Download dtu7ech03 pt 2 - Fort Thomas Independent Schools

Light and Telescopes
Modern Astronomy
Problems with ground-based
observing
Equipment
 Atmosphere

Good seeing
 Twinkling stars
 Reduction in available wavelengths of light


Light pollution
Good Seeing Conditions
Stable atmosphere
 Cool temperature
 Low humidity
 Long periods of stable weather
 Limited light pollution

Where would you construct a new observatory?
Mauna Kea Observatory Complex
13,796 above MSL
Copyright 1998, Richard Wainscoat,
All Rights Reserved
Nordic Optical Telescope, La
Palma, Canary Islands
Photo by Bob Tubbs.
Roque de los Muchachos Observatory
Credit: Nik Szymanek (ING), IAC, ENO
Gran Telescopia Canaries, La
Palma, Canary Islands
10.4 meter multimirror
reflector
Palomar Mountain Observatory,
San Diego County, CA
Courtesy of Caltech Astronomy
200-inch primary mirror
Near Atacama Desert in Chile
La Silla, Chile
ESO
European Organisation for Astronomical
Research in the Southern Hemisphere
Other Notables
Mount Wilson Observatory, Los Angeles,
California
 McDonald Observatory, Texas
 Kitt Peak Observatory, Tuscon, AZ
 Yerkes Observatory, Williams Bay, WI
 Cincinnati Observatory Center

Cincinnati Observatory Center
11” refractor (likely the oldest continuously
used telescope in the world)
16” refractor
(Photo courtesy COC)
Photos courtesy of David Wall
Angular Resolution
The measure of the smallest amount of
detail of an astronomical object that can
be detected by a telescope.
 Angular size is indicated by seconds (1”)
or fractions of seconds (0.01”).
 Unaided human eye (1’)
 Best without adaptive optics (0.3”)

Differences in Angular Resolution
http://grus.berkeley.edu/~jrg/CELT/ay250_012403.html
Angular resolution of ground-based
telescopes: a comparison
Best resolution: 0.00001” using radio data
from telescopes on opposite sides of the
Earth
 0.001”—VLBA across the US
 0.1”—VLA radio wave observatory in New
Mexico
 0.3” to 0.005”—Keck Observatory, Hawaii

Advanced Technology:
improvements in light gathering and
resolving power

Previous methods
long-exposure photographic plates
 Monster-sized primary lenses and mirrors
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
Today
Charged Coupling Devices (CCD)
 Active optics
 Adaptive optics
 Interferometry

New technology has created chargecoupled devices (CCDs) to gather light
more efficiently than photographic
plates.
These devices
produce images
with astounding
detail. Shown in
this picture are the
intricate details of
the Rosetta Nebula
5000ly away.
Ordinary Photography Versus CCDs
ORDINARY
PHOTOGRAPH
NEGATIVE
NEGATIVE
USING CCDs
COMBINED CCD
IMAGES USING
COLORED FILTERS
Active Optics
Primary mirror receives constant
adjustments to maintain best orientation.
 Aims the mirror (or mirrors) correctly.

Adaptive Optics



Computer-activated motors attached to primary
mirror or other mirrors reshape the mirror to
cancel out the twinkling effect caused by
atmospheric turbulence.
Produces even clearer images by deformation of
the primary mirror.
Keck Observatory—10 m “primary mirror” is
actually composed of 36 hexagonal mirrors. Sixinch center mirror is diameter deformable and is
adjusted up to 670 times per second.
Keck Observatory, Mauna Kea,
Hawaii
NASA
Courtesy W.H. Keck Observatory
Keck 1 Primary Mirror (10 m)
Credit: W. M. Keck Observatory/Gary Chanan
Back of individual hexagonal
reflector at Keck Observatory
(Photocredit: R. Underwood.)
Using adaptive optics to calculate the amount of twinkling of
our atmosphere, as well as changes to the shape of the
mirror, we can receive better images from ground based
telescopes.
IMAGES OF SATURN
GROUND BASED
WITH NO
ADAPTIVE OPTICS
GROUND BASED
WITH ADAPTIVE
OPTICS
Interferometery

Multiple telescopes interface to act as one giant
telescope

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increases light-gathering ability and resolution
produces a composite image having excellent angular resolution.
Uses the physical principle of wave interference to add or
subtract specific wavelengths of light.
Approaches


One site: very-large array (VLA), New Mexico (0.1” resolution)
and Keck, Hawaii (dual telescopes 0.04” resolution)
Multiple sites: very-long-baseline interferometry (VLBI)

