Textbook: Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. You also will need a calculator. Office Hours
Mine Tuesday, Thursday - 1:15-2:15pm Lederle Graduate Research Tower C 632 Neil Tuesday, Thursday - 11 am-noon Lederle Graduate Research Tower B 619-O
Homework We will use Spark https://spark.oit.umass.edu/webct/ logonDisplay.dowebct Homework will be due approximately twice a
week 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.
Final Monday 12/14 4:00 pm Hasbrouck 20
HW #5 There is a HW #5 replace which will replace your HW #5 score if you get a higher grade F = G M1 M2 r2
G = 6.67 x 10-11 m3/(kgs2) HW #6 Due today HW #7
Due next Thursday Atoms make up molecules H2O - water CO2 carbon dioxide CH4 - methane
Spectroscopy Spectroscopy is the study of the interaction between radiation and matter as a function of wavelength (). You can use spectroscopy to determine what is in
a body (planet, star, etc.) or atmosphere http://upload.wikimedia.org/wikipedia/commons/f/f5/Light_dispersion_conceptual_waves.gif How did scientists recently determine that there was water on the Moon?
Water on the Moon Grey - H2O and OH absorptions White line - NASA' Cassini spacecraft
Blue line - NASA's Moon Mineralogy Mapper instrument on the Indian Chandrayaan-1 spacecraft http://www.nasa.gov/images/content/388950main_ROGER_2-516.jpg Definitions Reflectance How much light an object reflects Absorption Light is absorbed and not reflected
Light cause water molecules to vibrate http://www.btinternet.com/~martin.chaplin/ vibrat.html How much water?
If you had a cubic meter of lunar soil, you could squeeze it and get out a liter of water Water has to be near the surface How do you use light to determine what is in an astronomical body
like a star? http://www.youtube.com/watch?v=9LrTeadnF6Q http://www.youtube.com/watch?v=VYbcMfLKeg What happens when
Energy levels where an electron can reside To go to a higher energy level, an electron needs to gain energy To go to a lower energy level, an electron needs to lose energy eV 1 eV = 1.6 x 10-19 Joules
Rules An electron can not jump to a higher energy level unless it gains energy from somewhere else Absorbs a photon Gains kinetic energy from an impacting particle
To go to a lower energy level, the electron must lose energy Emits a photon Electron jumps can occur only with the particular
amounts of energy representing differences between possible energy levels Heated hydrogen gas Emission line spectrum
White light through cool hydrogen gas Absorption line spectrum Types of spectra Emission radiation is emitted at characteristic wavelengths
Material is hot so electrons keep on bumping into each other and transferring kinetic energy to each other so they jump between particular energy levels Absorption radiation is absorbed at characteristic wavelengths
Radiation passes through the material http://www.astro.bas.bg/~petrov/herter00_files/lec07_04.jpg So why is this important Different elements have different number of
electrons Different elements have different energy levels for their electrons So Different elements can absorb light at specific
energies Different elements can emit light at specific energies So if you can measure the wavelength of the light from an astronomical body, you can determine whats in it
Emission line spectra How can you determine velocities of objects? Doppler Shift The wavelength of light changes
as the source moves towards or away from you Since you know the wavelength position of emission or absorption features If the positions of the features move in wavelength position, you know the source is moving
So Source moving towards you, wavelength decreases blueshift Source moving away from you, wavelength increases
1 nanometer = 1 x 10-9 meters Formulas for light vrad/c = shift rest rest
Rest wavelength of a line of hydrogen is at 656.285 nm You observe this line at 656.255 nm for a star
What is the velocity of this star? vrad/c = (656.255 -656.285)/656.285 nm vrad/c = -4.5712 x 10-5 vrad = -4.5712 x 10-5 *3 x 108 m/s = -13,700 m/s = -13.7 km/s It is blue-shifted so the motion is toward us
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 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
Stars and planets act can be modeled as blackbodies http://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpg
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