The Sun-Earth-Moon System Flashcards

Seasons and Earth's Movements

• Seasons change due to the tilt of Earth's axis relative to its orbit around the Sun.
• The September Equinox marks the first day of fall in the Northern Hemisphere.
• Earth completes one revolution around the Sun in 365.25 days, which defines a year.

Earth's Rotation

• On the first day of winter, Earth's northern axis points away from the Sun.
• Days and nights are caused by Earth's rotation, which takes approximately 24 hours to complete one full turn.
• The equator is the imaginary line dividing Earth into northern and southern hemispheres.

Equinoxes and Solstices

• An equinox occurs when Earth's axis is not tilted toward or away from the Sun, resulting in nearly equal day and night.
• A solstice is the day when Earth's rotation axis is at its maximum tilt toward or away from the Sun, indicating the start of summer or winter.

Moon Features and Phases

• Maria are large, dark, flat areas on the Moon's surface.
• The phases of the Moon refer to the illuminated portion visible from Earth, with waxing phases indicating increasing visibility and waning phases indicating decreasing visibility.

Eclipses

• A lunar eclipse happens when the Moon enters Earth's shadow, while a solar eclipse occurs when the Moon casts its shadow on Earth.
• The penumbra is the lighter, outer part of a shadow where partial light is blocked; the umbra is the central, darker part where light is completely blocked.

Tides and Energy

• Tides are caused by the daily rise and fall of sea level influenced by the gravitational pull of the Moon and Sun.
• Sun's energy reaches Earth primarily in the form of light and thermal energy, more concentrated at the equator than at the poles.

Earth's Stability and Directionality

• The Sun's gravity is the force that keeps Earth in orbit around it; if this force ceased, Earth would move in a straight line away from the Sun.
• Earth rotates counterclockwise, so celestial objects appear to move from east to west in the sky.

Seasonal Variations and Daylight

• During the December Solstice, the northern axis leans away from the Sun, marking winter in the Northern Hemisphere and summer in the Southern Hemisphere.
• Near the December Solstice, temperatures are cooler in the Northern Hemisphere due to reduced sunlight.
• The March Equinox results in nearly equal hours of daylight and darkness worldwide; it marks the start of spring in the Northern Hemisphere and autumn in the Southern Hemisphere.