Don

1
Dont Panic

• We are both learning how to use Astronomy Place.
• Remember to Join the Class
• There have been problems submitting answers
• In the future I will set up Angel to accept
  answers in the cases where you cant submit them
  to Astronomy Place
• If problems persist come to my office so we can
  work together
• For this time deadline is extended until Monday

2
Spaceship EarthWhat are the motions of spaceship
Eearth?

• Earth SPINS on its axis towards the EASTonce
  every 24 hours
• Earth ORBITS around the Sun once every 365.25
  days. Speed 1x105 km/hr.
• Earth, the Sun the Solar System all orbit
  around the center of the Milky Way galaxy once
  every 2.3x108 years. Speed 8x105 km/hr.
• The Milky Way is moving toward the Andromeda
  galaxy, speed 3x105 km/hr
• The Milky Way (along with the local group)
  partakes in the expansion of the universe.

3
Earth Spins (Rotates) on its axistoward the
East, once every 24 hours
4
Earth ORBITS around the Sunonce a year
What keeps the Earth in orbit and stops it from
flying off?
5
The Solar System ORBITS the center of the Milky
Way galaxy
Period 2.3x108 years What keeps it in orbit
so it doesnt fly off?
6
Our motion through the universeThe Milky Way is
moving through the universe 600 km/s
7
Expanding Universe Model - Balloon
8
The SeasonsWhat could produce our seasons - the
difference between summer and winter?

• Changing energy output by the Sun
• Changing amount of energy we receive from the Sun
• Distance from the Sun
• Orientation of the ground re. Suns light
  (Tilt of Earths axis of rotation)

9
Suns heating Distance
10
Suns heating Orientation
11
Suns heating Rays
12
The Cause of the Seasons
13
Why doesnt Distance Matter?

• Small variation for Earth about 3
• Distance does matter for some other planets,
  notably Mars and Pluto.
• Surprisingly, seasons are more extreme in
  N. hemisphere, even thought Earth is closer
  to Sun in S. hemisphere summer (and farther
  in S. hemisphere winter) because of
  land/ocean distribution

14
Moons Phases
15
Phases of the Moon
16
A Solar Eclipse
17
Eclipses

• The Earth Moon cast shadows.
• When either passes through the others shadow, we
  have an eclipse.
• Why dont we have an eclipse every full new
  Moon?

18
Planetary MotionUsually planets appear to move
toward the East re the stars. Occasionally, they
appear to move backward - toward the West, called
Retrograde Motion
19
Retrograde MotionView from Earth explained by
big circles epicycles
big circledeferent. Explains most of planets
motion
Epicycle, rolls on big circle. Explains
retrograde loop.
20
Retrograde Motion

• Like the Sun, planets usually appear to move
  eastward relative to the stars.
• But as we pass them by in our orbit, they move
  west relative to the stars for a few weeks or
  months.
• Noticeable over many nights on a single night, a
  planet rises in east and sets in west

21
Next Week

• I will be away Monday and Wednesday.Classes will
  occur in BPS 1410 as usual both days. Dr.
  Horace Smith will take over for me.

22
Assignment for Next Week

• Make sure you pick up homework dueWednesday Jan
  28(If you miss a Wednesday class, homeworkis
  linked to the course web pagehttp//www.pa.msu.ed
  u/courses/isp205/sec-3)
• Pre-class assignment for Monday Jan 26, is linked
  to the course web page and is to be done on Angel.