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44 Cards in this Set
- Front
- Back
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Accomplishment(s) of Aristotle
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Proved the Earth is a sphere. (shape of the earth)
Earth produced curved shadows on the moon, you see different stars in the sky moving north to south, all objects fall straight down. |
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Accomplishment(s) of Aristarchus
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Determined the relative sizes of the Earth, moon and sun in comparison to each other and the distances between each one.
Also deduced that the Earth must orbit the sun. Was not accepted yet. |
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Accomplishment(s) of Eratosthenes
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Determined the physical size of the Earth by comparing shadows in 2 different cities and using simple geometry.
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Accomplishment(s) of Hipparchus
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Revised many of Aristarchus' observations and discovered that the Earth experiences Precession (the north celestial pole circulates over time, changing direction. Entire process takes 26,000 years)
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Accomplishment(s) of Ptolemy
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Developed the Geocentric model. Explained retrograde motion using epicycles.
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Accomplishment(s) of Copernicus
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Developed the Heliocentric model. This model could explain retrograde motion without epicycles.
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Accomplishment(s) of Tycho Brahe
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Observed the night sky daily for 25 years. His positions were accurate to 1 arc minute.
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Accomplishment(s) of Joannes Kepler
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Worked under Tycho Brahe. Refined the Heliocentric model and developed the 3 laws of planetary motion.
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Accomplishment(s) of Galileo
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Made 5 observations to support the Heliocentric model.
1. Venus shows phases similar to the moon. 2. Jupiter has 4 bright moons. 3. Lunar features seem similar to Earth. 4. Sun is blemished with spots and rotates. 5. Uncountable stars in the Milky Way |
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Describe Kepler's 3 laws of planetary motion
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1. Planets orbit the sun in elliptical (oval) orbits.
2. A planet's speed varies inversely with distance. The closer the planet is to the sun, the faster it travels. 3. The farther out a planet is from the sun, the longer it takes to complete one orbit. Mass plays no role. |
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Describe how one would measure the size of the Earth (Eratosthenes)
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By measuring the difference in the sizes of shadows in different cities.
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List and explain Newton's 3 laws
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1. Conservation of momentum. An object will remain at rest or continue in motion at a constant velocity unless acted upon by an external force.
2. Force law. The acceleration an object experiences is related to the mass of the object and the force acting upon it. Greater the force, greater the acceleration. Lower the mass of the object, greater the acceleration. etc. 3. When 2 bodies interact, they exert equal and opposite forces onto each other. |
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Describe the differences between refractor and reflector telescopes
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Refractors use a curved lens for the object whereas reflectors use a mirror or mirrors.
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What effects does the atmosphere have on light that travels through it to the surface?
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The atmosphere disrupts light that comes through (causing stars to twinkle) and completely blocks certain wavelengths from getting through at all.
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Describe how astronomers compensate for the effects of the atmosphere when making observations?
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They place telescopes on top of tall mountains, in space, and use "adaptive" optics.
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Where would one place a telescope in order to observe gamma rays?
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In space. Gamma rays are completely blocked out by the Earth's atmosphere and cannot reach the surface of the Earth.
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Describe how astronomers can use light to determine relative temperature
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(Wien's Law). By observing the blackbody curve. If the peak of the wavelength of light is blue-shifted, the temperature is higher. If it is red-shifted, it is cooler.
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What is the photosphere, and what is it's average temperature?
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The photosphere is the bottom most layer of the sun, considered to be its surface. Its average temperature is 5800 K (11,000 F).
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What are sunspots and why do they occur? What is the temperature like in sunspots?
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Sunspots are magnetically active regions on the sun. They occur when magnetic fields wrap around the sun too many times and start to come out of the surface. The temperature is cooler than the surrounding photosphere.
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How long can a sunspot last and how long is the cycle?
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A single sunspot can last from hours to months. The entire cycle for sunspot activity is approximately 11 years.
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Does the sun rotate? If so, describe its rotation
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The sun does rotate. It rotates faster at the equator than the poles.
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What does the discovery of binary stars allow us to do?
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Binary stars allow us to determine the mass of the stars by measuring their orbit around each other.
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Define:
1. Apparent Magnitude (m) 2. Absolute Magnitude (M) 3. Apparent Luminosity (l) 4. Absolute Luminosity (L) |
1. (m) is the brightness of a star as seen from the Earth.
2. (M) is the brightness of a star if it is 10 parsecs away. 3. (l) is the measure of the amount of energy we receive on Earth from the star. 4. (L) is the measure of the total amount of energy the star releases. |
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1. Determine the distance between Earth and a star if M=10 and m=5.
