The bright star Antares embedded in dust and gases

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Through the course of history there have been many theories about the solar system
Early Greeks thought the Earth was the center of the solar system, with the stars, sun and moon revolving around the
Earth – the Geocentric Model
In 1543, a scientist proposed that the sun was the center of the solar system and the planets revolved around it – the Heliocentric Model

 Modern astronomers believe that the sun and planets condensed out of a nebula or large cloud of gas and dust.
 This idea is named the Nebular Hypothesis . It was first presented by the German philosopher
Immanuel Kant in the late 1700’s.
 Such clouds have been observed around stars other than our sun (e.g., Beta Pictoris)

Our solar system began as a rotating gas cloud or nebula that collapsed toward its center under the influence of gravity.
The condensing and contracting caused the cloud to begin to rotate, as it rotated the center became dense and the temperature reached about 10 million K
A condensation formed at the center, which is called a protostar.
The extremely high temperatures allowed for a process called nuclear fusion to occur
A flattened disk of matter surrounded the protostar, which began to shine and become a star, our sun.

The rising temperature from the sun removed the gas from the inner regions, leaving dust and larger debris
•Inner planets formed from solid debris
•Outer planets retained original gases
Planets established dominance in their regions of the solar system.
After almost all of the remaining gas, dust, and small debris was collected by the larger objects, the solar system took on the form we recognize today.

•We can look at young star systems developing today.
•The planets orbiting these stars are formed from the surrounding disks of gas and dust, called protoplanetary disks or proplyds.
Proplyd in the Orion
Nebula

5.
6.
7.
8.
1.
2.
3.
4.
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune http://www2.jpl.nasa.gov/galileo/sepo/education/nav/ss2.gif

Common Properties of
Planet Orbits in Our
Solar System
As viewed from above, all of the planets orbit the Sun in a counterclockwise direction.
The planets orbit in nearly the same plane (ecliptic). All planets except Pluto have an orbital inclination of less than
7 °.

http://www.nineplanets.org/overview.html

http://www.nineplanets.org/overview.html

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Pluto’s orbit, or plane of revolution, is tilted by 17 ° to the general solar system orbits
(ecliptic)
Pluto can also cut across Neptune’s orbit (but they can never collide)

 Plane of the Ecliptic: The orbits of the planets are mostly in the same plane.
 This plane is called the ecliptic and is defined by the plane of the earth’s orbit.
 The exception is Pluto, which is tilted quite a bit in comparison to the rest of the planets.
 The ecliptic plane is a remnant of the original, rotating nebular disk that formed the sun and planets

 Directions of Motion: The planets orbit in a counterclockwise direction around the sun
(when looking down upon the solar system from the sun’s north pole).
 All the planets, except for Venus, Uranus, and Pluto, rotate in the same direction as their orbits.

 The planets nearest to the Sun (Mercury,
Venus, Earth, and Mars) are relatively close together, while those farther away
(Jupiter, Saturn, Uranus, and Neptune) are more spread out.
 Most of the planets are in nearly circular orbits.

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The astronomical unit
(AU) is useful in measuring distances in the solar system
One AU equals the average earth-to-sun distance of 93 million miles
AU distances allow direct comparison to the earth which is equal to 1.0
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Distance in AU
0.4
0.7
1.0
1.5
5.2
9.5
19.2
30
39.5

Distance in AU (Earth = 1)
30
25
20
40
35
15
10
5
0
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

 Mercury 88 days
 Venus 224.7 days
 Earth 365.25 days
 Mars 1.88 years
 Jupiter 11.86 years
 Saturn 29.5 years
 Uranus 84 years
 Neptune 164.79 years
 Pluto 248.32 years
*Earth days and years

Revolution Periods (Earth = 1)
250
200
150
100
50
0
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Diameter (Earth = 1)
0.38
0.95
1.0
0.53
11.21
9.45
4.01
3.88
0.18

Diameter (Earth = 1)
12
10
8
6
4
2
0
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Mass (Earth = 1)
0.06
0.81
1.0
0.11
317.94
95.18
14.53
17.14
0.002

