A1 04 Telescopes

Optical Telescopes
LACC: § 5.1, 4, 5

• Optical Telescopes: Refracting vs. Reﬂecting
• Reﬂecting Telescopes: prime vs. Cassegrain
vs. Newtonian vs. Coudé
• Q: Why make telescopes so big?
Telescope technology is primarily about detecting
objects that are normally too dim or outside the
range of human vision.

Thursday, February 18, 2010 1

Optical Telescopes
Refracting
* Primary Lens *

Reﬂecting
* Primary Mirror *

Catadioptric
* Both *

http://www.meade.com/support/telewrk.html


Reﬂecting Telescopes

http://138.238.143.191/astronomy/Chaisson/AT405/HTML/AT40501.htm


Why Make Telescopes Big?
James Webb Space Telescope Areacircle = π•radius2
(JWST)
So, a telescope with
twice the diameter
(or radius) will have
four times the light
collecting area.
10x the diameter
would mean 100x the
light collecting area.
http://www.jwst.nasa.gov/comparison.html


Why Make Telescopes Big?
"Angular resolution" =
smallest angular separation
where you can still see that 2
objects are actually 2 objects
rather than 1 blobby object
• The human eye's angular
resolution = 1 arcminute
• The Hubble Space Telescope's
ang. resolution = 0.05
arcseconds
http://www.physast.uga.edu/~rls/astro1020/ch7/ovhd.html


Adaptive Optics
Temperature ﬂuctuations in
Earth's atmosphere act like small,
randomly sized and oriented
weak lenses that cause stellar
images to degrade and dance
(twinkle), limiting the resolution
and sensitivity of ground-based
telescopes. "Seeing," as these
effects are called, varies with the
site and conditions but never
vanishes. The only way to avoid it
is to launch a telescope into
space. Mauna Kea and, to a lesser
extent, Haleakala have better
seeing than most observatory
locations, yet even at these
exceptional sites, the atmosphere
Adaptive Optics (AO) System: The deformable mirror turns pinpoint sources of light
changes shape to remove the distortions in the lightwave (such as stars) into slightly fuzzy
before the light goes to the camera. blobs.

http://www2.ifa.hawaii.edu/newsletters/article.cfm?a=300&n=1


Optical Telescopes
LACC: § 5.1, 4, 5
• Optical Telescopes: Refracting vs. Reﬂecting
• Reﬂecting Telescopes: prime vs. Cassegrain
vs. Newtonian vs. Coudé
• Q: Why make telescopes so big?
A: Light Gathering Power
Angular Resolution (alternatives--
Interferometry, Adaptive Optics)


LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch. 5, pp. 131-132: 3. Give two reasons.

Due at the beginning of the next class period.
Test covering chapters 1-5 next class period.


Observing the Entire EM
Spectrum LACC: § 5.1, 4, 5
• Telescopes: Designs
• Our Atmosphere: Optical (Infrared) and Radio
Atmospheric Windows
• Space: Interstellar Dust is Transparent to
Infrared and Radio


The EM Spectrum

•

Credit: Philip Ronan who has
given permission to copy,
distribute and/or modify this
document under the terms of
the GNU Free Documentation
License, Version 1.2 or any
later version.

•

Download site: Wikipedia:
Image:EM spectrum.svg.

http://www.nhn.ou.edu/~jeffery/course/c_energy/energyl/lec001.html


EM Rad. & Earth’s Atmosphere

http://www.answers.com/topic/telescope?cat=technology


Radio Telescopes
All radio
telescopes are
ground based.
Why?

http://www.skyscan.ca/RadioTelescopes.htm


Radio image

Shells of ancient supernovas, cocoons surrounding newborn stars, and specks from distant
quasars highlight this tremendous vista.... The representative color image covers about 10 degrees
across on the sky ... in radio light. Diffuse bands of ionized gas ﬂow though a dominating region of
star formation, located about 6000 light-years away. Two prominent supernova shells visible
include the brown globule on the lower left and the white bumpy sphere on the upper right.
Prominent stellar cocoons are visible throughout the image as bright white knots. Far in the
distance, visible here as only red dots, quasars glow.
http://antwrp.gsfc.nasa.gov/apod/ap020218.html


Interferometry

Powerful arrays of telescopes, like the Very
Large Array (VLA) in New Mexico, can be
coordinated in such a way as to "see" radio
sources and having the effect of a single
dish nearly 20 miles across.

http://www.geocities.com/plasminojen/astro/radio_astronomy.html


Infrared Telescopes
NASA's Stratospheric Observatory for Infrared Astronomy

Earth’s atmosphere
blocks much of the
infrared radiation
that comes from
space. Placing
telescopes in orbit
overcomes this
problem; but for
infrared astronomy,
it’s not absolutely
http://www.skyscan.ca/RadioTelescopes.htm
necessary.


