Planetary Motion Flashcards
Kepler’s 2nd Law
Sweep equal areas in equal time I.e. Velocity increases near focus and decreases away from focus due to conservation of angular momentum
Kepler’s 1st Law
The orbit of a planet/body around the sun/foci is and ellipse with the sun/body and the foci
Kepler’s 3rd Law
The square of the orbital period is proportional to the cube of the semi-major axis (p^2 = a^3)
Orbital periods?
Sidereal period (star-relative) - 350 degrees one complete orbital revolution of a satellite relative to a star and body it is orbiting. Moon and sum are in line e.g. Moon 27.3 days Synodic period (sun-relative) - star, moon and earth are inline. Sidereal period (360 degrees) + moon has to move from m2 to m3 to be I'm line with sun
Addition of diagrams
Methods of orbital forcing?
Eccentricity (stretch) - the orbit is changed from a circular to an elliptical orbit every 100,000 years. This process is driven by the orbits of other planets in the solar system.
Obliquely (tilt) - the inclination of the planet (22.1 - 24.5 degrees)
Precession (wobble) - describes the gyroscopic motion of the earths axis generated by the sun and moon. The orientation of the earths axis with respect to the fixed stars (23,000 years)
How are relative distances measured in the solar system?
Inner planets - maximum elongation gives relative distances to the sun in AU. Right angled triangle. 1 AU from earth to sun
Outer planets - oppositions and quadrate gives relative distances to the sun. Second quadrate triangle (superior planet and earth in position two)
Addition of images
Calculating the period of a synodic planet?
Inferior planet - 1/P (sidereal orbit) = 1/E (earth orbit) + 1/S (synodic orbit)
Superior planet - 1/P (sidereal orbit) = 1/E (earth orbit) - 1/S (synodic orbit)
How do tidal forces effect bodies in the solar system?
Look at diagrams in the booklet
Satellite, rings on planets, planets & moons
How do tidal torques effect a body?
Effect on spin - small bodies get tidally despun rapidly compared to larger bodies that despin slower
Effect on body - important source of internal heat (e.g. Early moon and present Io) and can also break bodied up (Roche Limit)
How does resonance effect comets?
Asteroids have scattered irregular elliptical orbits and show no distribution pattern with distance from the sun.
Kidwood groups - clusters of asteroids closely related to orbital resonance with Jupiter
Asteroids residing In gaps are eventually expelled into chaotic highly eccentric orbits
What happens when asteroids are injected into jupiters orbit?
Chaos - asteroids are injected into jupiters 3:1 resonance
Regular interactions with Jupiter induce chaotic oscillations. After 1ma eccentricity is high enough to be earth-crossing
Nature, origin and evolution of Saturn ring?
Nature
Voyager 1 imaged
Rings are compositional Ice and methane on the outer rings however B and C have a complicated UV spectra
A & B ring - separated by the Cassini Division
C & D ring - broad faint structured interior (not visible from earth)
E ring - volcanic ejecta
F & G ring - discovered by Prometheus and pandora
Formations
1) Roche limit - break up and capture of comets by gravitational forces (tidal torque)
2) Synchronous radius - remains of primordial circumplanetary disc during the accretion of a planet
Evolution
Low velocity collisions causes rings to flattern and spread at a rate proportional to the diameter
Orbital damping - out of plane orbits are damped and particles collapse into a place normal to spin axis
Radical diffusion - inner particles move faster than other particles meaning rings spread out until particle number density is low enough to prevent collisions
Large objects e.g. Satellites cause sinks (deflections)
What is the synchronous radius?
The orbital radius in which a satellite orbits with the same angular velocity as planetary rotation
Tidal torques push particles outwards when orbits are being Rs (when equal create ring). However, possible stabilisation as electromagnetic forces may be greater than gravitational forces acting on the particles
Moons of Saturn and there effects due to tidal forces?
Janus & Epimetius
Every 4 months the moons come with 5 degrees of each other but does not collide instead the motion is reversed and paths are switched
Both films trend In the same direction. The inner moon moves faster as the inner moon catches up with the outer and switches places with the inner accelerates and outer decelerates. Known as the horse shoe effect
