Telescopes Flashcards
Law of Reflection
Angle at which the light beam hits the mirror of a telescope, angle of incidence, is exactly equal to the angle at which it is reflected, angle of reflection, applies to all flat mirrors
Focal Point
Where light beams are reflected to, all the beams crossing makes the image brighter
Snell’s Law
Light bends as it crosses into glass, if light enters at an angle it bends towards the normal, as the light exits it speeds up and bends away from the normal
Objective Lens
Primary lens, bends the light to the focal point, the bigger the lens the more light collected so the better the image
Refracting Telescope
Light is collected through a glass objective lens and light from the focal point is reflected to the eye piece for magnification
Chromatic Aberration
Since light of different frequencies travel at different speeds within the medium they have different focal points, causes the image to be blurry and have a colored haze surrounding it, only a problem for refracting telescopes
Achromatic lenses
Uses multiple types of glass to match color focal points
3 Powers of a Telescope
Light gathering power, resolving power, magnification power
Light-Gathering Power
larger the objective lens the more light gathered, allows you to see fainter objects proportional to the area of the objective lens
Resolving Power
Ability to distinguish fine details and separate two closely spaced objects, higher power gives better image
Magnification Power
How much larger an object appears through the telescope compared to naked eye, least important power
Magnifying Scale
Angular size (how much space it takes up in your field of view) in telescope / angular size to naked eye
Cons of high magnification
reduces field of view, darker image, can make things blurry if resolving power isn’t high enough, heightens imperfections in atmosphere, harder to keep objects in sight
How to get difference in light-gathering power
6m lens vs. 9m lens
(9^2 pie) / (6^2 pie) = x stronger
Magnification Power Equation
focal length of objective / focal length of eye piece
How to get better resolving power
larger objective lens, resolving power is reported by the smallest angular separation between objects that can be distinguished
Newtonian Telescope
Uses a concave primary mirror, then a flat 45 degree secondary mirror redirecting light to the side of the telescope at an eye piece, solved the problem of chromatic aberration
Cassegrain Telescope (Reflecting Telescope)
Uses a concave primary mirror then a convex secondary mirror, the reflected back down through the middle of the objective to an eye piece
Why reflecting telescopes are better than refracting telescopes
Can collect more light using mirrors, no chromatic aberration, mirrors are cheaper and easier to support, more compact and easier to maintain (Use reflecting in all major telescopes)
Why do stars twinkle?
There is turbulence in our atmosphere, moving pockets of warm and cold air, causing images to blur on and off
Turbulence
Mixing of air of different densities in the atmosphere causing light to hit the focal point off-center or at different times creating a blurry image
Adaptive Optics
Technology that helps with turbulence, uses flexible mirrors that can adjust in real-time, self-correcting loop
Top 5 Ground-Based Optical Telescopes
Gran Telescopio Canarias (GTC), Keck I and II, Very Large Telescope (VLT), Subaru Telescope, Southern African Large Telescope (SALT)
Gran Telescopio Canarias (GTC)
Canary Islands, Spain, 10.4 m, high-altitude, Largest single-aperture optical telescope in the world
