THE SUN |

The Sun does not spin or rotate as a solid body. The equator rotates faster than do the polar regions. Different layers inside the Sun also rotate at different rates than the layers immediately above them. This differential rotation is of course only possible because the Sun is a gaseous body (a big ball of gas). Even with the very high estimated pressures at the solar core, the central temperature is high enough to keep the matter in a gaseous state.

Models and measurements from helioseismology lead us to believe that the Sun is divided internally into 3 different regions. The core (about 20% of the solar diameter) is where the nuclear fusion reactions occur that power the Sun. The radiative zone extends from the core out to a radius of about 70% of the Sun. This region is so dense that we believe it can take up to one million years for the particles of heat and light (photons) generated in the core to work their way through it. The outer 30% of the solar diameter is the convection zone where motions are very turbulent. The top of this zone is the photosphere.

The Sun has a constantly changing magnetic field, which is to believed to be generated at the base of the convection zone by the motions there. This magnetic field, twisted by the differential rotation of the Sun, is believed to produce sunspots on the solar surface together with solar activity such as flares and coronal mass ejections that can be observed with special filters.

The solar atmosphere is divided into a lower atmosphere (the chromosphere) and the outer atmosphere (the corona). The corona extends out through the solar system as what we term the solar wind. The coronal temperature near the Sun is about 2 million degrees (K).

*APPROXIMATE SOLAR PARAMETERS*

Diameter = 1,400,000 km ( = 109 times the Earth's diameter )

Mass = 2 x 10^{30} kg ( 330,000 Earth masses )

Volume = 1.4 x 10^{27} m^{3} ( 1.3 million times Earth's volume)

Average density = 1400 kg m^{-3} ( 1.4 times the density of water)

Surface gravity = 270 m s^{-2} ( 27 x Earth's gravity )

Surface temperature = 6,000 K

Surface pressure = 1 kPa ( 1/100 Earth's sea level pressure of 101 kPa)

Core temperature = 15 million K ( estimated from models )

Core pressure = 2.3 x 10^{13} kPa

Core density = 150,000 kg m^{-3}

Average rotation rate = once every 27 days ( varies with latitude )

Luminosity = 3.8 x 10^{26} W

Fuel consumption = 5 millions tons of hydrogen per second

Fuel cycle - nuclear fusion ( 4 H atoms fuse to form a He atom )

Sunspot cycle period = 11 years

Age = 5,000 million years ( estimated from models )

MERCURY |

The surface of Mercury is covered by craters, and one large impact feature, named Caloris, is spread over 1300 km and has 'weird' terrain at its antipodal point. Of the four terrestrial planets (Mercury, Venus, Earth and Mars), only Mercury and the Earth have a global magnetic field.

*ORBITAL PARAMETERS FOR MERCURY*

Mean distance from the Sun = 57.9 million km (0.387 AU)

Orbital eccentricity = 0.206

Orbital inclination to the ecliptic = 7.01 degrees

Orbital period = 87.969 days

Mean orbital velocity = 47.9 km/sec

Advance in perihelion = 10 minutes of arc per century

*PLANETARY PARAMETERS*

Mass = 3.30 x 10^{23} kg

Mean radius = 2438 km

Mean density = 5430 kg/m^{3}

Gravity = 3.7 m/sec^{2} = 0.38 g (g = Earth gravity)

Escape velocity = 4.25 km/sec

Synodic rotation period (mean) = 115.9 days

Sidereal rotation period = 58.6 days (= 2/3 of orbital period)

Surface temperature range = 100 - 700 K

Inclination of equator to orbit = 1^{o} (approx)

Mean solar constant = 9940 W/m^{2}

VENUS |

*ORBITAL PARAMETERS FOR VENUS*

Mean distance from the Sun = 108.2 million km (0.723 AU)

Orbital eccentricity = 0.007

Orbital inclination to the ecliptic = 3.39 degrees

Orbital period = 224.70 days

Mean orbital velocity = 35.0 km/sec

*PLANETARY PARAMETERS*

Mass = 4.87 x 10^{24} kg

Mean radius = 6052 km

Mean density = 5243 kg/m^{3}

Gravity = 8.9 m/sec^{2} = 0.91 g (g = Earth gravity)

Escape velocity = 10.4 km/sec

Synodic rotation period (mean) = 116.8 days

Sidereal rotation period = 243.0 days (retrograde)

Surface temperature range = 650 - 750 K (estimates)

Inclination of equator to orbit = 177^{o}

Mean solar constant = 2614 W/m^{2}

Surface atmospheric pressure = 9,200 kPa

Surface atmospheric density = 65 kg/m^{3}

EARTH |

*ORBITAL PARAMETERS FOR EARTH*

Mean distance from the Sun = 149.6 million km (1.000 AU)

Orbital eccentricity = 0.017

Orbital inclination to the ecliptic = 0.00 degrees

Orbital period = 365.26 days

Mean orbital velocity = 29.8 km/sec

*PLANETARY PARAMETERS*

Mass = 5.97 x 10^{24} kg

Mean radius = 6371 km

Mean density = 5515 kg/m^{3}

Gravity = 9.8 m/sec^{2} = 1.00 g (g = Earth gravity)

Escape velocity = 11.2 km/sec

Synodic rotation period (mean) = 24.00 hours

Sidereal rotation period = 23.935 hours

Surface temperature range = 180 - 330 K

Inclination of equator to orbit = 23.45^{o} (approx)

Mean solar constant = 1376 W/m^{2}

Surface atmospheric pressure = 101 kPa

Surface atmospheric density = 1.23 kg/m^{3}

MARS |

*ORBITAL PARAMETERS FOR MARS*

Mean distance from the Sun = 227.9 million km (1.52 AU)

Orbital eccentricity = 0.093

Orbital inclination to the ecliptic = 1.85 degrees

Orbital period = 686.98 days

Mean orbital velocity = 24.1 km/sec

*PLANETARY PARAMETERS*

Mass = 6.42 x 10^{23} kg

Mean radius = 3389 km

Mean density = 3933 kg/m^{3}

Gravity = 3.7 m/sec^{2} = 0.38 g (g = Earth gravity)

Escape velocity = 5.0 km/sec

Synodic rotation period (mean) = 24.66 hours

Sidereal rotation period = 24.62 hours

Surface temperature range = 140 - 300 K

Inclination of equator to orbit = 25.19^{o} (approx)

Mean solar constant = 589 W/m^{2}

Surface atmospheric pressure = 0.6 kPa

Surface atmospheric density = 0.016 kg/m^{3}