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CSU / Astronomy / AA 100 / Why do we see phases of the moon?

Why do we see phases of the moon?

Why do we see phases of the moon?


School: Colorado State University
Department: Astronomy
Course: AA 100
Professor: Roger culver
Term: Fall 2015
Tags: lunar, MoonPhases Eclipse Vocabulary, Johannes Kepler, velocity, and Circumference
Cost: 50
Name: Study Guide for AA101 Miderm 1
Description: These are notes I took during lecture and after taking the quizzes, hopefully they help prepare for our exam!
Uploaded: 02/10/2017
5 Pages 42 Views 3 Unlocks

Notes for Midterm 1

Why do we see phases of the moon?

Lunar Phases/Eclipse Material 

● Waning​-shrinking 

● Waxing​-growing 

● The moon’s “face” appears the same to us due to its synchronous rotation (rotation on its axis taking the same time as its orbit) 

● The orbital period of the moon is 27.3 days (synodic) and its complete cycle phase cycle is 29.5 (sidereal) 

○ Slight elliptical orbit 

● The moon is 385,000 km away from the earth 

● The moon is a natural satellite (orbits naturally) 

● The moon wanders ½ degree per hour to the East or 12 degrees every day ● Complete phase cycle is 29.5 days 

When does the moon rise?

● The moon “glows” because it reflects sunlight 

● Why do we see phases of the Moon? 

○ NOT caused by the Earth’s shadow 

○ No matter where the moon is in its orbit, 50% is illuminated by the Sun ○ Earth can only see part of the sunlit moon 

○ Phases always shrink to the left and grow to the right 

○ Crescents are always closest to the sun 

● When does the Moon rise? 

○ Moonrise/Moonset depends on phase 

○ A new moon can only be “seen” during the day 

○ A third quarter moon can be seen from late evening through morning ● The moon rotates so the same side always faces the earth 

What is sidereal and synodic month?

If you want to learn more check out What did the peace of westphalia do?

● Synodic​ vs. Sidereal Month 

○ Sidereal Month-how long it takes the moon to orbit the earth (27.3) 

○ Synodic-how long it takes to orbit the earth (extra 2.2 days) 

● We don’t see an eclipse at every new or full moon because the moon’s orbit is inclined by 5 degrees 

● Because of this, the sun, moon and earth are online lined up twice a year ● Penumbra​-weaker shadow, partial, some sunlight is blocked 

● Umbra​-darker shadow, total shadow and all sunlight is blocked 

● Lunar eclipses can only occur in the moon’s full phase 

○ Penumbral Lunar Eclipse​-passes through penumbra (not very dark) ○ Partial Lunar Eclipse​-part of moon passes through the umbra Don't forget about the age old question of What happens when cultures collide?

○ Total lunar eclipse​-moon passes entirely through the umbra 

○ These are red because the atmosphere refracts and scatters sunlight ● Moon’s orbit+earth’s rotation=short eclipse 

● If the Earth is viewed above the north pole, it appears to be rotating clockwise

● To an observer in the Northern Hemisphere, the moon orbits the Earth in a counter closewise directions 

○ Week 1: New moon-Waxing crescent 

○ Week 2: First Quarter-Waxing Gibbous We also discuss several other topics like What is the importance of using a balance sheet?

○ Week 3: Full Moon-Waning Gibbous 

○ Week 4: Third Quarter-Waning Crescent 

● New moon 

○ Rising-6 am 

○ Meridian-12pm 

○ Setting-6pm 

● Waxing Crescent 

○ Rising-9am 

○ Meridian-3pm 

○ Setting-9pm 

● First Quarter 

○ 12pm 

○ 6pm 

○ 12am 

● Waxing Gibbous 

○ 3pm 

○ 9pm 

○ 3am 

● Full Moon 

○ 6pm 

○ 12am 

○ 6am 

● Waning Gibbous 

○ 9pm 

○ 3am 

○ 9am 

● Third Quarter 

○ 12am 

○ 6am 

○ 12pm 

● Waning Crescent 

○ 9pm 

○ 3am 

○ 9am Don't forget about the age old question of What are the core activities of scientific approach?

Solar eclipses 

○ Partial Solar Eclipse​-standing in the penumbra 

○ Total Solar Eclipse​-standing in the umbra

○ Annular Solar Eclipse​ (ring)-the size of the moon is a little bit too small to block all of the sun 

● Corona of the sun is very hot but very thin We also discuss several other topics like What would be an example of the use of the sociological imagination?

● Solar eclipse only occur in a new moon phase 

● Sidereal Day-23hr 56 min 

● Solar Day-24 hrs 

Quiz 1 Material

● The universe is 13.82 billion years old

● All the atoms that make up the composition of the universe (including human beings) were once inside a star.

● An astronomical unit (AU) refers to the Earth’s average distance from the sun (150 million km)

● Ecliptic-the Sun’s orbital path across the celestial sphere We also discuss several other topics like What are the changes to copyright law through recent history?

