1. Earth’s Moon and Solar System

2. Phases of the Moon
The apparent shape of the moon depends upon the changing relative positions of Earth
As the moon completes one revolution around Earth each month, the growing and shrinking lighted area makes the moon appear to change in shape
The moon’s periods of rotation and revolution are equal
Because of this, the same side of the moon always faces Earth

3. Phases of the Moon
One complete orbit of the moon around Earth takes about 27 days
A complete cycle of the moon’s phases takes 29 ½ days
This 2 ½ day difference occurs because as the moon orbits Earth, Earth orbits the sun
When the moon gets back to its original position, it must move through an extra angle of about 30° to compensate for Earth’s orbital motion around the sun

5. Eclipse of the Moon
An eclipse of the moon occurs when the full moon moves into Earth’s shadow
During a lunar eclipse, the moon turns a coppery red
You can still see the moon because sunlight is bent by Earth’s atmosphere, which causes a weak illumination of the moon

6. Eclipse of the Sun
An eclipse of the sun occurs when the new moon briefly moves in front of the sun
At this time the moon casts its shadow on Earth

7. Angular Diameter
Angular diameter is the angle formed between the sides of an object and your eye
The angular diameter of any object depends upon the actual size of the object and how far away it is from the observer

8. Angular Diameter of the Sun
Observations of the sun’s angular diameter tell us that Earth is closest to the sun in January and farthest from the sun in July
Seasonal variations result from the tilt of the Earth’s axis and Earth’s shape not from Earth-sun distance
The sun’s angular diameter is larger in winter and smaller in summer

9. Angular Size and Shape of Orbit
Because the moon seems to change size more than the sun, we can infer that changes in the relative distance between the moon and Earth are greater than changes in the relative distance between the sun and Earth
Since both changes are small compared to the magnitude of the average distance, we can infer that the orbit of the moon around Earth and the orbit of Earth around the sun are nearly circular

10. Earth-Moon Orbit

11. The Tides
Every point along the ocean experiences two low tides and two high tides per day
The difference between high tide and low tide is usually less than a meter (3 feet)
The cause of tides is gravitational attraction off the moon and the sun
The sun and moon pull on the water in the oceans and on the solid part of Earth

12. The Tides
The water of the oceans is pulled toward the moon, which causes high tide
Another high tide occurs on the opposite side of Earth, where the solid part of Earth is pulled away from the oceans
The highest high tides and the lowest low tides occur about twice a month near the full and new moon phases

13. The Tides

14. The Geometry of Orbits Planets revolve in an ellipse around the sun
An ellipse has two fixed points called foci that are on either side of the center of the axis
The sun lies at one focus and is not the center of Earth’s orbit

15. The Geometry of Orbits
If the two foci are located near the ends of the axis, an ellipse is long and narrow
Many comets have this type of path
If the foci move closer together, the shape of the ellipse becomes circular

16. Calculating Eccentricity (elongation) of an ellipse
Eccentricity = distance between the foci length of the major axis e = d/L

17. The Force of Gravity
Gravity is a force of attraction between objects that is dependent on the masses of the objects and the distance between them

18. Gravity and the Planets
Gravity is the force that holds the planets and other objects in the solar system in their orbits
Any object that orbits another object in space is known as a satellite
Earth is a satellite of the sun
The moon is Earth’s satellite

19. Gravity and the Planets
The elliptical path of any satellite is a result of inertia and gravity
Inertia is the tendency of an object to remain at rest, or, if it is moving, to move with the same speed in the same direction

20. Gravity and the Planets
If a satellite has a circular orbit, inertia and the force of gravity are constant
There is no change in speed, but there is a constant change in direction, producing a circular path

21. Gravity and the Planets
If a satellite has an elliptical orbit, gravity causes the speed to change
The satellite will move faster when it’s near its primary and slower when it’s farther away

22. Gravity and the Planets
The closer a planet is to the sun, the faster it moves in its orbit
Mercury, the planet closest to the sun, travels about 1.6 times as fast as Earth and 10 times the speed of Pluto

24. Planets of our Solar System
The planets can be divided into two groups
Rocky (terrestrial) planets
Mercury
Venus
Earth (density = 5.5 g/cm3)
Gas giants
Jupiter
Saturn
Uranus
Neptune

