The Solar System

1. The Solar System

2. History of Our Solar System • Geocentric Model – A.D. 140 Egyptian astronomer Ptolemy • Means Earth is in the center and everything else revolves around it • Explained most observations made at that time • Geo = earth • Centric = center

3. History of our Solar System • Heliocentric Model – early 1500s Polish scientist Nicolaus Copernicus • Means the Sun is in the center and everything else revolves around it • Galileo Galilei & other scientists later proved this model was correct • Helio = sun • Centric = center

4. What’s in Our Solar System? • Our Solar System consists of a central star (the Sun), the 8 planets orbiting the sun, moons, asteroids, comets, meteors, interplanetary gas, dust, and all the “space” in between them. • The 8 planets of the Solar System are named for Greek and Roman Gods and Goddesses.

5. Inner Planets: Mercury Venus Earth Mars Outer Planets: Jupiter Saturn Uranus Neptune Inner and Outer Planets

6. Planetary Orbits • Johannes Kepler, 1600, discovered that the orbit of a planet around the sun is NOT a CIRCLE but an ELLIPSE - • Looks like an oval that has been stretched • The force that holds the planets in orbit around the sun wasn’t understood until Isaac Newton’s discoveries about gravity. • Gravity & Inertia combine to keep the planets in orbit around the sun

9. The Relative Size of the Planets in the Solar System One astronomical unit (AU) = avg. distance from Earth to the Sun – 149,598,000 km

10. Exploring the Solar System • Modern technology – telescopes, piloted spacecraft, space probes, etc. • 1st artificial satellite – Sputnik, 1957 • 1st human to orbit Earth – Yuri Gagrin, April 1961 • 1st American in space – Alan Shepard, May 1961 • 1st man on the moon – Neil Armstrong, July 1969

11. The Sun • The sun’s energy comes from nuclear fusion(where hydrogen is converted to helium) within its core. This energy is released from the sun in the form of heat and light. • Remember: Stars produce light. Planets reflect light. • A star’s temperature determines its “color.” The coldest stars are red. The hottest stars are blue.

12. The 8 Planets of the Solar System • Planets are categorized according to composition and size. There are two main categories of planets: • Terrestrial (small & rocky) (Mercury, Venus, Earth, and Mars) • Gas Giants (Jupiter, Saturn, Uranus, and Neptune)

13. Characteristics of Small Rocky Planets • They are made up mostly of rock and metal. • They are very heavy. • They move slowly in space. • They have no rings and few moons (if any). • They have a diameter of less than 13,000 km. • They are much warmer on average

14. Mercury • Revolution period of 88 days. • Smallest & closest to the sun • Large iron core; geologically dead • Extreme temp fluctuations • Scientists believe there is ICE on Mercury! The ice is protected from the sun’s heat by crater shadows.

15. Venus • Its maximum surface temperature may reach 900F. • Venus has no moons and takes 243 days to complete an orbit. • Rotation is longer than revolution • Unusual rotation – rotates in the opposite direction to which it revolves • Thick atmosphere – mostly CO2 which raises the planet’s temp • Brightest object in Earth’s night sky • Often mistaken as a star

16. Earth • Earth is the only planet known to support living organisms. • Earth’s surface is composed of 71% water. • Water is necessary for life on Earth. • The oceans help maintain Earth’s stable temperatures. • Earth has one moon and an oxygen rich atmosphere.

17. Earth’s Moon • It takes the moon approximately 29 days to complete one rotation. The same side of the moon always faces us. • The moon’s surface is covered in dust and rocky debris from meteor impacts. • The moon reflects light from the sun onto the earth’s surface. • Hypothesis = the moon formed after an enormous collision early in Earth’s history

18. Earth-Moon System • Lack of an atmosphere causes the surface temp. to vary greatly • Evidence of ice near the moon’s N and S poles • Major features: • Maria – low, flat plains formed by ancient lunar lava flows; cover about 15% • Highland – surround Marias & are lightly colored; rough, mountainous ranges • Craters – round depressions caused by an impact of high speed meteoroids

19. Earth-Moon System • Thousands of craters are evidence that the moon is geographically dead • Little erosion • No plate motion

20. Phases of the Moon

21. Eclipses • Occurs when a shadow of one body in space falls on another • For an eclipse to occur on Earth, the sun, moon, and Earth must lie along a straight line • Infrequent because the plane of the moon’s orbit is tilted about 5 degrees • Solar – occurs when the moon casts a shadow on a portion of Earth’s surface • Lunar – occurs when Earth casts a shadow on the moon

23. Tides on Earth • Regular rise and fall of ocean waters • Caused mainly by differences in the moon’s gravitational pull on Earth

24. Mars • “Red Planet” – iron rich rocks • Like Earth, Mars has ice caps at its poles. • Mars has the largest volcano in our solar system: Olympus Mons. Olympus Mons is approximately 15 miles high. • Shows evidence of once having liquid surface water • Mars has two moons and takes about two years to complete an orbit.

