Astronomy Study Guide Notes

Astronomy Study Guide Notes - Astronomy Study Guide Notes...

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Astronomy Study Guide Notes 11: Planetary Systems: Ours and Others The Solar System By terrestrial standards, the density of matter in the solar system is extremely low, and the planets are separated by enormous gaps. Other than the Sun, no solar system object is self-luminous at visible wavelengths, and all shine by reflected sunlight From Earth, the moon and Venus, are the second and third brightest objects Contents The Sun (99.8% of total mass) 8 “classical” planets (0.1%) (Jupiter > sum of others) Tens of thousands of smaller rocky or icy “minor” planets, ranging in size down to a few hundred meters. The largest of these called, inc. Pluto, “dwarf planets” o Most members of asteroid belt between Mars and Jupiter or Kuiper Belt beyond Neptune Over 160 satellites; comets; meteoroids, dust, gas Systematic Characteristics of Planet Orbits Orbits for all lie close to the plane of the Earth’s orbit (ecliptic plane) Orbits, though technically ellipses, are nearly circular The direction of revolution of the planets in their orbits is the SAME; the direction of spin on the rotation axis is the same for most Orbits show systematic spacing: separation between orbits increases w/ orbit size The systematic must be the product of special physical conditions prevailing during formation of planets they provide information on process Segregation of Physical Properties Four “inner planets” (Mercury, Venus, Earth, Mars) very dissimilar from four large “outer planets” (Jupiter, Saturn, Uranus, Neptune) another clue about the formation process of the planetary system INNER (TERRESTRIAL) OUTER (JOVIAN) Size and Mass Small Large Density Large Small Composition Si, O, Al, Mg, Fe, Rocky H, He, Gas Giants Origin of the Solar System Catastrophic/tidal Theory: a passing star pulls material from Sun, which cools to form planets: o Would imply planets are rare, since close encounters are rare o Physically unlikely: expelled material would diffuse, not condense Nebular Theory: planets are byproducts of normal star formation o Planets form the cloud of debris surrounding a forming star o Would imply planets are common
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The Interstellar Medium and Star Formation We know stars are forming continuously out of the interstellar medium at a rate of about 1 solar mass/year throughout our galaxy: ISM is the dilute matter between stars Constitutes a few % of the mass of our galaxy Contents: Gas (atoms, molecules) and Dust Dust plays important role of a refrigerant for interstellar gas. Parts of the ISM, if well shielded by dust grains, can become very dense and cold these are the regions which are primed to turn into nurseries for newly born stars Planet Formation in the Nebular Theory 1. A dense, cold cloud in the ISM collapses under gravity 2. As it collapses, it spins up and flattens because of the conservation of angular momentum a rotating, flattened “protoplanetary” disk is a natural consequence
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Astronomy Study Guide Notes - Astronomy Study Guide Notes...

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