1. The Sun-Earth-Moon System

2. What is the moon? The moon is a natural satellite of Earth This means that the moon orbits Earth.

3. How was the moon formed? Theories about the moon’s formation Capture theory During the formation of the solar system, a large object came close to Earth and got caught in its gravitation.

4. Simultaneous formation theory Earth & the moon formed at the same time, of the same materials.

5. Impact theory A large object hit Earth 4.5 billion years ago. The resulting material was ejected into space and merged together.

6. What are the properties of the moon? The moon is bigger than most other moons in the solar system. It is 27% of Earth’s radius It has over 1% of Earth’s mass

7. Scale Size & Distance

8. The moon reflects the sun’s light, making it visible at night from Earth Albedo is the amount of sunlight reflected by an object The moon’s albedo is only about 0.07 (7%) Most of the sun’s energy that hits the moon is absorbed. This causes large differences in surface temperatures.

9. Radiation & Reflection of Sunlight 0.07(7%) 0.367 (36.7%)

11. The moon has no atmosphere This also contributes to large differences in surface temperatures because heat is not retained.

12. The moon’s surface is solid and rocky There is no erosion because there is no air or water So, craters and other markings are not “erased” over time Craters were caused by collisions with meteorites. Meteorites, known as asteroids when they are still in space, are pieces of planets left over from the formation of the solar system.

13. The lunar crater Daedalus, about 93 kilometers (58 miles) in diameter,.

14. What is the sun? The sun is the star at the center of our solar system. Earth (and everything else in our solar system) revolves around the sun.

15. What are the daily motions of the sun, Earth, & moon? Earth rotates on its axis one time per day. This makes it appear that the sun rises and sets, even though the sun does not orbit the Earth. This also accounts for the moon rising and setting.

16. How do eclipses occur? An eclipse is when one object in the sky blocks your view of another object in the sky Types of eclipses Solar eclipse Occurs when the moon blocks our view of the sun.

18. Lunar eclipse Happens when the moon passes through Earth’s shadow.

20. Stars, Galaxies, & Beyond

21. What is a star? A star is a massive, luminous ball of gas held together by gravity. Our sun is a star. A group of stars is called a constellation.

22. What powers a star? Stars are powered by nuclear fusion. Fusion is the combining of lightweight nuclei into heavier nuclei. Ex. Hydrogen combines to form helium.

24. Surface temperature—the temperature on a star’s surface

25. Composition—what a star is made of Composition can be determined through spectral analysis. Different elements emit different wavelengths of light. Spectral types are assigned letters (O, B, A, F, G, K, and M). All stars have similar compositions. 73% hydrogen 25% helium 2% other elements Temperature can also affect a star’s spectrum, so this must be accounted for.

27. How are stars classified? Stars are classified by their mass, luminosity magnitude, temperature, and diameter. A Hertzsprun-Russell (H-R) diagram is used to show the relationship between these variables.

28. H-R Diagram

30. What is the life cycle of a star? Star formation A nebula collapses as a result of gravity. The rotation of the collapsing nebula forces it into a disk shape. The hot condensed object at the center is a protostar.

32. Fusion begins The temperature inside the proto star becomes hot enough for fusion to begin. The star becomes stable because the pressure caused by fusion balances out gravity.

34. Red giant The star runs out of hydrogen to use as fuel. It starts to collapse & heat up in the core, but cools on the surface. Helium is then used as fuel for fusion.

36. White dwarf If the star has a low mass, it uses up the helium. Out layers become a planetary nebula again. The hot core that remains is a white dwarf.

38. Supernova If the star has a high mass, it continues fusing elements until iron is formed. There is a very dense iron core, with less dense layers outside of that. The iron core eventually collapses violently. After the collapse outer layers fall in, sending out shockwaves and causing an explosion

40. Neutron star The remaining collapsed core is a neutron star. It is made of neutrons. It is very dense. It spins very fast.

42. Black hole If a star is too massive it cannot form a neutron star. It will continue collapsing forever, compacting matter into a smaller and smaller volume. It is dense enough that its gravity even sucks in light. HOWEVER, the total mass of the star remains unchanged

44. What is a galaxy? A galaxy is a collection of stars, gas, and dust held together by gravity. Our galaxy is called the Milky Way

45. The Expanding Universe Scientists observe that galaxies are moving away from each other. This is true anywhere in the universe. Edwin Hubbel observed that most galaxies have redshifts in their spectra. When an object moves away, light waves are stretched out, causing longer (red) wavelengths. When an object moves toward you, light waves are compressed, causing shorter (blue) wavelengths.