1. The study of the moon, stars and other objects in space.
Astronomy
The study of the moon, stars and other objects in space.

2. Why Do We Have Seasons?
Because the Earth’s axis is tilted as it revolves around the sun

3. Earth’s axis is always tilted 23.5 o from the vertical
As Earth revolves around the sun, the north (top) end of its axis is tilted away from the sun part of the year, and toward the sun for part of the year
Our seasons ARE NOT caused by changes in Earth’s distance from the sun!

5. Solstices
The sun reaches its greatest distance north or south of the equator 2 times each year. These days are called solstices
Summer Solstice in Northern Hemisphere = day when sun is farthest north of the equator
Around June 21; longest day of year in that hemisphere
Winter Solstice in Northern Hemisphere = day when sun is farthest south of the equator
Around December 21; shortest day of year in that hemisphere
Exactly opposite for Southern Hemisphere

6. Equinoxes
Neither hemisphere is tilted toward or away from the sun 2 times per year
Halfway between the solstices
Equinoxes (equal nights)
Day and night are about 12 hrs long all across Earth
Vernal Equinox (Spring Equinox) around March 21
Autumnal Equinox around September 22

7. Gravity
Isaac Newton realized that there is a force between the Earth and the moon that holds the moon in orbit. It’s called gravity.
Newton’s Law of Universal Gravitation: every object in the universe attracts every other object

8. Strength of the Force of Gravity
The strength of the force of gravity between two objects depends on 2 things:
The masses of the objects (amount of matter), and
The distance between them
Force of gravity as mass
Force of gravity as distance
The force of gravity on an object is called weight.
Mass never changes but weight does, depending on where you are.

9. Why doesn’t the moon crash into Earth?
Because of inertia
The tendency of an object to resist a change in motion
Newton’s 1st Law of Motion says: an object at rest will stay at rest and an object in motion will stay in motion with a constant speed and direction unless it is acted on by a force (a push or a pull)
Think of a soccer ball in a car that has to stop short

10. So,
Gravity and inertia work together to keep Earth orbiting around the sun and the moon orbiting around the Earth.

11. Motions of the Moon
The same side of the moon always faces the Earth because 1 day on the moon = 1 year on the moon
The changing positions of the moon, Earth, and the sun cause the phases of the moon, eclipses and tides

12. Phases of the moon The moon does not produce light
It reflects light from the sun
The shapes of the moon we see are called phases
The moon goes through a full set of phases each time it makes a complete revolution around Earth.

14. The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth
The sun lights the moon so ½ moon is almost always in sunlight
The moon revolves around Earth so you see the moon from different angles
The half of the moon that faces Earth isn’t always the half that is sunlit

15. During the New Moon, the side of the moon facing Earth is not lit because the sun is behind the moon
As the moon revolves around Earth, you see more of the lighted side every day until you see it is fully lit (Full Moon)
As the moon continues to revolve, you see less and less of the lighted side. After 29.5 days, the cycle is done and a new moon occurs again
Waxing means growing
Waning means shrinking
Crescent shape is

16. Eclipses
Eclipses happens when either the moon’s shadow hits Earth or when the Earth’s shadow hits the moon.
When an object in space comes between the sun and another object, the first object causes a shadow on the second object, causing an eclipse.

17. 2 Types
Solar Eclipse – when the moon passes between the sun and Earth, blocking the sunlight from Earth
Lunar Eclipse – when the Earth passes between the moon and the sun, blocking the sunlight from the moon

20. Total Eclipse versus Partial Eclipse
Darkest part of shadow is cone-shaped shadow, & called the Umbra. Only people in the Umbra experience a total eclipse.
A larger part of the shadow is less dark, and is called the Penumbra. In the penumbra, part of the sun is still visible.
You are much more likely to see a total lunar eclipse than a total solar eclipse because a total lunar eclipse can be seen from anywhere on Earth

21. Tides
Tides = the rise and fall of ocean water that occurs every 12 ½ hrs or so. The water rises for about 6 hours, then falls for about 6 hrs.

22. What Causes Tides?
Caused by differences in how much the moon’s gravity pulls on different parts of the Earth
At any time, there are 2 places on Earth with high tides and 2 places on Earth with low tides.

24. High Tides and Low Tides

25. Spring Tides and Neap Tides
Spring Tide – the tide with the greatest difference between high tides and low tides
Produced by the combined gravitational forces of the sun and the moon on Earth
Occur 2x/month: at new moon and full moon
Neap Tide – the tide with the least difference between high tides and low tides
Produced by the sun’s gravitational pull at right angles to the moon’s gravitational pull
Occur 2x/month: at first quarter moon and at third quarter moon phases

27. About Earth’s Moon Surface Features Maria Craters Highlands
Dark flat areas of hardened rock from huge ancient lava flows
Craters
Large round pits from being hit by meteoroids
Highlands
Light colored features; mountains; cover much of moon’s surface

28. Moon’s Characteristics
Size/Density
Small compared to Earth; Diameter about ¼ Earth’s diameter
Moon’s density is like the density of Earth’s outer layers
Temperature
Much bigger differences in highs and lows than on Earth because no atmosphere on moon
Higher highs and lower lows than Earth

29. More Moon’s Characteristics
Atmosphere
None; weak gravity lets gases escape into space
Water
No liquid water
Signs that there may be large patches of ice near the moon’s poles

30. Origin Collision Ring Theory – current theory
About 4 ½ billion years ago when Earth was young, lots of rocky debris floating in space-some as big as planets
A planet-sized object hit Earth
Material from Earth and from the object got shot into Earth’s orbit and formed a ring
Earth’s gravity pulled the pieces in the ring together to form the moon
Video: Teachers' Domain: The Origin of the Moon