lecture22spring2009 - Astronomy100Dr.Rhodes Lecture Chapter...

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Astronomy 100 - Dr. Rhodes Lecture # 22 - 3/9/2009
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Chapter 10: Dwarf Planets and Solar System Debris The Discovery of Pluto An analysis of the orbital data of Uranus indicated that 98% of its orbital variation could be accounted for by the presence of Neptune; the remaining unexplained 2% variation led to the search for Planet X. In 1905 Percival Lowell initiated what would become a successful search for Planet X. Unfortunately, Lowell died in 1916 before Pluto was discovered. Clyde Tombaugh finally discovered Pluto at the Lowell Observatory in 1930.
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Chapter 10: Dwarf Planets and Solar System Debris The Discovery of Pluto Tombaugh used a blink comparator to compare two photos of the sky taken a few days apart. A moving object such as a planet will appear to jump from one spot to another as the observer quickly changes views from the first photograph to the second. Pluto was discovered 6° from where Lowell had predicted it would be found.
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Chapter 10: Dwarf Planets and Solar System Debris The Discovery of Pluto Pluto’s mass, however, is too small to cause the irregularities that had been seen in Uranus’s orbit. Later it was shown that these irregularities were not caused by another planet but were variations due to the limited accuracy of the available data. In conclusion, we now know that Pluto’s discovery was an accident, although without Lowell’s predictions, the search would not have been pursued so vigorously
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Chapter 10: Dwarf Planets and Solar System Debris The Discovery of Pluto Pluto as Seen from Earth In 1989 Pluto was as close to the Earth as it had been for 248 years. (From 1979 to 1999 Pluto was inside Neptune’s orbit.) Pluto’s average distance from the Sun is 40 AU, but its eccentric orbit causes it to vary in distance from 30 AU to 50 AU. Pluto is now heading for its aphelion point. Pluto’s orbit is tilted 17° to the ecliptic (no other planet is tilted more than 7°).
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Chapter 10: Dwarf Planets and Solar System Debris Discovery of Pluto’s Atmosphere and Moon
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