25. Beyond Mars • Asteroids – small, rocky bodies • Asteroid belt – beyond mars, orbiting the sun • Scientists hypothesize that asteroids are remnants of the early solar system that never came together to form a planet

26. Characteristics of Gas Giants • They are made up mostly of gases (primarily hydrogen & helium). • Massive & very light for their size. • Very cold temps • Move quickly in space. • They have rings and many moons. • They have a diameter of less than 48,000 km

27. Gas Giants • Rings – disk made of many small particles of rock & ice in orbit around a planet

28. Jupiter • Jupiter is the largest and most massive planet. • Composed mainly of hydrogen & helium • It’s diameter is 11 times bigger than that of the Earth’s. • Rotates rapidly – 1 day on Jupiter is less than 10 Earth hours • It takes about 12 years for Jupiter to orbit the sun. • Jupiter has at least 63 moons.

29. Jupiter’s Moons • Ganymede & Callisto – similar size to Mercury • Io & Europa – about the size of our moon • Europa – icy crust appears to rest on top of a liquid saltwater ocean; scientists hypothesize that Europa is the most likely place in the solar system to support life (other than Earth obviously)

30. Saturn • 2nd largest planet; most visible from Earth • Saturn is composed almost entirely of hydrogen and helium. • Saturn has many rings made of ice. Saturn’s rings are very wide. They extend outward to about 260,000 miles from the surface but are less than 1 mile thick. • Atmosphere is the largest of any planet • Lowest average density of any planet • Saturn has at least 56 moons, some of which orbit inside the rings! • Titan – larger than Mercury • It takes Saturn about 30 years to orbit the sun.

31. Uranus • Uranus is blue in color due to methane gas in its atmosphere. • Uranus has 11 dark rings surrounding it. • Uranus has at least 27 moons and takes 84 years to complete one orbit. • Very cold • Unusual tilt – lies nearly on its side @ more than 90 degrees

32. Neptune • Neptune has the fastest winds in the solar system: up to 2,000 km/hr. • Neptune is also blue in color due to methane gas in its atmosphere. • Neptune takes 165 years to orbit the sun and has at least 13 moons. • Large storms in its atmosphere – Great Dark Spot 1989

33. Dwarf Planets • Like a planet, spherical & orbits the sun directly • Unlike a planet – has not cleared the neighborhood around its orbit • Pluto – very small • Elliptical orbit • Tilted more than 90 degrees like Uranus

34. Comets & Meteoroids • Comet – dusty pieces of ice & rock that partially vaporize when they pass near the sun • Meteoroids – pieces of rock, usually less than a few hundred meters in size

36. Edge of the Solar System • Estimate thousands of solar system objects exist beyond Neptune’s orbit • Kuiper Belt – extends about 100 AU from Neptune; • Objects are mostly made of ice, dust, & rock • Pluto is found here • Oort Cloud – great reservoir of comets

37. Exploring the Universe

38. The Sun • Tremendous amounts of energy in the form of electromagnetic radiation • Produced in its central region by the fusion of hydrogen nuclei into helium nuclei

39. Forces in Balance • Astronomers estimate the sun will remain stable for another 5 billion years • Energy from nuclear fusion in the center of the sun causes ions to move faster, exerting an outward thermal pressure • At the same time, gravity pulls the gas inward

40. The Sun’s Interior • Core – nuclear fusion occurs; little more than ¼ of the sun • Radiation Zone – region of highly compressed gas; energy is transferred by the absorption & reradiating electromagnetic waves • Convection Zone – outer layer of the sun’s interior; energy is transferred outward mainly by convection currents

41. The Sun’s Atmosphere • Protosphere – innermost layer • Chromosphere – middle layer; gives off color • Corona – outermost layer

42. Features of the Sun’s Atmosphere • Sunspots – areas of gas in the photosphere that are cooler than the surrounding gases • Prominences – huge loops of gas that erupt from sunspot regions • Solar Flare – sudden release of energy from the sun usually near sunspots

43. Sun’s Energy The sun will eventually lose energy & become a white dwarf!!

44. Stars • Large, glowing ball of gas in space, which generates energy through nuclear fusion in its core • Closest star to Earth = Sun

45. Distances to the Stars • Light year – distance that light travels in a vacuum in a year; about 9.5 trillion years • Scientists cannot measure stars distances directly • Parallax – apparent change in position of an object with respect to a distant background

46. Properties of Stars • Classified based on their color, size, & brightness • Color & Temp – hottest stars are blue • Brightness – decreases as its distance from you increases • Apparent brightness – brightness of a star as it appears from Earth • Absolute brightness – how bright the star really is • Size & Mass – calculate the mass by observing the gravitational interaction of stars that occur in pairs

47. Star Composition

48. Hertzsprung-Russell Diagram

49. Hertzsprung-Russell Diagram • Used to estimate the sizes of stars & their distances, and to infer how stars change over time • Main Sequence Stars – about 90% of stars • The Sun lies in the middle of this band • Supergiants – less than 1%; very bright stars at the upper right of the diagram • White Dwarf – about 10% of stars; small, dense remains of low or medium mass stars

50. How Stars Form • Nebula – large cloud of gas and dust spread out over a large volume of space • Stars form in the densest regions of nebulae by the pulling by gravity • As the nebula contracts, it heats up • Protostar – contracting cloud of gas & dust with enough mass to form a star