25. Planets of our Solar System

26. Similarities Between Mercury and Earth’s Moon
Both the moon and Mercury are smaller than Earth
Both have a dark surface covered with craters from meteorites
Neither have a significant atmosphere
They are not protected from meteor impacts and their craters do not erode quickly
Soil samples would show no chemical weathering
They both have extreme temperatures
Both have very slow rotations making days and nights longer than on Earth

27. Planet Surface Temperatures
Are a result of the distance from the Sun
Hottest Planets are Mercury and Venus
Venus is a little hotter due to a very dense atmosphere of carbon dioxide producing a “greenhouse effect”
Earth and Mars are cooler because of the greater distance from the sun
Mars has a very thin atmosphere of mostly carbon dioxide with minimal “greenhouse effect”
The gas giant planets do not have “surface temperatures” as they are composed of gases that increase in density with depth and pressure

28. Earth is Unique
Earth is the only planet that has abundant liquid water
The presence of liquid water on Earth may be the reason why living organisms have not been detected elsewhere in the solar system
The Earth’s atmosphere is the only planet that has an atmosphere with abundant free oxygen that is released when plants extract carbon from carbon dioxide by photosynthesis

29. Asteroids
Located mostly between Mars and Jupiter in a belt of thousands of rocky objects
They range from the size of pebbles to 600 miles in diameter
A few have orbits that can cross Earth’s orbit

30. Meteors
Small solid particles from space can be caught by Earth’s gravity and dragged down through the atmosphere
As the objects fall, they are heated by friction with the Earth atmosphere and burn up, producing streaks of light (“shooting stars”) visible at night
Meteors that survive their fall and hit the ground are called meteorites

31. Comets
Icy objects which usually originate in a region outside of the planets
Some of them come close to the sun in very elliptical orbits
Heating by the sun causes them to partially vaporize producing a tail
Comets are visible for weeks and do not streak across the night sky

32. The Sun The nearest star to Earth
A star is a large, self-luminous body in space that creates its own energy
The sun gets its energy from nuclear fusion
Dark spots on the sun’s surface are known as sunspots
Sunspots are temporary storms visible on the surface of the sun
Sunspots come and go in cycles of about 11 years

33. Classifying Stars
The Hertzprung-Russell diagram is used to classify stars by temperature and size
Our sun is a fairly typical star
Although the sun Is brighter than most of the nearest stars, it is small compared with most of the stars we see at night

35. Galaxies A galaxy is a huge body of stars and other matter in space
Our own galaxy is called the Milky Way named for its faint white color
The sun is one of about 100 billion stars in the Milky Way

36. The Milky Way The Milky Way is a spiral galaxy
Our solar system is located in a spiral arm well away from the galactic center
The Earth and sun and other nearby stars orbit around the center of the Milky Way galaxy
It takes about 220 million years to complete this revolution

37. Spectroscopes
The light given off by stars is marked by dark lines in certain colors
A spectroscope is an instrument that separates light into its component colors
Since stars are primarily hydrogen and helium, the lines we usually see are in the orange, yellow, green and blue areas

38. Edwin Hubble
In the early part of the 20th century, Edwin Hubble discovered that light that reached Earth from distant galaxies shows special lines that are shifted toward the red end of the spectrum
He suggested that the red-shifted lines are evidence that distant galaxies are moving away from us
Observations of distant galaxies in all directions showed the red shift
The more distant the galaxy, the greater the red shift

39. Evolution of the Universe
The red-shift and other observations led scientists to the conclusion that the universe is expanding
Computer models that reverse the expansion, lead to the idea that at one time the universe was a concentrated object of incredible mass and density that exploded.
This theory of the origin of the universe is known as the “big bang”
Scientists can detect radiation remaining from the big bang
Scientists currently believe the universe is about 10 to 15 billion years old

40. The Size of the Universe
The distance light can travel in one year is called a light-year, which is about 10 trillion kilometers
Light could circle Earth seven times in one second
Light takes about one and a half seconds to get to the moon
Light from the sun takes about eight minutes to reach earth
Light from the nearest star (not our sun) takes about four years to reach us
The universe is thought to be about 25 billion light-years in diameter

41. The Future of the Universe
Some astronomers think that the expansion of the universe will continue forever
Some astronomers believe the force of gravity will eventually reverse the expansion and the universe will fall back together in the “big crunch”
Some astronomers think it is possible that the universe will pulsate between explosions and contractions