attention: exam this friday !! * exam covers the reading chapters 1-6 * sample questions on the web....
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ATTENTION:
EXAM this FRIDAY !! * Exam covers the reading Chapters 1-6* Sample questions on the web.
* 50 m.p. questions
HW – due Wednesday midnight
Distances between planets?
all orbital data, e.g. eccentricity and inclinations …. (Brahe, Kepler)
1 AU = 149.6 × 106 km
But, all in terms of the a = 1 of earth
How big is an AU?Halley’s idea to accurately find the scale factor:The transit of Venus
First accurate measurement1761 and 1769
1 AU = 149.6 × 106 km
Accurate positionsNew clocks!
aE
aM
We know the orbits of (say) Earth and Mars
We also know where on their orbits they'll be be at any given time
aE
aM
We know the orbits of (say) Earth and Mars
We also know where on their orbits they'll be be at any given time
d
So we can use analytic geometry to figure how far away a planet is from us at any given time
Planetary Diameters
Mercury .38Venus .95Earth 1Mars .53
Jupiter 11.2Saturn 9.4Uranus 4.0Neptune 3.9
km756,12eD
eDD /
Jovian
Terrestrial
Earth’s Mass: measure acceleration of gravity at surface g = 9.80 m/s2
2e
e
r
GMg
-2211 kg m N 106742.6 G
m 1038.6 6rkg 1098.5 24eM
Other planets ? …….
(from experiments here on earth)
Masses of the Planets ?
32
2
)(
4a
MmGP
sec mkg
-2211 kg m N 106742.6 G(from experiments here on earth)
Masses of the Planets ?
When something very small (m) orbits something very big (M)you can say to very good accuracy:
MMm
000,000,000,000,000,000,000,980,5
000,000,000,000,000,000,000,000,000,990,1
000,000,000,000,000,000,000,980,005,990,1
Masses of the Planets ?
32
2 4a
GMP
whence
2
324
P
a
GM
mass of a planet need something smallto orbit it!
Mercury 0Venus 0Earth 1Mars 2Jupiter 63Saturn 61Uranus 27Neptune 13
moons
Satellites!
Planetary Masses
Mercury .055Venus .82Earth 1Mars .11
Jupiter 318Saturn 95Uranus 15Neptune 17
kg1098.5 24eM
eMM /
Jovian
Terrestrial
The Terrestrial Planets
Mercury Venus Earth Mars
Small and rocky
700 K100 K
740 K 290 K 220 K
5.4 g/cc 5.2 g/cc 5.5 g/cc 3.9 g/cc
The Jovian Planets
Jupiter Saturn Uranus Neptune
Big and gassy/icy
125 K 95 K 60 K 60 K
1.3 g/cc 0.7 g/cc 1.3 g/cc 1.6 g/cc
Gas giants Ice giants
Some things to note:
• Planets and other stuff orbit sun in a plane.• All planets orbit ccw in near circular orbits.• Most planets (Venus and Uranus) rotate ccw.• Most big moons do the same thing.• Two very different types of planets.
The most famous TNO: Pluto!
Single frame NAVCAM image of Comet 67P/C-G taken on 11 September 2015, 319 km from the nucleus. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
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