Light and the Spectrum:

1
Chapter 5

• Light and the Spectrum
• Messages from Space

2
What is Light????

• Waves or Particles
• Wave Theory
• Light is a form a electromagnetic energy.

• Defined by its wavelength
• 400-700 nm or 0.4-0.7mm

3
What is EM Radiation?

• Energy transmitted as Waves
• At the speed of light! (300,000 km/s)
• Therefore, shorter wavelengths of EMR are higher
  in energy than longer wavelengths

• ?HIGH ENERGY
• LOW ENERGY?

4
What about light then?

• Ranges from 0.4 0.7
• Colors of the spectrum Take a look!
• ROY G. BIV

• ?Blue HIGH ENERGY
• Red LOW ENERGY?

VIB G. YOR ????
5
Effect of Atmosphere on EM Radiation
Deadly
?
?
?
6
Particle Theory

• Light is concentrated .
• Into individual units
  (not spread out as a wave)
• A bullet-like particle
• The PHOTON
• Einstein
• Photo-electric effect
• Light can knock electrons off metals ---- like
  a bullet!

7
So light is

• A Platypus!
• Sometimes like a duck
• Sometimes like a beaver
• But neither.
• The cop-out
• Light is a phenomenon!
• Define it as we need it!

8
Spectroscopy

• Wiens Law
• lmax K ? T
• Wavelength is inversely proportional to
  temperature.
• Hotter object emit shorter wavelengths.
• Blue light is (hotter colder) than red light.

9
Spectroscopy

• The study of the properties of the spectrum of
  different objects.
• For us. Stars.
• So why do different objects have different
  spectra (spectrum pl.)?
• Because of the objects temperature
• And its composition (chemistry)

10
Spectroscopy

• The study of the properties of the spectrum of
  different objects.
• For us. Stars.
• So why do different objects have different
  spectra (spectrum pl.)?
• Because of the objects temperature
• And its composition (chemistry)

11
Spectroscopy

• Blue stars are hot.
• Red stars are cool.
• How bout the Sun?

• Yellowish Star
• Moderate

12
Spectroscopy

• Cooler than the sun.

• Other objects

13
Spectroscopy

• Creates emission lines within a spectrum
• Narrow bands of colors.
• Take a look!!!

14
Telescopes

• Three Functions.
• Magnification
• Make an image larger
• Resolution
• Ability to discriminate fine detail
• Light-gathering power
• Ability to see fainter details

15
Telescopes

• Two Designs.
• Refractors (1st built)
• Use a lens to refract (bend) light
• Like your eye

• Problems with lenses
• Separating light (prism)
• Heavy, distorts image

16
Telescopes

• Reflectors preferred today
• Made with curved mirrors

• Mirrors reflect ALL light (no prism)
• Can be made LARGE and CHEAP
• Light-gathering capabilities far superior!
• UPSIDE DOWN IMAGE!!!!

17
Telescope Terminology

• Photography 101 !!!
• Objective
• LENS OR MIRROR
• Key ingredient OPTICAL QUALITY !!!!
• Focal Length
• Distance from objective to focus
• Key Ingredient LENGTH

• Aperture
• Diameter of the objective
• Key Ingredient SIZE
• LIGHT GATHERING

18
Optical Telescopes gt 3 m
19
Light Pollution
20
Major Telescopes in Space