Radio telescopes separated by thousands of kilometers (0.001”
resolution)
NONOPTICAL ASTRONOMY
Using interferometry to combine
the information from two or more
telescopes to create one image,
radio telescopes can be linked
together over large distances to
overcome the limits of resolution
for a single radio telescope.
The radio telescope in Greenbank,
West Virginia, has an off-center
secondary which does not block
incoming radio waves.
The Very Large Array (VLA) in central New
Mexico combines the signals from 27 radio
telescopes to either cover wide areas of the
sky or increase the resolution for a small area.
Beyond the Hindrance of the
Earth’s Atmosphere
Sky & Telescope illustration by Kevin Sartoris.
Ground Based Telescopes are Limited
Our atmosphere causes the stars to appear to shift in color and
brightness. This causes the star to appear to flicker. We call this
twinkling.
GROUND BASED TELESCOPES
BLURRED BY TWINKLING
TELESCOPES IN ORBIT ABOVE
OUR ATMOSPHERE AVOID THIS
PROBLEM
Light from cities scatters in our atmosphere reducing the
visibility of celestial objects. This is called light pollution, and
has been an increasing problem in recent years.
The view from Kitt
Peak National
Observatory of the
Tuscon, Arizona
skyline in 1959
The same skyline in 1972
The transparency of a material depends on the wavelength of
light. Earth’s atmosphere is relatively transparent to visible light
and radio waves, which are referred to as “windows” through
which we can view space from a ground-based telescope.
Not every wavelength of light passes through the Earth’s Atmosphere!
To avoid adverse effects of our atmosphere, we launch
telescopes on satellites that circle the Earth above the
atmosphere.
THE HUBBLE
SPACE
TELESCOPE (HST)
Using adaptive optics to calculate the amount of twinkling of
our atmosphere, as well as changes to the shape of the
mirror, we can receive better images from ground based
telescopes.
IMAGES OF SATURN
GROUND BASED
WITH NO
ADAPTIVE OPTICS
GROUND BASED
WITH ADAPTIVE
OPTICS
HUBBLE IMAGE
Images of Saturn
IN VISIBLE LIGHT
IN RADIO WAVES
NOTE: We use falsecolor images when
displaying data from
non-visible light.
Radio Wave Telescope, Arecibo,
Puerto Rico
The Spitzer Space Telescope will examine
infrared cosmos
Mirror Setup
Launched in 2003
Non Optical Images of the Sun Reveal Details which
Cannot be Observed in Visible Light
X-RAY
X-ray image
VISIBLE
Kitt Peak
National
Observatory
Different Views of Our Universe
We are familiar with the view of our
surrounding universe in visible light
Astronomers also study our universe using other
wavelengths of light to unlock its secrets
RADIO WAVES
INFRARED
X-RAYS
GAMMA RAYS
A space-based telescope for every
purpose…and for every wavelength!


Radio waves (see ground-based telescopes)
Microwaves

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Infrared light


Far Ultraviolet Spectroscopic Explorer (FUSE), Extreme
Ultraviolet Explorer (EUVE), Galaxy Evolution Explorer (GALEX)
X-rays

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Hubble Space Telescope (HST)
Ultraviolet light

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Infrared Astronomical Satellite (IRAS), Infrared Space
Observatory (ISO), Spitzer Space Telescope (SST)
Visible light

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Wilkinson Microwave Anisotropy Probe (WMAP)
Chandra X-ray Observatory (CXO), Multi-Mirror Telescope
(XMM-Newton)
Gamma Rays

Swift gamma ray bursts detector
Telescopes for Observing the Sun

Monitoring Aspects of the Sun

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Solar and Heliospheric Observatory (SOHO)
http://sohowww.nascom.nasa.gov/
Rauven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI)
Hard X-ray Spectrometer (HXRS)
Monitoring Space Weather


Advanced Composition Explorer (ACE)
Geostationary Operational Environmental Satellite
(GOES) Solar X-ray Imager (SXI)
Who’s Involved in Space
Exploration?

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National Aeronautics and Space Administration
(NASA)
http://www.nasajobs.nasa.gov/work/where.htm
European Space Agency (ESA)
German Space Agency (DSL)
Russian Space Agency (ROSCOSMOS)
Japanese Space Agency
Chinese Space Agency
And so on…
WHAT DID YOU THINK?
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What is light?
One form of electromagnetic radiation with both wave
and particle properties.
Which type of electromagnetic radiation is most
dangerous to life?
Gamma rays.
What is the main purpose of a telescope?
To collect as much light as possible.
Why do stars twinkle?
Rapid changes in the density of the Earth’s atmosphere
cause passing light starlight to change direction.
What type(s) of electromagnetic radiation can telescopes
currently detect?
Some can detect the entire electromagnetic spectrum.
Key Terms
active optics
adaptive optics
angular resolution
(resolution)
blocked light
blueshift
Cassegrain focus
charge-coupled device
(CCD)
coude focus
Doppler shift
electromagnetic radiation
electromagnetic spectrum
eyepiece lens
focal length
focal plane
focal point
gamma ray
infrared radiation
interferometry
light-gathering power
magnification
Newtonian reflector
objective lens
photon
pixel
primary mirror
prime focus
radio telescope
radio wave
redshift
reflecting telescope
reflection
refracting telescope
refraction
Schmidt corrector plate
secondary mirror
seeing disk
spectrum
spherical aberration
twinkling
ultraviolet (UV) radiation
very-long-baseline
interferometry (VLBI)
wavelength
X ray