Lecture 5
The (astro)Physics of Light and Telescopes

The Near Infrared Camera for the Keck I telescope is so sensitive it could detect the equivalent of a single candle flame on the Moon.

- Keck Observatory

 

Note: Next lunar eclipse is this Thursday Feb 21, 2008 !

Spectra

Three basic types of spectra:

1. continuous,
2. absorption line
3. emission line

Kirchhoff's 3 laws describe behavior among these spectra. [Chaisson p.89, figs 4.2 and 4.5]

Energy

Conservation of energy: energy can be neither created nor destroyed; it may be transformed, but the total does not change.

Table of common energy outputs

 

Waves

Waves carry energy (of motion) but do not actually transport material

Know three fundamental properties of waves:

• wavelength
• frequency
• velocity

 

Light and the Electromagnetic Spectrum

Visible light is only a small part of the complete electromagnetic spectrum [Chaisson Fig.3.9]

Textbook Note: figures in the book contain an inset spectrum icon

 

The Quantum Theory of the atom

Each element in the Periodic Table has unique fingerprint spectrum (e.g., even in nebula)... but how to explain?

Quantum Mechanics in 20minutes (c.f., page from Dirac's book)

Nice online timeline of Quantum Mechanics (local copy), including Bohr model of the atom for explaining Balmer Series in hydrogen [Chaisson p.93]

 

Optics and Telescopes

Nearly all telescopes work on the principle of collecting light and "bending" it to a focal point (or "prime focus")
[movie: short and long version]

Two main types of telescopes: Refractors and Reflectors [Chaisson Fig5.5]

The telescope you looked through in class was a Schmidt-Cassegrain reflector.

 

Know the Three Powers of a telescope (Chaisson section 5.1 on Optical Telescopes):

1. collecting area
2. resolution
3. magnification (third and least important, not even mentioned by Chaisson)

 

Noteworthy optical telescopes

• Hawaii's dormant Mauna Kea volcano is the 14,000 ft elevated home to several observatories (web)
  • Gemini (8.1meter mirror)
  • Keck Observatory which uses adaptive optics
• Hubble Space Telescope in orbit around Earth. Hubblesite

 

Invisible Astronomy

Effect of earth's atmosphere on different electromagnetic radiation.

Views of the Milky Way at different wavelengths

 

Noteworthy non-optical telescopes

• Radio:
  • VLA (pic1, pic2) radio telescopes in the desert in New Mexico
  • Arecibo in Puerto Rico
  • VLBA spread across the entire globe
• X-ray: Chandra X-ray Observatory in earth orbit
• Infrared:
  • Keck Observatory also has infrared instrumentation
    ("The Near Infrared Camera for the Keck I telescope is so sensitive it could detect the equivalent of a single candle flame on the Moon." !!)
  • ESA Venus Express orbiter (infrared and other wavelengths)

 

Reading

Chaisson text:

• Chapter 3 (sections 1, 2, 3)
• Chapter 4 (sections 1, 2, 3)
• Chapter 5 (sections 1, 2, 3, 4, 5, 7, 8)

Northwestern University Physics department has a nice Quantum Mechanics timeline

PBS Nova's interactive and historical demonstration of refractors and reflectors

Sky and Telescope magazine article on buying a telescope

The National Radio Astronomy Observatory educational page

Celestron's Telescope Basics (Celestron is the maker of my telescope, which you used in class)

 

Document URL: http://www.uh.edu/~jclarage/astr3131/lectures/5/5.html