Earth's Tilt and the Seasons - Detailed Notes

EARTH'S TILT AND THE SEASONS

WHAT IS THE SUN?

  • The Sun Overview:

  • The Sun is a star located at the center of the Solar System.

  • Composed primarily of hot gases, mainly hydrogen and helium.

  • Produces energy through nuclear fusion, which powers its radiance and warmth.

DISTANCE OF THE EARTH FROM THE SUN

  • Key Distances:

  • Aphelion: The point at which Earth is farthest from the Sun, approximately 152,500,000 km (94,500,000 miles).

  • Perihelion: The point at which Earth is nearest to the Sun, approximately 147,500,000 km (91,500,000 miles).

  • Distance varies throughout the year and affects seasonal variations.

SIZE AND SHAPE OF THE EARTH

  • Historical Understanding:

  • Ancient scholars, including Eratosthenes, recognized that the Earth is not flat.

  • Two thousand years ago, mathematical methods were used to deduce the Earth's shape.

  • Shape Description:

  • The Earth is an Oblate Spheroid, slightly flattened at the poles and bulging at the equator, not a perfect sphere.

  • Equatorial Diameter: ~12,756 km

  • Polar Diameter: ~12,714 km

  • A 42 km difference exists between the equatorial and polar diameters.

  • Causes of Oblate Shape:

  • Due to the centrifugal force resulting from Earth's rotation, the Earth's shape results in slight bulges, especially around the equator.

MOTION OF THE EARTH

  • Rotation:

  • The Earth rotates on its own axis from West to East completing this spin in 24 hours.

  • This rotation causes the cycle of day and night.

  • Revolution:

  • The Earth revolves around the Sun in a circular path, taking approximately 365 ¼ days.

  • This movement defines the length of a year.

THE EARTH’S TILT

  • Tilt Angle:

  • The Earth is tilted at an angle of approximately 23.5º.

  • Significant Latitudinal Marks:

  • Tropic of Cancer: 23.5º North

  • Arctic Circle: Latitude varies with seasons

  • Tropic of Capricorn: 23.5º South

SOLSTICES AND EQUINOXES

  • Solstices Description:

  • Solstice: Occurs when the Sun reaches its highest or lowest point in the sky at noon, marking seasonal extremes in day length.

  • Summer Solstice: Around June 21, when the Sun is directly over the Tropic of Cancer, resulting in the longest day of the year in the Northern Hemisphere.

  • Winter Solstice: Around December 21, when the Sun is directly over the Tropic of Capricorn, resulting in the shortest day of the year in the Northern Hemisphere.

  • Equinoxes Description:

  • An Equinox occurs when day and night lengths are nearly equal across the globe, due to the Sun being directly over the equator.

  • Autumn/Fall Equinox: Occurs around September 21, marking the start of autumn in the Northern Hemisphere and spring in the Southern Hemisphere.

  • Vernal/Spring Equinox: Occurs around March 21, marking spring in the Northern Hemisphere and autumn in the Southern Hemisphere.

SEASONS IN THE PHILIPPINES

  • Seasonal Variations:

  • Dry Season: December to February

  • Wet Season: May to October

  • Regions such as the Philippines experience tropical seasons, influenced by sun position and monsoon patterns.