Earth in Space

 

Next Article

 

Article Description:

 

Earth is a spinning, magnetized sphere of solid and molten rock, and it is one of eight planets in our solar system

 

 

Earth in Space 

Earth is a spinning, magnetized sphere of solid and molten rock. It is one of eight planets and numerous smaller bodies (moons, asteroids, and comets) that orbit the sun. Although Earth is spherical, it is not a perfect sphere. In the 17th century, Sir Isaac Newton reasoned that Earth’s rotation is sufficient to cause a slight flattening at the poles of the planet. In 1743 Newton’s hypothesis was verified when measurements proved Earth’s circumference at the equator to be slightly greater than the circumference around the poles.

 

 

Careful measurements during the mid-20th century showed that Earth measures 40,075 kilometers (24,901.5 miles) around the equator, but only 40,008 kilometers (24,859.7 miles) around the poles. Thus, Earth bulges slightly at the equator and is flattened slightly at both poles. This shape is called an oblate spheroid. Analyses of measurements taken from orbiting satellites show that the equatorial bulge is not exactly at the equator, but slightly to the south. For this reason, some earth scientists prefer to consider Earth slightly pear- shaped rather than an oblate spheroid.

 

Like all planets, Earth spins around a central axis with imaginary ends at the north and south poles. Each complete rotation of Earth, lasting about 24 hours, produces day and night. To human beings, the most important effect of Earth’s rotation is the rising and setting of the sun. The sun actually remains in the center of the solar system, only seeming to rise and set because Earth rotates on its axis and moves in reference to it.

 

Since Earth rotates toward the east, the sun seems to rise in the east and travel across the sky, setting in the west. During summer in the northern hemisphere, the sun appears to take longer to cross the sky and the days are longer than the nights. In the winter, the reverse is true—the nights are longer than the days. The explanation for this is that during summer in the northern hemisphere, the North Pole is tilted toward the sun. Consequently, sunlight falls on much more than half of the northern hemisphere. In winter, the South Pole is tilted toward the sun. As a result, the southern hemisphere during  winter in the northern hemisphere has long days and short nights.

 

 

 

© Digital Vision

EARTH as seen from space showing the demarcation between day and night.