ASTR 207 Lecture Notes - Lecture 2: Solar Wind, Giant Planet, Galilean Moons

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Bound orbits
Orbits in which an object goes around another object over and over again.(Gravity bounds object to
object)
Unbound orbit
Paths that bring an object close to another object just once.
Center of Mass
The point at which the two objects would balance if they were somehow connected.
Kinetic Energy
Energy of motion(Ex. planet moving around the sun)
Gravitational Potential Energy
Energy that an object has by virtue of its position in a gravitational field; an object has more gravitational
potential energy when it has a greater distance that it can potentially fall.(Ex. Earth because it would fall
towards the sun if it stopped gravitating).
Orbital Energy
The sum of kinetic and gravitational potential energies.Always stays the same for planets.(Has to do with
conservation of energy)
Gravitational encounter
In which two objects pass near enough so that they can each feel the effects of the other's gravity.Will
change the orbit
Escape Velocity
The speed necessary for an object to completely escape the gravity of a large body such as a moon, star
or planet.(Ex. Earth: 40,000km/hr or 11 km/s)
Tidal Force
A force that occurs when the gravity pulling on one side of an object is larger than that on the other side,
causing the object to stretch.
Tidal Friction
When tidal forces stretch an object, the process creates friction.
Synchronous rotation
When the orbital and rotational period for an object are the same.
The Sun
Largest and brightest object. Total mass in universe is 99.8%Composed of 98% hydrogen and helium, 2%
other elements.
Source of virtually all light in our solar system.
Mercury
Closest to Sun, smallest planet.Composed of rocks and metals.
Zero moons.
Desolate, cratered world with no active volcanoes, no wind, no rain, etc.
Very hot and cold extremes.
Venus
Second planet from the Sun. Composed of rocks and metal. Zero moons.
Nearly same size as Earth. Covered in clouds, which traps all heat making planet extremely hot.
Has mountains, valleys and craters, with signs of past volcanic activity. Spins retrograde. Venus dy longer
than Venus year
Venus
Surface shows past volcanic and tectonic activity, explains lack of craters. Erosion only minor factor due
to thick atmospheres (no rainfall and slow rotation)Is probably still geologically active today.
Earth
Third from the Sun. Composed of rocks and metals. 1 moon. Only planet with actual life.
Mars
Fourth from the Sun, last inner planet.2 small moons.
Large ancient volcanoes, one huge long canyon, polar ice caps make of frozen carbon monoxide (dry
ice).Evidence of past water by Curiosity rover.
Extinct volcanoes and large canyons from tectonic movement. Has largest volcano in SS.
Very thin CO2 atmosphere, means no rain.
Mars
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