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Lesson 3 Lecture 13Solar system has: 1 star, 8 planets, 5 dwarf planets, 139+ moons, countless small solar system bodies Sun> cantaloupe; Earth> a ball point; Jupiter>finger tip; Pluto>dust speckAll Planets orbit the Sun counter-clockwise as viewed from above Earth’s NPAlso true for rotations of the Sun and most planets. Except the rotations of Venus (backwards) and Uranus (on side) Moons orbit around planets counterclockwise. With only a few exceptions Also, the orbits of the planets are very close to circular (Mercury’s orbit is least circular of the 8 planets). The orbits of dwarf planets (like Pluto) and small solar system bodies can be very eccentric. The solar system is basically ‘flat’ and disk-shaped The planets revolve around the sun in orbits that lie close to a common plane.The orbit of Mercury, the planet closest to the sun, is tipped 7° to Earth’s orbit.The rest of the planets’ orbital planes are inclined by no more than 3.4°.Orbits of dwarf planets (like Pluto) and small solar system bodies can be very inclined. Two Basic Types of Planets Terrestrial Planets (Earth like)Closer to the Sun, closer together Smaller sizes and masses Higher densities Compositions: mostly rock and metal Solid surfaces Warmer surfaces Few moons No rings Low massJovian Planets (Jupiter like)Farther from the Sun, farther apart Larger sizes and masses Lower densities Compositions: hydrogen, helium, “ices”No solid surfaces Colder temperatures at cloud-tops Many moonsAll have ring systems The Sun is a huge, glowing ball of mostly hydrogen and helium gas at the center of our solar system. The sun provides light, heat, and other energy to Earth. Earth travels around the sun at an average distance of about 149,600,000 kilometers(92 million miles). The sun's diameter is about 1.4 million km (864,000 miles), approximately 109 times Earth's diameter. The Sun has 99.8% of the mass in the entire solar system! Its mass is roughly 2 X 1027 tons. This number would be written out as a 2 followed by 27 zeros - or about 333,000 times as massive as Earth. Inner Planets> Terrestrials> Mercury, Venus, Mars EarthMercury is a barren airless world -heavily cratered surface. -only 30% larger diameter than the Moon.
-Mercury orbits the Sun once every 88 days, and it has the most eccentric orbit of the 8 planets. -Mercury rotates once per 59 days (with respect to the stars), but eachsolar day lasts 176 Earth days (2 Mercury years). -Lack of an atmosphere and long days means daytime temperatures reach a balmy 430 C (801 F), nighttime temperatures plunge to -170 C (-279 F). Venus, Earth’s “Evil Twin” Venus’ surface is guarded by thick sulfuric acid clouds Venus’ size is closest to Earth’s, but HOT! 470°C (925°F)!Venus has an extremely thick CO2 atmosphere. Unlike the benign water vapor cloudson Earth, Venus’ clouds contain large amounts of sulfur dust and sulfur compounds, giving them a yellow-orange color.