Ch 26.2

1. Ch 26.2 History of solar system

2. Geocentric Model of the universe What do you think the word geocentric means? What does geo mean? What about centric? The word geocentric means earth centered. The geocentric model was the predominant model of the universe for thousands of years. People believed that the earth was at the center of the universe.

3. What is the new model of the solar system? • What do we now know as the center of the solar system? • The sun • Nicolaus Copernicus proposed the heliocentric model. • The heliocentric model means sun centered.

4. Movement of the stars • 6000 years ago astronomers were recording the movement of the stars across the skies. • They noted that stars moved across the sky, but they did not move in relation to one another. • They thought that the stars were holes in the celestial sphere with an intense light source behind them. • As the sphere moved, the stars moved.

5. Constellations and planets • Early astronomers notices that the same groups of stars moved together all the time. • Many cultures used the constellations to create calendars. • There were a few points of light that were not part of any constellation, and they wandered by themselves. • These points of light were planets, and astronomers assumed that these points of light were closer to earth than the other stars.

6. Retrograde motion • Early astronomers noticed that the planets moved eastward in front of the constellations. • Sometimes the planets stopped moving eastward and began to move westward for a few weeks. • Then the planet began to move eastward again.

7. Retrograde motion So why were the planets going backward? They weren’t! It just looked like they were. Retrograde motion occurs because each planet orbits the sun counterclockwise at a different distance and at a different speed.

9. Example • Earth moves faster in its orbit than Mars does. • Whenever Earth begins to pass Mars, Mars appears to move west (backward) among the stars. • After Earth has passed Mars , the motion of Mars appears normal again. • Think of it a being in a car. As you pass the car it looks like it is going backward.

10. Ptolemy and retrograde motion • Ptolemy developed the first model that could be used to predict the location of the planets. • He had to take retrograde motion into account.

11. Tycho Brahe • Tycho and his assistants studied the movement of the moon and planets through their orbits, rather than just at certain points. • His observations were the most precise made before the invention of the telescope. • Tycho dies before he was able to apply his data.

12. Johannes Kepler • Kepler was an assistant to Tycho Brahe. • Kepler found that the planets’ orbits were elliptical rather than round.

13. Kepler’s Laws of Motion Kepler’s first law: planets travel in elliptical orbits with the sun at one focus. Kepler’s second law: (the equal area law) Each planet moves around the sun, in such a way that an imaginary line joining the planet to the sun sweeps over equal areas of space in equal periods of time. The planets travel faster around when they are closer to the sun, but he couldn’t figure out why.

14. Kepler’s Third law • The third law is the harmonic law. The time it takes a planet to travel one orbit around the sun is its period. The third law of planetary motion stated that the period of a planet squared is equal to the cube of its mean distance from the sun. We can use this to find the mean distance between the sun and a planet if the period is known , or to find the period if the mean distance is known.

15. Newton and the law of gravity • Newton stated that what keeps the planets orbiting the sun is the force of gravity. • The law of gravity states that: Every mass exerts a force of attraction on every other mass. The strength of the force is proportional to each of the masses, and inversely proportional to the distance between them. This means that the bigger, an object is the more it will attract an object, and as the distance decreases, the force of attraction is greater.

16. Gravity Does the sun have a greater force of attraction on the planets, or do the planets have a greater force of attraction on the sun. The sun on the planets because it is more massive.

17. Gravity The law of gravity is why the planets move faster when they get closer to the sun.

18. The Inner Planets Chapter 27.1 Mercury Venus Earth Mars

19. Inner planets The inner planets are located near the sun. Characteristics: Rocky crusts Dense mantle layers Very dense cores All of the inner planets are said to be terrestrial or earthlike planets.

20. The solar system The planets in the solar system are divided into two groups: The inner planets and the outer planets. Inner planets : Mercury Venus Earth Mars

21. Outer Planets Jupiter Saturn Uranus Neptune These four are the Jovian planets, they are larger than earth. They are gaseous, less dense than earth, and have ring systems. Pluto is not a gas planet, it is the farthest away from the sun. It is considered a dwarf planet now.

