Earth In Space Lecture Notes

Key Definitions

  • Observation: The interaction of your senses with the environment.
  • Inference: A conclusion based on observations.
  • Prediction: An inference that indicates what will happen in the future.

Earth's Motion

Axis
  • The axis is an imaginary line around the center of Earth.
  • Earth is tilted on its axis at an angle of approximately 23.5^{\circ}, which is the primary reason for the variation in sunlight intensity.
Rotation
  • Definition: The spinning of Earth on its axis.
  • Direction: Earth rotates from West to East (counter-clockwise when viewed from the North Pole).
  • Cause: It results in day and night.
  • Duration: One full rotation takes 24\text{ hours} (1 day).
Revolution
  • Definition: The movement of Earth around the Sun in an orbit.
  • Orbit Shape: The path is an ellipse (an elongated circle).
  • Cause of Seasons: Seasons are caused by the Earth's revolution combined with its fixed axial tilt.
  • Duration: One full revolution takes 365.25\text{ days}. The extra 0.25 day accounts for a Leap Year every four years.

Seasons

Solstice
  • Definition: The point during the Earth's orbit around the Sun at which the Sun is at its greatest distance from the equator.
  • Summer Solstice: The longest day of the year (approx. June 21 in the Northern Hemisphere).
  • Winter Solstice: The shortest day of the year (approx. December 21 in the Northern Hemisphere).
Equinox
  • Definition: The point when the Sun is directly above the equator, resulting in nearly equal day and night length globally.
Key Dates
  • March Equinox: Marks the start of Spring (Vernal Equinox).
  • June Solstice: Marks the start of Summer.
  • September Equinox: Marks the start of Autumn (Autumnal Equinox).
  • December Solstice: Marks the start of Winter.

Tides

Definition
  • Tides refer to the rise and drop of ocean water levels along coastlines and beaches, occurring twice daily due to the cycle of high and low tides.
Cause
  • Gravity: Mainly caused by the gravitational pull of the Moon, and to a lesser extent, the Sun.
  • Tidal Bulges: Gravity pulls water toward the Moon, creating a bulge on the side facing the Moon and the opposite side.
Types of Tides
  1. Spring Tides: Occur during Full and New Moons when the Sun, Moon, and Earth align. This results in the highest high tides and lowest low tides.
  2. Neap Tides: Occur during Quarter Moons when the Sun and Moon are at right angles to each other, resulting in the least difference between high and low tides.

The Moon

  • The only natural satellite that orbits Earth.
  • Atmosphere: The Moon has almost no atmosphere, leading to extreme temperature fluctuations.
  • Orbital Period: It takes approximately 27.3\text{ days} to orbit Earth, but the cycle of phases (synodic month) takes 29\text{-}30\text{ days}.
Phases of the Moon
  1. New Moon
  2. Waxing Crescent
  3. First Quarter
  4. Waxing Gibbous
  5. Full Moon
  6. Waning Gibbous
  7. Last Quarter
  8. Waning Crescent

Solar and Lunar Eclipse

Shadows
  • Umbra: The darkest part of the shadow (total eclipse).
  • Penumbra: The lighter, outer part of the shadow (partial eclipse).
Lunar Eclipse
  • Occurs when the Earth passes between the Moon and the Sun (Alignment: Sun-Earth-Moon).
  • Can only happen during a Full Moon phase.
Solar Eclipse
  • Occurs when the Moon passes between the Earth and the Sun (Alignment: Sun-Moon-Earth).
  • Can only happen during a New Moon phase.

Cosmology and Big Bang Theory

Big Bang Theory
  • Proposes that the universe began as a single, extremely hot and dense point approximately 13.8\text{ billion} years ago and has been expanding ever since.
Cosmology
  • Distance Measurement: Space distances are often measured in light-years (the distance light travels in one year, approx. 9.46 \times 10^{12}\text{ km}).
Hubble's Law
  • Describes the expansion of the universe. Galaxies move away from us at speeds proportional to their distance.
  • Formula: v = H_0 d

Satellites

  • Natural Satellites: Celestial bodies orbiting planets (e.g., the Moon).
  • Artificial Satellites: Human-made objects launched into orbit for specific tasks.
    • Geostationary Orbit: A satellite that remains over the same spot on Earth by orbiting at the same rate Earth rotates.

Instructions for Educators

  • Encourage students to observe the Moon's phase nightly for a month to understand the synodic cycle.
  • Recommended Multimedia:
    • Cosmology and Big Bang Theory Overview
    • Interactive Hubble's Law Simulation