Astrophysics Flashcards
For a single lense to make an image appear to be diminished, where should the object be placed?
Beyond 2f
For a single lense to make an image appear the same size, where should the object be placed?
At 2f
The a single lens to make an image appear magnified, where should the object be placed?
Between f and 2f
For a single lens to make an image appear as a virtual object, where should the object be placed?
Below f
How does a CCD work?
1- a CCD is a silicon chip, divided into picture elements (pixels)
2- each pixel is associated with a potential well in the silicon
3- photons are incident on the CCD, and the photons within the semi-conductor cause the electrons to be released
4- the number of electrons liberated, is proportional to the intensity of the light
5- the electrons are trapped in the potential wells, and an electron pattern is built up that is identical to the image formed on the CCD
6- when the exposure is complete, the charged is processed to form an image
What is meant by quantum efficiency, and what are the values for a CCD vs the human eye?
Number of photons detected/ number of photons incident
CCD: 80% or more
Human eye: 1%
What is chromatic abrasion, and which type of telescope does it effect?
A colour distortion that creates an outline of unwanted colour along the edges of objects in photos, that effects refracting telescopes. (Blue first then red)
What is spherical abrasion, and what type of telescope does it effect?
It occurs when the mirror isn’t a perfect parabola, and it effects both types of telescope
What is the Rayleigh criterion?
2 objects will just be resolved when the first minimum in the diffraction pattern of one image coincides with the central maximum of the other
How can you improve resolving power?
Increase the size of the dish, or look at smaller wavelengths
State 3 optical advantages of reflecting telescopes over refracting telescopes
- mirrors don’t refract light, so they don’t suffer chromatic abrasion
- mirrors can be larger, and therefore have greater resolving power
- mirrors can be larger, and therefore have smaller minimum angular resolution
What is the maximum size of imperfections in a telescope dish can be?
Wavelength/ 20
What is 1 parsec?
The distance at which 1 AU subs tends an angle of 1 arc second
What is 1 arc second in degrees?
1/3600
What is meant by apparent magnitude?
The brightness of a star as seen from earth