The Effect of the Earth’s Rotation & Revolution

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 Rotation

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.

Coriolis Effect: Defection of wind due to rotation of Earth

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 Motions

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!

Effects of Earth’s revolution and tilt

The Earth’s revolution has several effects including the seasons and the variable duration of days/ nights. Also, the Earth’s tilt and axis relative to its orbital plane have a significant effect as well. This results in one hemisphere tilting toward the sun and the contralateral hemisphere tilting away. The hemisphere tilted towards the sun will experience warmer weather and longer daytime hours.

Whereas the hemisphere titled away from the sun will experience cooler temperatures and shorter daytime hours. This variation in daytime hours and average temperature cases by revolution and tilt results in the different seasons of the year. If the Earth were exactly perpendicular to its orbital plane, the seasons would not occur. It would also cause both hemispheres to experience approximately 12 hours of daylight and darkness during a 24-hour period. The Earth’s current axis is 23.5 degrees, if it were to be tilted more, this would result in warmer summers and colder winters. respectively.

For example, the summer solstice occurs when the Northern Hemisphere is at its maximum tilt toward the sun. During this period the sun will be directly overhead long the latitude of 23.5 degree N; otherwise known as the Tropic of Cancer. During the first day of summer, location along the latitude of 23.5 degree of the North pole experience 24hrs of daylight.

Altitude & Latitude

First, altitude describes how high a certain point is located above sea level. It mainly affects the climate in regions situated at high altitudes by making them cooler as the air pressure and temperature decreases. An example of a high-altitude region is the Himalayas, with an altitude of nearly 9000 meters, and fall in temperature from 0.2 to 1.2 degree Celsius every 100 meters.

These regions are typically characterized by high amounts of precipitation, strong winds and low levels of oxygen due to the lower air pressure. Altitude does affect climate, but primarily the local climate of a specific location; it does not contribute to affecting the entire planet’s climate. This thus downplays its significance in contributing to the Earth’s climate.

The further away a location is from the equator, the less sunlight it receives to heat the atmosphere because the sun’s rays are dispersed over a larger area of land as you move away from the equator due to the curvature of the Earth. As a result, places nearer to the equator such as the Sahara Desert tend to be hotter with a mean temperature of 30-40 degrees Celsius, as opposed to the polar regions with an average temperature of 0 to -40 degrees Celsius.

Evidence of the Earth’s Rotation and Revolution

Computing the speed of Earth’s revolution around the Sun:

•Circumference of Earth’s orbit = 940,000,000 kilometers

•Time for one revolution = 365 1/4 days = 8766 hours

•Speed of revolution = Distance/Time = 940,000,000 km / 8766 hr = 107,000 km/hr = 30 km/sec

•Uniform motion is difficult to detect. Although it is possible to detect the Earth’s circular motions, the effects are subtle, and were not detected until the 18th and 19th centuries, long after Copernicus proposed that the Earth was in motion.

The Coriolis effect was first described in 1835 by a French scientist by the name of Gustave Coriolis. If you are located at the equator, and fire a cannonball north or south, you find that the cannonball swerves to the east.

The net result of the Coriolis Effect:
In the Northern Hemisphere, projectiles swerve to the right. In addition, air rushing inward to a low pressure area will swerve to the right, and set up a COUNTERCLOCKWISE hurricane. 

In the Southern Hemisphere, projectiles swerve to the left, and air rushing inward to a low pressure area will set up a CLOCKWISE hurricane.

The Foucault pendulum was first demonstrated in 1851 by yet another French scientist; Jean Foucault. The Foucault pendulum is nothing more than a very long pendulum suspended from a well-oiled ball-and-socket joint overhead, so it is free to swing in any direction. 

Foucault set up such a pendulum in the Pantheon in Paris, and set it swinging north to south. As hours passed, however, the direction in which the pendulum was swinging moved around in a clockwise direction. After a while, the pendulum was swinging northeast-southwest; after a while longer, it was swinging east-west, then southeast-northwest, then north-south again.

What causes this change in the pendulum’s direction of swing? The rotation of the Earth, of course.

The important fact (independent of where you’re standing) is that the Earth and the pendulum’s swing are rotating relative to each other. If the Earth did not rotate on its axis, the direction of swing of a Foucault pendulum would remain fixed relative to the surface of the Earth.

When Copernicus proposed his heliocentric theory, his critics pointed out that if the Earth orbits the Sun once per year, then the Earth’s location in October (for instance) should be 2 astronomical units away from its location in April, half a year later. This change in the Earth’s location must cause the nearby stars to shift in apparent location relative to more distant stars.

Stellar parallax was searched for by astronomers from antiquity onward. However, prior to the invention of the telescope, stellar parallax was not observed.

There are two possible hypotheses:

(1) There is no stellar parallax because the Earth is stationary. This is the hypothesis put forward by the supporters of the geocentric universe.

(2) Stellar parallax exists, but it is too small to be detected, because the stars are too far away. This is the hypothesis put forward by Copernicus and other supporters of the heliocentric universe.

In fact, stellar parallax was first detected by Bessel (using a telescope) in the year 1837, nearly three centuries after the death of Copernicus. In general terms, parallax can be defined as the shift in the observed position of an object, resulting from a change in the observer’s location.

So, Copernicus was right:

•The Earth does rotate about its axis.

•The Earth does revolve around the Sun.

•The stars are very distant from the Sun.

However, Copernicus wasn’t vindicated by direct observational evidence until centuries after his death!