Astro-10 Chapter 6

How much greater is the light-collecting area of one of the 10-meter Keck telescopes than that of the 5-meter Hale telescope?

4

Suppose astronomers built a 20-meter telescope. How much greater would its light-collecting area be than that of the 10-meter Keck telescope?

4

In what wavelength range was interferometry first routinely used?

radio

What is the purpose of adaptive optics?

to eliminate the distorting effects of atmospheric turbulence for telescopes on the ground

How much greater is the light-collecting area of a 6-meter telescope than a 3-meter telescope?

Four(4) times

What do we mean by the diffraction limit of a telescope?

It is the angular resolution the telescope could achieve if nothing besides the size of its light-collecting area affected the quality of its images.

What do we mean by the diffraction limit of a telescope?

It is the best angular resolution the telescope could achieve with perfect optical quality and in the absence of atmospheric distortion

Which of the following studies is best suited to a time monitoring experiment?

studying whether a particular star's brightness is steady or variable

The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is:

above the Earth's atmophere

What causes stars to twinkle?

bending of light rays by turbulent layers in the atmosphere

Listed following are distinguishing characteristics and examples of reflecting and refracting telescopes. Match these to the appropriate category. Refracting telescopes

incoming light passes through the glass, very large telescope becomes top heavy, the worlds largest is 1 meter in diameter, galileos telescope

Listed following are distinguishing characteristics and examples of reflecting and refracting telescopes. Match these to the appropriate category. Reflecting telescopes

worlds largest telescope, most commonly used by professionals astronomers today, the hubble space telescope

What is meant by spectral resolution?

It is a measure of how close two spectral lines can be distinguished.

Which of the following statements best describes the difference between a refracting telescope and a reflecting telescope?

A refracting telescope uses a transparent glass lens to focus light while a reflecting telescope uses a mirror to focus light.

Shown following are five different colors of visible light that travel to Earth from the Sun. Rank these colors of visible light from left to right based on the altitude in the atmosphere where they are completely absorbed, from highest to lowest (Earth's surface). If two (or more) of the choices reach the surface, rank them as equal by dragging one on top of the other(s).

All stacked on each other

Shown following are the primary mirror arrangements and total light-collecting area of five different telescopes. Each mirror uses a different segmented arrangement, but assume that they are all equivalent in quality and in their ability to focus light. Also assume that the telescopes use identical detectors and have the same observing conditions. Rank the telescopes from left to right based on their ability to detect very dim objects, from greatest to least. To rank two (or more) telescopes as equal, drag one on top of the other(s).

All stacked on each other

Shown following are the primary mirror arrangements and total light-collecting area of five different telescopes. Notice that although the arrangements look similar to those in Part B, the light-collecting areas are not the same. Also listed is an amount of time (exposure time) that each telescope will be pointed at the same distant galaxy. Again assume that the quality of these mirrors, the detectors, and the observing conditions are identical. Rank the telescopes from left to right based on the brightness of the image each telescope will take of the galaxy in the time indicated, from brightest to dimmest. To rank two (or more) telescopes as equal, drag one on top of the other(s).

All stacked on each other

Which of the following is a principal advantage of CCDs over photographic film?

CCDs capture a much higher percentage of the incoming photons than does film.

Listed following are the names and mirror diameters for six of the world's greatest reflecting telescopes used to gather visible light. Rank the telescopes from left to right based on their light-collecting area from largest to smallest. For telescopes with more than one mirror, rank based on the combined light-collecting area of the mirrors.

Left to Right 1. Large Binocular Telescope Two 8.4-m mirrors 2. Keck1 : One 10-m mirror 3. Hobby-Ebberly : One 9.2-m mirror 4. Subaru One 8.3-m mirror 5. Gemini North: One 8.3-m mirror 6. Magellan 11: One 6.5-m mirror

If you wanted a radio telescope to achieve the same angular resolution as a visible-light telescope, it would need to be:

Much larger

________ astronomy uses dishes like satellite dishes to observe objects. In some cases, the dishes work together to form images at a much higher resolution than any one of them could achieve alone. An example is Very Large Array in New Mexico. _________ telescopes are very similar to optical telescopes, except that they use different detectors to sense the light. An example is the Spitzer ___________Space Telescope. Most of the ___________ wavelengths act enough like the visible wavelengths that we can use the same sorts of telescopes, with different detectors. An example is the Hubble Space Telescope. _________ telescopes have to gently redirect the light because it tends to go straight through things in its path. Mirrors are arranged so that the light just grazes them. An example is the Chandra Space Telescope. ____________ telescopes must be massive in order to intercept this high-energy light. An example is the Fermi ______________ Telescope.

Radio, Infared, Infared, Uktraviolet,X-ray, Gamma-ray, Gamma-ray

What does angular resolution measure?

The angular size of the smallest features that the telescope can see

Which of the following wavelength regions cannot be studied with telescopes on the ground?

Ultraviolet, X-rays

Shown following are six different types of light that travel to Earth from sources in space. Rank these types of light from left to right based on the altitude in the atmosphere where they are completely absorbed, from highest to lowest (Earth's surface). If two (or more) of the choices reach the same altitude or the surface, rank them as equal by dragging one on top of the other(s).

X-rays, most ultraviolet, most infared light, stacked on each other =most radio waves, green visible light

Interferometry uses two or more telescopes to achieve:

an angular resolution equivalent to that of a much larger telescope.

Suppose you want to determine the chemical composition of a distant planet or star. Which of the following will be most useful to have?

high spectral resolution

In what part of the electromagnetic spectrum do the biggest telescopes on Earth operate?

radio

Which of the following could not be measured by an observation that uses only imaging?

the rate at which a variable star brightens and dims

Which of the following could not be determined by an observation that uses only spectroscopy?

the size of a distant galaxy