2. Determine the distance between Earth and a star if M=4 and m=8. |
(M) at 0 is equal to 10 parsecs. m=M. Determine a value for (m) to find distance.
1. 5 = 10 / -5 = 0 / Star is 5 parsecs away (less than 10 parsecs). 2. 8 = 4 / 4 = 0 / Star is 14 parsecs away (more than 10 parsecs). |
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What is the HR (Hertzsprung-Russel) Diagram and what is its significance?
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The HR Diagram is a plot of the brightness of stars (M) as a function of their temperature/color/spectral type. Stars fall naturally onto certain areas of the diagram. 90% of stars are on the main sequence.
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What is the difference between magnitude and luminosity?
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magnitude is our perception of brightness from a star, and luminosity refers to the amount of energy we receive from a star.
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What is the most important parameter to the lifespan of a star?
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The star's mass. The more massive a star is, the shorter its lifespan will be.
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How do electrons produce light? What does electron quantization refer to?
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Electrons produce light when they transition from an outer to inner orbital, releasing energy.
Quantization refers to the electrons only absorbing or emitting specific amounts of energy. |
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Describe the difference between an absorption spectrum and an emission spectrum
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Absorption spectra are dark lines on a bright background, whereas emission spectra are bright lines on a dark background.
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What are the 7 spectral classes for stars?
What determines the spectral class a star would be in? |
O, B, A, F, G, K, M (Oh Be A Fine Girl Kiss Me)
Their temperature. |
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What is nucleosynthesis? Where does this occur?
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The process by which smaller atoms combine to form larger atoms. This process occurs in stars until they have reached the point of forming iron in the core. The process continues beyond iron during supernovas.
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What happens when a star exhausts its supply of hydrogen in the core?
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After a star has exhausted its supply of hydrogen in the core, hydrogen fusion stops. Hydrogen continues to burn in a shell around the core for a while afterward. Main sequence stars then turn into red giants. Stars with a mass less than 0.8M (M=mass of the sun) cannot evolve into a red giant under normal conditions.
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What are white dwarfs?
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The core remnants of stars whose fusion stopped because of electron degeneracy.
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What is electron degeneracy? (degenerate electron pressure)
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The outward pressure exerted by the electrons resulting from their being crowded together into too small of a volume. This forces low to medium mass stars to stop their fusion process at a certain point. Those stars will end their lives as a white dwarf.
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What is the Chandrasekhar limit?
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The maximum mass a white dwarf can have. 1.4M (M=mass of the sun)
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What is a type II Supernova? Which kind of stars undergo a type II supernova?
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A type II supernova is the explosion of a very massive star after its fusion process has reached a point where the entire core is iron. Only very massive stars can break through the degenerate electron pressure (electron degeneracy) to generate iron in the core, so only these stars under go a type II supernova.
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What is a neutron star? What is neutron Degeneracy?
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A neutron star is the possible remnant from a type II supernova. Neutron degeneracy is the outward force that works against the collapse of the star, similar to electron degeneracy.
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What are black holes?
What is the Schwarzschild radius? |
Black holes occur when the core of a very massive star collapses after undergoing a type II supernova, and neutron degeneracy fails. They are theorized to have a near 0 volume and near infinite density. No light escapes.
The Schwartzschild radius is minimum distance light can be from a black hole and still escape. |
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How could one detect a black hole?
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You would not be able to physically see it since no light can escape the black hole, but one can observe the mass swirling around it or the visible star the black hole is orbiting (if any).
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What is the apparent shape of the Milky Way (MW)?
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A narrow band that stretches from one horizon to another.
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Name and describe the different types of galaxies
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1. Spiral Galaxy: Pin-wheel shaped
2. Elliptical Galaxy: Spherical to Elliptical shaped 3. Irregular Galaxy: Random shapes |
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Explain the Hubble Law
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Galaxies are receding from each other with a speed proportional to their distance. The farther away a galaxy is, the faster it is receding. This suggests an expanding universe.
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Describe the Hubble Constant
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The Hubble Constant is the slope of the line in the Hubble Law graph. It is related to the age of the universe.
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Describe the differences between an open, closed, and flat universe.
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A closed universe describes a situation where the current expansion of the universe stops, and collapses on itself. An open universe describes a situation in which the universe expands forever without significant slowing. A flat universe is a universe that will expand forever WITH significant slowing, but never stopping.
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