20 terms

Ch 28 & 29 Sun-Earth-Moon System (SEM)

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Geocentric Model
"Earth-centered". An old, incorrect theory that said the Earth was the center of the universe and that the Sun, planets & stars orbited a stationary Earth.
Heliocentric Model
"Sun-centered". The current model of our solar system that places the Sun in the center and the planets orbiting the Sun.

This model provides an explanation for retrograde motion.
Retrograde Motion
The apparent backward motion of a planet in the sky. This problem was unexplainable by the geocentric theory. It is explainable using the heliocentric model.
Astronomical Unit
The distance scale used to measure objects in space. The distance from the Earth to the Sun is 1 Astronomical Unit (AU).
Kepler's First Law
Planets orbit the Sun in an ellipse, NOT a circle. An ellipse is a shape centered around 2 focus points. If the 2 foci are very close together a circle is formed. If the focus points are far away an oval is formed.
Eccentricity
Describes the shape of a planet's orbit. It is calculated using the ratio of the distance between the 2 foci to the length of the major axis.

Eccentricity range is 0-1. 0 is a perfect circle.

An eccentricity of 1 is a very elongated oval.
Focus (Foci is plural)
Two points that the elliptical orbit of a planet is centered on.
Newton's Inverse Square Law
Law that states the gravitational attraction between two objects is based on their masses AND the distance between them.
Axis Tilt
The angle between a planet's rotational axis at its north pole and a line perpendicular to its orbital plane.
Long-term climate change
Climate change caused by changes in the tilt of the Earth, shape of its orbit, and the change in positions of continent. (Changes over thousands to millions of years)
Short-term climate change
Climate change due to changes in the amount of energy released by the Sun, sudden events such as asteroid impact or volcanic eruption, etc. (Change occurs over decades to thousands of years)
Sunspot
A region of darker color on the Sun caused by explosions on the Sun's surface that release large amounts of energy
Rotation
The type of movement that occurs when an object is spinning on an axis. 1 full spin = 1 day.

Causes day & night.
Revolution
Orbit around another space object. 1 full revolution = 1 year.
Solstice
The day when the Sun reaches its greatest distance north (summer) or south (winter) of the equator
Equinox
The day when neither pole is tilted towards the sun. It happens two times a year on the 1st day of spring & 1st day of fall. Day and night are of equal length. The sun's rays are focused on the equator.
High Tide
The tide when it is at its highest level and waves reach farther inland.
Low Tide
The tide when it is at its lowest level and waves recede (move) farther into the ocean.
Spring Tide
Large tidal range which occurs when the Moon, Sun and Earth are aligned.

There is a large difference between high and low tide levels because the high tides are very high, and low tides are very low.
Neap Tide
Small tidal range that occurs when the moon is at a right angle with the Earth and the Sun;

The difference between high and low tides is small because the high tides are not very high tides and the low tides are not very low.