Astronomy 2- 2.2

What is the primary purpose of an astronomical telescope?

to collect a lot of light and bring it to a focus

The process occurring when photons bounce off a polished surface is called:

reflection

Which type of telescope has the simplest light path?

prime focus reflector

Which design is subject to chromatic aberration?

refractor

The tendency of a wave to bend as it passes from one transparent medium to another is called:

refraction.

The primary purpose of a telescope is to:

collect a large amount of light and bring it into focus.

What problem do refractor telescopes have that reflectors don’t?

chromatic aberration

A major advantage of a Newtonian reflector over a refractor is:

the elimination of chromatic aberration.

This design involves only one optical surface, a concave mirror.

prime focus reflector

Why are most large telescopes reflectors, not refractors?

Large, very clear lenses are harder to cast than more tolerant mirror blanks. Reflectors do not suffer from chromatic aberration like refractors do. Large mirrors need only one optical surface, achromats four surfaces to grind. Large lenses deform under their own weight, but mirrors can be supported. All of the above are correct.

Which design has a convex primary mirror and flat secondary mirror, with the eyepiece located on the top side of the telescope tube?

Newtonian reflector

The convex secondary mirror in this design focuses light down through a hole cut in the concave primary mirror.

Cassegrain reflector

The Atacama Large Millimeter Array achieves exceptional resolution by using exceptionally:

many radio antennas in a mobile array.

It is much easier to build large reflectors than large refractors.

True

Chromatic aberration affects refractor and reflector telescopes equally, unless they have very long focal lengths.

False

The primary purpose of an astronomical telescope is to magnify the images of distant objects, making them appear closer.

False

CCD detectors gather light 10-20 times faster than the most sensitive photographic film.

True

A convex lens is thinnest in its center; it refracts light to a focus, while a convex mirror reflects it to the focus instead.

False

Absorption of light passing through the glass is a bigger problem for Cassegrain reflectors than achromatic refractors.

False

To reach the Cassegrain focus, a hole must be cut in the center of the primary mirror.

True

The simplest scope design, by Isaac Newton, uses only a primary mirror.

False

You could more easily resolve a close double star with a blue filter than with a red one.

True

The amount of diffraction, and thus the resolution of the scope, depends upon:

the wavelength used and the size of the main telescope objective lens or mirror.

The angular resolution of an 8-inch diameter telescope is ________ better than that of a 2-inch diameter telescope.

4 times

It is diffraction that limits the ________ of a telescope’s objective.

resolution

What is the resolution of a telescope?

its ability to distinguish two adjacent objects close together in the sky

What type of telescope is the Subaru telescope (shown below)?

Cassegrain reflector

What is the light-gathering power of an 8-inch telescope compared to a 4-inch telescope?

4× better

What is the resolving power of the telescope?

the ability to distinguish adjacent objects in the sky

Compared to a 5-inch prime focus reflector, a 5-inch Newtonian reflector will:

have the same light gathering power.

Which method of astronomical measurement is the precise measurement of brightness?

photometry

A telescope with a 60 mm objective lens collects how many times as much light as does your eye’s 6 mm exit pupil?

100 times

It is diffraction that limits the ________ of a telescope of a given objective diameter.

resolution

Diffraction is the tendency of light to:

spread around corners.

What are two advantages of large scopes over smaller ones?

Large telescope have more light grasp and better resolution.

What type of telescope is the Hubble Space Telescope?

Cassegrain

The amount of diffraction a telescope creates depends upon:

the wavelength and the diameter of the telescope objective.

Green light has a shorter wavelength than orange light. In a 5-inch telescope, green light will:

provide better angular resolution than orange light.

The light gathering ability of a telescope is most dependent on the diameter of its primary objective.

True

Hubble Space Telescope is still the largest scope ever built.

False

The most important advantage of CCDs over film is that:

they record much more light in a given exposure time.

Refractor telescopes suffer from this separation of light into its component colors.

chromatic aberration

Which of these devices helps correct coma in fast reflectors?

Schmidt corrector plate

One advantage of the Hubble Space telescope over ground based ones is that:

in orbit, it can operate close to its diffraction limit at visible wavelengths.

The Schmidt corrector plate largely cures spherical aberration, giving a wide, flat field of view.

True

What is "seeing"?

a measurement of the image quality due to air stability

What problem does adaptive optics correct?

turbulence in the Earth’s atmosphere which creates twinkling

A mountain top is an especially good site for infrared telescopes since:

there you are closer to celestial objects. less air above means better seeing in many cases. you are above most of the carbon dioxide and water vapor in the atmosphere. the cold weather helps the sensitivity of infrared detectors. All of the above are factors.

What problem is adaptive optics designed to correct?

the effects of atmospheric turbulence

One reason for building telescopes on mountain tops is that they improve seeing by reducing the amount of air above the observer.

True

The Arecibo radio telescope is laid out like which optical telescope design?

prime focus reflector

What is true of radio telescopes?

They have poorer angular resolution than a refractor.

Which of the following is a problem inherent in all large radio telescopes?

Radio waves have long wavelengths, so radio telescopes have poor resolution.

Radio dishes are large in order to:

increase their angular resolution and collect the very weak radio photons.

Compared to optical telescopes, radio telescopes are built large because:

radio photons don’t carry much energy.

Optical telescopes are usually used only at night, but radio telescopes can be used day or night.

True

Radio telescopes have poorer angular resolution than optical telescopes because radio waves have a much longer wavelength than optical waves.

True

All radio telescopes are reflectors in design.

True

Compared with radio telescopes, optical telescopes can

resolve finer detail.

In astronomy, an interferometer can be used to:

improve the angular resolution of radio telescopes.

Which of the following greatly improves the angular resolution of radio maps?

use of interferometers

This design combines the radiation from two different telescopes to greatly enhance resolution via computer synthesis.

interferometer

Optical interferometry is more in use than radio interferometry.

False

In which part of the electromagnetic spectrum have astronomers been unable to get any information?

We now can access information in all spectral lengths.

Which of the following is currently supplying high resolution X-ray images from space?

Chandra

The design of modern X-ray telescopes depends on:

grazing incidence optics.

The name of the Infrared Orbiting Observatory launched in 2003 is the:

Spitzer Space Telescope.

The detectors on the Spitzer Space Telescope were cooled to near absolute zero in order to:

prevent the infrared radiation from the instruments interfering with the infrared signals from space.

The Chandra X-ray telescope must use:

grazing incidence optics to focus the short wavelengths.

Due to our ozone layer, ultraviolet astronomy must be done from space.

True

Galaxies look the same whether viewed in visible or X-ray wavelengths.

False