Infrared Telescopes
The Wide-ﬁeld Infrared Survey Explorer (WISE) is the latest
moon shown
for scale

visible light infra red
http://photojournal.jpl.nasa.gov/catalog/PIA12832
http://
antwrp.gsfc.nasa.gov/
apod/ap061228.html

http://www.sciencenewsforkids.org/
articles/20100106/Note3.asp


Visible vs. Infrared
Warm dust becomes visible when viewed in the ir.
(So ir telescopes must be cooled.)
Remember: interstellar dust blocks visible light, but not ir.

http://www.spitzer.caltech.edu/Media/happenings/20051208/


X-Ray Telescopes
Earth’s atmosphere
blocks the x-ray
radiation that
comes from space.
For this reason, all
x-ray telescopes
are placed in orbit.

http://www.geocities.com/wt2002friendz/schoolwork/telescope_gina_mei.html


X-Ray Image

Spanning over 25,000 light-years, comparable to the distance from the Sun to the center of our
own Milky Way galaxy, a cosmic jet seen in X-rays blasts from the center of Centaurus A. Only 10
million light-years away, Centaurus A is a giant elliptical galaxy - the closest active galaxy to Earth.
This composite image illustrates the jumble of gas, dust, and stars visible in an optical picture of
Cen A superposed on a new image recorded by the orbiting Chandra X-ray Observatory. The X-
ray data is shown in red. Present theories hold that the X-ray bright jet is caused by electrons
driven to extremely high energies over enormous distances. The jet's power source is likely to be
a black hole with about 10 million times the mass of the Sun coincident with the X-ray bright
spot at the galaxy's center.

http://apod.nasa.gov/apod/ap991028.html


Gamma Ray Telescopes

Solid state gamma ray
detectors in space or
optical reﬂecting
telescopes to detect
evidence of air showers.
http://imagine.gsfc.nasa.gov/docs/science/how_l2/gamma_detectors.html


Gamma Ray Image
Top: High Energy Stereoscopic
System (H.E.S.S.) telescopes in
Namibia, in South-West Africa. This
system of four 13 m diameter
telescopes is currently the most
sensitive detector of very high
energy gamma-rays.
Center: A larger picture of the
gamma ray sky as measured with
H.E.S.S.
Bottom Left: The green star
shows the position of LS5039 as
measured using radio telescopes, and
the white ellipse shows the gamma
ray position. In the upper-left
corner ... HESS J1825-137.
Bottom Right: A computer
simulation of the microquasar
LS5039, showing one possible
scenario where gamma rays are
generated in microquasar 'jets'.
http://www.mpi-hd.mpg.de/hfm/HESS/pages/press/old/PressRelease/
LS5039Press-2005/LS5039_Press_E.htm


Observing the Entire EM
Spectrum LACC: § 5.1, 4, 5
• Telescopes: Designs requirements for: radio,
infrared, visible/uv, x-ray, gamma ray
• Our Atmosphere: Optical (Infrared) and Radio
Atmospheric Windows
• Space: Interstellar Dust is Transparent to
Infrared and Radio


LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch. 5, pp. 131-132: 7. The different regions of the spectrum
are: radio, microwave, infrared, visible, ultraviolet, x-ray, gamma ray.

Due at the beginning of the next class period.
Test covering chapters 1-5 next class period.


Review for the Test 1 of 5:
Observational Astronomy
[10 pts] The History of Astronomy
• shape (Aristotle) and size (Eratosthenes) and of the [10 pts] Telescopes
Earth • Understand how the different kinds of optical
• Geocentric (Ptolemy) vs. Heliocentric telescopes work: refracting vs reflecting--prime,
(Copernicus), Galileo Cassegrain, Newtonian, Coudé; and non-optical
• Kepler (3 Laws or Planetary Motion), Newton (3 telescopes: radio, infrared, X-ray, gamma ray
Laws of Gravity, Universal Gravity) • Understand how the Earth’s atmosphere affects
observations (atmospheric windows--visible, radio)
[10 pts] Making use of the Heavens and telescope design (which ones can’t be ground
• Know the Celestial Sphere: RA, Dec, meridian, based--gamma ray, X-ray, ultraviolet)
zenith, N/S Poles, Celestial Equator • Understand how telescopes are built to improve
• Understand how the 23.5° axial tilt of the Earth their light gathering ability and angular resolution
affects the motion/position of celestial objects: (large primary mirrors, adaptive optics,
Arctic/Antarctic Circle, Tropic of Cancer/Capricorn interferometry)
• Know how the heavens can be used to mark time:
moon phases, eclipses, solar/sidereal day [10 pts] Figures/Illustrations
• Understand orbital mechanics and moon phases
[10 pts] Electromagnetic Radiation • Use a graphic showing the energy levels around an
• Understand how energy, frequency, and wavelength atom to determine what photon energies could be
relate to each other: v = f λ, E=hf absorbed/emitted; ID elements in a spectrum
• Know the order of the electromagnetic spectrum: • ID the type of telescope (refracting; reflecting--
radio, microwave, ir, visible, uv, x-ray, gamma ray prime, Cassegrain, Newtonian, Coudé, radio,
• Know how photon interact with atoms: energy infrared, X-ray, gamma ray) or spectra (continuous/
levels, types of spectra--continuous, absorption, thermal, emission line, absorption line) from a
emission line picture


A1 04 Telescopes

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to A1 04 Telescopes

Similar to A1 04 Telescopes (20)

More from Park University

More from Park University (20)

Recently uploaded

Recently uploaded (20)

A1 04 Telescopes