Chapter 6 Astro 100
What does angular resolution measure?
The angular size of the smallest features that the telescope can see.
Which of the following telescopes would benefit most from adaptive optics?
The Keck I telescope on Mauna Kea.
How can multiple telescopes work together ?
The technique of interferometry allows multiple telescopes to be linked in a way that allows them to obtain the angular resolution of a much larger telescope
What is the purpose of adaptive optics?
It reduces blurring caused by atmospheric turbulence for telescopes on the ground.
What are two basic designs of telescopes?
A refracting telescope forms an image by bending light through a lens. A reflecting telescope forms an image by focusing light with mirrors.
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.
What are the two most important properties of a telescope?
A telescope's most important properties are its light-collecting areas, which determines how much light it gathers, and its angular resolutions, which determines how much detail we can see inits images.
Which of the following best describes the principle advantage of CCDs over photographic film?
CCDs capture a much higher percentage of the incoming photons than film.
How does Earth's atmosphere affect ground based observations?
Earth's atmosphere limits visible-light observations to nighttime and clear weather. Light pollution can lessen the quality of observations, and atmospheric turbulence makes stars twinkle, blurring their images. The technology of adaptive optics can overcome some of the blurring due to turbulence.
Which of the following is not one of the three main categories of observation generally used by astronomers?
Filtering to look at just a single color from an object.
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.
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.
Which of the following wavelength regions can be studied with telescopes on the ground?
It allows two or more small telescopes to achieve the angular resolution of a much larger telescope.
What is a CCD?
It is an electronic detector that can be used in place of photographic film for making images.
Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes?
It is closer to the stars.
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.
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.
What do astronomers mean by light pollution?
Light pollution is light from human sources that makes it difficult to see the stars at night.
Consider two future observatories in space. Observatory X consists of a single 50-meter telescope. Observatory Y is an interferometer consisting of five 10-meter telescopes, spread out over a region 100 meters across. Which observatory can detect dimmer stars, and which one can see more detail in its images? (Assume all else is equal, such as quality of optics, types of instruments, and so on.)
Observatory X can detect dimmer stars and Observatory Y reveals more detail in images.
Which of the following studies is best suited to astronomical observations that fall into the category called timing?
Studying how a star's brightness varies over a period of 3 years.
Which of the following statements best describes the two principle advantages of telescopes over eyes?
Telescopes can collect far more light with far better angular resolution
How do we observe invisible light?
Telescopes for other than visible light often use variations on the basic design of a reflecting telescope. Radio telescopes use large metal dishes as their primary mirros. Infrared telescopes are sometimes cooled to very low temperature. X-ray telescopes use grazing incidence reflections rather than direct reflection.
Why do we put telescopes into space?
Telescopes in space are above Earth's atmosphere and the problems it causes for observations. Most important, telescopes in space can observe all wavelengths of light, while telescopes on the ground can observe only visible light, radio waves, and small portions of the infrared.
Which of the following is not a major reason why astronomers would like an observatory on the far side of the Moon?
Telescopes on the Moon could see objects in all parts of the sky equally well, whereas telescopes on Earth can see only portions of the sky that depend on their latitude.
How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?
The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.
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.
Suppose you point your telescope at a distant object. Which of the following is not an advantage of taking a photograph of the object through the telescope as compared to just looking at the object through the telescope?
The photograph will have far better angular resolution than you can see with your eye.
The stars in our sky twinkle in brightness and color because of ______.
turbulence in the Earth's atmosphere
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.
What do astronomers do with telescopes?
The three primary uses of telescopes are imaging to create pictures of distant objects, spectroscopy to study the spectra of distant objects, and timing to study how a distant objects brightness changes with time.
Which of the following best describes the development of astronomical telescopes over the past 65 years?
The world's most powerful telescope remained the same for most of this period, but in the past 20 years many new and more powerful telescopes have been built.
Which of the following is always true about images captured with X-ray telescopes?
They are always shown with colors that are not the true colors of the objects that were photographed.
How do we record images?
We record images with a detector such as photographic film or a CCD. Recorded images are more reliable than just seeing by eye and can record more light is we use a longer exposure time.
The Chandra X-ray Observatory must operate in space because:
X rays do not penetrate Earth's atmosphere.
How does your eye form an image?
Your eye begins rays of light to focus on your retina. Glass lenses work similarly, so distant objects form an image that is in focus on the focal plane
What is the angular resolution of the human eye?
about 1 arcminute, or 1/60 of a degree
Which of the following effects is caused by atmospheric turbulence?
twinkling of stars