# ASTR 206 Exam 1

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1. Geocentric Model
Earth is at the center of the solar system.
• Old Theory: Planets orbit around a point called an epicycle, and that the epicycle orbits the earth in an orbit called a deferent. Theorized by the ptolemaic system to explain why the planets appeared to travel east and then travel west briefly.
• In reality, retrograde motion occurs because when earth passes these planets due to its faster orbit, the planets appear to move backwards from Earth's point of view
3. Heliocentric Model
The correct model of the solar system. It states that the sun is at the center of the solar system.
4. Sidereel Period
The time (in earth years) that it takes for a planet to orbit the sun once
5. Inferior/Superior Planets
• -Inferior Planets: Planets inside of Earth's orbit (Mercury and Venus)
• -Superior Planets: Planets outside of Earths orbit (Mars, Jupiter, Saturn, Uranus, and Neptune)
6. Eccentricity
• A measure of how elliptical a planet's orbit is. 0 is a perfect circle and 1 is a straight line. maximum orbit eccentricity is .99.
7. Planetary Configurations
• -Opposition: When a superior planet behind the earth when looking from the sun. To the earth observer, it is at its highest point at midnight.
• -Conjunction: When a superior planet is behind the sun as seen from earth. It can only be seen during the day and is at its furthest point from earth.
• -Inferior Conjunction: When an inferior planet is in between the earth and the sun.
• -Superior Conjunction: When the sun is between an inferior planet and the earth. The planet is at its furthest point from earth.
8. Kepler's Laws
• -1st: The orbits of the planets are elliptical
• -2nd: A planet's speed varies as it moves around its orbit
• -3rd: The orbital period of a planet is related to the size of its orbit.
• P^2=ka^3 where P is a planets sidereal period in years and a is the planets semimajor axis in AU and k is the constant for the body in which the object is orbiting around.
9. Astronomical Unit
• 1 AU is the average distance between the earth and the sun. It is used as a reference to measure distances in our solar system.
• -1 AU: 1.5X10^8 km
10. The Elliptical Orbit of Planets
• -Perihelion: When a planet is at the closest point to the sun in its orbit. At perihelion, a planet is traveling its fastest speed.
• -Aphelion: When a planet is at its furthest point from the sun in its orbit. Here it is traveling at its slowest orbital speed.
• -Semimajor axis: The diameter of an elliptical orbit from end to end on the longest part of the ellipse.

11. Newton's Law of Universal Gravitation
• -Force of gravity= G (m1*m2/r^2)
• -G: Gravitational constant=
• 6.67x10^-11 Nm^2/kg^2
• -m1 and m2: Mass of each of the two objects in question
• -r: Distance between the centers of the two objects
• -The larger the mass of an object, the greater its gravitational pull. This is a linear relationship.
• -The further away an object is from another, the less its gravitational pull is by distance squared. This is an exponential relationship
12. Hohmann Transfer Orbit
• An elliptical orbit that transfers an object from one circular orbit, to another circular orbit
13. Langrange Points
• -A point between two large objects where gravitational pull from the two cancel each other out and an object that resides in this point can remain stationary.
• -Asteroids that are in langrange points are known as "Trojan Asteroids".
14. Yarkovsky Effect
Photons of light from the sun can alter the path that asteroids take by adding thermal energy, which can turn into kinetic energy. Its effect is small but since asteroids travel over long distances, a slight change in angle can have a drastic effect.
15. Revolutions in Planetary Science
• -Greek Philosophy:Geocentric Model. Observations made with the naked eye
• -Copernican Revolution: Began with Copernicus, heliocentric model, observations with telescopes possible. Galileo
• -Space Age: Began in 1960's with the launch of spacecraft into space for direct observation.
16. Important Astronomers Throughout History
• -Plato: Observed celestial bodies and inferred that the earth is at the center of the universe
• -Ptolemy: Introduced the concept of epicycles
• -Copernicus: Introduced the heliocentric model
• -Tycho Brahe: Observed a supernova, inferred that planets and stars are not constant. Best naked eye observer
• -Galileo: Used telescopes, found Jupiter's moons, craters and mountains on moon, tower of Pisa experiment, ruled out geocentric model by observing Venus
• -Kepler: Proposed elliptical orbits, came up with Kepler's laws
• -Newton: Universal laws of gravity, physics
17. Wavelength
• v=(lambda)W
• v= Velocity of wave
• (lambda)= Wavelength
• W= Frequency
18. Wave Terminology
• -Wavelegth: Distance between crests
• -Amplitude: Height of crest
• -Frequency: number of crests per second
• -Velocity: Speed/direction of wave
• -Interference: Waves add when they collide. Can be constructive or destructive
• -Diffraction: Waves bend going around corners
• -Doppler Effect: Waves compress of expand due to moving source. Useful to determine speed of wave emitters.
