8PTYS_206_comets - PYTS/ASTR 206 Comets q 1 Announcements s...

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PYTS/ASTR 206 – Comets 1 Announcements HW6 available today, due in a week Use Kevin as the TA for this one 2 In-class assignments left in 3 lectures
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PYTS/ASTR 206 – Comets 2 PTYS/ASTR 206 – The Golden Age of Planetary Exploration Shane Byrne – shane@lpl.arizona.edu Comets
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PYTS/ASTR 206 – Comets 3 In this lecture… Observations of comets What are comets? Composition and structure Cometary tails Ion and dust tails Where do comets come from? Orbits of comets Oort cloud Scattered Kuiper Belt
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PYTS/ASTR 206 – Comets 4 Comets have been known from ancient times Thought to foreshadow disasters and major battles Pre-telescopes the known solar system was a pretty empty place Moon and the Sun Mercury, Venus, Mars, Jupiter, Saturn And COMETS No Uranus No Neptune No planetary Moons (except ours) No Asteroids No Kuiper Belt Objects Observations of comets
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PYTS/ASTR 206 – Comets 5 People have recorded comet sightings for millennia 167 BC 687 AD 1986 AD
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PYTS/ASTR 206 – Comets 6 Ancient Greeks thought comets were atmospheric phenomena In the west this went unchallenged until telescopes came along Tycho Brahe’s parallax measurements proved this wrong Comets were much further away than the Moon Renaissance astronomers thought comets moved in straight lines through the solar system Even Kepler argued they shouldn’t follow elliptical orbits like the planets In the 1680s astronomers tracked a comet and showed it had an elliptical orbit
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PYTS/ASTR 206 – Comets 7 Newton finally settled this in his ‘Principia Mathematica’ (1687) Showed that comets moved in parabolic or elliptical orbits by the Sun’s gravity e = 1 A parabolic orbit
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PYTS/ASTR 206 – Comets 8 If they have orbits… then they’re periodic The same comet should come back In 1705 Edmund Halley connected the dots… Used Newton’s laws to figure out the orbit of many comets Comets seen in 1531, 1607, and 1682 were the same object Predicted a return in 1759 Halley’s comet has been seen ~30 times 687 AD 1986 AD 167 BC
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PYTS/ASTR 206 – Comets 9 Many telescopic observations of comets (including Halley’s comet) Even a few spacecraft missions Giotto & Vega Comet Halley
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8PTYS_206_comets - PYTS/ASTR 206 Comets q 1 Announcements s...

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