Motions of the Earth

Ch 22.2

• Rotationthe turning, or

spinning, of a

body on its axis.

• Two measurements

for rotation

• Mean solar day is the time interval from one noon to

the next, about 24 hours.• .

Sidereal day is the time it takes for Earth to make one complete rotation (360º) with respect to a star other than the sun—23 hours, 56 minutes, 4 seconds

• Revolution is the motion of a body, such as a planet or moon, along a path around some point in space.

• Perihelion is the time in January when Earth is closest to the sun.

• Aphelion is the time in July when Earth is farthest from the sun.

Plane of the Ecliptic• an imaginary plane

that connects Earth’s orbit with the celestial sphere.

Precession• Precession traces

out a cone over a period of 26,000 years.

• In about 13,000 years the N. Pole will be tipped towards the Star Vega

The Moon

• Perigee – the point where the Moon is closest to the Earth

• Apogee – the point where the Moon is farther from the Earth

Moon Phases

• The Moon takes about 27 days (27 days, 7 hours, 43 minutes, 11.6 seconds) to go all the way around the Earth and return to its starting position.

• The Moon's orbit around the Earth is a slightly squashed circle called an ellipse.

• Whilst the Moon is orbiting the Earth, the Earth is constantly moving because it is orbiting the sun. The Moon therefore travels slightly more than 360° to get from one new moon to the next. Thus the lunar month is longer.

Moon Facts• The moon moves toward the

east in our sky by about 12 degrees each day.

• The moon rises in the east and sets in the west

• The Moon is about 250,000 miles (384,400 km) from Earth.

• The moon orbits Earth at an average speed of 2,288 miles per hour (3,683 km per hour).

• The Moon travels at different speeds during different parts of its orbit. It moves slowest when it is at furthest distance from Earth. The Moon moves fastest in its orbit when it is closest to Earth.

• The moon is highly reflective and close to the Earth so it is very visible both day and night. The Moon gets close to the sun towards the beginning of the lunar cycle as travels around the sky. So it increases visibility during the day.

• We always see the same side of the moon because it spins once on its axis in the same amount of time it takes to orbit the Earth.

Lunar Eclipse

Solar Eclipse

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the

Moon and the Sun and the rotation of the Earth

• Spring tide

• When the Sun and the Moon are in alignment with the Earth, causing extreme tides

• Neap tide

• When the Moon, Earth and Sun are at right angles. Tides are less extreme due to the opposing pull of both Sun and Moon

The Highest Tide – the Bay of Fundy

• http://www.youtube.com/watch?v=hbzwzrZXUKA&feature=player_embedded

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