Sat, December 9, 2017 at 10:38 am GMT
Hello Barbara,Thank you for your Journal. I am using my time to write to you and I would like you to read the following topic.
Earth’s magnetic field.
Earth, on the right, is tiny in comparison
to the Sun, but its magnetic field extends
far outward.
In 1851, a French scientist named Léon Foucault took an iron sphere and swung it from a wire. He pulled the sphere
to one side and then released it, letting it swing back and forth in a straight line. A ball swinging back
and forth on a string is called a pendulum.
A pendulum set in motion will not change its motion, and so the direction of its swinging should not change.
However, Foucault observed that his pendulum did seem to change direction. Since he knew that the pendulum
could not change its motion, he concluded that the Earth, underneath the pendulum was moving.
An observer in space will see that Earth requires 23 hours, 56 minutes, and 4 seconds to make one complete rotation
on its axis. But because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a
little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is actually 24 hours. At
the equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles the movement speed is nearly
Foucault’s pendulum is now on display in
the Pantheon in Paris.
Imagine a pendulum at the North Pole.
The pendulum always swings in the same
direction, but because of Earth’s rotation,
its direction appears to change to observers
on Earth.
Planet Earth
Earth’s Revolution
For Earth to make one complete revolution around the Sun takes 365.24 days. This amount of time is the definition
of one year. The gravitational pull of the Sun keeps Earth and the other planets in orbit around the star. Like the
other planets, Earth’s orbital path is an ellipse so the planet is sometimes farther away from the Sun
than at other times. The closest Earth gets to the Sun each year is at perihelion (147 million km) on about January
3rd and the furthest is at aphelion (152 million km) on July 4th. Earth’s elliptical orbit has nothing to do with Earth’s
seasons.
Earth and the other planets in the solar
system orbit around the Sun. Although
the orbits are slightly elliptical, in this image
the ellipses are exaggerated.
During one revolution around the Sun, Earth travels at an average distance of about 150 million km. Earth revolves
around the Sun at an average speed of about 27 km (17 mi) per second, but the speed is not constant. The planet
moves slower when it is at aphelion and faster when it is at perihelion.
The reason the Earth (or any planet) has seasons is that Earth is tilted 23 1/2
o
on its axis. During the Northern
Hemisphere summer the North Pole points toward the Sun, and in the Northern Hemisphere winter the North Pole
is tilted away from the Sun
