Mastering Astronomy- Telescopes Assignment

These two photos were taken at the same time and same location near San Jose, California. The one on the left was taken using visible light. Considering the properties of the other parts of the electromagnetic spectrum, which type of radiation do you think was able to penetrate the dust and smog to obtain the image on the right?

Infrared

These two photos show the same region of space. One of them is taken in visible light. Note that stars are obscured in Photo 2 but are much easier to see in Photo 1. Considering the properties of the different bands of the electromagnetic spectrum, which spectral region do you think was used to take each photo?

Photo 1 (one with more stars) is infrared

Photo 2 (one with less stars, more cloudy) is visible

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

reflection

True or False

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

true

As telescopes become larger and larger, astronomers favor ________.

a) refracting telescopes, in part because as light bounces off of mirrors, some of it is absorbed; this doesn't happen with lenses

b) reflecting telescopes, in part because large lenses and mirrors sag under their own weight, and it is easier to support a mirror along its entire back side than it is to support a lens only around its edge

c) reflecting telescopes, in part because the angular resolution of refractors is limited by diffraction whereas the angular resolution of reflectors is not

d) refracting telescopes, in part because lenses are easier than mirrors to shape and polish accurately

b) reflecting telescopes, in part because large lenses and mirrors sag under their own weight, and it is easier to support a mirror along its entire back side than it is to support a lens only around its edge

True or False

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

true

True or False

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

false

True or False

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

False

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

a) magnification

b) wavelengths

c) resolution

d) light grasp

e) frequencies

c) resolution

True or False

In addition to visible light, Hubble can do some work in the infrared and ultraviolet portions of the spectrum.

true

Which type of telescope has the simplest light path?

a) Newtonian reflector

b) prime focus reflector

c) single lens refractor

d) achromatic refractor

e) Cassegrain reflector

b) prime focus reflector

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

a) provide better angular resolution than orange light.

b) reduce the effects of atmospheric turbulence.

c) come to the same exact focus as orange light.

d) allow dimmer stars to be observed.

e) provide worse angular resolution than orange light.

a) provide better angular resolution than orange light.

What is the resolution of a telescope?

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

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.

Astronomical sources emit electromagnetic radiation at various wavelengths. Some sources might emit just visible and infrared radiation. Other sources might emit gamma, UV, visible, and infrared radiation. Some of that radiation travels in the direction of Earth and can be detected with the right telescopes placed in the right locations. Some wavelengths can be read in the atmosphere. However, the majority of wavelengths are either read from space or Earth's surface. Which observations would require you to launch a telescope above the Earth's atmosphere? Please drag each observing mode below into either the ground-based (Surface) zone or space-borne (Space) zone, depending on the respective observing requirements.

Space Zone:

-X-ray observations

-Gamma-ray observations

-Far-UV observations

-Far-infrared observations

Surface Zone:

-Radio observations

-Visible (optical) observations

What is the primary purpose of an astronomical telescope?

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

Why are most large telescopes reflectors, not refractors?

a) Large, very clear lenses are harder to cast than more tolerant mirror blanks.

b) Large lenses deform under their own weight, but mirrors can be supported.

c) Reflectors do not suffer from chromatic aberration like refractors do.

d) Large mirrors need only one optical surface, achromats four surfaces to grind.

e) All of the above are correct.

e) All of the above are correct.

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

4 times

Which design is subject to chromatic aberration?

a) Newtonian reflector

b) Gregorian reflector

c) prime focus reflector

d) refractor

e) Cassegrain reflector

d) refractor

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

Cassegrain reflector

Chromatic aberration in lenses is a result of which wave property of light?

refraction

Refraction is the bending of light as it passes from one medium to another. Because it is wavelength dependent, different wavelengths bend by different amounts as they pass through a lens, causing chromatic aberration.

The amount of diffraction a telescope creates depends upon:

the wavelength and the diameter of the telescope objective.

True or False

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

true

How much better resolution would a 60 mm objective lens have than your eye's 6 mm exit pupil?

10 times

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

refraction.

If you want to make a very dim object appear much brighter in an image photographed through a telescope, which of the following factors are important?

diameter of the telescope and the length of the exposure

Which of the following is/are true when comparing radio telescopes to optical telescopes?

-radio telescopes can observe objects even when it's cloudy

-radio telescopes can observe objects in the daytime

There are fundamental differences between radio and optical telescopes, but they are both collectors of light, and we need to use both to observe very different phenomena.

The best frequency range in which to study the hot (million-kelvin) gas found among the galaxies in the Virgo galaxy cluster would be in the following region of the electromagnetic spectrum:

X-ray

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

have the same light gathering power.