When Knowledge Conquered Fear
Study Guide for Episode 3
Episode 3: When Knowledge Conquered Fear
People
• Edmund Halley used historical records of comet sightings to show that some of them make repeated appearances. The comet now named for him is a short-period comet, returning every 76 years.
• Robert Hooke made significant scientific contributions in mechanics (most notably, behavior of springs), gravitation, timekeeping, microscopy, and paleontology. In later life, he was often unwell, and he was involved in many disputes about priorities of discoveries.
• Isaac Newton formulated laws of motion and gravitation that allow us to understand planetary and stellar motion in great detail, to send satellites into orbit, to carry out space missions, and to simulate the motions of astronomical objects -- from asteroids to galaxies.
• Jan Oort proposed, from examination of comet orbits, that the solar system is surrounded by a sparsely populated shell of small objects, from which comes the long-period comets.
Ideas
• Tyson mentions Edmund Halley's method for determining the distance from Earth to Sun. This distance is called the astronomical unit (AU). The principles involved are described HERE. The method makes use of Kepler's third law of planetary motion, which relates the ratio of two planets' orbital period (loosely, the lengths of their years) to the ratio of their distances from the Sun.
• Having trouble imagining the scale of the Solar System, the Kuiper Belt, and the Oort Cloud? Me too. Cosmos uses re-scaling to help us grasp time in our universe, by referring us to the Cosmic Calendar. Let's re-scale the size the Solar System to fit onto a football field, with the Sun at one goal line, and Neptune at the other. Where would each planet lie? How big would the Sun and each planet be? Click HERE to find out.
Updates
• Edmund Halley discovered, by comparing accurate modern and historical star charts, that stars move slowly in different directions in the sky. Scientists recently spotted a small, red star moving across the sky rapidly enough that they could determine its recent path. Turns out that about 70,000 years ago, it passed through our Oort Cloud. Read more HERE.
• Such events are thought to the main producers of Oort-Cloud comets, more commonly called long-period comets. Two recent long-period comets were Hyakutake (1996) and Hale-Bopp (1997). Both were very bright because they were probably making their first trips to the inner Solar System. Did you see them? Read more about long-period comets HERE.
• Did you see Comet West in 1975? At its brightest, it was possible for astronomers to study it in daylight. Like many long-period comets, its orbit is not stable, and could range from 250,000 to one million years. Now that's a long-period comet! As it approached the sun, it broke up into at least four large pieces, giving further uncertainty to its future movements.
Additional Readings
• There is no longer any living person who has walked on the Moon. Read more HERE.
• Poem: "Astronomy", by A.E. Houseman. Read it HERE. What is the poem about? Do you know your astronomy well enough to understand all of it? What does astronomy do for the poem?
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People
• Edmund Halley used historical records of comet sightings to show that some of them make repeated appearances. The comet now named for him is a short-period comet, returning every 76 years.
• Robert Hooke made significant scientific contributions in mechanics (most notably, behavior of springs), gravitation, timekeeping, microscopy, and paleontology. In later life, he was often unwell, and he was involved in many disputes about priorities of discoveries.
• Isaac Newton formulated laws of motion and gravitation that allow us to understand planetary and stellar motion in great detail, to send satellites into orbit, to carry out space missions, and to simulate the motions of astronomical objects -- from asteroids to galaxies.
• Jan Oort proposed, from examination of comet orbits, that the solar system is surrounded by a sparsely populated shell of small objects, from which comes the long-period comets.
• Tyson mentions Edmund Halley's method for determining the distance from Earth to Sun. This distance is called the astronomical unit (AU). The principles involved are described HERE. The method makes use of Kepler's third law of planetary motion, which relates the ratio of two planets' orbital period (loosely, the lengths of their years) to the ratio of their distances from the Sun.
• Having trouble imagining the scale of the Solar System, the Kuiper Belt, and the Oort Cloud? Me too. Cosmos uses re-scaling to help us grasp time in our universe, by referring us to the Cosmic Calendar. Let's re-scale the size the Solar System to fit onto a football field, with the Sun at one goal line, and Neptune at the other. Where would each planet lie? How big would the Sun and each planet be? Click HERE to find out.
Updates
• