Transcript Planets & Motions

Next up: Focus on our solar
system
Three motions of Earth are:
– Rotation (spin on the axis)
– Revolution, a.k.a. orbit (around the sun)
– Precession (wobble of the rotation)
Major features of our planets and dwarf planets
Motions of the Earth: Rotation
Causes day & night (Two ways to measure)
Mean solar day (noon to noon) = 24 hours
Sidereal day (360o) = 23 hr, 56 min, 4 sec. Represents the time
required for a star to be in the identical position as the night
before.
Since the sidereal day is approximately 4 min shorter than the mean
solar day, we use the mean solar day to set our calendar.
Astronomers use the sidereal day.
Difference is due to the revolution or orbit of the earth around the
sun.
Sidereal day vs. solar day
360o turn
4 min
difference
Motions of Earth:
Revolution/Orbit
Elliptical orbit (a.k.a. oval!)
Perihelion = closest to sun, occurs about January
3
Aphelion = farthest from sun, occurs about July
4
Ecliptic = Imaginary plane that connects the
orbit of the earth with the celestial sphere.
Celstial Sphere?
Imaginary bubble of the
sky.
Ancient astronomers
thought it was REAL
The Truman show
QuickTime™ and a
decompressor
are needed to see this picture.
Ecliptic
Precession
The earth’s axis currently points at Polaris (North Star)
Eventually will be Vega
Not static! Traces a circle every 26,000 years.
A wobble, like a top.
Effects the seasons, and has been suggested that it relates
to global warming/cooling (alone = inaccurate due to
rate of warming trend).
Planets
• Formed from a nebula (cloud of dust and gas).
Cloud comes together due to gravity.
• Three Categories
– Terrestrial
– Jovian
– Dwarf
The Planets
Terrestrial planets(a.k.a. Inner/Rocky planets)
– Small
– Rocky
– more dense
– close to sun
– no rings
– thin atmosphere
– Mercury,Venus, Earth, Mars
The Planets
Jovian planets (a.k.a. Outer/Gaseous planets)
– Huge
– gas giants = thick atmosphere,
– much less dense (Saturn floats!),
– rings,
– beyond asteroid belt
– Jupiter, Saturn, Uranus, Neptune
The Planets
Dwarf planets
– Ceres, Pluto, Eris
– What is a Dwarf planet?
– Bigger than an asteroid, but not quite big enough.
– Caused astronomers to redefine exactly what a
planet IS.
Poor Pluto!
Planets must:
1. Orbit the sun.
2. Have enough mass to be round.
3. Dominate its orbit.
Pluto doesn’t dominate (dances with Charon)
Ceres doesn’t dominate, not round (asteroid belt)
Eris doesn’t dominate (space junk)
My Very Excellent Mother Just
Served Us Noodles - Terrestrial
Planets
Mercury -smallest inner planet, closest to the sun, no
atmosphere, revolves/orbits quickly, but rotates very
slowly, has the greatest temperature extremes
Venus-2nd planet from the sun, brightest “star” in the sky,
has recently active volcanism and tectonic activity,
“thick” atmosphere consisting of 97% CO2.
My Very Excellent Mother Just
Served Us Noodles - Terrestrial
Planets
Earth is next in line . . .
Mars - Appears reddish through a telescope with
white polar caps, has a very thin atmosphere,
large dust storms with hurricane force winds
(270 km/h) last for weeks; has mountains &
volcanoes, temperatures range from -70oC to
-100oC.
My Very Excellent Mother Just
Served Us Noodles - Jovian
Planets
Jupiter-Huge mass, hydrogen and helium
atmosphere, Great Red Spot, rotates rapidly,
appears banded, 28 moons resembling a small
solar system (Jupiter needed to have been
10X larger to be a star!), has rings
My Very Excellent Mother Just
Served Us Noodles - Jovian
Planets
Saturn- The ringed one! Similar to Jupiter in size,
atmosphere, and structure, winds reach 1500 km/hr,
stormy, 31 moons.
Uranus-rotates “lying down”, has rings
Neptune- rings, active atmosphere, 1, 000+ km/hr winds,
Great Dark Spot, 13 moons, nitrogen and methane
atmosphere, low temps = -200oC.
How big?
How big?
How big?
Looking ahead
First Lab: what we can observe in our sky.
Second lab: Debunking 2012.