Chapter 6 Flashcards
What is an astronomer’s most important tool?
A telescope
What are the two primary types of optical telescopes?
- Refracting
2. Reflecting
What does a reflecting telescope use for collecting and focusing incoming light?
A primary mirror, a secondary mirror, and an eyepiece on the side of the telescope
What does a refracting telescope use for collecting and focusing incoming light?
An objective lens & eyepiece
What is the focal plane?
The plane, perpendicular to the optical axis of a lens or mirror, on which an image is formed
What is the focal point?
The point at which light from a very distant object converges after being refracted or reflected
What is the focal length?
The distance from the lens or mirror to its focal point
What type of telescope does chromatic aberration occur in?
Refracting telescopes
How can chromatic aberration be corrected?
You add in a second lens that is made from a different kind of glass
What is chromatic aberration?
Its when the lens acts slightly like a prism. It bends different colored lights by different amounts
What is the best resolution that a given telescope can achieve?
Diffraction limit
What’s the advantage of launching a telescope above earth’s atmosphere?
They aren’t affected by astronomical seeing
Which dimensions of the refracting telescope determine its magnification?
Focal lengths of the objective lens / focal length of the eyepiece
Describe the advantages of reflecting telescopes over refracting telescopes
- No chromatic aberration
2. The mirror can be supported by a bracket on it’s back
What is spherical aberration?
Light from different parts of the mirror converge at different focal points due to the shape of the mirror
What are the two ways that you can correct spherical aberration?
- You can use a parabolic mirror instead of a spherical one
2. You can put a correcting lens in front of the mirror
What criteria would you employ to evaluate a telescope when you want to buy one? Explain
- Light-gathering power - Provides a brighter image
2. Resolving power - Provides sharp and crisp images
Compare an optical reflecting telescope and a radio telescope. How are they different?
Since radio waves are much longer, radio telescopes have to be bigger. Also, optical telescopes work during the night while radio telescopes work during the day
Compare an optical reflecting telescope and a radio telescope. What do they have in common?
They both use a curved reflecting surface to focus the incoming radiation
What is the optical window and the radio window?
They are wavelength regions where our atmosphere is transparent
Why isn’t there an X-ray window or an ultraviolet window?
Our atmosphere is not transparent to these wavelength ranges, so the waves aren’t able to reach the earth’s surface
Why do we need Gamma-ray, X-ray, UV and Infrared telescopes? Explain.
So we can study extremely hot objects
How do you find the magnification of a reflecting telescope?
Focal length of primary mirror / focal length of eyepiece
Explain the different designs of reflecting telescopes
You have a primary mirror and a secondary mirror, so your head doesn’t block some of the light
