Earth in MotionMs. Scott

Introduction Every object or body in the universe

is in motion. Earth itself is involved in a number of

different motions.• These motions are important for day and

night and the seasons Scientist have also discovered that the motions

of the earth in space bring about changes in climate and physical processes on earth

Differing Types of Movement

Just like humans, the earth is in constant motion.

Even though we are unaware of the motions of the earth- the biggest movements occur outside our experiences and/or senses

We are aware of smaller movements such as the rotation of the earth on its axis, and orbiting around the sun because that is what gives us day and night, and seasons.

Moving Galaxy Most scientists believe that all the

known galaxies in the universe are hurtling away at an incredible speed.• From Earth it looks like the galaxies are

moving away from us (same as if we were to be on a different planet)

• It is difficult to calculate the speed at which the galaxies are moving since there are no fixed points to use a reference

Moving Galaxy In addition to general movement, the Milky

Way is also spinning in space around a central axis like an enormous pinwheel

Our sun and solar system orbit the center of this galaxy along with over 100 billion other stars, taking about 175,000 years to complete one revolution.• It is estimated that the speed of the rotation of the

Milky way is about 250km/sec. and that the sun’s distance from the galactic center is 24, 000 to 26,000 light years away (one light year=distance of light travelled in one year (9.46 trillion kms)

The Moving Earth The term ‘revolution’ refers tot the

Earth’s orbiting of the sun.

The earth revolves around the sun at a speed around 108, 000km/hr, travelling 929 million km to complete a single rotation.

Moving Objects Speed of Movement (km/hr)

Earth Rotation on Axis (Equator)

1,660

Earth Orbit Around Sun 108,000

Sun Orbit Around Milky Way 900,000

Movement of Milky Way Galaxy

2,000,000

The Moving Earth The orbit of the Earth is eliptical The average distance from the sun is

150 million km. Presently the Earth is at its greatest

distance 152 million km form the sun on July 4th and its closest at 147 million km on January 3rd.

The Moving Earth The term aphelion refers to the point in

the orbit of the earth where it is the furthest from the sun

The term perihelion refers to the point in the orbit of the earth where it is closest to the sun.• The situation occurs approximately 21,000-22,000 • In 10500 to 11000 years, the earth will be closest

in July and furthest in January The shift is called the PRECESSION OF THE

EQUINOXES

The Moving Earth The Earth experiences a change in

the eccentricity of its orbit around the sun over a period of approximately 100,000 years.

The orbit goes from more nearly circular to much more elliptical and back again during this cycle

IT’S A FACT……… The Milky Way Galaxy and

everything in its vicinity are moving towards the “Great Attractor”, a cluster of 75,000 galaxies about 150 million light years from Earth, at a speed of 2,000,000 km/hr. • The journey will take about 100 billion years

to complete.

Earth’s Tilted Axis

Earth’s Tilted Axis The Axis of the earth is defined as the line

joining the North and South Poles, around which the Earth rotates.

The Earth is tilted at an average of 23.5 degrees from the plane of the elliptical• This means the sun shines more fully on one side

of the hemisphere than the other.• There are two times a year when the sun shines

equally on both hemispheres (March 21 and Sept 21) The spring and autumn equinoxes

Sun rays perpendicular at the Equator

Earth’s Tilted Axis The summer solstice occurs

approximately June 21st when the sun shines directly over the Tropic of Cancer in the Northern hemisphere

The reverse is true of the Southern hemisphere at this time- the winter solstice occur on or around December 21st , at which the sun’s rays are perpendicular to the Tropic of Capricorn

Earth’s Tilted Axis The tilt of the Earth’s rotational axis

causes the different seasons experienced in the high latitudes of the southern and northern hemispheres.

Earth’s Tilted Axis Another reason for higher summer

temperatures in the northern hemisphere is the fact that the sun shines for much longer during the day in the summer season.

The sun is directly about the horizon for all 24 hours in the aria that lies north above the Arctic Circle• In the southern hemisphere it is reversed

Earth’s Tilted Axis The Earth’s angle of tilt form the

plane of the elliptical varies form 21.5 degrees to 24.5 degrees over the course of about 40,000 years• This ‘wobble’ in the axis changes th

contrast between seasons. When the earth’s tilt is the greatest the Earth’s

winters are the coldest and the summers hottest. When the tilt is less, there is less difference between summer and winter.

Activity Looking through the Farmer Almanac

try to determine what years the Earth’s tilts were the greatest and the least.

Using the Atlas label the following accordingly:• Equator• Earth’s tilt• Tropic of Cancer• Tropic of Capricorn• North and South Pole