Optical TelescopesLACC: § 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.

1Thursday, February 18, 2010

Optical Telescopes

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

Refracting* Primary Lens *

Reflecting* Primary Mirror *

Catadioptric* Both *

2Thursday, February 18, 2010

Reflecting Telescopes

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

3Thursday, February 18, 2010

Why Make Telescopes Big?

http://www.jwst.nasa.gov/comparison.html

Areacircle = π•radius2

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.

James Webb Space Telescope (JWST)

4Thursday, February 18, 2010

Why Make Telescopes Big?

http://www.physast.uga.edu/~rls/astro1020/ch7/ovhd.html

"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

5Thursday, February 18, 2010

Adaptive Optics

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

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 turns pinpoint sources of light (such as stars) into slightly fuzzy blobs.

Adaptive Optics (AO) System: The deformable mirror changes shape to remove the distortions in the lightwave

before the light goes to the camera.

6Thursday, February 18, 2010

Optical TelescopesLACC: § 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)

Telescope technology is primarily about detecting objects that are normally too dim or outside the

range of human vision.

7Thursday, February 18, 2010

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.

8Thursday, February 18, 2010

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

Telescope technology is primarily about detecting objects that are normally too dim or outside the

range of human vision.

9Thursday, February 18, 2010

The EM Spectrum

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

• 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.

10Thursday, February 18, 2010

EM Rad. & Earth’s Atmosphere

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

11Thursday, February 18, 2010

Radio Telescopes

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

All radio telescopes are ground based.

Why?

12Thursday, February 18, 2010

Radio image

http://antwrp.gsfc.nasa.gov/apod/ap020218.html

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.

13Thursday, February 18, 2010

Interferometry

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

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.

14Thursday, February 18, 2010

Infrared Telescopes

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

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

necessary.

NASA's Stratospheric Observatory for Infrared Astronomy

15Thursday, February 18, 2010

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

http://photojournal.jpl.nasa.gov/catalog/PIA12832http://antwrp.gsfc.nasa.gov/apod/ap061228.html

The Wide-field Infrared Survey Explorer (WISE) is the latest

Infrared Telescopes

visible light infra red

moon shown for scale

16Thursday, February 18, 2010

Visible vs. Infrared

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

Warm dust becomes visible when viewed in the ir. (So ir telescopes must be cooled.)

Remember: interstellar dust blocks visible light, but not ir.

17Thursday, February 18, 2010

X-Ray Telescopes

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

Earth’s atmosphere blocks the x-ray radiation that

comes from space. For this reason, all x-ray telescopes

are placed in orbit.

18Thursday, February 18, 2010

X-Ray Image

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

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.

19Thursday, February 18, 2010

Gamma Ray Telescopes

http://imagine.gsfc.nasa.gov/docs/science/how_l2/gamma_detectors.html

Solid state gamma ray detectors in space or

optical reflecting telescopes to detect

evidence of air showers.

20Thursday, February 18, 2010

Gamma Ray Image

http://www.mpi-hd.mpg.de/hfm/HESS/pages/press/old/PressRelease/LS5039Press-2005/LS5039_Press_E.htm

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'.

21Thursday, February 18, 2010

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

Telescope technology is primarily about detecting objects that are normally too dim or outside the

range of human vision.

22Thursday, February 18, 2010

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.

23Thursday, February 18, 2010

Review for the Test 1 of 5:Observational Astronomy

[10 pts] The History of Astronomy• shape (Aristotle) and size (Eratosthenes) and of the

Earth• Geocentric (Ptolemy) vs. Heliocentric

(Copernicus), Galileo• Kepler (3 Laws or Planetary Motion), Newton (3

Laws of Gravity, Universal Gravity)

[10 pts] Making use of the Heavens• Know the Celestial Sphere: RA, Dec, meridian,

zenith, N/S Poles, Celestial Equator• Understand how the 23.5° axial tilt of the Earth

affects the motion/position of celestial objects: Arctic/Antarctic Circle, Tropic of Cancer/Capricorn

• Know how the heavens can be used to mark time: moon phases, eclipses, solar/sidereal day

[10 pts] Electromagnetic Radiation • Understand how energy, frequency, and wavelength

relate to each other: v = f λ, E=hf• Know the order of the electromagnetic spectrum:

radio, microwave, ir, visible, uv, x-ray, gamma ray• Know how photon interact with atoms: energy

levels, types of spectra--continuous, absorption, emission line

[10 pts] Telescopes• Understand how the different kinds of optical

telescopes work: refracting vs reflecting--prime, Cassegrain, Newtonian, Coudé; and non-optical telescopes: radio, infrared, X-ray, gamma ray

• Understand how the Earth’s atmosphere affects observations (atmospheric windows--visible, radio) and telescope design (which ones can’t be ground based--gamma ray, X-ray, ultraviolet)

• Understand how telescopes are built to improve their light gathering ability and angular resolution (large primary mirrors, adaptive optics, interferometry)

[10 pts] Figures/Illustrations• Understand orbital mechanics and moon phases• Use a graphic showing the energy levels around an

atom to determine what photon energies could be absorbed/emitted; ID elements in a spectrum

• ID the type of telescope (refracting; reflecting--prime, Cassegrain, Newtonian, Coudé, radio, infrared, X-ray, gamma ray) or spectra (continuous/thermal, emission line, absorption line) from a picture

24Thursday, February 18, 2010