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Test 1 Study Guide

by: Emily Notetaker

Test 1 Study Guide ASTR 1504 - 300

Emily Notetaker
GPA 3.9

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Astronomy: Exploring the Universe
Xinyu, Dai
Study Guide
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Popular in Astronomy: Exploring the Universe

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This 8 page Study Guide was uploaded by Emily Notetaker on Saturday February 13, 2016. The Study Guide belongs to ASTR 1504 - 300 at University of Oklahoma taught by Xinyu, Dai in Spring 2016. Since its upload, it has received 43 views. For similar materials see Astronomy: Exploring the Universe in Astronomy at University of Oklahoma.


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Date Created: 02/13/16
Test 1 Study Guide Chapters 2-5 Chapter 2 Celestial sphere-projection of Earth’s axes and equator into space Ecliptic- path of the Sun across the celestial sphere, tilted 23.5 degrees to equator Zenith-point of the celestial sphere directly overhead Nadir- point of the celestial sphere directly below, can’t be seen Earth is in the way Earth rotates counterclockwise as seen from above the North Pole. From the equator you can observe the entire celestial sphere within 24 hours Circumpolar Stars-stars that don’t set or rise just move in a circle around the celestial pole Polaris- star very near the North Celestial Pole, North Star Constellations- well defined regions of the sky Earth is tilted slightly to the ecliptic plane, so depending on where it is in its orbit the Sun will shine more directly on either the Northern or Southern hemisphere, causing the change of seasons. When your hemisphere is receiving more direct sunlight it is summer. Precession- Earth’s axis of rotation moves in a circle very slowly, once every 26,000 years, shifting the location of the celestial poles Synchronous Rotation- the Moon rotates once in the time it takes it to orbit the Earth, so we always see the some side Solar Eclipse-the Moon moves between the Sun and the Earth, casting a shadow on the Earth. Because the Moon is much smaller than Earth, the eclipse can only be seen within a very small area and doesn’t last long. Happen during the New Moon  Total eclipse-the Moon completely blocks the Sun  Partial Eclipse- the Moon blocks part of the Sun  Annular Eclipse- the Sun appears as a ring around the Moon Lunar Eclipse- the Earth moves between the Sun and the Moon, casting a shadow on the Moon. Because Earth is much bigger than the moon, the entire Moon will be in shadow, the eclipse can be seen from any point on Earth facing the moon at the time, and it will last longer than a solar eclipse. Happen during the Full Moon The Moon’s orbit is tilted 5 degrees from the ecliptic, which is why there isn’t a solar eclipse every New Moon and a lunar eclipse every Full Moon Chapter 3 Aristotelian Model  Geocentric or Earth-centered  Sun, Moon, stars, and planets orbit Earth in perfect circles  Celestial objects are perfect spheres  Couldn’t explain retrograde motion- the occasional apparent reversal of direction of the planets’ orbits Ptolemaic Model  Geocentric  Sun, Moon, stars, and planets orbit Earth in perfect circles  Each planet also orbits a point on its larger orbit of Earth, creating epicycles Retrograde motion caused by epicycles Copernican Model  Heliocentric or Sun centered  Planets, including Earth, orbit the Sun in perfect circles  Retrograde motion caused by Earth catching up to and passing other planets in orbit  Couldn’t accurately predict where a planet would be in its orbit at a given time Galileo- first to look at the sky with a telescope. Discovered four of the moons of Jupiter, craters on the Moon, spots on the Sun, and phases of Venus. Also discovered that objects of different mass fall at the same rate. Kepler’s 1 Law- planets’ orbits are ellipses. The Sun is at one focus and nothing is at the other Kepler’s 2 nd Law or Law of Equal Areas- if you imagine a line connecting the Sun and a planet, the area swept by this line during a set time interval will be equal at any point in the planet’s orbit. Kepler’s 3 Law-planet’s further from the Sun orbit more slowly. Period squared= distance cubed st Newton’s 1 Law-An object at rest will stay at rest and an object in motion will stay in constant motion unless acted upon by an outside force. Inertia nd Newton’s 2 Law- unbalanced forces are what cause changes in motion F=ma rd Newton’s 3 Law- Every action has an equal and opposite reaction Newton’s Law of Gravity- every object in the universe is attracted by gravity to every other object in the universe with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. F=G(m1xm2)/d^2. G=6.673x10^-11 Chapter 4 Light- behaves as both a wave and a particle Light as a Wave- changing electric and magnetic fields create an electromagnetic wave Wavelength= distance between crests of a wave Frequency- number of waves to pass a point each second Amplitude- height of a wave Wavelength and frequency have an inverse relationship λ-c/f Light as