Download Light and Telescopes Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015

Light and Telescopes
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Quotes & Cartoon of the Day
“We find them smaller
and fainter, in constantly
increasing numbers, and
we know that we are
reaching into space,
farther and farther, until,
with the faintest nebulae
that can be detected with
the greatest telescopes,
we arrive at the frontier of
the known universe.”
Edwin Powell Hubble
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Announcements
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Last Class
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History Galileo, Newton (right?)
Gravity & Tides
Intro to light
LT EM Spectrum
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
This Class
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LT EM Spectrum
Telescopes & Observatories
Light and the Atmosphere
Multi-wavelength Astronomy
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Electromagnetic Spectrum
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
The Electromagnetic Spectrum
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All these are the same thing as visible light
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Radio waves -- lowest frequency, longest wavelength, least energy per
photon
Gamma rays -- highest frequency, shortest wavelength, greatest energy per
photon
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WARMUP QUESTION
Which of the following has the shortest wavelength?
A. A photon of ultraviolet light.
B. Blue electromagnetic radiation.
C. An X-ray.
D. A radio wave.
E. Infrared radiation.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
LECTURE-TUTORIAL
EM SPECTRUM P. 47-49
Which of the following has the shortest wavelength?
A. A photon of ultraviolet light.
B. Blue electromagnetic radiation.
C. An X-ray.
D. A radio wave.
E. Infrared radiation.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
Consider green light with a wavelength of 550 nm
(0.00000055 cm). Light with a wavelength 1000 times
longer than this is most likely to be _____.
A. Infrared
B. Ultraviolet
C. Gamma Ray
D. Radio (excluding microwave)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Consider Xrays with frequency 1017 Hz. Light with a
frequency one millionth of this (i.e. 1011 Hz) is most
likely to be _____.
A. Ultraviolet
B. Gamma Ray
C. Microwave
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Evil aliens have
kidnapped you and placed
you in chamber with a
light source. There is a
large dial in front of you
marked “wavelength”. It’s
currently flooding the
room with light and the
dial reads 10-12 m. Which
way do you turn the dial?
A. Toward larger numbers -- fast!
B. Toward smaller numbers -- fast!
C. I leave it where it is.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WAVE- PARTICLE DUALITY
Light behaves like both wave and particle
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A wave is disturbance or oscillation (of a physical quantity),
that travels through matter or space, accompanied by a
transfer of energy
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example: water waves, sound waves
characterized by wavelength, frequency, speed
key property is interference
A particle in the physical sciences is a small localized
object to which can be ascribed physical properties.
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example: bullets, pebbles, sand grains, electrons, protons
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particles do not display interference
characterized by size, shape, speed,specific amount of energy,
mass, etc.
key property is the photoelectric effect
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Original Double-slit Experiment
Astronomy 1 - Elementary Astronomy
LA Mission College
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Particles Waving
Astronomy 1 - Elementary Astronomy
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Light behaves like both wave and particle
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Light displays interference
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Double-slit experiment
Wave behavior
Light deposits energy in discrete (quantized)
amounts
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depending only on wavelength
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The “particle of light” or “quantum of light” is
called a photon
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Particle behavior
photoelectric effect
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Telescopes and
Observatories
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Manipulating Light
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We commonly use lenses and mirrors to manipulate
light in the visible part of the spectrum
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all electromagnetic radiation follows the same basic
“rules” when it comes to how they interact with
matter.
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A radio dish is basically a mirror for radio waves.
Telescopes can use lenses, mirrors or a combination of
both to collect and focus light
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
TELESCOPES
What do you think?
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Why do Astronomers use Telescopes?
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Why do Astronomers Use Telescopes?
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To gather the faint light from distant objects
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This is the most important property of a telescope!
