Astro-Physics Flashcards
(24 cards)
Give two equations for magnification of a refracting telescope.
1) M = α / β
2) M = Fo / Fe (Focal Objective / Focal Eyepiece)
Define 1 arc minute.
1/60 of a degree
What is 1 degree in arc minutes
60 arc minutes
What’s the equation for angular size of an object
Diameter of object / Distance to eye or lense
List two “aberrations” of refracting telescopes
1) Chromatic Aberration
2) Spherical Aberration
What is meant by Chromatic Aberration
The refractive index of a lens is different for different wavelengths so different colours are brought to focus at different points. SHORTER WAVELENGTH => SMALLER FOCAL LENGTH
What is meant by Spherical Aberration
Due to manufacturing difficulties, imperfections in a lens cause rays further from the principle axis to be brought to focus closer to the lens.
What criteria must be met for a a refracting telescope to be in “normal adjustment”
- Objective and eyepiece lenses share a principle focus (separation = Fo + Fe)
- Must be focused at infinity (meaning everything in frame is in focus)
What is meant by the term Collecting power of a telescope
How much light enters the telescope hence determining the brightness of the observed image
What is the relationship between collecting power and telescope aperture
Collecting power is directly proportional to (Diameter of Aperture)^2
What is meant by the term Resolving Power of a telescope
How well the telescope can distinguish between two nearby objects
What is an airy disc
It’s a circular diffraction patter around a star’s image caused by diffraction at the telescopes aperture.
What is the Rayleigh Criterion
The minimum angular separation for two object to be resolved
When will the minimum angular separation for the Rayleigh Criterion occour
When the central maximum of one airy disc coincides with the first minimum of the second airy disc.
List 4 disadvantages of refracting telescopes
- Very difficult to create large lenses
- Large lenses can deform under their own weight
- Very difficult to manoeuvre quickly
- Suffer from chromatic and spherical aberration
List 4 advantages of reflecting telescopes
- Can be made of smaller composite mirrors
- Large single mirrors can be made fairly easily
- No chromatic or spherical aberration when using parabolic mirrors
- Light weight allows quick response to astronomical events
Give an equation linking the ratio of two star’s intensities and their apparent magnitudes.
(Intensity1 / Intensity2) = (100^0.2) ^ (m1-m2)
or in words
Intensity 1 over Intensity 2 is approximately equal to 2.51 to the power of the difference of the apparent magnitudes
What is 1 arcsecond in terms of distances
It angle subtended within a triangle of opposite length of 1 AU and adjacent length of 1 parsec
What is a CCD
A Charged Coupled Device,
Essentially an array of photosensitive pixels that rely on the photoelectric effect to produce a digital image
How does quantum efficiency of the eye compare to that of a CCD
CCD ~ 80% efficificent
Eye ~ 1%
What is meant by quantum efficiency
How well a detector can detect / capture photos for amplification for images
(Number Of Photons Detected / Number Of Photons Incident) * 100
What is meant by a parallax angle of 1
1 arcsecond angle within a triangle of opposite length of 1 AU and adjacent length of 1 parsec
Give the first stage in the life cycle of a star.
Clouds of hydrogen and dust called nebula exist in space.
Gravitational attraction between individual atoms causes denser clumps of matter to be formed.
This is referred to as gravitational collapse.
