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 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 Pencil Eye

How Do We See? Light Pencil Eye

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< 20 nanom High energy, short Ultraviolet20 nm microm Visible blue green yellow orange red Wavelength = micrometers Infrared1 microm - 1 mm Microwave1 mm - 1 cm Radio> 1 cm 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 mi away –If Sun = 3 ft diameter ball, Earth = raisin 100 m away, nearest star = distance to Sun

Atom nucleus electron e-e- proton neutron p+p+ n

Hydrogen e-e- p+p+ atomic number = 1 atomic mass number = 1

Hydrogen e-e- p+p+ n Deuterium isotope atomic number = 1 atomic mass number = 2

Helium e-e- p+p+ n e-e- n p+p+ atomic 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

p+p+ n e-e- n p+p+ atomic number = 2 atomic mass number = 4 What if an electron is missing? ion He +1

Temperature Measures motion of atoms (& molecules, ions, nuclei, electrons) Hotter = moving Faster kT = 1/2 m v 2 k=number T=temperature m=mass 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 & 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)