Earth and Moon System Quiz

Earth-Moon System

• The Earth-Moon system depicts the Earth and its moon, with the Earth positioned in front of the moon.

Shape of the Earth

• Ancient Mediterranean peoples visualized Earth as a flat disc, with the Nile River's mouth at the center and a vast ocean surrounding it.
• Greek philosophers like Pythagoras and Aristotle, during the 5th and 3rd centuries BCE, proposed a spherical Earth.
• During the Middle Ages, the flat Earth theory gained popularity, despite the spherical model being predominant in the culture of the time.
• Evidence for a spherical Earth includes the Earth's shadow during lunar eclipses (only a sphere casts a circular shadow), the progressively wider horizon as elevation increases, and the disappearance of a ship's hull below the horizon as it sails away (revealing the curvature).
• During the 16th century, the Magellan-Elcano expedition circumnavigated the globe, providing physical proof of a spherical Earth.
• Modern satellite imagery and space exploration further confirm the spherical shape, but with slight irregularities, like a flattened sphere at the poles.

Shape of the Earth: Further Details

• Earth's shape is not a perfect sphere; it's an oblate spheroid.
• The Earth's rotation causes it to bulge at the equator and flatten slightly at the poles.
• The oblate spheroid shape is approximated by an ellipsoid of revolution, which is formed by rotating an ellipse about its shorter axis.
• Earth's shape is more precisely described as a geoid, which accounts for the uneven distribution of mass within the Earth.

Earth's Coordinates

• Earth's coordinates are based on imaginary locations and lines.
• The North and South poles are the intersection points of the Earth's axis of rotation with its surface.
• The equator is a circle around the Earth formed by a plane perpendicular to the axis of rotation and passing through its center.
• Parallels are circles formed by planes parallel to the plane of the equator. They are used to measure latitude.
• Meridians are semi-circles connecting the two poles. They are used to measure longitude.
• Latitude measures the angular distance of a point from the equator (0° to 90° N or S).
• Longitude measures the angular distance of a point from a prime meridian, typically the Greenwich meridian (0° to 180° E or W).
• Altitude measures a point's height above sea level.

Motions of Earth

• Earth undergoes several motions including rotation, revolution, and very slow millenary motions.

Earth's Rotation

• Earth's rotation is a 360° spin about its axis, approximately every 23 hours, 56 minutes, and 4 seconds (sidereal day).
• Differences between the sidereal day and the solar day occur due to Earth's orbital motion around the sun.
• The Coriolis effect, a consequence of Earth's rotation, causes moving objects to deflect right in the Northern Hemisphere and left in the Southern Hemisphere.

Earth's Revolution

• Earth orbits the sun in an elliptical path called the ecliptic, lasting 365 days, 6 hours, 9 minutes, and 10 seconds (sidereal year).
• The varying distance from the Earth to the Sun within its orbit results in differing time periods.
• Earth's orbit results in the change of seasons.
• The tilt of Earth's axis relative to its orbital plane is responsible for the change of seasons.

Earth's Millenary Motions

• Earth's long-term motions over millennia also influence climate patterns.
• This includes precession (a slow wobble of Earth's axis), changes in orbital eccentricity, and variations in the tilt of Earth's axis.

Moon

• The moon is Earth's only natural satellite.
• Its physical characteristics include a diameter about 1/4 that of Earth and a mass about 1/81 that of Earth.
• Also, the surface gravity is roughly 1/6th that of Earth.
• The moon has no atmosphere, no liquid water, no weather, and no protection from asteroids.
• There's significant variation in its surface temperature between day and night.
• The surface is marked by highlands (called "terrae"). They are light-colored and highly cratered.
• The moon also has dark, smooth plains called "maria." These are mainly solidified lava.
• The moon has countless craters of varying sizes and forms.

Moon's Origin

• The most widely accepted theory for the Moon's formation is the giant-impact hypothesis.
• This theory suggests that a Mars-sized object (called Theia) collided with the early Earth, throwing debris into orbit which eventually coalesced to form the Moon.

Moon's Motions

• The moon rotates on its axis, taking approximately the same amount of time to rotate once as it does to orbit Earth.
• This results in the moon always showing the same face towards Earth.
• The moon revolves around Earth in an elliptical orbit.
• The moon's revolution around Earth and the Earth's rotation cause variations in moon visibility (phases).

Lunar Phases

• The varying illumination of the Moon by the Sun as viewed from Earth causes the different phases.
• There are various phases of the moon from new to full and back again.

Eclipses

• Eclipses occur when the Earth, Moon, and Sun align in a specific configuration.
• A solar eclipse occurs when the Moon passes between the Sun and the Earth, casting a shadow on Earth.
• A lunar eclipse happens when the Earth passes between the Sun and the Moon, casting a shadow on the Moon.

Test your knowledge about the Earth-Moon system and the historical perspectives on the shape of the Earth. This quiz covers ancient beliefs, scientific advancements, and modern evidence proving the Earth’s spherical shape. Challenge yourself with questions that span history and astronomy!