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Astronomy 101 Lecture #3
Today: Basic Principles LGP, Angular Resolution Plate Scale, Focal Ratio
Telescope Design Types of Telescopes Effective Focal Length Magnification
Reading: Ch. 6
Where there is an observatory and a telescope, we expect that any eyes will see new worlds at once. – Henry David Thoreau
●No light loss (reflection) ●Smaller f, compact design●Only one surface important●Support from back●Spherical and coma aberration
●Light loss (absorption) ●Large f (large telescope size)●Difficulty in manufacture●Large weight (support)●Chromatic aberration, f=f(λ)●Thermal Stability●Easy maintenance
Refractors
Telescope Types: Pros and Cons Astronomy 101 Lecture #3
Reflectors
The Largest Refractor The Yerkes Observatory
(University of Chicago) refractor was built in 1897. It has lens diameter of 40in and is 19.3 meters long. When it was built, it was the largest telescope in the world. It remains the largest refractor ever built.
Image credit: Yerkes Observatory
Astronomy 101 Lecture #3
Making Large Mirrors at University of Arizona
Image credit: Steward Observatory
The mirrors are made out of borosilicate glass on the honeycombed support structure.
The glass is melted, molded and spun into shape in a specially designed rotating oven.
The design was pioneered by Roger Angel at University of Arizona in the late 1980s.
LBT (8.4 m)
Magellan (6.4 m)
Astronomy 101 Lecture #3
Keck Telescope 10–meter Mirror
The primary mirrors consists of 36 hexagonal segments. Each is 1.8 meters wide and 3in thick,and weighs about one ton. They are alignedtwice a second to a precision of 4nm.
Image credit: Keck Observatory
Astronomy 101 Lecture #3
Diffraction Pattern for a Spherical Aperture – Airy Disk
Astronomy 101 Lecture #3
Resolving Two Stars
θmin = 1.22 λ/D
Image Credit: HST
Astronomy 101 Lecture #3
Types of Telescopes
Astronomy 101 Lecture #3
Equatorial Mount
RA axis
DEC axisDEC axis
Astronomy 101 Lecture #3
AltAz Mount
altitude axis
azimuth axis
Astronomy 101 Lecture #3
Astronomy 101 Lecture #3
Nasmyth Focus on Keck
Effective Focal Length
f eff=as
PS=1
f eff
Effective Focal Length
f eff=as
=
f p f s'
p
as= f s'
=a p
p= f p
p
PS=1
f eff
Effective Focal Length
f eff=as
=
f p f s'
p
as= f s'
=a p
p= f p
p
PS=1
f eff
Effective Focal Length
f eff= f p
f s / d s
f s/ d s− f p/ d p
TMO Telescope
f eff=f p f s
'
p
f eff= f p
f s / d s
f s/ d s− f p/ d p
