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Astro Midterm
| Question | Answer |
|---|---|
| Celestial sphere | rotates about the earth which causes the daily rise and set of the stars. Ancients believed that all heavenly objects were located on crystal spheres that encircled the earth |
| Celestial poles | On celestial sphere, where the celestial sphere rotates around. Are the intersections of the Earth's rotational axis with the celestial sphere |
| Celestial equator | is the projection of the Earths equatorial plane onto the celestial sphere |
| true size | magnitude of AB |
| angular size variable | c |
| Solid angle | angular area on the sky (d omega) is called this. is in units of steradians (sr) which is radians*radians |
| Refracting telescopes use | lenses |
| Reflecting telescopes use | mirrors. Reflector: shape is usually a parabola but can be spherical with the addition of a correction lens |
| Refractors | are heavy. lens/mirror must be polished to its precise shape within approximately 1/25th of the wavelength of light you are operating at |
| Reflectors | instead of lenses, reflectors have curved mirrors to focus light. can make them bigger than refractors. rigid backup structure reduces sag. |
| Prime focus telescopes | block part of the aperture (loses light collecting power and distorts the diffraction pattern |
| For reflectors, which type has a small pickoff (secondary)mirror on the side to send the light to? eye piece is on the side | Newtonian |
| For reflectors, which type has a small pickoff (secondary)mirror on the back to send the light to? eye piece on the back? | Cassegrain (requires a small hole to be cut in the primary mirror |
| Cassegrain | can make compact telescopes with long focal lengths (good for large fields of view. Has secondary mirror at the back with the eye piece |
| cons of refractor | more expensive, less compact, chromatic aberration, reduced light scattering |
| AZ | coordinates like N,W,S,E |
| Magnification | is the least important feature of a telescope and is actually controlled by the focal length of the eyepiece |
| f/4 means | f/D=4 or f=4D |
| The bigger the scope the | more radiation it collects in a given amount of time therefore the fainter the object it can detect in a given amount of time. This is actually one of the most important features of telescopes |
| What is the sensitivity of a telescope related to? | Its collecting area. |
| How does the size of a telescope's collecting area affect its sensitivity? | The bigger the 'bucket', the more photons it can collect in a given time |
| What does higher sensitivity in a telescope allow it to detect? | Fainter objects with smaller radiant flux/light intensity. |
| How can the sensitivity of a telescope be increased? | By increasing the amount of time it collects light. |
| What does the Rayleigh Criterion define? | The width of the intensity profile in diffraction. |
| What is the formula for the Rayleigh Criterion? | Sin(theta) = 1.22 * wavelength / D |
| What happens to the width of the diffraction pattern if the diameter of the telescope is increased while keeping the wavelength constant? | The width of the diffraction pattern gets smaller. |
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