The Effect of the Earth’s Rotation & Revolution
When watching the stars at night, they do appear to move very slowly. This is because the Earth is constantly moving. The Earth completes one “rotation” every twenty-four hours. A rotation is when the planet spins around once. The Earth rotates counterclockwise; this is why the Sun “rises” in the East and “sets” in the West. It is not the Sun’s movement that causes days, but rather the Earth turning around in front of the Sun. The Earth’s axis (the point at which it rotates around, for example, if you were to spin around while standing in one spot, your axis would be an imaginary line running through your head straight down to your feet) is in line with a star named “Polaris”. Polaris is also known as the “North Star” since it is directly above the Earth’s axis. Since this star is directly above the Earth’s axis, it does not appear to move, however the rest of the stars in the sky move around Polaris (for example: when you spin around, the object directly above your head does not appear to move but everything else seems to spin around that object). Polaris is only seen in the Northern hemisphere and it belongs to the Little Dipper constellation (it’s the last star at the end of the “handle”).
THE EFFECT OF THE EARTH’S REVOLUTION
Another type of motion is known as “revolution”. Revolution is when one object completes a circular path around another object. The Earth takes 365.24 days to revolve around the Sun. This is why a year is 365 days long. During the year the Earth is angled differently towards the Sun. These changing angles provide us with different Sun intensities and therefore we get four different seasons. Since the Earth is at different positions in space over the year, we see different constellations throughout the year.
UP [NORTH]: West DOWN [SOUTH]: East (On Surface)
Northern Hemisphere: Deflected to the right (clockwise)
Southern Hemisphere: Deflected to the left (counter-clockwise)
Trade Winds: high pressure wind blown to the west from 30N
Westerlies: deflected to the east
Earth is currently in a cool phase characterized by formation of glaciers (glacial maxima), followed by warm periods with glacial melting (interglacial periods). These glacial–interglacial cycles occur at frequencies of about 100,000 years. We are currently in an interglacial period; these have lasted about 23,000 years in the past. The last glacial maximum was about 18,000 years ago.
The glacial–interglacial cycles have been explained by regular changes in the shape of Earth’s orbit and the tilt of its axis—Milankovitch cycles.
Circular rotation causes glaciers to melt; more solar radiation; Elliptical= less radiation. The intensity of solar radiation reaching Earth changes, resulting in climatic change. The shape of Earth’s orbit changes in 100,000-year cycles. The angle of axis tilt changes in cycles of about 41,000 years. Earth’s orientation relative to other celestial objects changes in cycles of about 22,000 years.
THE EFFECT OF PLANET’S MOTION
Thousands of years ago, people were able to clearly see the night sky (no “light pollution”). The one thing they noticed is that five “stars” seemed to wander faster through the night sky than other stars. These “stars” were actually the planets Mercury, Venus, Mars, Jupiter, and Saturn. People called these objects “wandering stars”. Their names were then changed to planets which is after the Greek word “planetes” which means “wanderers”. All planets rotate on their axes and revolve around the Sun, however these times are different for each planet. Planets move through constellations as well. This motion usually takes a few weeks. Many constellations are named after animals. The Greek word for “animal sign” is “zodion”. This is why we have star groups called the zodiac constellations. Depending on which zodiac constellation was visible when you were born is the “sign” you have been assigned. For example: Aquarius, Leo, Gemini, Sagittarius, etc. Many people believe that zodiac signs determine certain traits and characteristics of people. This is known as “astrology” and is not a legitimate science based on truth or facts. Astrology is simply for entertainment.
Revolution Around the Sun vs. Rotation upon Axis
Revolve, as in orbiting the Sun? Yes, all the planets in our solar system orbit the Sun in the same direction Earth does. Some comets and asteroids orbit backwards, and some (more so comets than asteroids) orbit virtually perpendicular to the plane of Earth’s orbit.
Rotate, as to spin on ones axis (the thing that causes day and night on Earth)? Earth rotates counter-clockwise, as seen from above Earth’s north pole, the same direction it revolves around the Sun. But two planets (used to be 3, when Pluto was a planet) rotate clockwise – Venus and Uranus. Some might quibble about Uranus, as it spins on its side, but technically it rotates clockwise.
Why do they all revolve in the same direction, and most rotate in the same direction? Because of the way the solar system formed. It formed out of a nebula – a giant cloud of gas and dust in space. This cloud had a slight rotation to it. Gravity caused the dust and gas to come together, but since the nebula was spinning, it collapsed into a disk instead of a sphere. The center of the disk, that’s where the Sun formed. The rest of the disk (now rotating quite nicely) is where the planets formed. So all the planets revolve in the same direction because that’s the direction the original nebula was rotating.
Why do some planets now rotate backward? They got clobbered by one or more large asteroids while they were forming, which caused their rotation rate/direction to change. Earth got clobbered, too, at least once – that’s how we got our Moon!