ASTR Ch.6

Diffraction Limit

The angular resolution that a telescope could achieve if it were limited only by the interference of light waves; it is smaller (i.e., better angular resolution) for larger telescopes.

Timing (in astronomical research)

The process of tracking how the light intensity from an astronomical object varies with time.

Optical quality

The ability of a lens, mirror, or telescope to obtain clear and properly focused images.

Exposure time

The amount of time during which light is collected to make a single image

Light curve

A graph of an object's intensity agains time

Scattered light

Light that is reflected into random directions

Filter (for light)

A material that transmits only particular wavelengths of light

Image

A picture of an object made by focusing light

Secondary Mirror

A small mirror in a reflecting telescope, used to reflect light gathered by the primary mirror toward an eyepiece or instrument.

Adaptive Optics

A technique in which telescope mirrors flex rapidly to compensate for the bending of starlight caused by atmospheric turbulence.

Refracting telescope

A telescope that uses lenses to focus light

Reflecting telescope

A telescope that uses mirrors to focus light

Interferometry

A telescopic technique in which two or more telescopes are used in tandem to produce much better angular resolution than the telescopes could achieve individually.

CCD (charge coupled device)

A type of electronic light detector that has largely replaced photographic film in astronomical research.

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

A. High spectral resolution. B. High turbulence. C. A radio telescope. D. High angular resolution. -High spectral resolution.

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

A. It describes the maximum exposure time for images captured with the telescope. B. 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. C. It is the maximum size to which any telescope can be built. D. It describes the farthest distance to which the telescope can see. -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?

A. It is the lower surface of the telescope's primary lens or mirror. B. 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 C. It is the surface of the lens on the eyepiece, through which you would look to see objects in the telescope's field of view. D. It is the upper surface of the telescope's primary lens or mirror. -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 is the purpose of adaptive optics?

A. It reduces blurring caused by atmospheric turbulence for telescopes on the ground. B. It allows ground-based telescopes to observe ultraviolet light that normally does not penetrate the atmosphere. C. It allows several small telescopes to work together like a single larger telescope. D. It is a special technology that allows the Hubble Space Telescope to adapt to study many different types of astronomical objects. -It reduces blurring caused by atmospheric turbulence for telescopes on the ground.

What is the purpose of interferometry?

A. It reduces the twinkling of stars caused by atmospheric turbulence. B. It allows two or more small telescopes to achieve the angular resolution of a much larger telescope. C. It allows two or more small telescopes to achieve a larger light-collecting area than they would have independently. D. It is designed to prevent light pollution from interfering with astronomical observations. -It allows two or more small telescopes to achieve the angular resolution of a much larger telescope.

What do astronomers mean by light pollution?

A. Light pollution is a term used to describe the appearance of the sky in regions that are crowded with stars. B. Light pollution is light from human sources that makes it difficult to see the stars at night. C. Light pollution means contamination of light caused by chemicals in the Earth's atmosphere. D. Light pollution is a type of air pollution created by lightweight gases such as hydrogen and helium. -Light pollution is light from human sources that makes it difficult to see the stars at night.

Which of the following is not one of the three main categories of observation generally used by astronomers?

A. Spectroscopy to spread an object's light into a spectrum. B. Filtering to look at just a single color from an object. C. Imaging to get a picture of an astronomical objects. D. Time monitoring to track how an object's brightness varies with time. -Filtering to look at just a single color from an object.

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

A. Telescopes have much more magnification and better angular resolution. B. Telescopes can collect far more light with far better angular resolution. C. Telescopes can collect far more light with far greater magnification. D. Telescopes collect more light and are unaffected by twinkling -A refracting telescope uses a transparent glass lens to focus light while a reflecting telescope uses a mirror to focus light.

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

A. Telescopes have much more magnification and better angular resolution. B. Telescopes can collect far more light with far better angular resolution. C. Telescopes can collect far more light with far greater magnification. D. Telescopes collect more light and are unaffected by twinkling -Telescopes can collect far more light with far better angular resolution.

What does angular resolution measure?

A. The angular size of the smallest features that the telescope can see B. The number of electromagnetic waves captured by an image. C. The size of an image. D. The brightness of an image. -The angular size of the smallest features that the telescope can see (Therefore a smaller angular resolution is better)

Which of the following is always true about images captured with X-ray telescopes?

A. They show us light with extremely long wavelengths compared to the wavelengths of visible light. B. They always are made with adaptive optics. C. They are always very pretty. D. They are always shown with colors that are not the true colors of the objects that were photographed. E. They always have very high angular resolution. -They are always shown with colors that are not the true colors of the objects that were photographed.

What is the angular resolution of the human eye?

A. about 1 arcminute, or 1/60 of a degree B. about 1 degree C. about 1 milliarcsecond D. about 1 arcsecond (1/3600 of a degree) -about 1 arcminute, or 1/60 of a degree

Which of the following effects is caused by atmospheric turbulence?

A. diffraction of light B. magnification of images C. twinkling of stars D. light pollution -twinkling of stars (Therefore, there is no twinkling if you view stars from space, above Earth's atmosphere)

Which of the following wavelength regions can be studied with telescopes on the ground?

A. infrared, visible, and ultraviolet light. B. radio, visible, and very limited portions of the infrared and ultraviolet regions C. all light with wavelengths longer than ultraviolet wavelengths D. all light with wavelengths shorter than infrared wavelengths -radio, visible, and very limited portions of the infrared and ultraviolet regions (Other parts of the electromagnetic spectrum require telescopes in space)

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

A. lens B. retina C. pupil D. optic nerve -retina

Pixel

An individual "picture element" on a CCD

Spectrograph

An instrument used to record spectra

Light pollution

Human-made light that hinders astronomical observations

Infrared light

Light with wavelengths that fall in the portion of the electromagnetic spectrum between radio waves and visible light

Turbulence

Rapid and random motion

Grazing incidence (in telescopes)

Reflections in which light grazes a mirror surface and is deflected at a small angle; commonly used to focus high-energy ultraviolet light and X rays.

Light-collecting area (of a telescope)

The area of the primary mirror or lens that collects light in a telescope

Spectral Resolution

The degree of detail that can be seen in a ; the hight the spectral resolution, the more detail we can see

Prime Focus (of a reflecting telescope)

The first point at which light focuses after bouncing off the primary mirror; located in front of the primary mirror.

Primary Mirror

The large, light-collecting mirror of a reflecting telescope

Focal plane

The place where an image created by a lens or mirror is in focus.

Imaging (in astronomical research)

The process of obtaining pictures of astronomical objects.

Frequency

The rate at which peaks of a wave pass by a point, measured in units of 1/s, often called cycles per second or hertz.

Angular Resolution

The smallest angular separation that two pointlike objects can have and still be seen as distinct points of light (rather than as a single point of light).