Astronomy — The Planet Earth
Earth
- Distance from the Sun: 93,000,000 miles
- Time for one solar circuit: 365.25 days
- Time for one axial rotation: 1 day
- Diameter: 8,000 miles
- Circumference: 25,000 miles
- Orbital speed: 67,000 miles per hour
- Speed of rotation at the equator: 1000 miles per hour
- Total mileage of one solar orbit: 586,920,000 miles
- Earth’s core is:
- Hot (7000 degrees Kelvin)
- Dense (14 gm/cm3)
- Composed of molten nickel and iron
- 3600 miles in diameter
- The four main phases of Earth’s history are:
- Differentiation
- Cratering
- Flooding
- Slow surface evolution
- The Earth, other planets in our solar system, and moons in our solar system formed 4.6 billion years ago. The oldest rocks found on Earth are 3.7 billion years old.
- The Earth’s magnetic field is a result of its rapid rotation and its molten core. This describes the dynamo effect.
- Earth is a good reflector – it reflects 40% of all the sunlight that strikes it.
- The reasons for our seasons are:
- Our elliptic orbit? No! We are actually closer to the Sun during winter than during summer.
- The tilt of Earth’s axis? Yes! We receive the Sun’s rays at a more direct angle during summer.
- Tides:
- Moon’s gravitational pull is stronger on the near side of the Earth than it is on the Earth’s center, thus the rocky surface on the near side bulges up a few centimeters.
- The same effect on ocean waters is much more pronounced and noticeable. There is a bulge on the side away from the Moon also because Moon’s gravity pulls more strongly on Earth’s center than on the far side.
- As the earth rotates, the tidal bulges remain fixed along the Earth-Moon axis.
- At new Moon and full Moon, the Sun and Moon combine to produce exaggerated tidal bulges (spring tides). At first and third quarter moon, the Sun and Moon pull at right angles to each other, producing modest tides (neap tides).
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