Astronomy: Chapter 4

Question 1

List the constituents of the electro-magnetic spectrum and discuss their relative wavelengths and energies.

Answer 1

• The electromagnetic spectrum is simply the types of electromagnetic radiation arranged in order of increasing wavelength.
• Visual: violet, indigo, blue, green, yellow, orange, red. Closer to violet side have a higher frequency, more energy, and shorter wavelength (they are hotter). Closer to the red side of the electromagnetic spectrum have a lower frequency, less energy, and longer wavelengths and they are colder.
• Infrared: beyond the red end of the visible. your eyes are not sensitive to this radiation, but your skin can sense some of the heat.
• Radio: longer than infrared radiation. used for AM radio transmission
• microwave: beyond infrared. used for radar and long-distance telephone communications
• Ultraviolet UV: to the left of violet. Shorter wavelenghts than violet.
• X rays: shorter wavelengths than UV
• Gamma rays: shorter wavelengths than X rays.

Question 2

Discuss the relationship of the aperture of a telescope and its light-gathering power and resolving power.

Answer 2

• Telescope Aperture: The telescope main optical element, be it a lens or a mirror.
• Light gathering power: determines how bright objects viewed in the scope will appear. (increases with a bigger aperture so that more light is collected.)
• Maximum Resolving Power: How much fine detail it can reveal. (increases with a bigger aperture so that finer detail is revealed with less diffraction.)
• The larger the aperture (fatter), the more you will see.

Question 3

What determines the magnifying power of a telescope? Give a numerical example of a calculation of magnification.

Answer 3

Focal length of the primary mirror or lens divided by the focal length of the eye piece.

ex. Focal length of 700mm and eyepiece of 14mm has magnifying power of 503

Question 4

What problems led Isaac Newton to invent the reflecting telescope? Also, list some advantages of reflectors over refracting.

Answer 4

Chromatic aberration: the distortion of light at different wavelengths so they are scattered slightly and produce a fuzzy image.
- Refracting lenses suffer from an optical distortion that limits their usefulness. they cause chromatic aberration. Lens must be pure and flawless because light needs to pass through it.

Question 5

What is meant by “adaptive optics”; how odes it work, and why is it so important in astronomy today?

Answer 5

Adaptive Optics: Thinner mirrors and computer-controlled systems that constantly correct distortion in a mirror’s shape to ensure peak performance.
- helped with reducing the blurring of the earth’s atmosphere.

Question 6

Explain how radio telescopes work and discuss their advantages and disadvantages.

Answer 6

• Radio telescope: telescope that gathers radio radiation.
• radio waves from celestial objects, like visible light waves, penetrate Earth’s atmosphere and reach the ground. The Dish reflector of a typical radio telescope focuses the radio waves so their intensity can be measure. Because radio wavelengths are so long, the disk reflector does not have to be as perfectly smooth as the mirror of a reflecting optical telescope.

Question 7

What is VLA and VLBI and what is gained by hooking radio telescopes together?

Answer 7

• VLA: Very Large Array consists of 27 dishes spread in a Y-pattern across the New Mexico desert. It is operated as an interferometer, the VLA has the resolving power of a radio telescope up to 36 km (22 miles) in diameter.
  VLBI: Very Large Base Inferormeter.
• separated telescopes combined to produce a virtual telescope with the resolution of a much larger-diameter telescope.

Question 8

What kinds of objects can best be studied by infrared, ultraviolet, and x-ray astronomy?

Answer 8

• Infrared: can be sense, heat.
• Ultraviolet: best for the study of thermal radiation and spectral emission lines.
  X - ray astronomy: Elliptical galaxies.

Question 9

Describe several types of imaging systems used by astronomers and discuss their advantages and disadvantages.

Answer 9

CCD: Charged Coupled Device; It is sensitive to light and can be utilized as an image sensor for astronomical pictures. They have to be cooled to minimize residual images.

Photographic plate: the first recording device used with telescope; it records the brightness of objects,but with only moderate precision.

Array Detectors: detect faint and bright objects. Digitized. More sensitive than a photographic plate.