Download Light and Telescopes II

Lecture 7
Light and Telescopes II
Advanced Telescopes
Announcements
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Details about the May Term Observational
Astronomy course.
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McM May Term runs May 14 to June 1
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Class meets 5 days a week, 9 – 11:55 am
Prerequisite is college algebra (and this course)
Travel costs will probably run about $600, depending
on the number of students.
Observing trip to Arizona expected to be the middle
week, subject to telescope scheduling.
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Side trips planned for The Grand Canyon and Beringar
Crater (aka Meteor Crater).
Review - What Is A Telescope?
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Telescope – An
instrument for
collecting and
focusing
electromagnetic
radiation (light).
Review - What Are Telescopes For?
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MYTH: The main
function of a telescope is
to magnify a distant
object.
THIS MYTH IS FALSE!
The main function of a
telescope is to make the
image of a distant object
brighter and sharper!
Traditional Telescopes
The 4-m
Mayall
Telescope at
Kitt Peak
National
Observatory
(Arizona)
Advances in Modern Telescope Design
Modern computer technology has made
possible significant advances in telescope
design:
1. Lighter mirrors with lighter support structures,
to be controlled dynamically by computers
Floppy mirror
Segmented mirror
2. Simpler, stronger mountings to be controlled by
computers
Segmented Mirror Telescope
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Mirror segments fit
together like a puzzle.
Computers align the
mirror segments
Keck I & II Telescopes
are each 10 meters
Hobby-Eberly
Telescope at McDonald
Observatory in Texas is
a 9.2 meter segmented
mirror design
Examples of Modern Telescope Design
Design of the Large
Binocular Telescope
(LBT)
The Keck I telescope mirror
Examples of Modern Telescope Design
The Very Large Telescope (VLT)
8.1-m mirror of the Gemini Telescopes
Interferometry
Recall: Resolving power of a telescope depends on
diameter D:
amin = 1.22 l/D.
This holds true even
if not the entire
surface is filled out.
• Combine the
signals from several
smaller telescopes to
simulate one big
mirror 
Interferometry
Keck Interferometer
Instruments On The Telescope
Imaging devices
 Photometer
 Spectrograph
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Imaging Devices
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Drawing what was seen
through the telescope
Photography greatly
increased the "light
gathering power" of the
telescope by allowing
an image to build up on
the film.
Electronic (digital)
cameras utilizing CCD
(charge-coupled
device) chips have
taken the place of film
in many applications in
the last few years.
CCD Imaging
• More sensitive than
CCD = Charge-coupled device
photographic plates
• Data can be read
directly into computer
memory, allowing easy
electronic manipulations
Negative image to
enhance contrasts
False-color image to visualize
brightness contours
Photometer
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Measures the
intensity of the light
from a celestial object
very accurately
Often used to monitor
variable stars
Data can be read
directly into a
computer for analysis
Photometry Projects
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Variable stars
Novas &
supernovas
Eclipsing binaries
Eclipsing planets
The Spectrograph
Using a prism (or a grating), light can
be split up into different wavelengths
(colors!) to produce a spectrum.
Spectral lines in a spectrum
tell us about the chemical
composition and other
properties of the observed
object
Daily Quiz 9 – Question 1
In which device do astronomers take
advantage of chromatic aberration?
A.
B.
C.
D.
The primary mirrors of reflecting
telescopes.
The primary lenses of refracting
telescopes.
The prism.
The photometer.
Radio Telescopes
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The other major type of
ground based telescope.
Four parts:
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The Dish – collects and
focuses radio signals from
space.
The Antenna – absorbs the
radio energy and sends it
through a cable to the
amplifier.
The Amplifier – artificially
makes the radio signal
stronger.
Computer – actually
digitally records the signal
for later analysis.
Radio Astronomy
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Radio waves from space
are produced by a variety
of sources.
Many related to magnetic
fields, or very interesting
astronomical objects (e.g.
black holes).
Radio waves are not
absorbed by dust in
space, so we can see
“through” dust clouds that
block optical telescopes.
Radio Astronomy
Recall: Radio waves of l ~ 1 cm – 1 m also
penetrate the Earth’s atmosphere and can be
observed from the ground.
The Largest Radio Telescopes
The 100-m Green Bank Telescope in
Green Bank, WVa.
The 300-m telescope in
Arecibo, Puerto Rico
Radio Interferometry
Just as for optical telescopes, the resolving power of
a radio telescope is amin = 1.22 l/D.
For radio
telescopes, this
is a big
problem: Radio
waves are
much longer
than visible
light
 Use
interferometry to improve resolution!
Radio Interferometry
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Radio signals are digitally
combined by computers
to produce a “virtual”
radio telescope with a
dish as large as the
distance between the
telescopes in the
network.
Lets us produce virtual
radio telescopes with
enough resolving power
to read a newspaper on
the moon (if it was a
“radio newspaper”).
