Earth, Moon, and Sun



Astronomy PT 1

• The relative position of the Earth, Moon and Sun cause many things to happen such as, moon phases, eclipses, solstices, and equinox.

• All things in the universe are in motion, for instance;

o The earth is rotating (spinning)

o The earth is in orbit, or revolves around the sun (goes around the sun)

o The moon is rotating

o The moon is revolving around the earth

o All of the motions above are going counterclockwise.

• The reason earth has day and night is because of the rotation of the earth

• Because earth rotates counterclockwise, the sun appears to “rise” in the east, and “set” in the west

• The moon also rises in the east, and sets in the west for the same reason.

• Actually, all things in space move across the earth’s sky from east to west; for instance stars move from east to west because of the earth’s rotation.

• The seasons happen on the earth because of the tilt of the earth combined with the revolution (orbit) of the earth

• The moon also orbits the earth counterclockwise

• The first day of summer is called the summer solstice—the suns rays are the greatest distance North of the equator. This is the longest day of the year, and the sun is at its highest point in the sky.

• The first day of winter is called the winter solstice—the suns rays are the greatest distance South of the equator. This is the shortest day of the year, and the sun is at its lowest point in the sky.

• We always see the same face of the moon because the moon rotates at the same speed as the moon orbits the earth(about one month)

• Gravity is what governs (controls) all motion in the universe—it is a pulling force

• Inertia is the resistance to a change in motion—if something is moving forward, it wants to continue to move forward (remember the car moving and hitting the brakes…you still go forward).

• Gravity and inertia are the reasons why the moon doesn’t come crashing into the earth as well as why the planets don’t go crashing into the sun.

• The moon orbits the earth approximately every 28 days (almost a month).

• The earth rotates once every 24 hours

• The earth revolves or orbits the sun once every 365 1/4 days

• The moon goes through 8 phases every time it orbits the earth(about once a month)

• The phases are in order starting from the new moon…. New moon, waxing crescent, 1st quarter, waxing gibbous, full moon, waning gibbous, 3rd quarter, waning crescent, and back to new moon.

• Because the moon goes through an entire phase cycle in about one month, each phase changes approximately every 3 ½ days. (so, if a new moon is in the sky, 3 ½ days later you would see a waxing crescent, and 3 ½ days later you would see a 1st quarter, etc..)

• The phases of the moon look like the following:

New Waxing 1st waxing Full waning 3rd waning

Moon Crescent quarter gibbous moon gibbous quarter crescent

[pic]

• Eclipses are when one thing blocks the sun from another thing.

o When the earth blocks the sun from shining on the moon, it is called a lunar eclipse.

o When the moon blocks the sun from shining on the earth, it is called a solar eclipse.

• Lunar eclipses can only happen during a full moon phase

• Solar eclipses can only happen during a new moon phase

• When an eclipse happens, one large body casts a shadow on another body. The darkest part of the shadow is called the umbra.

• The lighter part of the shadow is called the penumbra.

• Note the positions of the moon in the above picture… as the moon revolves counterclockwise, it shows how each phase forms.

• Geocentric/Heliocentric Notes

• For many, many years, people believed that the earth was the center of the solar system, as well as the universe. The people believed that everything revolved around the earth. The first scientist who proposed this idea was Ptolemy. He called this “earth-centered” solar system a geocentric model. Geo meaning earth, and centric meaning centered. His theory held as true for nearly 1500 years.

• Many years after Ptolemy, another astronomer came along and proposed that the earth was not in the center at all, but instead the sun was in the center. This scientists name was Nicolaus Copernicus. He proposed the sun was in the center, and he called this the heliocentric model. Helio comes from the Greek helios meaning sun. Again, centric meaning center, so heliocentric means sun in the center.

• Copernicus had difficulty proving this, but another scientist named Galileo Galilei was able to prove this heliocentric theory by using a telescope. He was the first scientist to use the telescope for astronomy. Galileo discovered that the planet Venus had phases just like our moon. This could not happen unless Venus was going around the sun. He also discovered that Jupiter had 4 large moons orbiting it; this showed that not everything revolved around the earth.

• Both Copernicus and Galileo were correct with the sun being in the center, but they thought the orbits of the planets were round. In this, they were wrong. It was Tycho Brahe and Johannes Keppler who discovered that the orbits of planets and moons were elliptical (oval shaped, and also called ellipses). Using math and science, Keppler showed that the shapes of the orbits could not be perfectly round because the orbital speed increased at points closer to the sun, therefore, they must have been ellipses.

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