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Moon Project • Tonight is CLEAR. Do project!!! • Locate the Moon with respect to the STARS on the star map (NOT the horizon) – You need to find star patterns you recognize in the sky and on the map to determine where the Moon is – Depending on the time of night you look the Moon will be in different parts of the sky, but on a single night always close to the same stars. Announcements • 30 students have still not registered and joined our class on Astronomy Place. • The assignment for Monday is a review with questions taken from past ISP205 exams. It will be posted on Angel by Thursday evening. It is good practice for the quiz and mid-term exam. • Assignments on Angel and Astronomy Place can be done over until you get a perfect score. These are easy points. Assignments, Activities & Quizzes = 25% of grade. More Announcements • Quiz and Review - Monday Feb 9 • 1st Mid-Term Exam - Wednesday Feb 11 Will cover chapters 1-6 (sections 6.1-3 only) Objectives: Light (from syllabus) • Describe the Structure of an atom • Describe how energy is stored in atoms • Describe the relation between temperature and motion • Describe the ways in which light acts as a wave and as particles • Describe the different types of light in the electromagnetic spectrum and the relation between type of light, wavelength, energy and temperature of the source of the light. What is a FACT & what is a THEORY? Write your name and student ID on your index card and write your own statement of what is a FACT and a THEORY, with one example of each. Then we will discuss your ideas. Why is Light important? We can’t touch, hear or smell the stars. ALL of our INFORMATION about the rest of the universe (except for some samples returned from the Moon) comes to us via LIGHT. Big Picture • Light carries information about the atoms that produced it. We need to understand the interaction between Light and Atoms. • There is more to light than meets the eye. The visible light that our eyes can see is only a small portion of the complete electromagnetic spectrum. • The properties of light, especially the amount of light of different energies - its spectrum - gives us information about distant objects. Different portions of the spectrum contain different pieces of the story of a distant object. How Do We See? Light Eye Pencil How Do We See? Light Eye Pencil How do we see? • An object must give off light and our eye must receive the light in order to see the object. • That light might be emitted by the object (e.g. a light bulb or the Sun) • Light from another source can be reflected off the object (e. g. a pen reflecting light from a bulb or the Moon reflecting sunlight) • If there is no light, can’t see the object. Light is an Electromagnetic WAVE • A wave is a moving pattern • Light is a changing pattern in the electric and magnetic force (e.g. shaking a rope) • Properties of waves: – Wavelength () = distance between waves – Period (P) = time between waves – Frequency (f) = number of waves per unit time (analogy busses on Grand River Ave.) • Waves transport energy Light as a Wave • For light: = cP – c = speed of light • P = 1/ f • The higher f is, the smaller is, and vice versa. • Our eyes recognize f (or ) as color! Light is a stream of PHOTONS • A particle is a thing • Light is also a stream of particles called PHOTONS • Properties of photons – Frequency (f) – Energy, e = hf = hc/ (h=number called Planck’s constant) Higher frequency = shorter wavelength = higher energy Spectrum of Light • Visible light is only a small part of the electromagnetic spectrum • Lowest enegy light is radio • Highest energy light is gamma rays Visible Light Spectrum of Light X-rays Ultraviolet Visible Infrared Microwave Radio < 20 nanom 20 nm - 0.4 microm blue green yellow orange red 1 microm - 1 mm 1 mm - 1 cm > 1 cm High energy, short Wavelength = 0.4 0.7 micrometers Low energy, long Matter is made of ATOMS • Atom is nucleus orbited by electrons – Nucleus - composed of protons (+ charge) & neutrons (0 charge) – Electrons (- charge) orbit nucleus attracted by electric force • Electric Force – Produced by charge – Opposite charges attract, like charges repel – Decreases with increasing distance • Element is determined by number of protons in nucleus Atoms • Crude Model: Atom = solar system – If person = proton or neutron electron = cotton candy orbiting 100 km (60 mi) away (Flint) – If nucleus = raisin, electron = 400 m away, next atom is 2.5 - 25 mi away – If Sun = 3 ft diameter ball, Earth = raisin 100 m away, nearest star = distance to Sun Atom electron nucleus p+n proton neutron e- Hydrogen e- p+ atomic number = 1 atomic mass number = 1 Hydrogen Deuterium e- isotope p+ n atomic number = 1 atomic mass number = 2 Helium e- p+p+ nn eatomic number = 2 atomic mass number = 4 Atoms • Neutral Atom - number of electrons = number of protons – Usual state at LOW temperatures • Ion - some or all of electrons have been knocked out of atom – Usual state at HIGH temperatures What if an electron is missing? ion e- p+p+ nn atomic number = 2 atomic mass number = 4 He +1 Temperature • Measures motion of atoms (& molecules, ions, nuclei, electrons) • Hotter = moving Faster kT = 1/2 m v2 k=number m=mass T=temperature v=speed Not a required equation Temperature Scales Emission & Absorption of Light Photons are emitted or Absorbed when an electron changes its Energy Assignment for Monday • Monday - QUIZ Chapters 1-6.3 & Review • Assignment for Monday - Sky Assignment 7, review questions on Angel (posted Thursday) • Problems with Astronomy Place or Angel - clear browser cache & cookies and try again (instructions linked to course web page and on Angel)