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OU ASTR 1514 - Exam 1 Study Guide

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ASTR 1514 1st Edition Exam # 1 Study Guide Motions in the sky- The North and South poles have the most circumpolar stars (Never rise or set)- The equator Contains most equatorial stars (Rise and Set), this indicates that more stars are visible at the equator - Ex: Near the poles have the most circumpolar stars, Ontorio Canada has more circumpolar stars that Mexico City. - Intermediate latitude: The angle from the pole to horizon is equal to the latitude. - AU = Astronomical Unit, the average distance from the Earth to the sun. 150 million kilometers. Motion of the Moon- The orbit of the moon is approximately 29.5 days around the Earth- The moon shines by reflecting light from the sun, only being halfway lit. - The moon orbits in the same direction as the Earth around the sun - Synchronous Rotation – Moon completes one full rotation in one full orbit around theEarth- Moon Phases1. New Moon – Can’t be seen2. Waxing crescent – Illuminated increased size crescent3. First Quarter – Half of the moon’s front surface is visible4. Waxing gibbous – Moon is not round but very close 5. Full Moon – Moon is big and illuminated to appear round6. Waning gibbous – Appears smaller than waxing gibbous7. Third Quarter – Half of the moon is lit8. Waning crescent – Small portion of the moon is illuminated- Full moon is directly overhead at midnight- Each phase of the moon is about 3.5 days long- First quarter moon sets at midnightKeplers Laws- Paralax – Effect or position or direction of an object appears to differ when viewed from different positions. - Retrograde motion – Planets farther away from the sun appear to move in a backwards direction. - Geocentric – The universe is centered about the Earth (Ptolemaic universe)- Heliocentric – The universe is centered about the Sun (Copernicus)Keplers First Law- Planets have an elliptical orbit around the sun. 1. Each ellipse contains an eccentricity: How elongated the ellipse is, and how far apart the foci are. 2. Nearly circular ellipses have very small eccentricity and the foci are close together3. Long thin ellipses have an eccentricity closer to 1 and the foci are far apart. Ex: Earth eccentricity = approx.. 0.0167Kepler’s Second Law- Law of Equal Areas- Orbits sweep out equal areas in equal amount of times- Applies to only one planet at a time- Planets orbits are fastest when closest to the sun Kepler’s Third Law- A planets orbital Period squared is proportional to it’s average distance from the sun cubed. - Meaning that Planets the are closer to the sun have a faster orbit. Newton’s First Law- A body continues at rest or in uniform motion in a straight line unless acted upon by some force. - Ex: You are traveling on a bike and hit a curve, unless acted upon by gravity, you could continue flying through the air at a constant velocity. Newton’s Second Law- Unbalanced forces cause changes in motion.Ex: Speeding up with a gas pedal in car (accelerating), and slowing down with brake pedal (decelerating)- Change in direction is a change in motion, Driving around a curve, speed not changing but direction is - A larger force will result in a larger acceleration. - Force = (Mass)(Acceleration)- Force has a direct relationship with acceleration.- Acceleration has an inverse relationship with mass. - Ex: It requires a greater force to push a heavier kart compared to a light one. Newton’s Third Law- Forces occur in Action-Reaction pairs.- The two forces are equal in size- The two forces have opposite directionsEx: Astronaut in space throws an item to push himself backwards, the two astronaut and item exert an equal force on each other in opposite directions.Gravity- Gravity is a force therefore it has an acceleration- Acceleration of gravity is approx.. 9.81m/s2 - The force that you feel depends on the force of gravity and the mass of your body content. - Weight = (Mass)(9.81)- Force of gravity is what we mean by weight.Properties of Gravity- Gravity is an attractive mutual force between ant two objects with mass. - Depends on the scale of the masses and the distance between them. - The greater the mass than the greater the attraction and greater the force. - The greater the distance then the weaker the force and attraction. - Distance has an inverse relation with Force of gravity. Gravity and Orbits- Orbits are one body falling around another due to gravity. - Less massive object is a satellite of more massive object.Light- Light provides the predominant information that astronomers use to understand astronomical objects- We collect light through telescopes to determine an astronomical objects temperature, composition, and speeds and more. - Light moves at a constant speed – 300,000 km/s in a vacuum. - Measured by Rhoemer when he was observing Jupiters moons.- Light will travel faster in less dense materials. - Light is a wave of combined electricity and magnetism, called an electromagnetic wave. Properties of Waves- Wavelength: Length between the crests of a wave- Amplitude: Height of the wave- Frequency: The number of waves that pass by each second.- Period: Time it takes a wave to complete one cycle- Long wavelength means low frequency- Short wavelength means high frequency- Wavelength = Speed of light (300,000 km/s ) divided by the frequency.- Wavelength has an inverse relationship with frequency. - Violet light has a shorter wavelength than red light therefore it has a higher frequency. - Light behaves as both a wave and particle. - Photon – Particle of light- Photons carry energy: Energy = h (constant) times the frequency.- Energy has a direct relationship with frequency- High energy photons = light with larger frequency. - Low energy photons = light with lower frequency- Violet light has higher energy and higher frequency than redlight - Light is a wave because it exhibits interference, waves interact with one another to become stronger - Ex: Light from a laser pointer exhibits interference therefore it is a waveTelescopes- In a perfectly dark sky away from city lights and pollution we can see about 4500 stars in the night sky in each hemisphere. - In a larger city with plenty of light pollution only about 35 stars are visible. - Telescopes collect light to see distant objects- Aperture of a telescope is much larger than a human eye so they collect more light- Bigger the aperture the more light that they collect.How telescopes work- Because light is a wave it is refracted when it enters a medium. -


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