To resolve details of these objects
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The bigger the telescope, the more light it gathers
By creating a detailed image
Magnification is relatively unimportant, but the image
may be magnified for viewing or for optimal capture of a
digital image, etc
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
There are two main types of telescopes
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Refractors
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Think Pirate’s Spyglass
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Refractors have a large
lens or lenses, normally
at the front of the
telescope, which are the
primary optical
component
Galileo’s Telescopes were
Refractors
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
There are two main types of telescopes
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Reflectors
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Most modern telescopes are
reflectors -- also called
Newtonians
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including the Hubble Space Telescope
Reflectors have a large mirror at
the back of the telescope, which
is the primary optical
component
http://www.company7.com/orion/graphics/
Atlas10wManAtEyepc353500.jpg
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Terminology
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The “main” lens or
mirror is called the
Primary or Objective
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In reflecting telescopes
there is second mirror,
to re-direct the light
path. This is called the
Secondary
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Chrmomatic Aberration
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Light slows down in
glass
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returns to c on exit
Causes it to bend
Violet light bends/slows
more than red light
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Lenses cause colored
fringes called
chromatic aberration
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effect can be
minimized, but not
eliminated
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Refractors vs. Reflectors
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Refractors
Advantages
Rugged
Sealed Tube
Relatively Simple design
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Disadvantages
Chromatic Aberration
Heavy
Difficult to make glass
optically perfect
Astronomy 1 - Elementary Astronomy
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Reflectors
Advantages
Can be made very large
Glass does not have to be
optically perfect
Can be made thin &
therefore light
No chromatic aberration
Disadvantages
Design is more complex
with more optical
components
LA Mission College
Levine F2015
Bottom line
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A reflector is usually the best choice for an amateur
backyard telescope or a professional telescope.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
Astronomers use large telescopes primarily because
large telescopes
A. have a bigger field of view
B. have larger magnification
C. gather more light
D. None of the above
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Which of the following is an undesirable characteristic
of a refracting telescope?
A. Resolving power
B. Harmonic convergence
C. Chromatic aberration
D. Atmospheric coherence
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
All other things being equal, you’ll buy the telescope
with the ______________ that fits your budget and space/
weight limitations.
A. Largest diameter primary mirror
B. Largest diameter secondary mirror
C. eyepiece with the largest magnification
D. tube with the longest length
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
THE EFFECT OF THE ATMOSPHERE
AND ENVIRONMENT
Transmission of the Atmosphere
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Astronomical observations from the ground are mostly
constrained to visible light and radio wavelengths.
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Near-infrared and submillimeter observations are also
possible
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The ideal site for an observatory
Paranal Observatory (ESO), Chile
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At high altitude -- stiller, drier air
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Good seeing
Excellent Weather
In the middle of nowhere
Best ground-based sites include: Atacama Desert and Paranal in
Chile, Mauna Kea in Hawaii, Antarctica
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The ideal site for an observatory
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Altitude, weather, isolation....
From a high-flying aircraft or balloon!
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Kuiper Airborne observatory
SOFIA
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The ideal site for an observatory
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Altitude, weather, isolation....
Space! No atmosphere. No weather. No neighbors!
$$$ and usually very limited lifespan. Cosmic Rays
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Hubble Space Telescope
Spitzer Space Telescope
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
You want to build an observatory that can study the
ultraviolet emission from stars and galaxies. You
should plan to locate it _____.
A. on a high, dry desert plateau
B. in space
C. the site doesn’t matter much
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Most of the _____ light from astronomical objects
reaches the surface of the Earth.
A. Visible and Ultraviolet
B. Infrared and Visible
C. Visible and Radio
D. Gamma Ray and Visible
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Which of the following wavelength ranges reaches the
Earth from astronomical objects only in a few small
windows and except for those windows requires a high
flying aircraft, balloon or space-based telescope to
make observations?
A. Infrared
B. Ultraviolet
C. Radio
D. X-ray
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Multiwavelength Astronomy
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Astronomers observe across the Electromagnetic spectrum
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Gamma rays
X-rays
the ultraviolet (UV)
visible light
the infrared (IR)
submillimeter & radio
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WHAT WE LEARN ABOUT AT
DIFFERENT WAVELENGTHS
Infrared: More than Your Eyes Can See
Astronomy 1 - Elementary Astronomy
LA Mission College
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Xray & Gamma Ray Astronomy
Compton Gamma Ray
Observatory
Image Credit: NASA
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Hot objects & violent events
matter heated to millions of degrees
cosmic explosions, high speed collisions, material moving at extremely high speeds.
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Black Holes
Supernovae
White dwarfs & pulsars
Hottest part of Sun’s atmosphere
observatories must be in space
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Infrared Astronomy
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Old, cold & dusty objects
space based observatories or
high-flying aircraft.
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A few narrow bands from Earth
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heat radiation from cool
objects
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penetrate thick interstellar
dust
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star-forming regions
central areas of our galaxy
Cool stars
Spitzer Space Telescope
NASA/JPL-Caltech/R. Hurt (SSC)
cold interstellar clouds
star-forming galaxies
planets
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Radio ( & Microwave) Astronomy
Very Large Array
(VLA)
Image courtesy of
NRAO/AUI
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Very cold objects, traces atomic and molecular hydrogen
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Radiation left over from the Big Bang
supernovae
quasars
interstellar gas and molecules
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WRAP-UP
Topic for Next Class
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Solar System Overview
Astronomy 1 - Elementary Astronomy
LA Mission College
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Reading Assignment
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Astro: 5&7
Astropedia: 5 & 11
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Homework
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none yet
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015