MOTIONS OF EARTH AND MOON
Earth = 8000 miles in diameter
Distance to Milky Way galaxy = 100,000 lightyears
Local group of galaxies = 10,000,000 lightyears
Light travel time from the sun to the earth is 8.3 min
LTT Sun to Neptune is about 4 hrs
Big Empty contains Oort Cloud which is light weeks to 1 LY across
When comets collide, they fall to the sun and get new, long, elliptical orbits
The Big Bang was about 14 billion yrs ago
As comets approach the sun, their ices begin to evaporate
Andomeda galaxy is 2 million LY away
The Virgo Cluster contains 2000 galaxies centered 50 MLY away
The Hubble Deep Field shows galaxies 12 Billion LY in space and time
1st generation of stars made of hydrogen and helium
2nd generation of stars made hydrogen and helium and 1/10,000 of ?
BRIEF HISTORY OF THE UNIVERSE
The “Obvious” View 1/30/13
Declination- degrees north or south of celestial equator
Right ascension- measured in hrs, min, and sec eastward from position……….
Earth’s Orbital Motion
-The 12 constellations the Sun moves through during the year are called zodiac; path is ecliptic.
-Ecliptic is plane of Earths path around the sun; at 23.5 degrees to celestial equator.
Northernmost point (above celestial equator) is summer solstice, southernmost is winter solstice; points where path crosses celestial equator are vernal and autumnal equinoxes.
Combination of day length and sunlight angle gives seasons.
Time from one vernal equinox to next is tropical year.
Precession- Rotation of Earth’s axis itself; makes one complete circle in about 26,000 years
The Motion of the Moon
The moon takes about 29.5 days to go through whole cycle of phases – synodic month.
Phases are due to different amounts of sunlit portion being visible from Earth.
Time to make full 360 degrees around earth, sidereal month, is about 2 days shorter than synodic month.
Eclipses don’t occur every month bc Earths and the moons orbits are not in the same plane.
Earth is between the moon and sun.
Partial when only part of the Moon is in shadow.
Total when all is in shadow.