emits) a photon (light).

6. Spectroscopy
Spectroscope – instrument used to determine the composition, temperature and speed of objects.
Spectroscopes that are used to observe objects in space are made of a prism combined with a telescope

7. Types of Spectra There are 3 types of spectra: Continuous spectrum
Emission spectrum
Absorption spectrum

8. Continuous Spectrum Unbroken band of colors Ex: Rainbow
Comes from 3 sources:
Glowing (hot) solid
Glowing liquid
Hot, compressed gases deep inside a star

9. Emission or Bright Line Spectrum
Spaced series of lines of different colors and brightness
Comes from a glowing, thin gas or vapor
Ex: neon gas
Each element has a unique bright line spectrum
This is like the element’s fingerprint, and allows us to identify it in distant objects!

10. Emission Spectra
Photo:

11. Absorption or Dark Line Spectrum
Series of dark lines within a continuous spectrum
Occur where light is absorbed
Dark lines are in same places as bright lines for a particular element
Form when source passes through a cool gas

12. Absorption Spectra
Photo:
vtam/EN/show.asp?XH16

13. Absorption or Dark Line Spectrum
The sun’s spectrum is an absorption spectrum:
Hot, compressed gases in sun’s center radiate a continuous spectrum
Gases pass through outer, cooler layers and are absorbed
The sun’s spectrum has 1000’s of dark lines
67 elements have been identified on the sun

14. Solar Spectrum

15. Absorption or Dark Line Spectrum
Absorption spectra are used to determine the composition of planets’ atmospheres
Planets shine by reflecting light from the sun
If spectrum shows dark lines that are not part of sun’s spectrum, then they are caused by substances in the planet’s atmosphere

17. Doppler Effect in Spectra
Doppler effect – a motion-induced change in observed wavelength (car ex.)

18. Doppler Effect in Spectra
Dark lines in stars’ spectra are shifted slightly right (towards blue) or left (towards red) of the bright line spectrum of the element

19. Doppler Effect in Spectra
Red shift – if shifted toward the red end, means longer wavelengths coming from star and star is moving away
Blue shift – if shifted toward the blue end, means shorter wavelengths coming from star and star is moving toward us