Astronomy 1904
Wayne K. Trail
Spring 2008
Chapter 6 Review
Note: you should not use this as a substitute for your notes and the book.
What is refraction? What does light do when it enters a medium other than a vacuum?
What can you say about rays of light coming from a distant object? (They are parallel.)
What is the name of the place where parallel rays meet after they pass through a
refracting lens? (The focal point.) The distance from the lens to the focal point is called
the focal length.
What are the two basic types of telescopes? How do they differ?
What is the objective of a telescope? (It is the primary lens or mirror.)
What are the two main uses of a telescope? (magnification and brightening)
What are the two most important properties of a telescope? Light-gathering area and
angular resolution.
What is the light-gathering power of a telescope most dependent on? (The diameter of the
objective.) Greater light gathering power gives greater detail.
What is chromatic aberration? Not all colors of light are refracted at the same angle in
glass, so when light passes through a lens, the colors are focused at slightly different
focal lengths. This can make the image a little “color fuzzy.”
What is the law of reflection?
Why don’t most modern research telescopes have eyepieces? (they have CCD’s for
imaging or spectroscopes)
What are the 4 disadvantages of a refracting telescope (uses a lens instead of a mirror).
What are some advantages of a reflecting telescope (uses a mirror instead of a lens)? If
you block out part of the objective (cover part of the mirror), will part of the image be
blocked out?
How did Sir Isaac Newton get the image from his reflecting telescope out of the
telescope? (He inserted a mirror near the focal point and reflected the image through the
side to the eyepiece.)
What is angular resolution? How can you improve angular resolution? (Get a larger
objective.)
What are active or adaptive optics? (They are techniques in which you change the shape
of the mirror while using it, to adjust for atmospheric effects.)
What is a CCD? It is the heart of a digital camera.
What is interferometry? Connecting several telescopes together electronically so they act
like a much larger telescope.
Why are radio telescopes sometimes arranged in large arrays? So they can be used as a
giant telescope. The effective diameter of the giant telescope is the size of the array.
What can we learn about objects by examining them with a radio telescope? (We can
learn about magnetic fields and hence something about their interiors.)
Why do x-ray and gamma ray telescopes have to be in space?
Why do radio telescopes need to be so large? Because radio waves have long wavelength
and good resolution improves as the diameter of the telescope increases relative to the
wavelength being viewed.
Active optics
Diffraction grating
Angular resolution
Eyepiece lens
Astronomy 1904
Wayne K. Trail
Focal point
Magnification
Optical telescope
Radio telescope
Refraction
Spring 2008
Focal length
Interferometry
Objective lens
Focal plane
Light-gathering power
Objective mirror
Pixel
Refracting telescope