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INTRO
In astronomy,
observation usually
precedes theory.
Ex/ New solar syst.; acc. univ.
Telescopes have grown in size and
complexity and now cover the
entire EM spectrum
I. Optical Telescopes
A. Telescope: A “light bucket”
used to capture
incoming photons
& concentrate them
into a focused beam
for analysis.
B. Types of Telescopes
1. Refractors: A glass lens bends
(refracts) incoming light rays to
a focus. Eyepiece magnifies.
Yerkes
Observatory
2. Reflectors: A curved mirror (the
primary mirror) reflects incoming
rays to a focus.
Eyepiece magnifies.
D. Reflector Design
1.Newtonian:
Secondary mirror
reflects light to
side eyepiece.
Subcategory:
Dobsonian
2. Cassegrain:
Secondary mirror
reflects light back thru
a hole in the primary mirror.
II. Telescope Size & Resolution
A. Light-gathering power: Larger
collecting area - brighter image.
2
1. Brightness ~ Diameter
Ex/ 10” aperture is 25 x brighter
than 2” aperture
(or 25 x faster exposure)
2. Largest: VLT in Chile (16 m)
Keck I & II in Hawaii (14 m)
TMT (2018); Giant Magellan Telescope (2016)
Ch. 5 Example Problem
How long would it take a telescope with
a 9” aperture to produce the same
image that a 3” scope can make in 45
min.?
The VLT
GranTeCan
Canary Islands
GMT: 7 8.4-m mirrors
B. Resolving Power: Ability to
make sharp images of faint objects
or to distinguish between 2 adjacent
objects in the sky.**
aka
Angular Resolution
C. Atmospheric Blurring
1. Hinders ground-based scopes
Ex/ “twinkling” stars
2. Best locations- high, dry, & dark
Ex/ Arizona; Chile; Hawaii
3. Another solution - space.
Ex/Hubble (1993) - 20 x
better than previous best
Pic Du Midi, French Pyrenees
D. Adaptive Optics: Mirror changes
shape to compensate for atmosphere.
a. Lasers pierce atmosphere,
create “artificial star”
b. Some now sharper than Hubble!
Ex/ Subaru (IR), Keck, VLT
III. Radio Astronomy &
Interferometry
A. Radio telescopes
1. Only since the‘50’s Grote
2. Pioneers- Karl Jansky, Reber
3. Curved metal dish focuses
radio waves to a focal point.
4. Instruments located at
the prime focus.
B. Large Size Necessary
1. Signals are faint
2. Long wavelength radio diffracts
greatly - poor resolution
a. Surface doesn’t have to be
smooth like optical scopes
b. It’s easy to make them large
Ex/ Largest:
Arecibo – 1000 ft. wide!(305 m)
Green Bank, West Virginia - largest moveable radio dish
C. Value of Radio Astronomy
1. 24 / 7
2. Thru clouds, rain, snow
3. Objects visibly dim may be
strong radio sources. Ex/
*4. Radio penetrates dust
in space.
Ex/ Center of our galaxy
D. INTERFEROMETRY
1. Interferometer: Data from 2 or
more scopes combined.
Ex/ VLA in N. Mex (27 dishes)
ATA (2007)- 42 dishes ALMA (2012) - 66
Square Kilometer Array (2020)
- 150 dishes
2. Behaves like a single dish
whose diameter is the distance
between dishes. Ex/ Compound eye
Allen Telescope Array (so far..)
Single Dish of the VLA
VLA in New Mexico
ALMA
Largest Telescopes 2015
Refractor (lens)
Yerkes Obs.
1m
Single mirror
GranTeCan
Keck I & II
Optical
interferometer
VLT
Keck
Arecibo
10.4 m
10 m
16.4 m
14.6 m
305 m
Single radio dish
Array (1 location) ATA (phase 1)
VLA
ALMA
42 dishes
27 dishes
66 dishes
IV. Space Telescopes
A. Microwave satellites
1. COBE (1990’s) - Measured the
cosmic microwave background
Proof of the Big Bang!
2. Planck (2009)
B. INFRARED Astronomy
1. Long wavelength IR
penetrates clouds in space.
2. Good for star or planet-forming
clouds of warm dust & gas.
3. Mountaintops Ex/ Subaru
4. Airplanes Ex/ SOFIA
5. Or Space Ex/ Spitzer
James Webb Space Tel. (2018)
SUBARU
SOFIA
James Webb Space Telescope
~ 6.5 m
mirror
Launch in
2018 (?)
Infrared
C. Visible light:
1.Hubble Space
Telescope
2. Spherical
aberration
corrected 1993
3. Final repair
D. ULTRAVIOLET Astronomy
1. Used for hot stars
2. Done by high-altitude balloons
3. Or satellites Ex/ Galex, Hubble
E. X-RAY Astronomy
1. No ground - only satellites
2. Used 4 violent events (black holes)
3. Special design (difficult to focus)
Ex/ Chandra (1990’s)
X-ray
detectors
F. GAMMA RAY Astronomy
1. Can’t be focused
2. Counted by special detectors
3. Scarce (~ 1 detection per day)
4. Occasional “bursts”, or GRB’s
a. Hypernova – really massive star
explodes / black hole formed
b. Colliding binary neutron stars
5. Compton Gamma Ray Observatory
(1990’s - 2000)
6. SWIFT
(2004)
7. Fermi Gamma-Ray Space Telescope