Planets

c. Students know how to use astronomical units and light years as measures of distances between the Sun, stars, and Earth.

d. Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own light.

e. Students know the appearance, general composition, relative position and size, and motion of objects in the solar system, including planets, planetary satellites, comets, and asteroids originally thought to be stars are now known to be distant galaxies.

The Nine planets are currently known in the solar system:

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

They vary greatly in size and appearance.

For example, the mass of Earth is 6 × 10²⁴ kg and the radius is 6.4 × 10⁶ m.
Jupiter has more than 300 times the mass of Earth, and the radius is ten times larger.

The planets are very different in their

Distance to the Sun
Period of Reolution about the Sun
Period of rotation about their own axis
Tilt of their axis
Composition
Appearance.

The composition of the planets falls into two main categories:

The inner planets (Mercury, Venus, Earth, and Mars) tend to be relatively small and are composed primarily of rock.
The outer planets (Jupiter, Saturn, Uranus, and Neptune) are generally much larger and are composed primarily of gas
Pluto is composed primarily of rock and is the smallest planet in the solar system

Their size varies greatly:

All the planets are much smaller than the Sun.

Spectral Type of Star	G2 V
Age	4.5 billion years
Mean Distance to Earth	150 million km
Rotation Period (at equator)	26.8 days
Rotation Period (at poles)	36 days
Diameter	1.4 million km
Mass	1.99 x 1030 kilograms
Composition (number of atoms)	92.1% Hydrogen, 7.8% Helium
Temperature (photosphere)	5,780 K
Energy Output (luminosity)	3.83 x 1033 ergs/sec

Namesake	Messenger of the Roman Gods
Mean Distance from Sun	57.9 million km
Orbital Period	88 days
Orbital Eccentricity	0.206
Orbital Inclination to Ecliptic	7˚
Inclination of Equator to Orbit	0˚
Rotational Period	58 d 39 m
Diameter	4,879 km
Mass	0.06 of Earth’s
Density	5.43 g/cm3
Gravity	0.38 of Earth’s
Atmosphere (primary components)	Oxygen, Sodium, Helium

Namesake Roman Goddess of Love and Beauty

Mean Distance from Sun 108.2 million km

Orbital Period 224.695 days

Orbital Eccentricity 0.007

Orbital Inclination to Ecliptic 3.4˚

Inclination of Equator to Orbit 177.3˚

Rotational Period 243 d (retrograde)

Diameter 12,100 km

Mass 0.82 of Earth’s

Density 5.24 g/cm³

Gravity 0.91 of Earth’s

Atmosphere (primary component) Carbon Dioxide

Mean Temperature at Solid Surface 457 ˚C

Number of Moons 0 Number of Rings 0

Significant Dates
1962	Mariner 2 (U.S.) flew by Venus; verified high temperatures.
1970	Venera 7 (U.S.S.R.) soft-landed on Venus.
1972	Venera 8 (U.S.S.R.) landed on Venus; transmitted nearly an hour of data.
1974	Mariner 10 (U.S.), bound for Mercury, flew by Venus; tracked global
	atmospheric circulation with visible and ultraviolet imagery.
1975	Venera 9 (U.S.S.R.) sent the first surface pictures of Venus via its
	orbiter.
1978	Pioneer Venus Orbiter (U.S.) radar mapped Venus; Pioneer Venus
	Multiprobe (U.S.) dropped four probes through Venusian clouds.
1983	Venera 15 and 16 (U.S.S.R.) provided high-resolution mapping radar
	and atmospheric analyses.
1984	Vega 1 and 2 (U.S.S.R.) dropped off landers and balloon probes at
	Venus while en route to Halley’s comet.
1989	Magellan (U.S.) was launched toward Venus.
1990–94	Magellan (U.S.) mapped 98 percent of the surface of Venus using

Mean Distance from Sun	149,597,890 km
	(1 astronomical unit, or AU)
Orbital Period	365.26 days
Orbital Eccentricity	0.0167
Orbital Inclination to Ecliptic	0.00005°
Inclination of Equator to Orbit	23.45°
Rotational Period	23 h 56 m
Diameter	12,756 km
Mass	5.9742 x 1027 g
Density	5.515 g/cm3
Gravity	980 cm/s2