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The Planet Earth

© Copyright 2000, Jim Loy

The Earth (see the spacecraft Galileo photo on the left) is the only planet known to have life. Its distance from the sun is in what I call the Baby Bear zone, not too hot and not too cold, but just right. The Earth's atmosphere is rich in oxygen (21% oxygen, 78% nitrogen, 1% argon and other gasses) which makes animal life possible. This atmosphere is the result of plants, which have converted a carbon dioxide dominated atmosphere into the atmosphere that we have now.

The Earth is a terrestrial (rocky) planet, as are Mercury, Venus, and Mars. It is the densest planet, being mostly molten iron. The core is solid iron, surrounded by molten iron. The crust is rocky. The Earth is a double planet (Earth+Moon). Besides the Earth and Moon, tiny Pluto has a moon that is as large, compared to the planet's size. The Earth has large oceans and continents, Jupiter's moon Europa seems to have a world wide ocean under the ice. The continents seem to move around due to convection, plate tectonics. No other planet seems to do this. The Earth has a relatively strong magnetic field (see Magnets).

The Earth's orbit is very nearly circular. The tilt of the Earth's spin axis gives us The Seasons.

Here are some data about the Earth:

• Distance from the sun:
  • perihelion (closest): 91.4 million miles
  • semi-major axis (mean distance): 1 AU (astronomical units, Earth=1) or 150 million km (93 million miles)
  • aphelion (farthest): 94.5 million miles
• Orbit:
  • Period of revolution around the sun: 365.25636 days
  • Orbital eccentricity (circle=0): 0.016710
  • Orbital inclination (tilt): 0 degrees
  • Velocity: 18.50 miles per second
• Rotation:
  • Synodic (solar) day 24 hours
  • Siderial day: 23 hr 56 min 4.1 sec
  • Rotational inclination (tilt): 23 degrees 26' 21.412"
• Mass (Earth=1): 1 (5.9742 x 10^24 kg)
• Mean radius: 3960 miles (equator: 6378.136 km (3963 miles), poles: 3950 miles)
• Mean density (Earth=1): 1
• Gravity at surface (Earth=1): 1
• Mean Temperature at surface: 59 degrees Fahrenheit
• Moons: 1 (The Moon)

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