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Space Systems 2
NYS Earth & Space Sciences
Term | Definition |
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Kepler's Laws of Planetary Motion | Three fundamental laws discovered by Johannes Kepler in the early 1600s that describe how planets orbit the Sun. These laws replaced the ancient belief in circular orbits and provided the foundation for understanding planetary motion. |
Kepler's 1st Law (Law of Ellipses) | All planets orbit the Sun in elliptical paths, with the Sun located at one of the two foci of the ellipse. This law established that planetary orbits are not perfect circles but elongated ovals. |
Kepler's 2nd Law (Law of Equal Areas) | A line connecting a planet to the Sun sweeps out equal areas in equal time intervals. This means planets move faster when closer to the Sun and slower when farther away, ensuring the orbital speed varies throughout the orbit. |
Kepler's 3rd Law (Law of Harmonies) | The square of a planet's orbital period is proportional to the cube of its average distance from the Sun. Mathematically expressed as T² ∝ a³, where T is the orbital period and a is the semi-major axis. |
Ellipse | An oval-shaped geometric figure where the sum of distances from any point on the curve to two fixed points (foci) remains constant. Planetary orbits follow this shape rather than perfect circles. |
Foci | Two fixed points inside an ellipse used to define its shape. For planetary orbits, the Sun occupies one focus while the other focus remains empty. The closer the foci are to each other, the more circular the ellipse appears. One foci is called a “focus.” |
Major Axis | The longest diameter of an ellipse, passing through both foci and the center. Half of this distance is called the semi-major axis, which represents the average distance between a planet and the Sun. |
Eccentricity of Orbits | A measure of how elongated or "stretched out" an elliptical orbit is, ranging from 0 (perfect circle) to 1 (extremely elongated). Most planetary orbits have low eccentricity values, making them nearly circular. |
Perihelion | The point in a planet's orbit where it is closest to the Sun. At this position, the planet moves at its fastest orbital speed according to Kepler's 2nd Law. |
Aphelion | The point in a planet's orbit where it is farthest from the Sun. At this position, the planet moves at its slowest orbital speed. |
Heliocentric Longitude | The angular position of a celestial body as measured from the Sun's perspective, using the Sun as the reference point. This coordinate system places the Sun at the center. |
Geocentric Longitude | The angular position of a celestial body as measured from Earth's perspective, using Earth as the reference point. This is how we observe and measure positions of objects in the sky from our planet's surface. |
Phases of the Moon | The different appearances of the Moon as seen from Earth, caused by the changing relative positions of the Moon, Earth, and Sun during the Moon’s orbit around Earth. |
Tides | The periodic rise and fall of sea levels on Earth, caused by the gravitational pull of the Moon and Sun on Earth's oceans. |
Season | The changes in weather patterns and daylight hours throughout the year, caused by the tilt of Earth’s axis and its orbit around the Sun. |
Cyclically | Occurring in a repeated pattern over time, as seen in the regular cycles of the Moon’s phases, eclipses, tides, and seasons. |
Moon’s Orbit | The path the Moon follows as it revolves around Earth, influencing the phases of the Moon, the occurrence of eclipses, and the strength of tides. |
Earth’s Orbit | The elliptical path Earth follows as it revolves around the Sun, determining the seasons by changing the amount of sunlight different parts of Earth receive throughout the year. |
Sun | The central star in our solar system, providing light and heat, and playing a key role in the cycles of seasons, tides, and eclipses due to its gravitational and positional relationship with Earth and the Moon. |
Solar Eclipse | An event where the Moon passes between the Earth and the Sun, temporarily blocking the Sun's light and casting a shadow on Earth. |
Gravitational Pull | The force exerted by a celestial body, like the Moon or Sun, which influences the movement of other bodies and the occurrence of tides on Earth. |
Waxing Moon | The period when the illuminated portion of the Moon visible from Earth is increasing. This occurs from new moon to full moon, including the waxing crescent, first quarter, and waxing gibbous phases. |
Waning Moon | The period when the illuminated portion of the Moon visible from Earth is decreasing. This occurs from full moon to new moon, including the waning gibbous, third quarter, and waning crescent phases. |
Lunar Eclipse | An astronomical event that occurs when Earth passes between the Sun and Moon, causing Earth's shadow to fall on the Moon. This can only happen during a full moon when the three bodies are aligned. |
Umbra | The darkest, central part of a shadow where light is completely blocked. During a lunar eclipse, the Moon passes through Earth's umbra, appearing dark red or copper-colored due to atmospheric refraction of sunlight. |
Penumbra | The lighter, outer part of a shadow where light is only partially blocked. During a lunar eclipse, the Moon may first pass through Earth's penumbra, causing a subtle dimming before entering the umbra. |
Solar Eclipse | An astronomical event that occurs when the Moon passes between Earth and the Sun, casting a shadow on Earth's surface. This can only happen during a new moon when the three bodies are aligned. |
Apparent Motion (of Sun) | The Sun's observed movement across the sky from east to west each day, caused by Earth's rotation on its axis. The Sun appears to follow different paths throughout the year due to Earth's tilted axis and orbital motion. |
Axis of Rotation | An imaginary line passing through Earth's center from the North Pole to the South Pole, around which Earth rotates once every 24 hours. This rotation causes day and night cycles. |
Earth's Tilt (23.5°) | The angle at which Earth's rotational axis is tilted relative to its orbital plane around the Sun. This tilt is responsible for seasonal changes in temperature, daylight hours, and the Sun's apparent path across the sky. |
Path of the Sun | The apparent track the Sun follows across the sky during the day, which changes throughout the year due to Earth's tilted axis. The path is highest in summer and lowest in winter for observers in the Northern Hemisphere. |
Solar Altitude | The angle of the Sun above the horizon at any given time and location. Solar altitude changes throughout the day (highest at solar noon) and throughout the year (highest during summer solstice). |
Changing Sunrise & Sunset (SRise & SSet) | The variation in times when the Sun rises and sets throughout the year, caused by Earth's tilted axis and orbital motion. Days are longer in summer and shorter in winter due to these changing sunrise and sunset times. |
Vertical Rays | Sunlight that strikes Earth's surface at a 90-degree angle (perpendicular to the surface). Vertical rays deliver the most concentrated solar energy and occur at solar noon along specific latitudes that change throughout the year, creating the seasons. |