Wednesday January 27th 1999
Announcements:

Lecture notes:
Class 8

What to expect on exam

• 50 questions multiple choice
• Emphasis on material from class
• 5-8 questions on material in book not covered in class
• main topics not details
• not tricky

A few questions on constellations
simple math questions - Kepler's laws Newton's law of universal gravitation
can take test papers away and test answers outside
can see how you did
curved so don't worry too much about exact numerical score
no makeups

Review of Constellations

• ursa major
• ursa minor
• bootes
• lyra
• hercules
• cygnus
• polaris
• arcturus
• vega

plane of ecliptic
circumpolar rotation about polaris

Scientific notation
large numbers and small numbers
math with scientific notation
Basic practical astronomy things
why day and night?
why seasons? - not distance of earth from sun
why phases of moon? - not earth blocking sun's light
why different stars in winter and summer?
precession of the earth's rotation axis
phases of Venus
why we never see mercury and venus at midnight
eclipses - lunar eclipse full and partial
                - solar eclipse - full and partial

parallax - parallax angle is smaller for a more distant object
astronomers use it as a tool to measure distances to nearby objects
use orbit of earth to get big baseline

orbits of the planets

• Copernicus - heliocentric model ( but wrongly thought circular
• orbits)
• Kepler - elliptical orbits - sun at focus
•     equal areas in equal times - faster when closer
• p² yrs = a³ au
• Newton - law of universal gravitation F= (Gm₁m₂)/(D²)

Electromagnetic radiation

•  made when charges move around
•  moves at c = 30 billion cm/s
•     - universal constant
•     - speed limit for universe
• strictly speaking light not a wave or particle but does have
• wave-like and particle-like aspects
• when speaking of light as a wave should know wavelength
• frequency and amplitude
• high temp high energy short wavelength high frequency bluer color
• low temp low energy long wavelength redder color

broad electromagnetic spectrum

• radio waves
• microwaves
• infrared
• optical
• ultraviolet
• x-ray
• gamma ray

Atom
protons - positively charged in nucleus determine type
neutrons - neutral in nucleus
elections - negatively charged outside nucleus

held together by electric attraction of opposite charges
ground state and excited state
how this relates to absorption line and emission line spectra.