Chapter 6 Astronomy

When your eye forms an image, the _____ plays a role analogous to the detector in a camera.

retina

The light-collecting area of an 8-meter telescope is _____ times that of a 2-meter telescope.

16

How much more light does an 8-meter telescope gather than a 2-meter telescope?

16 times as much

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

Brightest to Dimmest all the same

Which of the following best describes why radio telescopes are generally much larger in size than telescopes designed to collect visible light?

Getting an image of the same angular resolution requires a much larger telescope for radio waves than for visible light.

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).

Highest to lowest xrays ultraviolet infrared radio and visible 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

Highest to lowest altitude all the same

What is the purpose of interferometry?

It allows two or more small telescopes to achieve the angular resolution of a much larger telescope.

Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes?

It is closer to the stars.

Which of the following best describes what we mean by the focal plane of a telescope?

It is the place where, if we mounted film or an electronic detector, we could get a clear (not blurry) image of an object viewed through the telescope.

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

Reflecting world's largest telescope The Hubble Space Telescope Most commonly used by professional astronomers today Refracting incoming light passes through glass very large telescopes become "top-heavy" Galileo's telescopes The world's largest is 1-meter in diameter

This x-ray image was taken by the Chandra X-ray Observatory. Without knowing anything more about the object that is shown, what can you conclude from looking at this image?

Some parts of the object emit more x-rays than others.

Which of the following studies is best suited to astronomical observations that fall into the category called time monitoring?

Studying how a star's brightness varies over a period of 3 years.

Which of the following telescopes benefits most from adaptive optics?

The Keck I telescope on Mauna Kea

What does angular resolution measure?

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

Why does the Sun's image look distorted in shape at sunset?

The distortion arises because of the way air affects the paths of light.

Suppose that two stars are separated in the sky by 0.01 arcsecond, and you observe them with a telescope that has an angular resolution of 1 arcsecond. What will you see?

The light from the two stars will be blended together so that they look like one star.

Suppose you have two small photographs of the Moon. Although both look the same at small size, when you blow them up to poster size one of them still looks sharp, while the other one becomes fuzzy (grainy) looking. Which of the following statements is true?

The one that still looks sharp at large size has better (smaller) angular resolution than the one that looks fuzzy.

The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see?

The photo will seem to show only one star rather than two.

Which of the following is not a reason why telescopes tend to be built on mountaintops that are relatively far from cities and are in regions with dry climates?

The thin air on mountaintops makes the glass in telescope mirrors less susceptible to warping.

Why are astronomers interested in building observatories capable of detecting neutrinos, cosmic rays, and gravitational waves?

These things are not forms of light, and therefore can provide different types of information than light about objects that emit them.

What is the primary reason that we launch X-ray telescopes into space rather than building them on the ground?

X-rays from space do not reach the ground.

Suppose you have a camera attached to a telescope, and you want to record an image of a faint galaxy. Which of the following will help the most?

a lot of pixels and a long exposure time

What are the two most important properties of a telescope?

angular resolution light-collecting area

If our eyes were sensitive only to X rays, the world would appear __________.

dark because X-ray light does not reach Earth's surface

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).

greatest ability to lowest ability All the same

If you had only one telescope and wanted to take both visible-light and ultraviolet pictures of stars, where should you locate your telescope?

in space

The James Webb Space Telescope is designed primarily to observe __________.

infrared light

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.

largest to lowest area Large binocular: two 8.4 Keck 1: 10 Hobby- Ebberly: 9.2 Subaru: 8.3 Gemini North:8 Magellan: 6.4

This photo shows a satellite dish on a house. In essence, the dish is _________.

the primary mirror of a radio telescope

Which of the following effects is caused by atmospheric turbulence?

twinkling of stars

X-rays from space do not reach the ground.

visible light radio waves

The Chandra X-ray Observatory must operate in space because __________________________.

x-rays do not penetrate Earth's atmosphere