To Prepare for the quiz on Wednesday Sept 13th (20 mins of review, 30 mins multiple choice)

• Read the textbook,
• go through the sessions on the website,
• check that you understand the following concepts - not just definitions but how things work.

1. Speed of Light = Distance / Time -> Distance = Speed of Light x Time
2. Astronomical Scales

Light-year = Distance = Scale between stars
Sun-Earth Distance = Astronomical Unit = 8 Light-minutes = Scale of Solar system
3. Apparent vs. Actual Motion

e.g.: Apparent motion = stars East -> West, Actual motion = Earth’s spin
4. Celestial co-ordinates - controlled by Earth’s spin axis — always points in same direction (Polaris)
5. Latitude = Angle between Polaris and North Horizon
6. Longitude = time that Sun crosses the meridian in Greenwich Mean Time (1 hour = 15 degrees)
7. Solar vs. Sidereal Days Due to Earth's orbital motion around Sun - Solar Day is 4 mins longer than a Sidereal Day. Stars rise 4 mins earlier each day.
8. Seasons Caused by the 23.5 degree tilt of the Earth's spin axis - which tilts towards the Sun during summer.
9. Size of Earth - Eratosthenes was able to measure the size of the Earth using simple geometry and measuring an angle of the Sun in the sky and a distance between 2 place - to an accuracy of 1% - 2000 years ago.
10. Precession Wobble of Earth's spin axis over 26,000 years. Causes slow change in direction of celestial poles and seasonal appearance of constellations.
11. Lunar Phases - due to changing illumination as seen on Earth as the Moon orbits the Earth.
12. Apparent vs. Actual Motions of the Moon:

Apparent Motions:
Moves 13° East each day (at same of day)
Rises 53 minutes LATER each day.
Location is within ± 5° of the ecliptic.
Actual Motions:
Moon orbits Earth, Earth orbits the Sun.
Orbital period of Moon relative to the stars (sidereal month = 27.3 days) is a little shorter than relative to the Sun (lunar month = 29.5 days).
Orbital plane of the Moon is tilted 5° from the ecliptic plane
13. Eclipses -

Lunar - Earth's shadow on the Moon
Solar - Moon's shadow on the Earth
Requires the Sun - Earth - Moon to be in a line (hence does not happen frequently due to the 5° tilt of Moon's orbit out of the ecliptic plane)
The Moon's orbit is not exactly circular so that the Moon is sometimes closer/farther from the Earth so that the angular size of the Moon is bigger/smaller -> Moon over/under-covers the Sun.
14. Parallax

Parallax is how we measure the distance to astronomical objects.
The farther away an object the less it appears to move when you 'blink'.
The bigger the baseline, the bigger the parallax angle.
15. Cosmology based on science vs myth

Early cosmologies were based on myths. Greek astronomers built a cosmology based on rational argument and observations - they built (mental) models based on mathematics (geometry).
16. Lack of Parallax caused conviction that Earth could not be moving

Despite very careful observations, the bright (presumably near stars) could not be detected to move relative to the background stars. Since it seemed unlikely that the stars could really be so very far away, the logical conclusion was that the Earth had to be stationary.