19 Flashcards
(21 cards)
Why are telescopes better than the human eye for observing distant objects?
Because they gather more light using larger apertures, improving brightness and resolution.
What formula is used to calculate the light-gathering power (LGP) of a telescope?
LGP ∝ D², where D is the diameter of the mirror or lens.
What is the angular magnification of a telescope?
m = -fo/fe, where fo is the focal length of the objective and fe is the focal length of the eyepiece.
Why are large refracting telescopes difficult to build?
Large lenses sag under their own weight, are expensive to make, and cause chromatic aberration.
What are the advantages of reflecting telescopes over refracting ones?
They can be larger, avoid chromatic aberration, and are structurally supported from behind.
What is a Newtonian focus in a reflecting telescope?
It uses a flat mirror to redirect light to the side of the telescope for easier viewing.
What limits the resolution of any optical device like a telescope?
Diffraction, due to the wave nature of light.
What is the formula for the diffraction limit (Rayleigh’s criterion)?
θ = 1.22 λ / D
What does a smaller angular resolution mean?
Better resolving power—ability to distinguish closely spaced objects.
What are the units and conversion for angular resolution?
Radians or arc-seconds (1° = 3600 arc-seconds)
What three factors improve telescope observations?
More light larger telescope,longer exposure
Smaller angular resolution , larger telescope
Atmospheric effect
Adaptive optics go to space top of mountain
What are adaptive optics?
Technology that corrects for atmospheric distortion by adjusting the mirror shape in real-time.
Why do we place telescopes in space?
To avoid atmospheric distortion and absorption of non-visible radiation.
Which wavelengths can pass through Earth’s atmosphere?
Visible light and radio waves.
Name telescopes specialized for non-visible wavelengths.
HST (visible, UV, IR), Chandra (X-ray), Spitzer (IR), CGRO (Gamma-ray), LIGO (gravitational waves).
What does LIGO detect?
Gravitational waves—ripples in spacetime from cosmic events.
What is light pollution?
Bright city lights that limit our ability to see stars clearly.
What is the advantage of segmented mirrors like JWST?
Easier to build large-diameter telescopes by assembling smaller segments.
How is exposure time related to light gathering?
LGP ∝ Area × Time; longer exposure allows more detail in images.
What is the diffraction pattern from a circular aperture?
A central bright spot surrounded by concentric rings of alternating brightness.
Chromatic Aberration
an optical distortion that causes a lens to focus different colors of light at slightly different points, resulting in color fringing or a “color blur” along the edges of objects in an image
