Chapter 5
If two radio telescopes work together, which of the following is the size of the effective telescope?
It is equal to the distance between the telescopes.
Why does diffraction occur?
Light has wavelike characteristics.
What is the resolution of the Hubble Space telescope focusing visible light? It's mirror is 2.4 meters in diameter.
0.047 arc sends
What is the resolving power of a 2-meter-diameter telescope focusing visible light?
0.057 arc seconds
Based on what you learned about light, select all of the correct statements from the following list.
A photon is a particle of light. High frequency photons carry more energy than long wavelength photons. Light can act both as a wave and a particle. All electromagnetic waves travel at the speed of light.
Why are there arrays of many more than two radio telescopes working together?
Additional telescopes in between the two farthest-separated telescopes increases the gathering power and resolving power of the effective telescope.
Why have no large refracting telescopes been built since 1900?
All of the below. (Refracting telescopes suffer from chromatic aberration. Making large glass lenses without interior defects is difficult. Refracting telescopes have several surfaces to shape and polish. Large glass lenses are more difficult to support than large mirrors.)
Why are short tunes an advantage for large telescopes?
All of these (Short tubes weigh less than those of refracting telescopes. Short tubes can fit inside a smaller observatory building. Short tubes can be supported with less vibration.)
The highest quality telescopes ever made have been termed "diffraction-limited" and can be described by which of the following statements?
All of these. (Diffraction fringes are visible around every point of light. The telescope has the highest resolution possible for its diameter. Further improvements in the quality of the optics would no improve the image.)
Astronomers build large-diameter telescopes for which of the following reasons?
All of these. (To see fine detail in image. To increase the resolving power. To reduce the size of the diffraction fringes in the image.)
Why are telescopes in different locations working together especially desirable for radio telescopes?
Because radio telescopes have such poor resolution.
When telescopes in different locations work together, it is called which of the following?
Interferomtery
Which power of a telescope is the least important?
Magnifying power
What do large diameter; gently curved convex (thicker in the middle) lenses and large diameter gently curved concave (thinner in the middle) mirrors have in common?
They both have long focal lengths and can be used as primary light collectors for a telescope.
Which of the following is true of reflecting telescopes?
They focus light by bouncing ti off of optical surfaces.
Why do the pupil's of a cat's eye open wider at night?
To increase light gathering power.
The visible part of the electromagnetic spectrum can be divided into seven color bands: red, orange, yellow, green, blue, indigo, and violet (from long to short wavelength). A single photon of which of these colors has the greatest amount of energy?
Violet
Rank the following types of electromagnetic radiation in order of decreasing wavelength: infrared, gamma-ray, radio, ultraviolet, visible
greatest: radio, infrared, visible, ultraviolet, gamma-ray: least
Rank the following colors of visible light in order of increasing wavelength: blue, green, red, yellow
least: blue, green, yellow, red :greatest
Rank the following colors of visible light in order of increasing frequency: green, red, violet, yellow
least: red, yellow, green, violet :greatest
The entire electromagnetic spectrum can be divided into seven bands: radio, microwave, infrared, visible, ultraviolet, X ray, and gamma ray (from longest to shortest wavelength). To which of these two bands is Earth's atmosphere the most transparent?
visible and radio
Of these two telescopes shown here, which will allow you to see dimmer objects?
The telescope on the left.
Imagine that you looked through a telescope 0.5 meters in diameter at a pair of stars 0.1 seconds of arc apart. Which of the following would be true?
The two stars would be visible as a single point of light.
Based on what you learned about telescopes, select all the correct statements from the following list.
Recently built modern telescopes are reflectors.
In this figure you can see that different wavelengths of light are refracted (bent) by different amounts. Which wavelengths are bent by the greatest amount?
Short wavelengths.
The detail visible though even the highest quality telescope is limited by which of the following?
The diameter of the telescope.
In a telescope, which of the following is the optical element with the shortest focal length?
The eyepiece.
Which of the following is a reason that reflecting telescopes have shorter tubes than refracting telescopes?
The light goes up the tube then back down.
Refracting telescopes are so called for which of the following reasons?
The light is bent to a focus.
What is the biggest advantage of a reflecting telescope?
The light never passes though glass.
Which of the following is the first thing light hits when it enters a telescope?
The primary lens or mirror.
Astronomers are both hindered and assisted by chromatic aberration. In which device is chromatic aberration a big problem for astronomers?
The primary lenses of refracting telescopes.
