Telescopes, Observatories, Data...
Transcript of Telescopes, Observatories, Data...
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Intro to Galaxies Telescopes 1
Telescopes, Observatories,
Data Collection
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Astronomy : observational science
only input is the light received
• different telescopes, different wavelengths
of light
• lab experiments with spectroscopy,
properties of matter and radiation
• space probes to measure conditions in
our own solar neighborhood
• use technology to ‘tweak’ the models,
simulations, graphics
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VISIBLE ASTRONOMY (Optical)
visible wavelengths - 4000 A - 7000 A
detectable with human eye
optics : science of controlling the direction
of light
Light travels in space in a straight line,
a light ray - particles of light (photons) moving
in a straight line.
Change the direction using lenses, mirrors,
prisms.
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Refraction
Light crosses one boundary to another,
it changes direction - it is bent.
The amount that light is bent is dependent
on what color it is, i.e., what wavelength.
Blue is bent more than red - the shorter
the wavelength, the more it is bent.
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Reflection
Light bounces off a surface and rebounds
at the same angle it had when coming in.
Reflection does NOT depend on the
wavelength of the light.
Science of optics uses refraction and
reflection to make images.
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image : gather light rays into the same
alignment they had when they
left the object
visual representation of the object
lens : smoothly curved surface, rays
are bent, and converge to a point
a lens brings light rays to a focus
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extended object : something more than
a point source of light
a lens brings rays from an
extended object to a focus where
an image is formed - usually
upside-down and smaller
focal length : distance from lens to image
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Hubble Space Telescope - Deep Field
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mirror : a polished surface that reflects
light - if flat, image is not distorted;
if curved, image is distorted
smoothly curved mirror will bring
all light to a focus
f-ratio : important property that describes
a lens or mirror
f-ratio = focal length
diameter
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Large diameter => small f-ratio
=> brighter the image
telescope : instrument to gather light &
allow you to examine an image
objective : lens or mirror that brings light
to a focus
eyepiece : allows you to examine the image
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Refracting Telescope
objective is a lens (Galileo’s telescope)
problem: not all the colors in the light
come to focus at the same point
- chromatic aberration
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Reflecting Telescope
objective is a mirror (Newton’s telescope)
light does not separate into colors, so no
problem with color haloes
cheaper to make
can be made much larger
have to figure out how to look at the image
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Reflecting Telescopes
Newtonian - small mirror, tilted at 45 deg.
to the path of the light
Cassegrain - hole in the objective
secondary mirror in the light path
“fold” the path of light
cheaper to build
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Functions of a Telescope
• Gather Light
“light bucket” - collect
photons, bring them to focus
objects seen in a telescope are brighter
than they appear to the naked eye
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LGP (Light Gathering Power)
LGP is proportional to (diameter)2
amount of light depends on the area of
the objective
a mirror with 2 times the diameter will
have times the LGP 4
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Some Comparisons
• human eye : diameter = 0.5 cm
telescope : diameter = 50 cm
How do the LGP’s compare ?
The telescope is 50/.05 = 100 times bigger
in diameter.
The telescope is (100)2 (=10,000) times
better for gathering light.
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• Hale Telescope - 5 m (Mt. Palomar)
Mayall Telescope - 4 m (Kitt Peak)
How do the LGP’s compare ?
Hale is 5/4 times bigger than the Mayall
in diameter.
LGP is (1.25)2 = 1.563 times better in
gathering light.
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• Resolve fine detail
resolution : ability to separate things
that appear close together
into separate images
resolution is measured in angular measure
example: 10 cm diameter telescope has a
resolution of 1.4 arc sec
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If the separation is more than
1.4 arcsec, you’ll see them as
separate stars with this telescope.
If the separation is less than
1.4 arcsec, you’ll see them as
a big blob with this telescope.
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Resolution is inversely proportional
to diameter
Resolution 1
diameter
Smaller resolution is better for learning
about details.
2 X the diameter means resolution
is twice as small (i.e. 2 times
better)
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Human eye has a resolution of 1 arcmin.
Things that affect resolution :
seeing : turbulence in the atmosphere
distorts and blurs the image
measured in arcsec
Solution : put telescopes in space !
Resolution would be limited by the optics
of the telescope NOT by the Earth’s
atmosphere.
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• Magnify the Image (least important) magnification : apparent increase in an
object’s size compared to
naked eye observation
MP = focal length of the objective
focal length of the eyepiece
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What’s next?
very light materials
remote observing
very large mirrors in segments
adaptive optics
telescopes in space
telescopes on the moon?
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Invisible Astronomy
wavelengths not seen by the human eye
wavelengths that are generated by very
different physical processes
allow us to discover astronomical objects
we wouldn’t ordinarily have seen
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Milky Way in Radio
Vesta
VLA
Arecibo
Gamma Ray Moon
http://antwrp.gsfc.nasa.gov/apod/ap971214.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap971214.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970908.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970908.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970727.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970727.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970412.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970412.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970210.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970210.html
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Earth’s Atmosphere
Radiation that has traveled for billions of
years to get here is blocked in the last 100 km
of the journey by our atmosphere !
IR - blocked by water vapor
UV and X-ray blocked by the ionosphere,
above 100 km
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• ground-based (radio, IR)
• space-based - rockets, balloons,
airplanes, satellites, spacecraft
RADIO ASTRONOMY
Parabolic dish, focuses the EM rays (in
radio wavelengths) to a focal point
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Radio Telescopes
detector (receiver) is placed at the focal
point, translates the radio signal to a voltage
which is then measured and recorded
computer then generates a map of these
intensities
can observe day or night, even on cloudy
days for the longer wavelengths
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larger than optical telescopes (100 m!!!)
drawback is poor resolution
resolution also depends on wavelength
being observed
long wavelengths, poor resolution
SOLUTION : interferometers to create
effectively larger diameter telescopes
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Two (or more) telescopes act like
parts of one big telescope.
Interferometer
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VLA - Very Large Array, Socorro, NM
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VLBA - Very Long Baseline Array
radio dishes from Hawaii to the
Virgin Islands
resolution of 2 x 10-4 arcsec
adding radio telescopes on the moon would
give a resolution of 10-6 arcsec
http://www.aoc.nrao.edu/vlba/html/thesites.html
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IR Astronomy
• some wavelengths from the ground
• need high, dry climate
• optics are much the same as for optical
astronomy
• detectors must be different, cooled to 2 K
advantages:
less hindered by interstellar dust
cool objects can be detected
things not seen in visible can be detected
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Space-Based IR
balloons, satellites
IRAS - international collaboration
mapped the sky - 200,000 IR sources
many related to the process of
starbirth
UV, X-Ray, Gamma Ray - done from space
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IR Astronomy
• some wavelengths from the ground
• need high, dry climate
• optics are much the same as for optical
astronomy
• detectors must be different, cooled to 2 K
advantages:
less hindered by interstellar dust
cool objects can be detected
things not seen in visible can be detected
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Space-Based IR
balloons, satellites
IRAS - international collaboration
mapped the sky - 200,000 IR sources
many related to the process of
starbirth
UV, X-Ray, Gamma Ray - done from space
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Hubble Space Telescope (HST)
2.4 meter mirror
goal : faint objects with high resolution,
0.1 arcsec resolution
1200 A to 10,000 A
most expensive astronomical project to
date
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Hubble
Space
Telescope
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Image Collection
• images taken by detectors
photographic plates
CCD’s (charge coupled devices)
• computer visualizations, false-colors
• intensity maps
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CCD = Charge Coupled Device
Each cell is
called a pixel. A
pixel captures
photons and
counts them
individually.