Transcript Telescopes - University of Hawaii

Optics and Telescopes
Kathy Cooksey
Acknowledgements Tyler Nordgren & Julie Rathbun University of Redlands
Johnny B. Holmes Christian Brothers University
Outline
• Optics and telescopes
• Understand different
types
• Why does size matter?
• Why put them in
space?
Refraction & Lens-users Eq.
1
1
1
=
+
f
o
i
as o approaches infinity
i approaches f
f
o
f
i
Refraction & Lens-users Eq.
f>0
1
1
1
=
+
f
o
i
o > 0 AND o > f
i > 0 AND i > f
f
f
o
i
Refraction & Lens-users Eq.
1
1
1
=
+
f
o
i
as o gets smaller,
i gets larger
f
f
o
i
Refraction & Lens-users Eq.
1
1
1
=
+
f
o
i
as o approaches f,
i approaches infinity
f
f
o
i
Refracting Telescope
Two lenses: How does it work?
objective lens
eyepiece
fo
fe
Refracting Telescope
Two lenses:
objective lens
eyepiece
fo
fe
Model Optical Rail
• http://www.school-forchampions.com/science/experiments/simo
pticsmirror.htm
• Magnification
• Image Inversion
• Multiple optics
– Image re-inversion ;)
Purpose of Telescope
1. Increases amount of light we see:
Sensitivity is proportional to collecting area.
If one telescope is 3 times bigger than another, then it can see
32 = 9 times fainter objects.
2. Increases detail (resolution) we see:
Resolution is inversely proportional to telescope diameter.
If one telescope is 3 times bigger than another, then it can see 3
times smaller angles (3 times smaller objects or detail).
Sensitivity
• Telescope size doubled from left to right
Andromeda Galaxy Copyright by AURA
Resolution
(a) 10’
(b) 1’ (10 times bigger than a)
(c) 5” (12 times bigger than b)
(d) 1” (5 times bigger than c)
Human eye: 0.5’ in visual range
Andromeda Galaxy Copyright by AURA
Side Note: Exposure Time
• Point telescope, open shutter, and expose for
a long time (integration)
• Gather more photons and improve image
• Human eye has limited integration time
Telescopes & Light
• Collect “light”
– Visible light is just part of whole spectrum of “light”
• Light is all astronomers have!!!
• Electromagnetic spectrum (EM): whole range of
varieties of “light”:
– Example: visible light comes from lamp in your house
– Example: radio waves come from radio station
– Other types of radiation: microwaves, infrared and
ultraviolet light, X-rays, and gamma-rays
EM Radiation
Radio
γ-ray
UV
Optical and infrared
X-ray
Types of Telescopes
Refracting Telescope
Two lenses (as we made)
objective
lens
eyepiece
fo
fe
Yerkes 40-in Refractor
Optical
All modern astronomy
telescopes are reflectors
Use mirrors for primary optic
Reflecting Telescope
Light from far away
mirror
focuses
light
Problem: how do we get to focused light without blocking
incoming light?
Reflecting Telescope
Light from far away
mirror
focuses
eyepiece
light
Solution #1: If mirror is big enough (say100 to 200 inches in
diameter), we can sit right in middle and won’t block much
light - this is called prime focus.
Arecibo 300-ft
Reflector
Radio
Reflecting Telescope
Light from far away
eyepiece
mirror
focuses
light
Solution #2: Use secondary mirror to reflect light off to side
of telescope - this is called Newtonian focus.
Reflecting Telescope
Light from far away
primary mirror
focuses
light
eyepiece
Solution #3: Use secondary mirror to reflect light out back
of telescope - this is called Cassegrain focus.
Hooker 100-in Reflector
Optical
Some Large Optical Telescopes
Location, location, location
Aperture
(meters)
10.0
Name
Keck
Keck II
Location
Mauna Kea,
Hawaii
Comments
mi rror composed of 36 segments
future optical interferometry!
9.2
Hobby-Eberly
Mt. Fowlkes,
Texas
very inexp ensive: sphe rical
segmented mir ror; fixed
eleva tion; spectroscopy only
8.3
Suba ru
Mauna Kea,
Hawaii
NAOJ
Cerro Parana l,
Chil e
now operate indep enden tly in the
future will be unit s of Very Large
Telescope
Antu
8.2
Kueyen
Melipal
Yepun
Gemi ni North
8.0
3.0
Mauna Kea,
Hawaii
Gemi ni South
Cerro Pachon,
Chil e
Shane
Moun t
Hamilt on,
Calif ornia
twins
Lick Observatory
Keck Twin
10-m
Reflector
Optical & IR
Keck Primary Mirrors
• Large!
– Formed by 36 individual
hexagonal segments
• All must be kept
positioned relative to their
neighbors
– To accuracy of four
nanometers, or 1,000 times
thinner than human hair
Lick Observatory
Nickel 40-in
Shane 120-in
Lick Observatory
Adaptive Optics Teaser
Atmospheric Seeing
Hubble Space
Telescope
Ground - KPNO 4.0m
Copyright NOAO /AURA/NSF
Space - HST – 1.0m
Summary
• Refracting telescope: primary lens
• Reflecting telescope: primary mirror
– All modern telescopes
• Sensitivity: amount of light
– Proportional to collecting area
• Resolution: detail
– Inversely proportional to telescope diameter
• Bigger is better
• Space is atmosphere free