1. Chapter 24 Sec. 1 Light Sec. 2: Tools of Astronomy

2. 24.1 Electromagnetic Radiation
Electromagnetic waves
--> Range of electric and magnetic waves that travel through
space
transfer energy
Classified based on wavelength
travel through space
travel at the speed of light—~300,000,000 m/s
Include:
Ultraviolet (UV) light=sunburns
Infrared radiation=heat
Visible light
X-rays
Microwaves
Radio waves
Gamma rays (CT scans)

3. Light is ... Nature of Light Behaves like a wave
Similar to swells in the ocean
Wavelength
Distance from crest to crest
Behaves like a particle
Photon
Small packet of light energy

4. Spectroscopy Spectroscopy
Study of the properties of light that depend on wavelength
Break light into the various colors, each with its own wavelength
Three types of Spectra
Continuous
Absorption
Emission

5. Spectroscopy: Continuous
Uninterrupted band of light
Emitted by an incandescent solid, liquid, or gas under pressure.

6. Spectroscopy: Absorption
Continuous spectrum produced when white light passes through cool gas under low pressure.

7. Spectroscopy: Emission
Series of bright lines of particular wavelengths produced by a hot gas under low pressure.
Used to study the spectrum of a star:
Spectral lines act as “fingerprints”
Lines identify elements present  star’s chemical composition

8. Electromagnetic Spectrum: the continuum of radiation released by star --classified by wavelength (red longer, blue shorter) --wavelength=distance between the peaks on a wave --frequency=the # of waves that pass a point per second As wavelength decreases, freq. increases they are inversely proportional

9. Doppler Effect
The Doppler Effect:
Sound Waves
Electromagnetic Waves
Apparent change in frequency of electromagnetic or sound waves caused by the relative motions of the source of the observer.
Used to determine whether a star or other body in space is moving away from or toward Earth.
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10. 24.2 How Is This Used By Astronomers?
Telescopes:
Refracting telescope
Reflecting telescope
Both types have 3 properties that aid astronomers:
Light-gathering power
Resolving power
Magnifying power
Interferometry:
combines several telescope images to make a very detailed image
VLT (Very Large
Telescope
@ European
Southern
Observatory
(reflecting)

11. Refracting Telescope Lenses bring light into focus
Bends (refracts) light
Objective lens
produces image by bending light from distant object light area called focus (central point)

12. Refracting Telescope Yerkes Observatory Wisconsin 40” diameter lens
63’ long tube

13. Reflecting Telescope Reflects light off a concave mirror
Focuses image in front of the mirror
Advantages:
Most large optical telescopes are reflectors
Light does not pass through a mirror  glass for a reflecting telescope doesn’t have to be of optical quality

14. Reflecting Telescope
Keck Telescopes Hawaii

15. Detecting Invisible Radiation
Radio Telescopes
Observations using radio wavelengths
Focuses incoming radio waves on antenna
Absorbs and transmits waves to amplifier

16. Radio Telescopes Advantages:
Less affected by turbulence in the atmosphere, clouds and the weather
No protective dome is required  reduces cost of construction
Can “see” through interstellar dust clouds that obscure visible wavelengths

17. Space Telescopes
Orbit above Earth’s atmosphere and thus produce clearer images then Earth-based telescopes
Hubble Space Telescope
1st space telescope built by NASA
Put into orbit around Earth April 1990
Other Space Telescopes
Study X-Rays: NASA uses Chandra X-Ray Observatory (launched in 1999)
Study Visible and Gamma Rays: Compton Gamma-Ray Observatory
Infrared: James Webb Space Telescope

18. James Webb Space Telescope
Infrared vision that will peer back over 13.5 billion years to see the first stars and galaxies forming out of the darkness of the early universe.
Will launch in 2018 from European Spaceport located near Kourou, French Guiana on a rocket. (The mission lifetime is years.)