**Eighth Grade Earth and Space Science**

Hi,

The diagram Earth’s revolution around the Sun shown below represents Texas’ 8th Grade Science Standard:

**TEKS 8.7A.**

*Model and illustrate how the tilted Earth rotates on its axis, causing day and night, and revolves around the Sun causing changes in seasons.*

The dates for 2014 and 2015 seasons in the Northern Hemisphere are correct, thus students can use this model to determine the start of each season.

The

**X**marks on the diagram indicate the location of Earth on its path around the Sun for each month of the year. Students can use the model to locate the general position of Earth on any day of the year.PDF Copy of the Earth’s Revolution Around the Sun Diagram: TEKS 8.7A Earth Revolution Model

Make note that Earth’s axis is an imaginary line through the Earth. The points where Earth’s axis exits are called the North Pole and the South Pole.

**FYI:**The needle of a compass DOES NOT point toward the North Pole. Instead, a compass needle points toward Earth’s Magnetic North Pole. The magnetic north pole of Earth changes location. Google the location of Earth’s magnetic north pole during a specific year.

**Velocity of Earth’s Rotation**

The Earth is in constant motion.

The Earth **rotates** (spins about its axis) once every 24 hours. It is this motion that causes daylight and nighttime.

Students can calculate the velocity of Earth’s rotation.

**At the equator, the circumference of the Earth is 40,070 kilometers, and the day is 24 hours long.**

**V = D ÷ t; Velocity equals distance divided by time.**

Note: The difference in speed and velocity is that velocity is always in a specific direction. Earth rotates toward the East.

**V =**

**40,070 kilometers**

**÷ 24 hours** =

**1670 kilometers/hour ( 1070 miles/hr)**Since Earth is a sphere, the circumference is greatest at the equator and decreases at

**latitudes**north or south of the equator.

Math Enrichment: The velocity at different latitudes can be determined by this formula:

Math Enrichment: The velocity at different latitudes can be determined by this formula:

Cosine of Latitude x 1670 kilometers/hour= velocity at a specific latitude

**Example:**At latitude 45 degrees (North or South) the velocity would be:

Cosine (45) = 0.707, thus the velocity of Earth at latitude 45 degrees would be—- 0.707 x 1670 kilometers/hour= 1180 kilometers/hr

**Velocity of Earth’s Revolution Around the Sun**

As Earth rotates on its axis it

**revolves**around the Sun.Earth rotates 365 days during its yearly trip around the Sun. The path or orbit that Earth traces out each year is slightly elliptical, but assuming it to be a circle, the circumference would be equal to 2 x pi x radius. The radius used will be the average distance of Earth to the Sun, which is 149,597,890 km.

The average distance Earth travels each year is 2 x Pi(149,597,890)km.

Thus the velocity of Earth revolution around the Sun is: V = 2 x Pi(149,597,890)km ÷ 1 year

What is the velocity of Earth’s Revolution in km/hr

Clue: Once the distance (circumference is determined) divide by the number of hours in one year.

Answer:

velocity=107,300 km/h (67,062 miles per hour) counterclockwise (looking down on the North Pole)

**Seasons**

Point out that because the Earth’s axis it tilted in reference to the Sun, when the Northern has winter the Southern Hemisphere is enjoying summer. In Sept, its fall in the Northern Hemisphere and spring in the Southern Hemisphere.

Students need to know that when Earth’s North Pole (axis exiting the Northern Hemisphere) is pointing toward the Sun, the Northern Hemisphere is receiving the most direct Sun rays, thus it is summer-location 10. Note that the North Pole points away from the Sun in location 4. In location 1 and 7, the North Pole and South Pole of Earth receive equal amounts of direct sun rays, thus these are called Equinox positions.

Use the ASK JANICE Tab on the Navigation bar above if you have a question.

Janice VanCleave