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Astronomy Earth and Moon Solar System Stars and Galaxies Effects of Gravity • Gravity – force of attraction between any two objects • Mass – amount of matter that an object contains • Orbit – curved path that an object follows as it revolves around another object Earth’s Movement • Revolution – movement of one object in its orbit around another object; a single revolution takes about 365 days • The various positions of the Earth in relation to the Sun will cause seasons in some parts of the world • Solstices – Sun is directly on the Tropic of Cancer or Tropic of Capricorn • Equinoxes – Sun is directly on the Equator Moon’s Movement • Revolves completely around the Earth in about 29 days • Rotates on it’s axis about once every 29 days • Therefore, we always see the same side of the Moon • Phase – change in the Moon’s appearance as it orbits the Earth • 4 main phases: New, First Quarter, Full, Third Quarter Eclipses • Lunar eclipse – passing of the Moon through the Earth’s shadow; Earth is between the Sun and the Moon • Solar eclipse – passing of the Moon between the Earth and the Sun; Moon casts a shadow on the Earth Solar Eclipse Lunar Eclipse Tides • Tides – regular rising and falling of the Earth’s major bodies of water • Moon’s gravity causes ocean water to pile up on the side of the Earth facing the Moon • Other factors that affect tides are wind, ocean temperature, and water flowing into the ocean Moon’s Surface • Maria – low, flat plains on the Moon’s surface that appear as dark areas • Crater – circular low area surrounded by a rim, usually caused by an object hitting the ground • Apollo Missions: Between 1969 and 1972, seven trips to the Moon. – Measure moonquakes, moon rocks and dust, approximately 4.6 billion years old – No other people have visited the Moon since. The Solar System • Star – glowing ball of hot gas that makes its own energy and light • Planet – large object in space that orbits a star, such as the Sun • Moon – natural satellite that orbits a planet • Solar system – a star, such as the Sun, and all of the objects that revolve around it in space. The Solar System The Sun • Made of hydrogen (H) and helium (He) • Rotates on an axis; parts rotate at different rates • Temperature: Outer 5,500 °C, Inner 15,000,000 °C. • Nuclear reactions fuse two hydrogen atoms to make one helium atom Parts of the Sun • Atmosphere – envelope of gas surrounding an object in space • Photosphere – inner layer of the Sun’s atmosphere that gives off light • Chromosphere - middle layer of the Sun’s atmosphere that can be seen during an eclipse; has a distinctive red color • Corona – outer layer of the Sun’s atmosphere • Sunspots – cooler areas of the Sun that give off less energy The Inner Planets • Inner planets: Mercury, Venus, Earth, Mars; closest to the Sun • All are solid and have a high density • Similar in size and have a low mass • Rocky Mercury • Closest to the Sun • Fastest moving; revolves in 88 days • Virtually no atmosphere • Many craters • Surface Temperature: 427 °C facing Sun, -187 °C away from Sun Venus • Hottest planet: 460 °C • Greenhouse effect: warming of the atmosphere because of heat trapped by Sun • Rotates from east to west; 243 Earth days Earth • Mild surface temperature that changes little • Dense protective atmosphere • Only planet to have liquid water Mars • Reddish color; iron oxide • Similar rotation with Earth; 24 hrs, 38 min. • Longer revolution; 687 Earth days • Thin atmosphere; colder • Two moons • Only frozen water exists The Outer Planets • Jupiter, Saturn, Uranus, Neptune • Made of frozen gas and liquid, with a small solid core • All have a ring system • Large size and high mass • Low density • Many moons • High gravity Jupiter • Largest planet • Colorful bands of gases where storms take place • Fast rotation; 10 hours • Great Red Spot; spinning windstorm which has lasted 300 years Saturn • • • • • Second largest planet 1000 individual rings, most visible and largest Stormy bands of clouds along the surface Rotates quickly; 11 hours Revolves once every 29 years Uranus • Rotates on its side; once every 17 hours • Revolves once every 84 years • At least 11 rings and 22 moons Neptune • Greenish blue atmosphere because of methane gas • Four rings • Great Dark Spot – as big as the Earth • Rotates once every 16 hours • Revolves once every 164 years Pluto • No longer considered a planet; dwarf planet • No rings and thin atmosphere • One moon • Crosses Neptune’s orbit part of the time • Rotates once every 6 days • Revolves once every 248 years. Other Objects in Solar System • Asteroids – rocky objects, smaller than a planet, that orbit a star • Asteroid belt – region between Mars and Jupiter where most asteroids orbit Sun • Meteor – brief streak of light seen when an asteroid enters the Earth’s atmosphere and burns up • Meteorite – asteroid that hits the surface of a planet or moon after traveling through space • Comet – ball of ice, rock, frozen gas, and dust that orbits the Sun Asteroids Meteors and Meteorites Comets Stars • Stars shine because of a process called fusion • Fusion – process by which particles combine to form a new particle • The source of energy for the Sun is hydrogen fusion • By combining hydrogen atoms, the Sun produces a constant supply of energy in the form of heat and light. Stars • Magnitude – brightness of a star; determined by distance from Earth and amount of energy • Apparent magnitude – how bright a star looks • Absolute magnitude – how bright a star actually is if all the stars were the same distance from the Earth • The more negative the magnitude, the brighter the star. • Color – blue is hottest, red is coldest Distance to Stars • Light-year – distance that light travels in one year – 1 light-year = 9.5 trillion kilometers • Astronomical Unit (AU) – the distance between the Earth and the Sun – 1 AU = 149,598,000 kilometers • Parallax – the apparent shift in a star’s position because the position of the Earth – Used to measure distances of starts Distance to Stars The Life of a Star • A star’s life cycle begins in a nebula, a cloud of gas and dust in space. • Balance between gravity and fusion. Gravity causes a collapse, fusion causes heat and expansion • Main sequence star – star, like our Sun, that is fusing gases together giving off light and heat. The Life of a Star • As fusion uses up hydrogen, the star expands to about 100 times it’s original size – Red Giant. • Gravity overtakes the mass of the star, and it collapses. • Temperature begins to increase and the outer layer is blown off forming a nova; brilliant explosion of a Red Giant. • Center of nova becomes a small, white, hot dense star – white dwarf The Life of a Star • Star more massive than the sun, as it uses up hydrogen, it becomes a supergiant • Supergiant collapses and becomes a supernova, a brilliant explosion of a supergiant. • After the gases have left, a neutron star may remain; very small, very dense star • However, if gravity is large, a black hole may form; a region in space with tremendous gravity that light cannot escape. Constellations • Constellation – pattern of stars seen from the Earth Galaxies • Galaxy – group of billions of stars • Our galaxy is the Milky Way galaxy – 100,000 light years thick and 10,000 light years wide • Three types based on shape: – Elliptical – Irregular – Spiral