geography

Earth's Rotation and Day Length

Equinox Definition: Occurs when the Earth's rotation axis is perpendicular to the sunlight, leading to equal amounts of day and night across the globe (12 hours each).
Circle of Illumination: An imaginary line that divides day and night, cutting through all latitudes.

Definition: The latitude where the sun is directly overhead (90 degrees) at noon on any given day.
Declination Range: Varies between 23.5° North (Tropic of Cancer) and 23.5° South (Tropic of Capricorn).
Importance: Determines day length and the angle of the sun in the sky, influencing seasonal changes and climate.

Daylight Variation: Greater variations in daylight exist at higher latitudes compared to the equator.
Northern Hemisphere:
- Fall Equinox: Around September 20, marking the onset of fall.
- Summer Solstice: Around June 21, causing the highest sun angle and longest days.
- Winter Solstice: Around December 21, resulting in the lowest sun angle and shortest days.

Solar Angle (Altitude): Angle of the sun above the horizon at solar noon.
Calculation Formula:
- Solar Angle = 90° - Latitude ± Solar Declination
Key Points:
- Add declination if it’s in the same hemisphere.
- Subtract if it's in the opposite hemisphere.

North Pole: Experiences extreme day lengths ranging from 24 hours of daylight to 24 hours of darkness.
Equator: Stays consistent with approximately 12 hours of daylight and 12 hours of night year-round.

Concept: Refers to how the angle of the sun affects energy intensity reaching the Earth's surface.
Implications: A higher sun angle means more concentrated solar energy, while a lower angle diffuses the energy over a larger area, reducing intensity.

Atmospheric Interaction: The amount of atmosphere solar rays pass through influences the energy received on the surface.
- More atmosphere = Less energy reaching the ground due to scattering, absorption, and reflection.
Impacts of Path Length: Longer path lengths (e.g., low sun angles) lead to diminished energy and colder temperatures despite longer daylight hours.

Types of Earth's Motion:
- Tilt (Obliquity): Changes between approximately 22° to 24.5° over 40,000 years.
- Eccentricity: Variation in the Earth's orbit from nearly circular to elliptical over 100,000 years.
- Axial Precession: The wobble of Earth's axis over roughly 26,000 years.
Ice Age Conditions: Favorable conditions for ice ages require two out of the three cycles to align, while exiting an ice age requires all three to align.

Energy Definition: The capacity to do work, defined as the movement of matter.
Types of Energy:
- Potential Energy: Energy stored due to an object's position.
- Kinetic Energy: Energy of motion.
- Thermal Energy: A subtype of kinetic energy related to temperature and heat transfer.

Conduction: Energy transfer through direct contact.
- Example: Touching a hot skillet. Only energy transfers, not matter.
Convection: Energy transfer through the movement of a fluid (liquid or gas).
- Example: Boiling water; hot water rises, carrying energy.
Radiation: Transmission of energy as electromagnetic waves (e.g., heat from the sun).
- Relevant to the atmospheric sciences, affecting weather patterns.

Rule 1: All objects emit radiation continuously across various wavelengths.
Rule 2: Hotter objects emit more radiation than colder ones (Stefan-Boltzmann Law).
Rule 3: As temperature increases, energy is emitted more at shorter wavelengths (Wien’s Law).
Rule 4: Good absorbers of energy are also good emitters (emissivity concept); related to the Earth's radiation dynamics.

Definition: The measure of solar energy received at the upper atmosphere, approximately 1,364 watts/m².
Importance: Indicates the intensity of solar radiation reaching the Earth, essential for understanding solar energy balance.

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