All Celestial Objects Undergo Some Type of Motion. Planetary Motion Can Be Either

SNC1PPlanetary Motion

Planetary Motion

All celestial objects undergo some type of motion. Planetary motion can be either

Revolution

The eight planets in our solar system travel

Planetary orbits are elliptical.

It takes earth to revolve around the sun

Rotation

As the earth revolves around the sun, it also rotates .

An axis is an around which an object rotates.

Day and Night

In the time that it takes the earth to make s. There are 365 days in a year.

Using a calendar with 365 days every year would result in a loss six hours per year. Adding a day ever four years fixes the problem. (Leap Year)

The Four Seasons

To understand why seasons change, consider the earth’s orbit around the sun, as well as the earth’s orientation in this orbit.

The earth is spinning or rotating on its axis (an imaginary line from the North pole to South pole) while orbiting around the sun.

The axis of rotationwith respect to the plane of orbit.

When the earth is oriented as it is in the picture, the sun’s rays that strike earth’s surface perpendicular to the surface are not hitting the equator, but instead are hitting just north of the equator.

In this orientation the Northern hemisphere receives more sunlight than the Southern hemisphere. This is

As the earth progresses around the sun, the angle between the axis of rotation and the orbital plane stays the same.

When earth, moves counterclockwise around the sun, summer changes to fall in the Northern hemisphere. The sun’s rays strike the equator perpendicular to the surface so the amount of sunlight that reaches the two hemispheres is equal.

Three months later, the sun’s rays strike perpendicular to the earth’s surface just south of the equator. This causes

Finally, when the most intense sunlight is once again at the equator, spring has arrived to the Northern hemisphere.

Solar Noon

Due to the earth’s motion, sunlight does not strike everywhere on the earth at the same time.

The time of day when the is called solar noon.

It may be solar noon in Toronto, but it is not Solar noon in Winnipeg! This makes time keeping difficult.

Time Zones

Earth has been divided into regions that have standard time, called a time zone. In that time zone, all clocks are the same time.

Solstices and Equinoxes

Solstice

oWhen the earth’s axis is .

oThis occurs twice a year.

Equinox

oBetween the two solstices there two days on which , called equinoxes.