Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine [e-mail]

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Astronomy 101The Solar SystemTuesday,
Thursday230-345 pmHasbrouck 20Tom
Burbinetomburbine_at_astro.umass.edu
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Course

• Course Website
• http//blogs.umass.edu/astron101-tburbine/
• Textbook
• Pathways to Astronomy (2nd Edition) by Stephen
  Schneider and Thomas Arny.
• You also will need a calculator.

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Office Hours

• Mine
• Tuesday, Thursday - 115-215pm
• Lederle Graduate Research Tower C 632
• Neil
• Tuesday, Thursday - 11 am-noon
• Lederle Graduate Research Tower B 619-O

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Homework

• We will use Spark
• https//spark.oit.umass.edu/webct/logonDisplay.dow
  ebct
• Homework will be due approximately twice a week

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Astronomy Information

• Astronomy Help Desk
• Mon-Thurs 7-9pm
• Hasbrouck 205
• The Observatory should be open on clear
  Thursdays
• Students should check the observatory website at
  http//www.astro.umass.edu/orchardhill for
  updated information
• There's a map to the observatory on the website.

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Final

• Monday - 12/14
• 400 pm
• Hasbrouck 20

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No class this Tuesday

• Space Station Bound A Day in the Life of a
  Scientist Astronaut with Cady Coleman '91PhD
• Tuesday, October 13, 2009 400 pm
• Engineering Lab II Room 119
• Free Admission

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HW 5 (replace)

• Due Today

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HW 7

• Due next Thursday

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HW 8

• Due next Thursday

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October 9 (Tomorrow) 730 AM

• LCROSS (Lunar Crater Observation and Sensing
  Satellite)
• LCROSS spent Upper-Stage Centaur Rocket will
  crash into the Moons South Pole
• LCROSS will then follow into the Moon
• Looking for water
• http//www.youtube.com/watch?vNQ8d2Oacv2M

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New Rings around Saturn

• Seen in the infrared by the Spitzer Telescope
• Made of dust and ice Dust is 80 Kelvin
• Lies some 13 million km from the planet
• Tilted 27 degrees from main ring plane
• 50 times more distant than the other rings and in
  a different plane.
• Probably made up of debris kicked off Saturn's
  moon Phoebe by small impacts.

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Why infrared for dust?

• Cold things give off more light in infrared than
  visible

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Blackbody

• A black body is an object that absorbs all
  electromagnetic radiation that falls onto it.
• Perfect emitter of radiation
• Radiates energy at every wavelength

http//www.daviddarling.info/images/blackbody.jpg
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• Stefan-Boltzman Law - energy radiated per unit
  surface area of a black body in unit time is
  directly proportional to the fourth power of the
  black bodys temperature
• Wiens Law - blackbody curve at any temperature
  has essentially the same shape as the curve at
  any other temperature, except that each
  wavelength is displaced, or moved over, on the
  graph

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• Stars and planets act can be modeled as
  blackbodies

http//www.astro.ncu.edu.tw/contents/faculty/wp_ch
en/Ast101/blackbody_curves.jpg
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Blackbody curves

• http//www.mhhe.com/physsci/astronomy/applets/Blac
  kbody/frame.html

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http//www.rap.ucar.edu/general/asap-2005/Thur-AM2
/Williams_DoD_Satellites_files/slide0005_image020.
gif
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Power

• Power is in Joules/second Watts

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Stefan-Boltzman Law

• Emitted power per square meter of surface sT4
• Temperature in Kelvin
• s 5.7 x 10-8 Watt/(m2K4)
• For example, if the temperature of an object is
  10,000 K
• Emitted power per square meter 5.7 x 10-8 x
  (10,000)4
• Emitted power per square meter 5.7 x 10-8 x (1
  x 1016)
• Emitted power per square meter 5.7 x 108 W/m2

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Wiens Law

• Wavelength of Maximum intensity of the blackbody
  curve peak 2,900,000 nm
• T
  (Kelvin)
• ?max 2,900,000/10,000 nm
• ?max 290 nm
• 1 nanometer 1 x 10-9 meters
• ?max 290 nm 2.0 x 10-7 meters

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When you observe an astronomical body

• You measure intensity
• Intensity amount of radiation

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When you see an object in the sky

• You measure its brightness
• Its brightness is a function of its
• Distance from Earth (can be calculated from
  orbit)
• If star
• -Luminosity - is the amount of energy a body
  radiates per unit time
• If planet
• Albedo
• Size

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Inverse Square Law

• The apparent brightness varies inversely by the
  square of the distance (1/d2)
• If the Earth was moved to 10 Astronomical Units
  away, the Sun would be 1/100 times dimmer
• If the Earth was moved to 100 Astronomical Units
  away, the Sun would be 1/10000 times dimmer

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• If the Earth was moved to 1 x 108 Astronomical
  Units away, the Sun would be
• A) 1 x 10-12 times dimmer
• B) 1 x 10-14 times dimmer
• C) 1 x 10-16 times dimmer
• D) 1 x 10-18 times dimmer
• E) 1 x 10-20 times dimmer

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• If the Earth was moved to 1 x 108 Astronomical
  Units away, the Sun would be
• A) 1 x 10-12 times dimmer
• B) 1 x 10-14 times dimmer
• C) 1 x 10-16 times dimmer
• D) 1 x 10-18 times dimmer
• E) 1 x 10-20 times dimmer

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Luminosity-Distance Formula

• Apparent brightness Luminosity
• 4? x
  (distance)2
• Usually use units of Solar Luminosity
• LSun 3.8 x 1026 Watts

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Magnitude System
brightest asteroid
4 Vesta

• Brighter lower number

http//www.astronomynotes.com/starprop/appmag.gif
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Magnitude difference Relative intensity
0 1
1 2.51
2 6.31
3 15.8
4 39.8
5 100
10 104
15 106
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Initially

• Everybody observed with their eyes

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Figure 7.1
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Parallel light
Lens
Figure 7.2a
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Figure 7.2b
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Why are Telescopes better than your eyes?

