Transcript Astronomy 103

Solar System and Earth
30 Sep: Solar System and Earth
05 Oct: Earth-Moon
07 Oct: Terrestrial Planets
12 Oct: Mars Close-up
14 Oct: Jovian Planets
19 Oct: Asteroids, comets, etc
21 Oct: Planet formation
26 Oct: Extra-Solar Planets
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Solar System
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9 planets going around Sun
Other than that the solar system is
practically empty. Most of that is
near perfect vacuum.
Large: about 12 billion km across
This image shows the sun and 9 planets
approximately to scale.
The order of these bodies are Sun, Mercury, Venus,
Earth, Mars, Jupiter , Saturn, Uranus, Neptune, Pluto
Average Distance from Sun (AU)
Mercury
0.39
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
0.72
1.00= about
1.52
5.20
9.54
19.18
30.06
39.5
1.5 10 m
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Scientific Notation
Express numbers in a general form,
A × 10n,
which is convenient for both large and
small numbers.
1.5 10 m  150 m
2
1.5 10 m  1,500 m
3
1.5 10 4 m  15,000 m
...
1.5 10 m  150,000,000,000 m
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Question
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If something happens at Sun (e.g.
Explosion), we know the event
(a) immediately
(b) about 3 sec after
(c) about 8 min after
Answer
(c) About 8 min after
Note: in only one second,
light can circumnavigate the Earth
more than seven times
Solar System
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Orbits are almost in a plane (within a
few degrees) and close to circular.
Mercury and Pluto are most eccentric
and have highest inclination.
Masses
of 9 Planets
Earth
?
Jupiter
Sun:
332,946 (Earth Mass)
Much heavier!!
Saturn
Pluto
Neptune
Uranus
Mars
Earth
Venus
Mercury
The nine planets are often further classified as follows
Terrestrial Planets (inner 4 planets)
Mercury, Venus, Earth and Mars
small, high density, low mass, rocky
little or no atmosphere
Jovian Planets (next 4)
Jupiter, Saturn, Uranus and Neptune
Massive, low density, gaseous
probably no solid surface
Pluto: ball of ice and rock,
not much the larger than the largest asteroids
Mars
Terrestrial
Rocky, no atmosphere
Neptune
Jovian
Gaseous, no solid surface
Terrestrial
Small, high density
Jovian
Massive, low density
Pluto
Composition
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Two ways to find out what the
planets are made of
(1) Go There! (Mars and Venus)
(2) Spectroscopy – either from Earth
or from a spacecraft passing by
or in the orbit around the planet
Compositions
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Terrestrial planets are rocky
- silicon, iron compounds
Jovian planets are gaseous –
hydrogen, helium, methane,
ammonia, carbon monoxide,
carbon dioxide, water vapor etc.
Water on Mars!
greeting card from my hockey mate at Jerusalem
Other Solar Stuff
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Moons: small bodies that orbit
Planets
Asteroids: small bodies that orbit
Sun.
Comets: dirty snowballs in highly
elliptical orbits around Sun
Asteroids
Most of them are between Mars and
Jupiter: Asteroid Belt
 The composition is similar to that of
terrestrial planets (rocks and metals)
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Comets (Ices, rocks)
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Comets have ices covering them, and
these vaporize and produce a gas halo
around the comet when it comes close to
Sun.
Kuiper belt comets : from extended wedge
of asteroids beyond the orbit of pluto, 30100AU
Oort cloud comets: from very extended
halo of comets, probably it extends to
100,000AU.
Question
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What is the farthest Planet to the sun?
(a) Mars
(b) Mercury
(c) Earth
(d) Moon
(e) Pluto
Answer
(e) Pluto.
Sometimes Neptune is further, but it
is not a choice.
Question
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Which of these is not a Planet?
(a) Mars
(b) Mercury
(c) Earth
(d) Moon
(e) Pluto
Answer
(d) Moon.
Mars is either a planet or a candy bar,
Mercury is either a planet or a metal,
and Pluto is either a planet or a
cartoon dog. Moon most definitely is
not a planet.
Question
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What is the closest Planet to the Sun?
(a) Mars
(b) Mercury
(c) Earth
(d) Moon
(e) Pluto
Answer
(b) Mercury.
Question
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Which of these takes the least time
to travel around the Sun?
(a) Mars
(b) Mercury
(c) Earth
(d) Moon
(e) Pluto
Answer
(b) Mercury.
Kepler’s Law