Radio Interferometry
The Very
Large Array
(VLA): 27
dishes are
combined to
simulate a
large dish of
36 km in
diameter.
Even larger arrays consist of dishes spread out over the entire U.S.
(VLBA = Very Long Baseline Array) or even the whole Earth (VLBI =
Very Long Baseline Interferometry)!
Daily Quiz 9 – Question 2
Radio telescopes are often connected together to
do interferometry. What is the primary problem
overcome by radio interferometry?
A.
B.
C.
D.
Poor light gathering power.
Poor resolving power.
Poor magnifying power.
The low energy of radio photons.
Science of Radio Astronomy
Radio astronomy reveals several features,
not visible at other wavelengths:
• Neutral hydrogen clouds (which don’t emit any
visible light), containing ~ 90 % of all the atoms
in the Universe.
• Molecules (often located in dense clouds,
where visible light is completely absorbed).
• Radio waves penetrate gas and dust clouds, so
we can observe regions from which visible light
is heavily absorbed.
Infrared Astronomy
Most infrared radiation is absorbed in the lower
atmosphere.
However,
from high
mountain
tops or highflying air
planes,
some
infrared
radiation
can still be
observed.
NASA infrared telescope on Mauna Kea, Hawaii
Space Astronomy
Able to observe at all wavelengths of
the electromagnetic spectrum
 Increased resolving power because
of almost perfect "seeing" in space
 Increased light gathering power
because of the extremely black
background in space
 Observe almost continuously
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Space Astronomy
NASA’s Space Infrared Telescope
Facility (SPITZER TELESCOPE)
Warm objects glow in
infrared, so IR telescopes
must be cooled to very low
temperatures.
Daily Quiz 9 – Question 3
Why must far infrared telescopes
be cooled to a low temperature?
A.
B.
C.
D.
To reduce interfering heat radiation emitted by the
telescope.
To protect the sensitive electronic amplifiers from
overheating by sunlight.
To improve their poor resolving power.
To improve their poor magnifying power.
Space Infrared Astronomy
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Here is a picture of the
“freezing dust” (blue
cloud) surrounding a
nursery of newly-forming
stars in a nearby nebula!
The dust shroud is about
-200ºF! The stars inside
are MUCH hotter.
This dust is so cold it
would be invisible to
optical telescopes!
Ultraviolet Astronomy
• Ultraviolet radiation with l < 290 nm is
completely absorbed in the ozone layer of
the atmosphere.
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Ultraviolet astronomy has to be done from
satellites.
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Several successful ultraviolet astronomy
satellites: IUE, EUVE, FUSE
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Ultraviolet radiation traces hot (tens of
thousands of degrees), moderately ionized
gas in the Universe.
Ultraviolet Astronomy
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This picture of the
Andromeda Galaxy
shows where all of
the most recently
formed stars are in
the galaxy.
Notice all the new
stars are arranged in
spiral patterns
twisting out of the
galaxy’s center!
X-ray Astronomy
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Must be done from
space
Extremely high
energy radiation
(black hole
accretion disks).
Requires special
grazing incidence
telescopes
X-Ray Astronomy
• X-rays are completely absorbed in the atmosphere.
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X-ray astronomy has to be done from satellites.
X-rays trace hot
(million degrees),
highly ionized gas
in the Universe.
NASA’s
Chandra X-ray
Observatory
Chandra X-ray Observatory
X-Ray Astronomy
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Many of the colored
“dots” in this image
are not what you think
they are! They’re
huge black holes!
Every one of them is
at the center of a
distant galaxy!
Sagittarius A* Black Hole
Gamma-Ray Astronomy
Gamma-rays: most energetic electromagnetic radiation;
traces the most violent processes in the Universe
The Compton
Gamma-Ray
Observatory
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Must be done
from space
Gamma rays
can not be
focused, so
only detectors
are used
Gamma Ray Astronomy
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If you had gamma-ray
eyes, this would be one
of the brightest objects in
the night sky (up to a
short while ago).
It’s a type of object called
a quasar, and it’s actually
8 billion light years away!
You’re looking at photons
that are almost twice as
old as the sun and the
Earth!
Daily Quiz 9 – Question 4
Why are near infrared telescopes located
on mountaintops and ultraviolet
telescopes in Earth orbit?
A. The primary infrared blocker, water vapor,
is mostly in the lower atmosphere.
B. The primary ultraviolet blocker, ozone, is
located high in the atmosphere, far above
mountaintops.
C. Ultraviolet telescopes require the low
temperature of space to operate.
D. Both A and B.
The Hubble Space Telescope
• Launched in 1990;
maintained and
upgraded by several
space shuttle service
missions throughout
the 1990s and early
2000’s
• Avoids
turbulence in
the Earth’s
atmosphere
• Extends
imaging and
spectroscopy
to (invisible)
infrared and
ultraviolet
For Next Time
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Read Units 23 and 24 for Monday.
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Remember that the Homework is due
Monday as well.
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Happy Valentine’s Day!