22. Mercury • Mercury is the planet closest to the sun. • It has the shortest orbital period of 88 earth days. • Mercury is the smallest of the terrestrial planets. • Mercury is smaller than Earth, its diameter is about 38% that of Earth. • The gravity on Mercury is also less than Earth. • It also has a weak magnetic field, about 1% as strong as the Earth.

23. Mercury • The surface of Mercury has many impact craters just like our moon. • These formed when huge rocks and other pieces of debris smashed into the surface. • Mercury also has smooth plains that may have been formed by lava flowing out of surface cracks.

24. Mercury • Mercury turns on its axis once every 59 days. This is very slow compared to its location to the sun. • The daytime temperatures of Mercury get to greater than 400 °C. • At night the temperature can be -200 °C. • Mercury has a very weak gravity which prevents it from having any atmosphere. • The temperature gets so hot during the day that the particles can escape into space because of the low gravity.

25. Pictures of Mercury

26. Venus: Earth’s sister planet • Venus is known as Earth’s sister planet because they are close to one another, they are similar in diameter, mass, and gravity. • Venus has almost no magnetic field as opposed to Earth. • Venus rotates from east to west, it is the only planet to do this. • It rotates on its axis very slowly, one rotation takes 243 days.

27. Venus continued • Venus orbits the sun in 225 days, this means that one day on Venus is longer than one year on Venus. • The atmosphere of Venus is CO2, nitrogen, and sulfuric acid. The sulfuric acid give the clouds a yellow color. • The surface of Venus is very hot. The CO2 in the atmosphere acts like a greenhouse. CO2 traps heat that is radiated from the surface and keeps the temperature high. • The surface temperature on Venus is 475 °C.

28. The surface of Venus • We can not see the surface of the planet, but we do know what it looks like from radar mapping. • There are many volcanoes, faulting, and impact craters. • 80% of the surface is covered in lava. • It is unclear if Venus is currently a tectonically active planet. • The atmospheric pressure is 90 times greater than on Earth.

29. Morning and Evening stars • Both Mercury and Venus can be seen as morning and evening stars, depending on if they are in front or behind us in our orbit. • Evening star: behind • Morning star: in front • Mercury is harder to see than Venus because it is closer to the sun, is smaller, and less bright than Venus.

31. Mars • The fourth planet from the sun and the first planet outside of Earth’s orbit. • It takes Mars 687 days to orbit the sun. • It has a diameter about half the size of the Earth. • The gravity on Mars is about 2/5ths of the Earth. • Has a very weak magnetic field.

32. Mars • Mars has four seasons due to the tilt of its axis just like which is very similar to the Earth. • Each Martian season is about twice as long as the Earth seasons, because the Martian year is twice as long as Earth. • Mars is farther away from the sun, so it is colder than the Earth. • On a summer day on Mars the temperature can reach 27°C . • On a winter night the temperature can drop to -133°C.

33. Mars • Mars has a thin atmosphere made of mostly CO2, nitrogen, and argon. • The atmospheric pressure is less than 1% of the Earth because the atmosphere is so thin. • Mars has polar ice caps, which are water ice covered by frozen CO2. • The ice caps shrink and grow with the seasons. • There are some seasonal dust storms that cover the planet.

34. The surface of Mars • The northern hemisphere of Mars is a smooth lowland plain of volcanic material with few craters. • The southern hemisphere is a highland fractured by many large craters and cut by small channels. • There are also several extinct volcanoes. The largest is Olympus Mons. This is also the largest volcano in the solar system.

35. The surface of Mars • There is no plate tectonic activity on Mars, we know this because there is only one solid plate. • There is also a canyon system as long as the united states is wide. • Liquid water can not exist on Mars because it either freezes, or boils away.

36. Life on Mars • Is their life on Mars? • There was probably once liquid water, so it is possible that life once existed on Mars. • If there is still liquid water somewhere on Mars it is possible that there is primitive life on Mars.