Open Stax Astronomy - CH6

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

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

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

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.

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

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

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;

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

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

Radio and radar observations are often made with the same antenna, but otherwise they are very different techniques. Compare and contrast radio and radar astronomy in terms of the equipment needed, the methods used, and the kind of results obtained.

A. Radio - The dish reflector of a radio telescope a spectrometer and a detector, the dish acts like the mirror of a reflecting telescope, collects and focuses radiation. Can detect far away objects

B. Radar - radio dish can be used as a radar telescope if it is equipped with a powerful transmitter as well as a receiver.

C. Emitted from earth bounced from an object to receive it and radar emitter is required, can only detect closer objects

Look back at Figure 6.18 of Cygnus A and read its caption again. The material in the giant lobes at the edges of the image had to have been ejected from the center at least how many years ago?

A. Material was ejected at least 160,000 years ago

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.

What was the problem with the Hubble Space Telescope and how was it solved?

A. After it was launched, scientists discovered that the primary mirror had a slight error in its shape.

B. They installed a corrector plate which improved camera before releasing HST back into orbit.

Describe the techniques radio astronomers use to obtain a resolution comparable to what astronomers
working with visible light can achieve.

A. Radio Astronomers use an interferometer to sharpen their images by linking two or more radio telescopes together electronically

B. astronomers combine a large number of radio dishes into an interferometer array

What kind of visible-light and infrared telescopes on the ground are astronomers planning for the future? Why are they building them on the ground and not in space?

Large Synoptic Survey Telescope (LSST), an 8.4-meter telescope, 2021.

They are building on the ground because it is too costly to put in space. (heavy)

Describe one visible-light or infrared telescope that astronomers are planning to launch into space in the future.

A. James Webb Space Telescope (JWST), which is expected to be ready in about the year 2018.

B. JWST telescope will be launched into a solar orbit to avoid interference from Earth's strong infrared glow.