Astronomical Universe ASTRO 001
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This 0 page Study Guide was uploaded by Lila Brekke I on Sunday November 1, 2015. The Study Guide belongs to ASTRO 001 at Pennsylvania State University taught by Staff in Fall. Since its upload, it has received 61 views. For similar materials see /class/233014/astro-001-pennsylvania-state-university in Astronomy and Astrophysics at Pennsylvania State University.
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Date Created: 11/01/15
Astro 001 Glossary Astronomical Unit AU average distance of the Earth from the Sun over the course of a year equivalently the semimajor axis of Earth s orbit blueshift the shifting of light to higher bluer frequencies due to motion of a source towards an observer circumpolar stars stars that are never seen to set from a given location conjunction alignment of two or more bodies as seen from Earth when only one planet is mentioned alignment of that planet with the Sun deferent primary circle of motion for the planets Sun and Moon in the geocentric systems of Aristotle Ptolemy and others ecliptic or ecliptic plane the circle on the celestial sphere defined by the motion of the Sun with respect to the fixed stars over the course of a year equivalently the plane through the Solar System defined by Earth s orbit epicycle secondary additional circle upon a circle of motion for the planets Sun and Moon in geocentric systems of Aristotle Ptolemy and others geocentric Earthcentered Sun revolving around the Earth heliocentric Suncentered Earth revolving around the Sun inferior conjunction when a planet is seen to be in conjunction with the Sun and on the near side of the Sun as viewed from Earth opposition when one body is seen to be in the opposite direction from another body when viewed from Earth when only one planet is mentioned when that planet is in the opposite direction from the Sun parallax the apparent motion of nearby objects with respect to more distant objects due to motion of the observer pole star when a particularly bright star is located close to the North or South celestial pole it may be called a pole star prograde motion when a planet moves from West to East with respect to the fixed stars as viewed from Earth quadrature when a planet or the Moon is seen to be at a 90degree angle with respect to the Sun as viewed from Earth redshift the shifting of light to lower redder frequencies due to motion of a source away from an observer or to other physical effects retrograde motion when a planet moves from East to West with respect to the fixed stars as viewed from Earth semimajor axis half the length of the major longer axis of an ellipse usually denoted as a Note that the semimajor axis of a circle is its radius sidereal month the duration of the Moon s orbit around the Earth measured with respect to the fixed stars Solar mass the mass of the Sun superior conjunction when a planet is seen to be in conjunction with the Sun and on the far side of the Sun as viewed from Earth synodic month the duration of the month as measured by the Moon s phases Astro 001 Laws amp Equations Kepler s Laws 1 The planets move in ellipses with the Sun at one focus 2 The speed of each planet s motion varies during the orbit such that equal areas are swept out in equal times by an imaginary line connecting the planet and the Sun The orbital period measured in years P and the semimajor axis measured in AU a of each planet satisfies the relation P2 a3 03 Newton s Laws of Motion 1 Objects at rest remain at rest and objects in motion remain in motion unless subject to an external force 2 Force is proportional to mass times acceleration Fma 3 Every force has an equal and opposite counterforce Newton s Law of Gravity The magnitude of the gravitational force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them F G In M I2 Newton s Revision of Kepler s Third Law m M P2 a3 Here M is the mass of the Sun and m the mass of the planet measured in solar masses The Nature of Light 39 The speed of light 0 is a constant 39 Frequency and wavelength are inversely proportional v c A 39 Energy per photon is proportional to frequency E h v 39 Flux decreases as the square of distance because it spreads out over the surface of a sphere F L 4 7 I2 Doppler shift The change in frequency or wavelength of light is roughly proportional to the speed of relative motion divided by the speed of light Simple version Avv 2 AN We More complex accurate version Avv 2 AM We 1 v2cz Note that signs are ignored in these equations Blackbody Radiation Equations 1 The peak frequency of a blackbody is proportional to its temperature vpeak k T 2 The total emission of a blackbody is proportional to the fourth power of the temperature L k T4 Table 1 Properties of the Earth and Moon Tilt of MoonEarth plane Table 2 Properties of the Planets Planet Distance Period Mass Density Temp C Rotation Tilt AU yr Ma water minmax time Mercury 039 024 0056 54 170430 58d 7 Venus 072 061 082 42 472 243d 178 Earth 10 10 10 555 5050 24h 23 Moon 0012 335 170130 29d 6 Mars 15 19 011 33 14020 24h 37m 24 Jupiter 52 119 318 134 130 9h 50m 1 Saturn 95 294 95 069 180 10h 39m 2 Uranus 192 84 145 129 220 17h 14m 98 Neptune 301 165 172 166 216 16h 03m 2 Table 3 Planetary Atmospheres Object Atmosphere Table 4 Some Atomic Weights Mercury None Element Atomic Weight Venus Thick CO2 Hydrogen H 1 Earth Thick N2 02 trace CO2 Helium He 4 Mars Thin 002 Carbon C 12 Jovian Very thick Nitrogen N 14 planets H He CH4 NH3 Oxygen O 16 Titan Thick CH4 NH3