19. Visible Light Spectrum
• -Blue light has a shorter wavelength (more energy) than red.
• -Light has the same property as gravity where as distance increases, intensity decreases by the square of the distance value
• -I=Isource(Rsource/r)^2
• -Isource: Intensity at source
• -r: location where we want to know intensity
• -The higher the temp, the shorter the peak wavelength (hot things red, hotter things blue)
20. Wein's Law
lambda max (peak wavelength)= 0.0029 Km/T
21. Index of Refraction
The rate of refraction of light traveling through a medium. It is calculated by dividing the speed of light in a vacuum by the speed of light through the given medium
22. Using Spectroscopy to Identify
• -Lines in the spectrum give the composition of the body
• -Shape of spectrum line gives the temperature of the body
23. Orrin of Light
• -Everything that's heated emits electromagnetic radiation (glows)
• -Wavelength of the light (color) depends on temperature
• -Every atom and molecule emits or absorbs light at a specific wavelength (can serve to fingerprint the object and see what element it is made of)
• -This is because of transitions in electron shells
• -A hypothetical object that emits its own radiation at all wavelengths
• -It's peak wavelength is determined by its temperature
• -Blackbodies absorb radiation that is edited to them
• -Finding peak wavelength:  F= (Stefan-Boltzmann constant) T^4
• F is peak wavelength, T is temperature in kelvin
25. Solar System Age
Age of solar system is determined by radioactive dating meteorites, specifically carbonaceous chondrites, which are a small class of stony meteorites that contain high levels of organic compounds, who's presence indicates that the object has not been heated significantly, indicating that they have not changed since universe formed.
Half life, you already know this. But you didn't know the solar system is 4.56 Billion years old
27. Solar System Formation
Our solar system is made from the solar nebula. Hydrogen and helium float around in space in clouds. These clouds rotate very slowly. As a common center of mass forms, the gas is attracted inwards towards the center. The center heats up as pressure increases until thermonuclear fusion occurs, and a star is born. As more of the cloud is sucked in, it picks up speed in the direction it was spinning, much like a figure skater who pulls their arms in. Centrifugal force turns this rotating mass into a disk, or the PROTOPLANETARY DISK. This disk is the solar system.
28. Solar System Formation Part 2
• The Protoplanetary disk is the reason that the planets all rotate on a single plane and in the same direction.
• -To Explain placement of terrestrial planets and jovian planets, you can use condensation. Iron and nickel (terrestrial planets) condense at high temperatures, allowing them to be close to the sun. Hydrogen and helium have low condensation temperatures, so they have to be further from the sun to condense
29. Internal Structure of Planets
• -Terrestrial planets have a metallic core, rocky mantel, and a crust. The proportions of each differ for each planet.
• -Jovian planet interiors have the same composition but with each in a different state of matter
30. Volcanoes
• To have an active volcano, the planet requires heat.
• -Larger planets cool more slowly.
• -Heat from the interior is released through the surface
• -Larger terrestrial planets are geological active for longer
31. Impact Cratering
• -Planets with many impact craters have dormant geological systems
• -Number of impact craters can be used to determine the age of a surface
• -Usually smaller bodies have more impact craters because their geological systems die quicker
32. Atmosphere
• To have an atmosphere, the planet must have gas, be cool enough to not escape, and must have a large enough mass to have a gravitational pull to keep the gas there.
• -Big cool planets are the most likely to have an atmosphere
33. Magnetic Fields
• -Most planets in our solar system have a magnetic field
• -To have a magnetic field, the planet must metals like iron in the liquid (molten) state and be moving
• -Jovian planets, which have stronger magnetic fields, have liquid metallic hydrogen or ionized water at their cores
34. The Sun
• -Most massive object in the solar system
• -Formed at the same time as the planets, all from the same material (in the same protoplanetary disk)
• -Thermonuclear fusion keeps the sun alive, it is the energy source of the sun
35. Solar Wind
• -The solar 'cornea', or the sun's outer atmosphere, is continually expanding and continues off into space.
• -Solar wind is a plasma, in the 4th state of matter
36. Asteroid/Kuiper Belt
• -Asteroid belt is between Mars and Jupiter (terrestrial and jovian boundary)
• -Kuiper belt is beyond the orbit of Neptune (the last planet). Pluto is considered a large Kuiper Belt Object
37. Zodiacal Light
A ring of dust around the sun, likely from asteroids in the asteroid belt or comets
38. Heliosphere
A Cavern that houses our solar system carved out of interstellar gas by solar wind
 Author: tigre671 ID: 296212 Card Set: ASTR 206 Exam 1 Updated: 2015-02-19 05:40:34 Tags: ASTR 206 Exam1 Folders: Description: Study guide for ASTR 206 Exam 1 Show Answers: