Astronomy Mid Term Final – Flashcards
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Expansion of the Universe and the role of gravity.
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The more distant the galaxy is, the faster it moves away. Therefore, the entire Universe is expanding. The galaxies in the local group are held by gravity. Distances between galaxies increases with time.
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Distance units in astronomy: astronomical unit (A.U.), light year.
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1 lightyear = 9.46x10^12 or about 300,000 kilometers per second. 1 Astronomical unit = 1.5 x 10^8 km
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Coordinates on Earth (longitude, latitude) and on the celestial sphere (right ascension, declination).
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Latitude: North and South (right ascension on the celestial sphere), longitude is East and West(declination).
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The Earth's rotational axis tilt and its consequences (seasons).
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The earth's tilt is the reason we have seasons when the tilt is pointed towards the sun, that's when that place has summer.
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Solar and Lunar eclipses.
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Lunar eclipses: Total, partial, and penumbral. Solar eclipses: Total, partial, and annular.
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Constellations: asterisms and modern definition.
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Asterisms: Patterns of stars seen in the sky long ago. There are 88 constellations defined in the 1920's.
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Main components of the scientific process (hypothesis, theory, observation).
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hypothesis - answer to an observation, observation - what you observe. Theory - a hypothesis that has been proved to be true over and over again.
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Physical quantities and their units: distance, speed, velocity, acceleration, force, energy.
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Speed is a rate of covering distance. Speed = distance/t. Velocity = speed and direction. Acceleration: a change in velocity. Velocity has both value and direction, speed represents the absolute value of a velocity. acceleration measures a change in velocity. Force = mass x acceleration. Friction is a force.
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Types of energy (kinetic, potential, radiative, mass (rest) energy).
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Kinetic - energy of motion potential - stored energy, one form is gravitational potential energy, which depends on gravity and how far it can fall as a result. Radiative energy - the energy carried by light. Thermal - a form of kinetic energy, the collective kinetic energy of many individual particles within a substance. Often measured in Kelvin (K) Mass (rest) energy - Discovered by Albert Einstein, rest energy is potential energy stored within the mass of an object. E = mc2
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Newton's Laws (including the Law of Gravitation) - (3)
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1. In the absence of a net force, an object moves in a straight line with a constant velocity (or keeps resting). 2. Force = mass x acceleration 3. For any force, there always is an equal and opposite reaction force. Universal Law of Gravitation: Every mass attracts every other mass, attraction is directly proportional to the product of their masses, attraction is inversely proportional to the square of the distance between their centers. Fg(9.8m/s2)=G(6.67x10^-11) x M1-M2/d2
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Kepler's Laws (3)
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Laws of Planetary Motion 1. The orbital of each planet is an ellipse with the sun at one focus. 2. As a planet moves around its orbit, it sweeps out equal areas in equal times. (The closer a planet is to the sun the faster it goes and vice-versa) 3. p2=r3 or the planet's orbital squared is equal to its semi major axis cubed.
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Conservation of energy, momentum, and angular momentum Laws.
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Momentum is the product of mass and velocity P=m x v. The total momentum of an isolated system is conserved. Angular momentum = m x v x r. In the absence of net torque (twisting force), the total angular momentum of a system remains constant.
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Electromagnetic (EM) waves (regions of the EM spectrum, basic properties of EM waves, wavelength, frequency).
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The shorter the wavelength the higher the frequency. Radio, Infrared, Visible spectrum, Ultraviolet, X-Ray, and Gamma rays.
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The Doppler effect.
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Similar shifts in wavelengths of visible light. Light moving toward us is blue-violet aka blueshift, light moving away from us is red aka redshift. Can determine from rest wavelengths aka stationary wavelengths.
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Atomic structure (protons, neutrons, electrons, atomic numbers, masses, isotopes).
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92 Chemical elements have been identified in the Universe. Nearly 20 more have been created artificially. Each chemical element is made from a different type of atom. Atoms are made from particles called protons, neutrons, and electrons. Protons and neutrons form the nucleus in the center of the atom. Electrons surround the nucleus.
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Types of radiation spectra and processes (absorption, emission, continuum, spectral lines).
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Light can interact with matter in 4 basic ways: It can be emitted by the process of emission. It can be absorbed (i.e. your hand) by the process of absorption. If something allows light to pass through it is transmitting the light in a process called transmission. If light bounces in one direction it is called reflection. When the bounce is random it is called scattering.
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What is the age of the Universe?
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14 billion years. (13.6)
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What is the age of the Solar System?
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4.6 billion years.
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Roughly, how many stars are in the Milky Way galaxy?
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100 billion.
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Roughly, how many galaxies are in the Universe?
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500 billion.
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What is a galaxy?
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A great island of stars in space, containing from a few hundred million to a trillion or more stars, all held together by gravity and orbiting a common center.
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Why does the Milky Way look like a band from the Earth?
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Because you can see the Milky Way all around Earth. If we were too far we'd only be able to see it from one point, if in the center we would be blinded by the light.
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What is the meaning of the universal expansion?
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It means that galaxies are moving away from us but our galaxy and solar system stays the same.
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Is the Solar system expanding?
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No.
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Is the Milky Way expanding?
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No.
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Zenith
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Point directly overhead.
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horizon
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Boundary between the Earth and the sky.
