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18 Cards in this Set
- Front
- Back
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What was William Herschel looking for when he discovered Uranus? What made Herschel particularly suited for discovering planets? In what 2 ways did Uranus reveal itself to Herschel as a planet? What is it about Uranus' orbit that caused it to be considered a planet instead of a comet? What is the origin of Uranus' name?
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He was looking for stellar parallax when he discovered Uranus. He used to build his own telescopes and built one of the largest telescopes of the time in his backyard to observe the skies. He realized it was a planet because it moved relative to the stars rather than with the stars. Also, when he increased magnification of the body, it appeared to become larger. This is different than stars because stars remain point-like in shape when magnified. Uranus was seen to have a near circular orbit around the Earth which deemed it a planet. Uranus was the Greek God of the sky, father of Saturn and grandfather of Jupiter.
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What did Kepler believe existed between the large space between Mars and Jupiter? Explain why Bode's Law supported this idea.
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Kepler believed there was an undiscovered planet in the large space. Bode’s law was a numerical trend that he applied to the orbits of the planets; however there was one value in between Mars and Jupiter which did not apply to a planet. He believed this meant there was an undiscovered planet for this value.
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What is the name of the object found in 1801 between Mars and Jupiter? What was this object finally classified as, and why? What is this object a part of?
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Ceres was the name given to the large body found in this area. It was later classified as an asteroid because it was small (smaller than our moon). It is a part of the asteroid belt in between Jupiter and Mars.
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What caused Adams and Leverrier to suspect the existence of a planet beyond Uranus? When this planet was found, what was it named, and why?
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Uranus’ orbit was seen to deviate from its usual nearly circular path so they believed that there must be a planet beyond Uranus that is causing the deviation due to the planet’s gravitational pull. This planet was found in 1846 and was named Neptune (greek god of the sea) because of its blue colour.
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How were the masses of Uranus and Neptune 1st measured? How do their masses compare with the other planets? Based on the masses and sizes, what do we know about their densities and compositions?
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By observing each planet’s moons they could use Kepler’s laws to determine the mass of the planets. They are more massive than the other planets but when comparing the mass to their size they are not very dense. This suggests they are made up of a lot of light-density matter such as gas so they are deemed “gas giants”.
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What is today's theory for why all the planets in our solar system orbit the Sun in the same direction and in roughly the same plane? What is the observational evidence for this theory?
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The theory is that stars are born of nebulas that spin fast enough to form a star at the centre with interstellar dust orbiting around it. This interstellar dust spinning around the star is called the circumstellar disk and the debris in it eventually clumps together as gravitational forces pull in more debris to form masses of debris. These masses of debris eventually become large enough to resemble planets which explains why they will all be spinning in the same direction and same plane as the circumstellar disk. It was observed that nebulas have rings around them either made of gas (bright rings), rocky debris (dark rings) or a combination of both which are believed to result in solar systems after many millions of years.
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What is today's theory for the asteroid belt? What about planetary rings?
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Asteroid belts are what happens when there are other planets that exhibit enough gravitational force on the space debris to prevent it from clumping together into planets and instead stay as debris. Planetary rings are the same except moons prevent the formation of other bodies and they occur in the orbits around planets instead of the orbit around the sun.
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What 3 attributes are unique to the 4 planets beyond Mars? What is the current explanation for this?
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The outer planets beyond Mars are all gaseous, ringed and have numerous moons (massive). The reason for this is that the outer planets had more matter available to collect in the circumstellar disk and as their mass grew their larger gravitational attraction could collect more debris and more gas making them massive and gaseous. The fact that they were more massive allowed them a larger gravitational pull to collect debris to orbit them to create moons
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Which planets are the terrestrial planets? What is the current explanation for their lack of gas?
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Venus, Mercury, Earth and Mars are all terrestrial planets. Since they are inner planets they had less debris available to them so as they formed, their hard core formed first and never had a chance to grow large enough to form a large gas layer like the outer planets.
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What is the current theory for the origin of Mars' two moons? What is the evidence to support this theory?
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It is believed that Mars’ moons were large asteroids from the asteroid belt that were knocked out of the belt and fell into Mars’ gravitational pull. Mars’ moons are not spherical and represent asteroids more than planets. Also, they move retrograde to the planets (clockwise rather than counter clockwise) which contradicts that they were part of the original formation of the solar system.
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Why is it unusual for Earth to have such a large moon? What is the current theory for the origin of Earth's moon?
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Usually the inner planets are believed to have been too small to have a moon form around them. It is believed that Earth’s moon was the product of a large collision of a Mars-sized body with Earth. This ejected a lot of debris into space which was caught in Earth’s gravitational pull which eventually formed our moon.
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What belief about Mars was popularized by Percival Lowell, and why? Was he right?
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He popularized the belief of an intelligent Martian civilization on Mars. He believed that there were intricate trenches built on Mars which could only be the product of an intelligent civilization. He was wrong; they were just optical illusions of shadows cast by Mars’ natural canyons.
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Why was there suspected to be a planet beyond Neptune?
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Neptune’s mass had been recalculated and they saw that the new mass did not account for the deviation of Uranus’ orbit alone. They believed there had to be a planet beyond Neptune which helped in the deviation of Uranus’ orbit.
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When Lowell's predicted planet was finally detected, what was it named, who named it, and why did she choose this name?
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It was named Pluto for the god of the underworld since it was dark and gloomy. It was suggested by a little girl in England at the time.
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Why did the discovery of Pluto turn out to be a coincidence?
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Because when Neptune’s mass was recalculated again, it turned out that the new mass indeed accounted for the deviation of Uranus’ orbit alone and Pluto was too small to have played a role in it.
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The discovery of what kind of objects motivated the IAU to define the conditions for being a planet? Where are these objects? What was the significance of the object now known as Eris?
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The discovery of KBOs had forced the IAU to redefine the definition of the term planet. These objects are all beyond Neptune and are pieces of ice debris. Objects like Eris (which was larger than Pluto) made IAU question what to define a planet because if Pluto was one, there would be many more just like it or bigger.
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What are the IAU's planet conditions? Which condition(s) does Pluto fail? What condition(s) do comets fail? What condition(s) do asteroids fail?
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A planet must orbit the sun, be a sphere by its own gravity and it must have cleared the debris around its orbit. Pluto fails the third condition because it is part of the ice belt beyond Neptune. Comets and some asteroids are excluded due to the second condition. Kuiper Belt Objects are excluded because of the third condition.
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What is Pluto now considered? What are the condition(s) for this type of object? Is this type of object expected to be common in our solar system?
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Pluto is now considered a Dwarf Planet because it only fails the third criteria of a planet. A Dwarf Planet is anything that satisfies the first two criteria of a planet. This object is expected to be very common in our solar system but cannot be confirmed until we have methods of telling whether distant planets are spherical or not
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