EARTH

Is the Earth closer to the sun in winter than in summer in the Northern Hemisphere?
Yes. However, the Earth’s axis, the line around which the planet rotates, is tipped 23.5 degrees with respect to the plane of revolution around the sun.

Does the rotation speed of the Earth vary?
Yes. The rotation speed is at its maximum in late July and early August and at its minimum in April.

The circumference of the Earth:
The Earth is an oblate – a sphere slightly flattened at the poles and bulging at the equator. The distance around the Earth at the equator is 24,902 miles (40,075 kilometers). The distance around the Earth through the poles is 24,860 (40,008 kilometers).

The distance from the Earth to the Moon:
Since the moon’s orbit is elliptical, its distance varies form about 221,463 miles (356,334 kilometers) at perigee (closest approach) to Earth, to 251,968 miles (405,503 kilometers) at apogee (farthest point), with the average distance being 238,857 miles (384,392 kilometers.

Why does the moon always keep the same face toward the Earth?
Only one side of the moon is seen because it always rotates in exactly the same length of time that it takes to revolve about the Earth. This combination of motions (called “captured rotation”) means that it always keeps the same side toward the Earth.

A light year defined:
A light year is a measure of distance, not time. It is the distance that light, which travels in a vacuum at the rate of 186,000 miles (300,000 kilometers) per second, can travel in a year (365 ¼ days). This is equal to 5,870 billion miles or 9,460 billion kilometers.

How many layers in the Earth’s atmosphere?
The atmosphere, the “skin” of gas that surrounds the Earth, consists of five layers that are differentiated by temperature:

The troposphere – is the lowest level; it averages about 7 miles (11 kilometers). Most clouds and weather form in this area.

The stratosphere – ranges between 7 miles (11 kilometers) to 30 miles (48 kilometers) above the Earth’s surface. Temperature rise slightly with altitude to about 32°F (0°C).

The mesosphere – (above the stratosphere) extends from 30 miles (48 kilometers) to 55 miles (85 kilometers) above the Earth. Temperatures decrease with altitude to 130VF (-90°C).

The thermosphere – is between 55 miles (85 kilometers) to 435 miles (700 kilometers). Temperatures in this layer range to 2696°F (1475°C).

The exosphere – beyond the thermosphere, applies to anything above 435 miles (700 kilometers). Temperature has no meaning in this layer.

The ionosphere – is a region of the atmosphere that overlaps the others, reaching from 30 miles (48 kilometers) to 250 miles (402 kilometers). The air is ionized (electrified) in this area and it affects the transmission and reflection of radio waves.

Blue Sky defined:
The sun interacting with the Earth’s atmosphere makes the sky blue.

Weight of the Earth:
It is estimated to weigh 6 sextillion tons, 588 quintillion short tons (6.6 sextillion short tons).

Highest and lowest points on Earth:
The highest point on land is the top of Mt. Everest (in the Himalayas on the Nepal-Tibet border) at 29,028 feet (8,848 meters) above sea level. The lowest point on land is the Dead Sea between Israel and Jordan which is 1,312 feet (399 meters) below sea level.

How much of the Earth is land and how much water?
30% or 57,259,000 square miles (148,300,000 square kilometers) is land. 70% or 139,692,000 square miles (361,800,000 square kilometers) is water.

Dead Sea defined:
The Dead Sea, on the boundary between Israel and Jordan, is called “dead” because nothing can live in it. It has a salt content of 25%. Because it is the lowest body of water on the Earth’s surface, any water that flows into the Dead Sea has no outflow. As the water evaporates, dissolved minerals are left in the sea.

Tsunami defined:
A tsunami is a giant wave set in motion by a large earthquake occurring under or near the ocean which causes the ocean floor to shift vertically. The vertical shift pushes the water ahead of it, starting a tsunami.

How strong was the earthquake that hit San Francisco on April 18, 1906?
8.3 on the Richter scale, causing 700 deaths and 500 million in damage. The October 17, 1989 earthquake measured 7.1 on the Richter scale, killing 67 people and causing billions in damage.