Astronomy Chapter 3: Telescopes Test Questions

Flashcard maker : Livia Baldwin
List 3 advantages of reflecting telescopes over refracting telescopes
– the lens in a refracting telescope focuses red and blue light differently. This deficiency is known as chromatic aberration.
– As light passes through the lens, some of it is absorbed by the glass.
– A large lens can be quite heavy therefore it tends to deform by its weight.
– A lens has two surfaces that must be accurately machined and polished, which can be a difficult task. A mirror has only one surface
How does earths atmosphere affect what is seen through an optical telescope
Atmospheric turbulence produces continuous small changes in the optical properties of the air between the star and our telescope (or eye).
The light from the star is refracted slightly, again and again, and the stellar image dances around on the detector (or retina).
what are the largest optical telescopes used today?
Currently, the largest (and highest) optical telescopes are the twin Keck instruments atop Mauna Kea in Hawaii operated jointly by the California Institute of Technology and the University of California.
What advantages does the hubble space telescope have over ground base telescopes.
A telescope placed above the atmosphere, in Earth orbit, can achieve resolution close to the diffraction limit.
It has a 2.4-m mirror and a diffraction limit of 0.05″, giving astronomers a view of the universe as much as 20 times sharper than that normally available from even much larger ground-based instruments.
What are the advantages of a CCD over a photograph?
More Efficient and Digital Format
CCDs are much more efficient than photographic plates, recording as many as 75 percent of the photons striking them, compared with less than five percent for photographic methods.
CCDs produce a faithful representation of an image in a digital format that can be placed directly on magnetic tape or disk, or even sent across a computer network to an observer’s home institution for analysis
Why do radio telescopes have to be very large?
because the radio waves they are picking up are very large.
What is interferometry and what problem in radio astronomy does it address
It is the combination of telescopes that are far apart to get a picture. The downside is the image quality is poor.
Compare the highest resolution attainable with optical telescopes to the highest resolution attainable with radio telescopes
optical- level .1 arc second
radio- 10 arc minute (w/o interferometry) but using it you can get to .1 arc second
What special conditions are required to conduct observations in the infrared?
For most infrared observations, astronomers must place their instruments above most or all of Earth’s atmosphere.
What are the main advantages of studying objects at many different wave lengths?
By comparing the features visible in each, multi-wavelength observations can COMPLEMENT each other, greatly extending our perception of the universe around us.
The main advantage of the HST is the increased amount of nighttime viewing it affords (T/F)
The term “seeing” is used to describe how faint an object can be detected by a telescope (T/F)
One of the primary advantages of CCD’s over photographic plates is the formers high efficiency in detecting light (T/F)
Radio telescopes are large in part to improve their angular resolution which is poor because of the long wavelengths at which they are used to observe the skies (T/F)
Infrared astronomy can only be done from space (T/F)
Gamma-ray telescopes employ the same basic design that optical instruments use (T/F)
Because gamma rays have very short wavelengths, gamma ray telescopes can achieve extremely high angular resolution (T/F)
The main reason that most professional research telescopes are reflectors is that _______?
large mirrors are easier to build than large lenses
If telescope mirrors could be made in odd sizes, the one with the most light gathering power would be a triangle with 1-m sides; a square with 1-m sides;a circle with 1-m diameter;or a rectangle with two 1-m sides and two 2-m sides?
Rectangle that’s 1 by 2
The primary reason professional observatories are built on the highest mountaintops is to ______?
Reduces atmospheric blurring
When multiple radio telescopes are used for interferometry, resolving power is most improved by increasing ______?
the distance between telescopes
The Spitzer Space Telescope is stationed far from earth because it _____?
Earth is a heat source and the telescope must be kept very cold
The best way to study young stars hidden behind interstellar dust clouds would be to use_______?
Infrared light
optical telescope
the most common type of telescope that collects and focuses visible light for closer observation. The simplest optical telescope contains an objective lens and a lens in the eyepiece of the telescope
refracting telescope
uses lenses to gatehr and focus light. Cannot focus images perfectly, distorts images if lens is too large
reflecting telescope
uses mirrors to gather and focus light. I sused by most professional astronomers. Focuses all colors of light to the same focal point, can use large mirrors to gather light and flaws in the glass don’t affect the collected light
2 disadvantages of refracting telescopes
their lenses focus different colors of light at different distances, which means the images cannot be exactly focused. Second, if the objective lens is too big, it will sag and images will be distorted
3 advantages of reflecting telescopes
1. mirrors can be large, which allows reflecting telescopes to gather much light.
2. they use mirrors and light doesn’t eneter the glass, so any damages in the glass don’t distort the image.
3. their mirrors focus all colors of light to the same focal point so all colors of light from and abject can be seen and focused.
Blocked wavelengths from earth
infrared rays, and X-rays
unblocked wavelengths from earth
gamma rays, visible light, microwaves
Radio telescopes
are larger than optical telescopes because radio wavelengths are much longer than optical wavelengths. The surface can also be more flawed than the lenses and mirrors of an optical telescope

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