Earth Science: Structure and Motions

Shape of the Earth

• The Earth is slightly bulging at the equator and flattened at its poles.

Earth's Motions

• Rotation: The Earth rotates on its axis, completing one rotation in 23 hours, 56 minutes, and 4 seconds. This causes day and night.
• Revolution: The Earth revolves around the Sun in an elliptical orbit, completing one revolution in 365.25 days.

Magnetic Field of the Earth

• The Earth's magnetic field is generated by the movement of molten iron and nickel in the liquid outer core.
• The magnetic field is responsible for the auroras (northern and southern lights) observed in the thermosphere.

Earth's Seasons

• The Earth's tilt is responsible for the seasons.

Layers of the Earth

• Crust: Thin and outermost layer, composed of two types:
  • Continental Crust: Less dense, made up of rocks like granite.
  • Oceanic Crust: Denser, made up of rocks like basalt.
• Mantle: Thickest layer, located beneath the crust, with increasing temperature as depth increases.
• Outer Core: Found 2,900 km below the Earth's surface, composed of liquid iron and nickel, with a temperature of up to 2000 ℃.
• Inner Core: Hottest layer, where iron and nickel are solidified due to the immense pressure.

Kepler's Laws of Planetary Motion

• 1st Law (Law of Orbits): Planets orbit the Sun in elliptical paths, not circular.
• 2nd Law (Law of Areas): The imaginary line connecting a planet to the Sun sweeps equal areas in equal intervals of time.
• 3rd Law (Law of Periods): The farther a planet is from the Sun, the longer it takes to orbit.

Newton's Laws of Motion

• 1st Law (Law of Inertia): An object at rest stays at rest, and an object in motion remains in motion at a constant speed and direction unless acted upon by a net external force.
• 2nd Law (Law of Acceleration): The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F = ma).
• 3rd Law (Law of Interaction): For every action, there is an equal and opposite reaction.

Earth's Moon

• The Moon is the Earth's only natural satellite.
• Lunar craters are formed from volcanic activity, collisions, and impacts with other celestial objects.
• Tides are affected by gravitational attraction between the Moon, Earth, and the Sun.
  • Spring Tide: Occurs when the Sun, Earth, and Moon align, resulting in higher high tides and lower low tides.
  • Neap Tide: Occurs when the Sun, Earth, and Moon are at right angles, resulting in smaller tidal variations.

Eclipses

• Occur when the Sun, Earth, and Moon align in a straight path.
• Shadows are formed during eclipses:
  • Umbra: The darkest part of a shadow.
  • Penumbra: The lighter part of a shadow.
  • Antumbra: A conical shadow behind the umbra.
• Solar Eclipse: Occurs when the Moon passes between the Sun and Earth, blocking the Sun's light.
  • Total Solar Eclipse: The Moon completely covers the Sun, creating the darkest part of the shadow (umbra).
  • Partial Solar Eclipse: Only part of the Sun is covered.
  • Annular Solar Eclipse: The Moon is far from Earth and appears smaller than the Sun, creating a ring (annulus) of sunlight around the Moon.
• Lunar Eclipse: Occurs when the Earth passes between the Sun and Moon, casting its shadow on the Moon.
  • Total Lunar Eclipse: The Moon is entirely within the Earth's shadow.
  • Partial Lunar Eclipse: Only part of the Moon is within the Earth's shadow.