• They can observe light in different wavelength
  regions (eyes can only see visible light)
• They can collect more light than eyes
• They can be built to compensate for the
  distorting effects of the atmosphere

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Refracting telescope
Figure 7.6
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Reflecting Telescope
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Reflecting Telescopes
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Resulting image inverted
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All large modern telescopes are reflectors

• Since light passes through the lens of a
  refracting telescope,
• You need to make the lens from clear,
  high-quality glass with precisely shaped surfaces

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It is

• Its easier to make a high-quality mirror than a
  lens

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Also,

• Large lenses are extremely heavy

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Also

• Lens focuses red and blue light slightly
  differently
• Called chromatic aberration

http//en.wikipedia.org/wiki/FileLens6a.svg
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Also

• Light can be absorbed by the glass as it passes
  through the glass
• Minor problem for visible, but severe for
  ultraviolet and infrared light

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Size of a telescope

• Diameter of its primary mirror or lens
• Light collecting area is proportional to the
  diameter squared since
• Collecting area ? r2
• E.g., 8-meter telescope

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a
b

• Telescope that took image b is twice as big as
  telescope that took image a
• Larger the telescope, more detail can be seen

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• Telescope on Mauna Kea (14,000 feet high)
• Telescope is Japanese Subaru 8-m telescope

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Atmosphere

• Atmosphere can absorb light
• Atmosphere can scatter light
• Atmosphere can distort light (twinkling)

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Twinkling

• Twinkling of stars is caused by moving air
  currents in the atmosphere.
• The beam of light from a star passes through many
  regions of moving air while on its way to an
  observers eye or telescope.
• Each atmospheric region distorts the light
  slightly for a fraction of a second.

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Advantages of space-based telescopes

• It can be open 24 hours, 7 days of week
• Do not have to worry about distorting effects of
  atmosphere
• There is no extra background of light due to
  scattering of light in the Earths atmosphere
• Observe in more wavelength regions

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Figure 7.20
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http//www.scienzagiovane.unibo.it/English/radio-w
indow/images/radiazioni-em.jpg
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• Infrared light absorbed by molecules

http//www.ucar.edu/learn/1_3_1.htm
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Not all light from a star reaches Earth
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Light in space can be affected by dust
http//www.ipac.caltech.edu/2mass/outreach/survey.
html
http//en.wikipedia.org/wiki/FileRayleigh_sunligh
t_scattering.png
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It does not help

• That you are closer to the stars

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To measure light

• In the past, they used photographic plates
• Now they use CCDs (charge-coupled devices)
• CCD are electronic detectors
• CCDs are chips of silicons

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Figure 7.5
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CCDs

• CCDs convert light into electrons

Shared the 2009 Physics Nobel Prize for their
discovery
William Boyle George
Smith
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How do they work?

• The CCD is made up of pixels.
• As the light falls on each pixel, the photons
  become electrons due to the photoelectric effect.
  The photoelectric effect happens when photons of
  light hit the silicon of the pixel and knock
  electrons out of place.
• These electrons are then stored.
• Essentially, the charge in each row is moved from
  one site to the next, a step at a
  time. This has been
• likened to a bucket row or human chain,
  passing buckets of water down a
  line.
• As these buckets of electrons reach the end of
  the line they are dumped out and measured, and
  this analog measurement is then turned into a
  digital value.
• Thus, a digital grid is made which describes the
  image.

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Color separation for digital cameras

• Colored filters

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CCDs

• CCDs can collect 90 of photons that strike them
• Photographic plates can only collect 10 of the
  photons
• CCDs are split into squares called pixels
• Data is in electronic form

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Hubble Telescope

• Can observe in visible, infrared, and ultraviolet
  wavelength regions
• Named after Edwin Hubble, the father of modern
  cosmology

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Hubble (launched in 1990)
Telescope is the size of a school bus 2.4 m
mirror
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Initially

• Hubbles primary mirror was polished to the wrong
  shape
• Was too flat at the edges
• Was barely 2.3 micrometers out from the required
  shape (1/50 the width of a human hair)
• Images were not focused as well as they could be
• Later shuttle mission fixed this problem by
  installing a number of small mirrors

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http//dayton.hq.nasa.gov/IMAGES/SMALL/GPN-2002-00
0064.jpg
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Jupiter
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• http//video.nationalgeographic.com/video/player/s
  cience/space-sci/exploration/hubble-sci.html

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Hubble replacement

• The first major components of the new James Webb
  Space Telescope are now being assembled.
• While Hubble is the size of a bus, the new James
  Webb will be the size of a jetliner.
• Will launch in 2014
• James Webb is a former NASA administrator during
  the Apollo program

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• http//www.youtube.com/watch?vSpkrVw_E6Nw

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Any Questions?