Chapter 5 Flashcards
If a telescope has a resolving power of 0.1 sec of arc, what do two stars 1.5 seconds of arc apart look like through this telescope?
two separate blobs of light
Most of Galileo’s telescopes had objective lenses which were only about 2 cm in diameter. Theoretically, should he have been able to resolve two stars 14 seconds of arc apart? (Hint: resolving power in seconds of arc = 0.113/diametr of objective (in meters)
Yes, because the objective is sufficiently large.
Which is better, the resolving power of an 8-m telescope on Earth without adaptive optics or that of the 2.5-m Hubble Space Telescope?
Hubble Space Telescope
A spy satellite orbiting 500 km above Earth is supposedly capable of counting individual people in a crowd. Roughly what minimum-diameter telescope must the satellite carry? (Hint: Use the small-angle formula. Assume that a human is about 0.5 m from shoulder to shoulder.)
56 cm
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
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
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
Why have no large refracting telescopes been built since 1900?
All of these choices are correct.
Which power of a telescope might be expressed as “0.5 seconds of arc”?
resolving power
Which power of a telescope is the least important?
magnifying power
Which theoretical power of an optical telescope is determined by the diameter of the primary mirror or lens?
light-gathering power and resolving power
What advantage do the builders of large telescopes today have over the previous generation of telescope builders?
All of these choices are correct.
In which device do astronomers take advantage of chromatic aberration?
the prism
Which power of a large ground-based optical telescope is severely limited by Earth’s atmosphere on a cloudless night?
resolving power
What do the newer light-sensitive electronic CCD chips do better than the older photographic plates coated with light-sensitive chemicals?
All of these choices are correct.
What is a disadvantage of radio telescopes compared to optical telescopes?
All of these choices are correct.
Radio telescopes are often connected together to do interferometry. What is the primary problem overcome by radio interferometry?
poor resolving power
Which is not a type of electromagnetic wave?
sound
Which is something that all electromagnetic waves have in common?
All of these choices are correct.
Which type of telescope is more expensive?
for the same size objective, refractors
Why do nocturnal animals usually have large pupils in their eyes?
To gather more light, so they can see better at night.
Which is the reason that radio telescopes are often put in valleys?
interference
Which reason to build a large radio telescope also applies to optical telescopes?
better resolution
Which reason for building a large telescope applies only to radio telescopes?
long wavelength light
Which could be a disadvantage of a thin or “floppy” telescope mirror?
It tends to sag under its own weight.
You see a telescope advertised as 200 power.
What quality of a telescope is probably being advertised?
magnifying power
You see a telescope advertised as 200 power.
What qualities of a telescope are important to you as a potential buyer?
All of the these choices are important.
Not long ago, an astronomer said: “Some people think I should give up photographic plates.”
What device could replace photographic plates in astronomy?
CCD
Which is true about a prism spectrograph?
It divides light into the individual components of its spectrum.
When telescopes in different locations work together, it is called which of the following?
interferometery
Why are telescopes in different locations working together especially desirable for radio telescopes?
because radio telescopes have such poor resolution
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 do radio telescopes have such poor resolution?
because radio waves have such a long wavelength
Which is better observed by an X-ray telescope than an infrared telescope?
hot gas trapped in galactic clusters
