Light and telescopes. Just by analyzing the light received from a star, astronomers can retrieve information about a star’s. Total energy output Surface temperature Radius Chemical composition Velocity relative to Earth Rotation period. What is light?. Electricity. Magnetism.
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Just by analyzing the light received from a star, astronomers can retrieve information about a star’s
Time-dependent magnetic field
creates time-dependent electric field,
and vice versa
c = 300,000 km/s = 3*108 m/s
f = c/l
Differentcolors of visible light correspond to different wavelengths.
High flying air planes or satellites
Need satellites to observe
1 nm = 10-9 m
1 Å = 10-10 m = 0.1 nm
Visible light has wavelengths between 4000 Å and 7000 Å (= 400 – 700 nm).
E = h*f
h = 6.626x10-34 J*sis the Planck constant.
The energy of a photon does notdepend on the intensity of the light!!!
1 eV = 1.6x10-19 J
c = 3x108 m/s
1 Angstrom = 10-10 m
Speed of light in matter:
cm = c/n, where
n is refractive index
Note: n is a function of
Matter in space consists of the same atoms as matter on Earth
Physical laws should be the same
We can still learn something about the stars!
Astronomers use telescopes to gather more light from astronomical objects.
The larger the telescope, the more light it gathers.
(SLIDESHOW MODE ONLY)
Refracting Telescope: Lens focuses light onto the focal plane
Reflecting Telescope: Concave Mirror focuses light onto the focal plane
Almost all modern telescopes are reflecting telescopes.
Can be corrected, but not eliminated by second lens out of different material.
1. Light-gathering power: Depends on the surface area A of the primary lens / mirror, proportional to diameter squared:
A = p (D/2)2
2. Resolving power: Wave nature of light => The telescope aperture produces fringe rings that set a limit to the resolution of the telescope.
Resolving power = minimum angular distance amin between two objects that can be separated.
amin = 1.22 (l/D)
For optical wavelengths, this gives
amin = 11.6 arcsec / D[cm]
(SLIDESHOW MODE ONLY)
3. Magnifying Power = ability of the telescope to make the image appear bigger.
The magnification depends on the ratio of focal lengths of the primary mirror/lens (Fo) and the eyepiece (Fe):
M = Fo/Fe
A larger magnification does not improve the resolving power of the telescope!