● There are 60 arcseconds (“) in 1 arcminute (‘), and 60’ in 1 degree (3600” in one degree) ● Circumpolar-orbit contained in one’s horizon 

● The reason for seasons- the tilt of Earth’s axis accounts for sunlight to hit the Earth differently depending on the time of year (Earth’s position in its rotation around the sun) ● Polaris appears very near the celestial pole, so it can be used to find North 

Quiz 2 Material 

● Eratosthenes measured Earth in 240 BC and estimated it was 42,000 km but it was 40,000 km 

● He did this by comparing the maximum altitude of the Sun in two cities at different latitudes 

● part/total=difference/360=dist/circumference 

● Prograde motion: over many nights, planets slip eastward against the sky ● Retrograde motion:occasionally planets slip backwards (westwards) against the sky over many nights 

○ They move on small circles that move on larger orbits around the Sun ● The Sun never goes in retrograde motion 

● When saturn is going through a period of retrograde motion, Earth is passing Saturn in its orbit while they are both on the same side of the Sun 

● Lunar eclipses are more common than solar eclipses because the Earth casts a bigger shadow than the moon 

● Ancient people could not detect stellar parallax because they lacked the equipment necessary to measure very small angles 

● Stellar parallax is more apparent the closer a star is. Stars that do not exhibit stellar parallax are very far away 

● The seven days of the week are named after the seven objects seen to the naked eye that move along the constellations 

● In Ptolemy’s model of the Universe, the Sun was between the orbits of Venus and Mars

● Although Copernicus was correct in his heliocentric model of the universe, he did not take into account that the planets’ eliptical orbits 

○ He marked their orbits as circular, so his prediction of their positions was not accurate 

● Copernicus died in 1543, the year he published his book suggesting a heliocentric universe 

Quiz 3 Material 

● When a planet is referred to as having a highly eccentric orbit, this means it is much closer to the Sun in some parts of its orbit than others 

● Tycho Brahe, a mentor of Galileo, was responsible for collecting data which led to Kepler’s discovery of the elliptical orbit of planets.​ He also proved that comets existed beyond Earth’s atmosphere. 

● Galileo observed many things which led to his conclusion of a Heliocentric universe. He did not prove this observation (Copernicus did) but his evidence was extensive enough that this model of the universe was accepted. 

○ Although he made many observations, stellar parallax was not one of them, this was made by Friedrich Bessel. 

● To somebody on Venus, Earth would appear to be full while Venus is in its full phase. ● Kepler’s third law (P^2=a^3) gives us this information 

○ A planets period is not relative to its eccentric orbit or mass 

○ The closer a planet is to the sun, the higher its speed 

○ Orbits sharing the same semi-major axis share the same period as well ● If an object has an orbital period of 8 years, its average distance from the sun is 4 AU ○ This conclusion can be drawn from Kepler’s third law 

○ P=8, 8 squared=16 

○ 16=a cubed 

○ Take the cube root of 16 and that gives you 4 (a is always in Astronomical Units) ● Kepler’s 2nd law-planet’s move faster near the sun and slower further from the sun, so it “sweeps” (which refers to an imaginary line that connects the planet and the sun) equal areas in equal times 

● Weight=mass x gravity 

● Due to the fact that astronauts are in a constant state of freefall, they appear “weightless” 

● Newton’s law of universal gravitation states that the gravitational pull on an object is proportional to its mass 

○ Therefore, two objects of the same mass will have the same gravitational force on an object, whereas an object twice the size as another object will have twice the gravitational force 

● Velocity refers to acceleration AND direction 

● Radiative energy is energy carried by waves not yet in the form of matter, such as light waves.

● Temperature measured the average kinetic energy (energy of motion) of particles in an object/substance 

● Newton’s universal law of gravitation also states that the gravitational force on an object is inversely proportional to the distance between it an another object 

○ Therefore, if you triple the distance between two objects, the gravitational force is decreased by 3 squared or 9 

● The tides of Earth’s oceans are caused by the change in gravitational force exerted by the moon as it orbits the Earth 

● Tides are highest during the moon’s new and full phases due to its alignment with the sun, which adds to the gravitational force. 

● Tides are lowest at first and third quarters of the moon. 


○ Velocity=distance/time (and direction) 

○ Kepler’s 3rd law: P^2=a^3 

○ Circumference=(2pi)r 

● Velocity=distance/time along with its direction 

● Acceleration: change in velocity/change in time 

● Force:a push or pull that causes an object to accelerate 

● Newton Developed laws of motion and gravity, he also studied the nature of light, built the first reflecting telescope and invented calculus 

○ Inertia:objects move at constant velocity until acted upon by an outside force ○ Law of Acceleration: F=ma (mass is the amount of matter in an object) ○ Action-Reaction: For every force, there is always an equal and opposite reaction

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