Who are some important astronomers? Copernicus: first to state moon orbited around Earth and everything revolved around Sun. Also known as the heliocentric model. Galileo: observations of Venus supported Copernicus’ findings Kepler: calculated that planets had elliptical orbit and planets closer to Sun travel faster than those farther away
Danish astronomer Tyco Brahe (1546- 1601) had an island observatory and the best measurements of the positions for all known planets (Mercury, Venus, Mars, Jupiter, and Saturn) and the Moon.
What did Tycho and Kepler discover? At that time, many astronomers believed that planets orbited around the sun in perfect circles, but Tyco’s accurate measurements for Mars didn’t fit a circle. Instead, the mathematician Johannes Kepler found that the orbit of Mars fit an ellipse the best…
What is the first law of planetary motion? 2 foci All planets orbit the sun in an elliptical orbit. An ellipse is a geometric shape with 2 foci instead of 1 central focus, as in a circle. The sun is at one focus with nothing at the other focus. Eccentricity: 0= perfect circle 1=elongated oval FIRST LAW OF PLANETARY MOTION
PerihelionAphelion Perihelion: When Mars or any another planet is closest to the sun. Aphelion: When Mars or any other planet is farthest from the sun.
What is the second law of planetary motion? A B An imaginary line drawn from the center of the sun to the center of the planet will sweep out in equal areas in equal intervals of time Kepler also found that Mars changed speed as it orbited around the sun: faster when closer to the sun, slower when farther from the sun… But, areas A and B, swept out by a line from the sun to Mars, were equal over the same amount of time.
What is the third law of planetary motion? Kepler found a relationship between the time it took a planet to go completely around the sun, and the average distance from the sun What does this mean? As a planet/satellite increases radius from the sun it takes longer to make a revolution. For example: Mercury's orbital period is 88 days and Plutos is 248 years.
What is an Astronomical Unit? 1 AU: 150 million kilometers or 93 million miles Roughly the mean difference in distance between the Sun and Earth
What are the Terrestrial Planets? Mercury, Venus, Earth & Mars ▫“Earth-Like” Rocky Planets ▫Largest is Earth ▫Only in the inner solar system (0.4 to 1.5 AU) Rocky Planets: ▫Solid Surfaces ▫Mostly Silicates and Iron ▫High Density: (rock & metal) ▫Earth, Venus, & Mars have atmospheres
What are the The Jovian (Gas Giant) Planets? Jupiter, Saturn, Uranus & Neptune Largest Planets: at least 15 times mass of Earth. Only in the outer solar system (5 to 30 AU) No solid surfaces (mostly atmosphere) Low density Many moons Gas Giants: (Jupiter & Saturn) Thick H/He atmosphere, liquid hydrogen mantle, ice core Ice Giants: (Uranus & Neptune) Ice/rock core & mantle, thin H/He atmosphere
What are Dwarf Planets? Defined by the IAU in 2006 Dwarf Planets: ▫Ceres: first of the Asteroids, discovered in 1801 ▫Pluto: trans-Neptunian object discovered in 1930 ▫Eris: trans-Neptunian object discovered in 2005 ▫Haumea (trans-Neptunian, suspected) ▫Makemake (trans-Neptunian, suspected)
What are the most giant moons in the solar system? Moon: any natural satellite orbiting a planet or dwarf planet Giant Moons: ▫Earth: The Moon (Luna) ▫Jupiter: Io, Europa, Ganymede, & Callisto ▫Saturn: Titan ▫Neptune: Triton Many smaller moons, both rocky & icy. Only Mercury & Venus have no moons.
What are Kuiper Belt objects? Class of icy bodies orbiting beyond Neptune. Found only in the outer Solar System (>30AU) Densities of 1.2 to 2 g/cc (mostly ices) Examples: Pluto & Eris (icy dwarf planets) Kuiper Belt Objects (30-50AU) Charon, Pluto’s large moon Sedna & Quaor: distant large icy bodies
What are The Leftovers (small bodies)? Asteroids: leftovers from the formation of the solar system Made of rock & metal (density 2-3 g/cc) Sizes: Few 100km to large boulders Most are found in the Main Belt (2.1-3.2 AU) Meteoroids: material that falls toward Earth and enters the atmosphere. Bits of rock and metal Sizes: grains of sand to boulders Meteor: meteoroid that burns up in the atmosphere creating a streak of light Meteorite: meteoroid that collides with the ground without burning up in the atmosphere. Comets: small, icy bodies with eccentric orbits around the sun. Composite rock & ice “dirty snowballs” Longs tails of gas & dust are swept off them when they pass near the Sun.
Is Pluto and planet? What to consider? Size? Shape? Orbit? What is it made of?
What is the IAU Definition of a Planet? In 2006, the International Astronomical Union (IAU) came up with the following definition of a planet: orbits the Sun has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape (i.e., it is spherical), has cleared the neighborhood around its orbit, is not a satellite
What is the IAU Definition of a Dwarf Planet? In 2006, the International Astronomical Union (IAU) came up with the following definition of a dwarf planet: orbits the Sun has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape (i.e., it is spherical), has not cleared the neighborhood around its orbit, is not a satellite