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meridian
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Imaginary half circle stretching from the horizon due South, to Zenith and the Horizon due North.
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altitude angle
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Angle between, the observer, sun, and the horizon.
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equinox
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Tilt of the Earth is neither toward or away from the sun.
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solstice
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Earth's tilt is as far as it gets towards/away from the sun.
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Why do we have seasons?
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Because of the Earth's tilt. 23 degrees
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What is a typical shape of a planetary orbit?
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An ellipse.
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Why do not we see a lunar eclipse every month?
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A lunar eclipse occurs when the Moon enters the Earth's shadow. A solar eclipse occurs when the Moon's shadow falls on the Earth. They do not happen every month because the Earth's orbit around the sun is not in the same plane as the Moon's orbit around the Earth. If you were to draw a little Earth in orbit around a little sun on a piece of paper, then you would not be able to accurately draw the Moon's orbit on that same piece of paper. Sometimes the Moon will be above the paper, other times below it. Only when the Moon is crossing the plane of the Earth's orbit (the paper) just as it is lining up with the Earth and Sun will an eclipse occur.
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There are more solar eclipses than lunar eclipses: why is it easier to observe a lunar eclipse?
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Lunar eclipses last 2 - 4 hrs while solar eclipses last only a few minutes. Also, lunar eclipses can be seen by the entire night side while lunar eclipses can only be see from certain angles.
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Who were the most influential figures in the history of astronomy and what is their contribution to the science?
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Copernicus: Late 1500's, started a scientific revolution by proposing the heliocentric model of the Solar System. Nevertheless, his major assumption was that planet's followed perfectly circular orbits. Johannes Kepler: Student of Tycho, took all of his teacher's data and proposed his three laws. Newton - Planetary motion. Galileo - telescopes.
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What is retrograde motion and how was it explained by the Ptolemaic and Copernican systems?
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Retrograde motion is when a planet appears to go backwards. This was explained by epicycles.
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What is geocentric system?
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The belief that the Earth is the center of the planets.
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What is heliocentric (Sun-centered) system?
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The belief that the sun is the center of the solar system.
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What is the ultimate direct proof that the Earth is not stationary, not the center of the Solar system?
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Stellar parallax.
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What is the place of the visible light in the electromagnetic (EM) spectrum?
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In the middle, 400nm - 700nm
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What are the main parameters of an EM wave (wavelength, frequency, amplitude)?
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The longer the wavelength the lower the frequency. Radio waves, infrared, visible spectrum (red to violet) ultra violet rays, X-rays and Gamma rays.
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What kind of frequencies (wavelengths) and energies do different types of photons have (for example, X-rays have high frequencies, low wavelengths, and high energies)?
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radio (longest), infrared, visible spectrum, ultraviolet, X-rays, gamma rays (shortest)
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How a photon's energy and frequency (wavelength) are connected?
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photon's are particles of light, light is determined by wavelengths or frequency (how many peaks pass any given place per second).
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What is the difference between mass and weight?
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Mass: The amount of matter in your body. Weight: The force that a scale measures when you stand on it. Includes both mass and forces including gravity, acting on your mass.
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What is weightlesness?
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A constant state of free fall.
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Velocity
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Both the speed and direction.
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Acceleration
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The way that velocity changes in any way. Speed, direction, or both.
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Momentum
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Product of an object's mass and velocity. Momentum = mass (velocity)
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Angular Momentum
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Circling momentum. Any object that is either spinning or moving along a curved path.
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What is the acceleration of gravity?
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The acceleration of a falling object. 9.8 meters per second.
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What elementary (subatomic) particles make up atoms?
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Protons, electrons, and neutrons.
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What is the atomic structure?
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The structure of an atom, theoretically consisting of a positively charged nucleus surrounded and neutralized by negatively charged electrons revolving in orbits at varying distances from the nucleus, the constitution of the nucleus and the arrangement of the electrons differing with various chemical elements.
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What elementary particle is responsible for emitting radiation in atoms?
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electrons/photons
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What happens when radiation is emitted or absorbed by an atom?
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It emits light. Electrons are changing levels.
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What is speed and what is velocity?
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Speed is how far an object will go in a certain direction. Velocity is both the speed AND the direction an object is going in.
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What does the law of conservation of angular momentum state and what are its consequences?
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As long as there is no external torque, the total angular momentum of a set of interacting objects cannot change. In other words, as radius decreases, velocity increases because the product (of mvr) must stay the same.
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What is the law of energy conservation are how does it work?
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Energy can neither be created or destroyed. Objects can only gain or lose energy by transferring energy to other objects.
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1. Draw a Sun's path on a certain day of the year as viewed from a certain place on Earth.
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....
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2. Calculate the amount of some form of energy (potential, kinetic) that an object with certain physical quantities (mass, velocity, height) has.
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KE = ½ mv2 km/hr acceleration of gravity: (mass) 9.8 m/s (height)
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3. Calculate the amount of radiation (power) from a complex body of a certain temperature and surface area.
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σT^4 = 5.67 x 10^-8 watt/m2 x K4
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4. Calculate the maximum wavelength or frequency of the radiation from a complex body of a certain temperature and figure out what spectral range it is in.
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Wien's Law - wavelength max = 2.9 x 10^6/T. 300,000 km/s/ 537nm
