Open Stax Astronomy - CH6

What is a charge-coupled device (CCD), and how is it used in astronomy?

A. A CCD is a modern detector similar to the detectors used in video camcorders B. High Pixels cameras, record brightness and color of image and computers sort info to create photo

When astronomers discuss the apertures of their telescopes, they say bigger is better. Explain why.

A. A bigger aperture allows you to use more magnification, produces image with higher resolution. Also collects light making for a sharper image and can detect fainter sources than a smaller one

Why do astronomers place telescopes in Earth's orbit? What are the advantages for the different regions of the spectrum?

A. Getting above the distorting effects of the atmosphere is also an advantage at visible and Infrared wavelengths. To bypass earths disadvantages like clouds, storms and moisture having an telescope in space eliminates all of earths distractions.

Why is it difficult to observe at infrared wavelengths? What do astronomers do to address this difficulty?

A. It is difficult to distinguish between the amount of heat radiation that reaches Earth from other stars and galaxies, and the greater heat radiated by the telescope itself and our planet's atmosphere. B. To solve this problem, astronomers must protect the infrared detector by cooling and also by storing the detector in space or mountains

List the largest-aperture single telescope currently in use in each of the following bands of the electromagnetic spectrum: radio, X-ray, gamma ray.

A. Radio - 305-m , Arecibo, Puerto Rico B. X-ray - Chandra , earths satellite in space C. Gamma Ray - FERMI, in space

What is meant by "reflecting" and "refracting" telescopes?

A. Reflecting Telescopes use a mirror rather than a lens to form an image B. Refracting Telescopes a long tube with a large glass lens at one end, uses a lens as its main optical element to form an image

What are the three basic components of a modern astronomical instrument?

A. Telescope (mirror/lens) , For collecting visible light. B. An Instrument, Sorts the incoming radiation by wavelength. C. Detector, a device that senses the radiation in the wavelength regions selected. Then it records the observations.

Name the two spectral windows through which electromagnetic radiation easily reaches the surface of Earth and describe the largest-aperture telescope currently in use for each window.

A. Visible Light, Radio Waves B. Radio - 305-m , at Arecibo, Puerto Rico ; Visible Light - 10.4m Mirror, Canary Island

. Suppose you are looking for sites for a visible-light observatory, an infrared observatory, and a radio observatory. What are the main criteria of excellence for each? What sites are actually considered the best today?

All of them must be free of electromagnetic interference Visible Light- Cloud free and dark skies Infrared- Cloud free and dry Radio- flat ground The best for visible and infrared- Mauna Kea The best for radio- VLA (Socorro, New Mexico)

What would be the properties of an ideal astronomical detector? How closely do the actual properties of a CCD approach this ideal?

An ideal detector should have high detection efficiency, a large format, should be able to count photons, register arrival time, register photon energy, should be cheap and simple. CCDs have high detection efficiency and a large format.

Many decades ago, the astronomers on the staff of Mount Wilson and Palomar Observatories each received about 60 nights per year for their observing programs. Today, an astronomer feels fortunate to get 10 nights per year on a large telescope. Can you suggest some reasons for this change?

Because of the increased usage of computers, astronomers are able to analyze the pictures taken by the telescopes on their computers rather than having to look through the telescopes themselves.

Compare the eye, photographic film, and CCDs as detectors for light. What are the advantages and disadvantages of each?

Eye - Easy and cheap; imperfect because we process w/ our imperfect brain, short integration time Film - Photographic plate that makes a permanent record; only about 1% of the light contributes to the chemical change that makes the image, expensive inefficient CCDs - light can be collected over longer periods of time similar to cellphone cam hoked to a telescope;

. The dean of a university located near the ocean (who was not a science major in college) proposes building an infrared telescope right on campus and operating it in a nice heated dome so that astronomers will be comfortable on cold winter nights. Criticize this proposal, giving your reasoning.

Must be away from light (campus bad) Must be low humidity (near ocean bad) and a heated dome would create infrared radiation that would interfere with the astronomical signal

The Hooker telescope at Palomar Observatory has a diameter of 5 m, and the Keck I telescope has a diameter of 10 m. How much more light can the Keck telescope collect than the Hooker telescope in the same amount of time?

The Keck telescope can collect 4times than the Hooker Telescope.

The largest observatory complex in the world is on Mauna Kea, the tallest mountain on Earth. What are some factors astronomers consider when selecting an observatory site? Don't forget practical ones. Should astronomers, for example, consider building an observatory on Denali (Mount McKinley) or Mount Everest?

There is no light pollution on Mauna Kea. Also, it easily accessible compared to Mount Everest. Not only that, but Mount Everest and Mount McKinley are very cloudy areas that get in the way of observations. Mauna Kea is cloudless.

Why are the largest visible-light telescopes in the world made with mirrors rather than lenses?

the use of a small secondary mirror allows more light to get through the system and to see the image clearer