Presentation on theme: "Actual Earth Motions. Rotation The Earth spins upon an imaginary line that runs through the planet from the North to South pole known as an axis. The."— Presentation transcript:
Actual Earth Motions
Rotation 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 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
Evidence of Rotation The Coriolis Effect 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
Evidence of the Coriolis Effect can be seen in global pattern of winds, large storms and ocean currents. The Coriolis Effect
Revolution The Earth moves around the Sun once a year (365 ¼ days) – roughly at a rate of 1° per day.
Evidence of Revolution Change in Constellations 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.
Evidence of Revolution Seasonal Change 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.
Evidence of Revolution Change in Sun’s Diameter 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).
Evidence of Revolution Doppler Effect of Stars 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.
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.