The original light
detector the
human eye
Maximum sensitivity about 550nm
Angular
resolution about 1 arcminute
alpha/360 deg / 2 pi d or alpha = s 360 deg / 2 pi d
For very small angles alpha [arcseconds] = 206265 s /d
The modern camera is the CCD
How to focus light Reflection
or Refraction
Telescopes:
Refractor
objective is a lens example
Reflector
objective is a mirror example
other types
Keck
What do you want to pay for
in a large telescope?
Light
collecting area proportional to (diameter of objective)2
Angular
resolution (resolving power)
Diffraction limit of the telescope in arcseconds
=
2.5 x 105 wavelength of light/diameter of the telescope
=
2.5 x 105 lambda/D
resolved stars unresolved
stars
Why magnification is not
important.
Magnification
= focal length of objective /focal length of eyepiece
Spectroscopy
A different kind of resolution low
and high
Timing
OGLE search for variables light curve phased light curve
What our atmosphere does.
Seeing
image motion, blurring
Scintillation
twinkling
One
solution HST
Another
solution Adaptive
Optics even for Neptune
And then there is the weather, so pick a good dark site
Except in the radio where even bad weather won’t stop you
Radio telescopes
RE: resolution proportional
to wavelength /diameter
so 1” at 20cm is 40km telescope!
Solution is interferometers
and arrays in which
resolution is proportional to wavelength/distance between receivers
VLA 27
telescopes 25m over 36km
VLBA 10
telescopes, resolution 0”0001 or so
Radar
Infrared
1 -40mm various windows, longer wavelength- space (IRAS)
Microwave Anisotropy
Probe the Cosmic Microwave Background
Ultraviolet
Hubble Space
Telescope * the Hubble Deep Field
X-ray
Gamma rays
Crab nebula in radio IR Optical X-ray
The Milky Way in Gamma-ray
X-ray
Visible
IR
Radio
If you can afford it get a
close-up.
Earth-orbiters
Voyager2 to the Giant Planets – the Grand Tour
Orbiters
Landers/probes
Sample Return
