Astronomy Assignment Six.

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

infrared light.

The twin 10-m Keck telescopes can work together to obtain better angular resolution through a technique known as _____.

interferonmetry.

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 is always true about images captured with X-ray telescopes?

They are always displayed in false color.

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

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

What is the purpose of adaptive optics?

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

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

ultraviolet X rays (Both B & C)

Which of the following forms of light can be observed with telescopes at sea level?

visible light radio waves.

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

above Earth's atmosphere.

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

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

The twinkling of stars is caused by:

motion of air in our atmosphere

Can the Hubble Space Telescope resolve the two stars?

No.

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.

-Large Binocular Telescope: Two 8.4-m mirrors. -Keck I: One 10-m mirror. -Hobby-Ebberly: One 9.2-m mirror. -Subaru: One 8.3-m mirror. -Gemini North: One 8-m mirror. -Magellan II: One 6.5-m mirror.

Large telescopes often have small fields of view. For example, the Hubble Space Telescope's (HST's) advanced camera has a field of view that is roughly square and about 0.06 degree on a side. Calculate the angular area of the HST's field of view in square degrees.

0.0036 square degrees.

Find three telescopes that you could buy for under $1000 and evaluate each on the following criteria: light-collecting area, angular resolution, construction quality, and portability. Give each telescope a rating of 1 to 4 stars (4 is best) and state which one you would recommend for purchase.

1)Celestron Nexstar 6 SE Telescope Rating: 3 2)Orion 8946 SkyQuest xt10 classic dobsonian telescope. Rating:4 3)Skywatcher 10' collapsible dobsonian telescope rating:3

The angular area of the entire sky is about 41,250 square degrees. How many pictures would the HST have to take with its camera to obtain a complete picture of the entire sky? Express your answer using two significant figures.

1.1 x 10^7 pictures.

What is the angular separation of the two stars? Give your answer in arcseconds. Express your answer using two significant figures.

1.5×10−2 ′′

Now remember that humans have two eyes that are approximately 7 centimeters apart. Estimate the diffraction limit for human vision, assuming that your "optical interferometer" is just as good as one eyeball as large as the separation of two regular eyeballs. Express your answer using two significant figures.

1.8 "

How does this compare to the diffraction limit of a 10-meter telescope? Express your answer using two significant figures.

1300

Calculate the diffraction limit of the human eye, assuming a wide-open pupil so that your eye acts like a lens with diameter 0.8 centimeter, for visible light of 500-nanometer wavelength. Express your answer using two significant figures.

16 "

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 that two stars in a binary star system are separated by a distance of 90 million kilometers and are located at a distance of 130 light-years from Earth. What is the angular separation of the two stars? Give your answer in degrees. Express your answer using two significant figures.

4.2×10−6 ∘

Suppose astronomers built a 80-meter telescope. How much greater would its light-collecting area be than that of the 10-meter Keck telescope? Express your answer using two significant figures.

64

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 are equal.

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 are equal.

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 are equal.

How does a camera record light? How are images affected by exposure time? What are pixels?

Cameras record light by focusing light through a lens onto a detector. A shutter controls the exposure time; the longer the exposure time, the more light is collected. Pixels are the individual "picture elements" on the detector; in principle, more pixels means better resolution.

A radio telescope and an optical telescope of the same size have the same angular resolution.

False.

Sort each of the astronomical questions below into the appropriate bin based on the type of observation you would need to perform to answer it.

Imaging : -How large is the Andromeda Galaxy? -What are the major surface features of Mars? -Are stars in the Orion Nebula surrounded by dusty disks of gas? Spectroscopy : -What is the chemical composition of the Crab Nebula? -What is the temperature of Jupiter's atmosphere? -Is the star Vega moving toward us or away from us? Time Monitoring: -Is the X-ray emission from the galactic center steady or changing? -Does the star Mira vary in brightness?

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.

Each of the following statements describes an astronomical measurement. Place each measurement into the appropriate bin based on the type of telescope you would use to make it.

Infrared telescope : -Determine the surface temperature of Venus. -Study a dense cloud of cold gas in space. Visible light telescope: -Obtain a spectrum of the sunlight reflected by Mars. -Measure the brightness of a star that is similar to our Sun. X-ray telescope: -Observe the hot (1-million K) gas in the Sun's corona. -Look for high energy radiation from a supernova.

What are the two key properties of a telescope, and why is each important?

Light collecting and angular resolution. Light collecting tells how much light it can collect at once. Angular resolution is the smallest angle to distinguish seperate stars,

What do astronomers mean by light pollution?

Light pollution refers to light used for human activities that brightens the sky and hinders astronomical observations.

Suppose that two stars are separated in the sky by 0.1 arcsecond. If you look at them with a telescope that has an angular resolution of 0.5 arcsecond, what will you see?

One point of light that is the blurred image of both stars.

Why do astronomers need different telescope designs to observe across the electromagnetic spectrum?

Photons of different energy behave differently and require different collection strategies.

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

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

______ separate the various colors of light, allowing astronomers to determine stellar composition and many other stellar properties

Spectrographs.

Which of the following statements best describes the two principal advantages of telescopes over eyes?

Telescopes can collect far more light with far better angular resolution.

The lens in your eye forms an upside-down image of the world.

True.

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 light Most infrared light 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.

The ______ of the Hubble Space Telescope is better for shorter (bluer) wavelengths of light than for longer (redder) wavelengths of light.

angular resolution.

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

four times

The Chandra X-ray observatory focuses X rays with ____ mirrors.

grazing incidence.

A 10-meter telescope has a larger ____ than a 4-meter telescope.

light-collecting area.

The large research observatories on Mauna Kea use giant ______.

reflecting telescopes.

Galileo's telescope designs using lenses were examples of ____.

refracting telescopes..

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

Which of the following is not a good reason to place observatories on remote mountain tops?

to be able to observe at radio wavelengths