Variations in Earth’s Orbit

Our solar system formed when a supernova sent

energy through a large nebula of gas, dust, and

ice, causing the material to spin and collect into the Sun and the

planets.

The nine planets are located in

very predictable patterns as they

orbit the Sun.Due to

conflicting gravity between Jupiter and the

Sun, there is also an asteroid belt between Mars

and Jupiter

Johannes Kepler’sThree Laws of

Planetary Motion1. The orbit of every planet is an ellipse with the sun at one focus.2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time.3. The square of the time taken for a planet to complete one orbit is proportional to the cube of its mean distance from the Sun.

1. The orbit of every planet is an ellipse with the sun at one focus.

2. A line joining a planet and the sun sweeps out equal areas during equal intervals of

time.

The planets travel faster when closer to the Sun (perihelion) and slowest when furthest

from the Sun (aphelion)

3. The square of the time taken for a planet to complete one orbit is proportional to the cube of its mean distance from the Sun.

The closer the planet is to the Sun, the shorter time it takes to orbit the Sun

The path on which the planets, including Earth,

orbit the Sun is called the Plane of the Ecliptic.

Both the Moon and the Sun exert a gravitational "tug" on the Earth's equatorial bulge, trying to

pull the Earth's equatorial region into alignment with the Ecliptic plane.

This tug, along with the rotational motion of the Earth on its axis, the revolution of the Earth around the

Sun, and the revolution of the Moon about the Earth, cause the Earth to wobble about its axis of rotation,

similar to the motion of a spinning top. This motion is called Precession.

During precession, the angle of Earth’s tilt does not change. What are changes is our view of

the stars. Currently, Polaris lies directly over the north pole, but in about 12,000 years, Vega

will be over the north pole.

The time it takes for Earth to complete one precession

period is 26,000 years.

During a precession period, the vernal

equinox travels through each of

the zodiac constellations.

This is the Dawning of the Age of Aquarius

Just as Earth’s equatorial plane is inclined at an angle, the moon’s “equatorial” plane is also tilted or inclined on a 5 degree angle in

respect to its orbit around Earth.

The Moon does not orbit the center of the Earth, rather, they both revolve around the

center of their masses called the barycenter.

Notice that how the Earth is also moving slightly

http://www.youtube.com/watch?v=uGBANgbRkws

The sun acts on the earth and its moon as one entity with its center at the barycenter. Since

the earth revolves around the barycenter, which in turn orbits the sun, the earth follows a wobbly

path around the sun.

Due to this wobbly path, the distances

between the Sun and Moon, in relation to Earth vary resulting

in a variation in their forces on the Earth.

When the force from the Moon on the Earth is at it greatest, the Moon tries to align Earth’s equatorial

plane with its own equatorial plane, causing a slight change in the tilt of Earth’s axis of about ½

degree each way on an 18.6 year cycle.

This periodic change in Earth’s tilt is called nutation

and leads to periodic harsher seasons.