Mass (Earth = 1)
350
300
250
200
150
100
50
0
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
3
Average Density (kg/m
3
)
5430
5250
5520
3950
1330
690
1290
1640
2030

Density (Earth = 1)
0,8
0,7
0,6
0,5
1
0,9
0,4
0,3
0,2
0,1
0
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Planet Days (Earth

1)
58.6462
243.0187
0.99727
1.025957
0.41354
0.42637
0.71806
0.67125
6.3872

Rotational Period (Earth = 1)
250
200
150
100
50
0
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Ave Temp ( °F)
354 °
867 °
45 °
-81 °
-186 °
-202 °
-337 °
-364 °
-380 °

Average Temperature (Earth = 1)
20,00
15,00
10,00
5,00
0,00
Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
-5,00
-10,00

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In mass, the sun represent 99% of the solar system
The smallest planet, Mercury, has a diameter of 3031 mi
Pluto, the previous smallest planet, has a diameter of 1457 mi
The largest planet, Jupiter, has a diameter of 88,700 mi
Earth = 7926 mi
Ganymede, the largest moon of
Jupiter, is larger than Mercury, yet
Ganymede is not considered a planet because it revolves around
Jupiter http://www.nineplanets.org/datamax.html

Two Basic Groups of Planets
TERRESTRIAL (earth-like)
Small size, low Mass
Higher density
Mostly rock
Mercury, Venus, Earth, Mars
JOVIAN (Jupiter-like)
Large size, massive
Low density
Mostly gas
Jupiter, Saturn, Uranus,
Neptune

 Terrestrial or Rocky planets —Composed of rock and metal:
Mercury, Venus,
Earth, Mars
 Jovian or Gas planets —Composed primarily of the gases hydrogen and helium:
Jupiter, Saturn,
Uranus, Neptune

 Small Planets —
Diameters less than
13,000 km: Mercury,
Venus, Earth, Mars
 Giant Planets (Gas
Giants) —Diameters greater than 48,000 km: Jupiter, Saturn,
Uranus, Neptune

 Inner Planets —
Mercury, Venus,
Earth, Mars
 Outer Planets —
Jupiter, Saturn,
Uranus, Neptune

 Inferior —Closer to the sun than earth:
Mercury and Venus
 Superior —Farther from the sun than earth: Mars, Jupiter,
Saturn, Uranus,
Neptune

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Classical —Known since prehistoric times, visible to the unaided eye:
Mercury, Venus,
Mars, Jupiter, Saturn
Modern —Discovered in modern times, visible only with telescopes: Uranus,
Neptune, (Pluto)

Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Rocky or
Gas?
Small or
Giant?
Inner or
Outer?
G
G
G
G
?
R
R
R
R
S
S
S
S
G
G
G
G
S
I
I
I
I
O
O
O
O
O
S
S
S
S
S
I
I
N/A
S
Inferior or
Superior?
Classical or
Modern?
C
C
?
C
C
C
M
M
M

 Planets:
 Mercury
 Venus
 Earth
 Mars
 Ceres (dwarf)
 Jupiter
 Saturn
 Uranus
 Neptune
 Pluto (dwarf)
 Eris (dwarf)
 Makemake (dwarf)
Eris
•Two Categories: Planets and Dwarf Planets
(dwarfs beyond Neptune are “Plutoids”)
•Today’s astronomers recognize only 8 planets

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If the sun were an orange, the earth would be a grain of sand thirty feet away.
Jupiter would be a cherry pit located one block from the sun.
Saturn would be another cherry pit located one block from Jupiter.
Pluto would be a grain of sand 10 blocks from the sun.
The nearest star to our sun (Alpha Centauri) would be represented as another orange 2000 miles from the sun.

Jupiter from Fantasia
(Disney)
 The planets have been given the Roman names of gods from ancient Greece.
Roman
 Mercury, Venus, Mars, Jupiter, Saturn
Greek
 Hermes, Aphrodite, Ares, Zeus, Kronos
The modern planets, Uranus, Neptune, and
Pluto, are also Roman gods