Particle-particles called photons carry energy at the speed of light. The amount of energy a particle carries is directly related to the light frequency E-hf h=6.63x10^-34 Visible light makes up a very small part of the electromagnetic spectrum, with wavelengths between 350nm (violet) and 750 nm (red) Spectrum- light separated by frequency. A rainbow is the visible light spectrum Refracting Telescope- use lenses t focus light Reflecting Telescope- use concave mirrors to focus light shorter focal length and light than refracting. Radio Telescope-detect radio waves. Need to be large because radio waves have large wavelengths. Can be connected in an interferometric array to improve resolution. Resolution- smallest detail that can be separated αmin=1.22λ/D Charge Coupled Devices (CCD)- photons strike a grid and are converted to pixels. Creates very high-resolution images. Spectrograph/Spectrometer-separates light into a spectrum. Allows scientist to look at specific wavelengths Atmosphere absorbs gamma rays and x rays, and most infrared and ultraviolet light. To observe these wavelengths telescopes must be built at very high altitudes or in space Astronomic Seeing-limit on resolution due to the atmosphere. Pockets of gas at different temperatures act as lenses, distorting the light and causing blurry images. Adaptive Optics- telescopes use a flexible mirror to adjust for atmospheric distortion. A telescope on Earth can get an image as clear as the Hubble Space Telescope Chapter 5 Molecular Cloud- cold, dense cloud of dust and gas in the space between stars Molecular Cloud Cores- particularly dense areas of the molecular cloud that collapse under their own gravity Protostar- center of molecular cloud, heats up as it collapses. Converts gravitational energy to thermal energy. Becomes a star if it reaches 10millon K and begins to turn hydrogen into helium. Must be at least 0.08 times as massive as the Sun for this to happen Brown Dwarf- protostars not large enough to become stars Conservation of Angular Momentum- the momentum of a rotating object stays constant in the absence of an outside force. Dependent on velocity and diameter. Accretion Disk- wide disk that forms around protostar, conserves angular momentum as the cloud collapses. Material in the disk forms planets, moons, asteroids, and other objects in the star system Particles in the disk collide and stick together and smaller particles are blown into larger ones by gas motion. Planetesimal- object in the disk 1km in size, large enough to pull in objects near its orbital path and grow more quickly. May eventually become a planet Refractory Materials- materials such as rock and metal that don’t melt or evaporate even at high temperatures, concentrated towards the center of the disk near the star Volatile Materials- materials such as water ice, ammonia, and methane that melt or evaporate at moderate temperatures, concentrated towards the edge of the disk far from the star. Planet- round body that orbits a star, large enough to clear other objects from its orbital path and smaller than 13 Jupiters Terrestrial Planet- planet made of refractory materials, Mercury, Venus, Mars, and Earth Giant Planet- planet made of volatile materials; most of the mas is gas. Jupiter Saturn, Uranus, Neptune Primary Atmosphere- gas pulled in from the disk as the planet forms. Giant planets have enough mas to hold the primary atmosphere but terrestrial planets lose it. Secondary Atmosphere- gas released from the center of the planet due to volcanic activity Exoplanets- planets orbiting a star other than the Sun. first discovered in 1992. 5 methods for location Spectroscopic Radial Velocity Method- an orbiting planet causes a star to move. Motion can be detected using the Doppler Effect if the star is on the same plane as Earth  The Doppler Effect- motion causes a change in the wavelengths of light from an object. Wavelength will be smaller and light blueshifted if the object is moving towards you. Wavelength will be longer and light redshifted if the object is moving away. Transit Method- if an orbiting planet moves between its star and the Earth, the light from the star will dim slightly. Can be detected by continuously measuring the brightness of a star. Gravitational Lensing- if a planet passes between the Earth and a background star the planet’s gravitational field will act as a lens and the light from the star will be slightly brighter. Also known as microlensing because the effect is so slight. Astrometry- precisely measuring the location of a star in the sky. If a star has an orbiting planet it will orbit the center of gravity between itself and the planet, and he motion can be observed from above. Movement is slight and difficult to measure, but the previous three methods won’t work if the isn’t on the same plane as Earth. Direct Imaging- directly photographing the planet. Difficult to find a dim planet close to a bright star, and requires extended observation to confirm that an object is a planet and not a background object or a brown dwarf.


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