# Actual Earth Motions.

## Presentation on theme: "Actual Earth Motions."— Presentation transcript:

Actual Earth Motions

Rotation The Earth’s axis is tilted 23 ½ ° from perpendicular.
The Earth spins upon an imaginary line that runs through the planet from the North to South pole known as an axis. The Earth’s axis is tilted 23 ½ ° from perpendicular. The Earth rotates at a rate of 15° per hour from west to east.

Evidence of Rotation The Foucault Pendulum
The Foucault pendulum when swinging freely will move in a predictable way. The pendulum “appears” to move in clockwise fashion over time. In reality, the Earth is rotating underneath the pendulum making the pendulum “appear” to shift position over time.

The Foucault Pendulum

The Coriolis Effect Evidence of Rotation
The tendency of objects to veer away from a straight-line path is known as the Coriolis Effect. Objects tend to veer to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This “deflection” of an object from a straight-line path is due to the rotation of the Earth underneath an object set into motion. The object “appears” to veer or be deflected from its original target. In fact, the target has changed its position due to the Earth’s rotation.

The Coriolis Effect

The Coriolis Effect Evidence of the Coriolis Effect can be seen in global pattern of winds, large storms and ocean currents.

Revolution The Earth moves around the Sun once a year (365 ¼ days) – roughly at a rate of 1° per day.

Change in Constellations
Evidence of Revolution A constellation is a group of stars that form a pattern in the sky. Throughout the year different constellations can only be observed during different seasons. Change in Constellations

Evidence of Revolution
The seasons we experience on our planet are a result of the revolution of the Earth around the Sun and the 23 ½ ° tilt of the Earth’s axis. Because of the Earth’s tilt, areas of the planet receive varying amounts of sunlight throughout the year – leading to seasonal change. Seasonal Change

Change in Sun’s Diameter
Evidence of Revolution The Earth’s orbit around the Sun is slightly elliptical. The Earth at one point in its revolution is closer to the sun (perihelion). The Earth is furthest from the sun at aphelion. The Sun’s apparent diameter seems to change as the earth revolves around the Sun (Larger in perihelion; smaller in aphelion). Change in Sun’s Diameter

Doppler Effect of Stars
Evidence of Revolution As the Earth revolves around the Sun, it will travels towards a particular star one half of the year and travel away from it the second half of the year. Movements “to and from” stars can be seen as slight “blue and red” shifts in starlight. Doppler Effect of Stars

Earth’s Motions and Time
Local Time: Time based on rotation of the Earth reflected in “apparent” motions of the Sun. Solar Noon: The time of the day when the Sun reaches its highest altitude in the sky. Solar Day: The time it takes the Earth to rotate from one solar noon to the next solar noon. Mean Solar Day: Average rate at which the Earth rotates from one solar noon to the next. Mean Solar Time: 24 hours = 1 day! Time Zones: 15° wide bands of meridians established to reflect mean solar time.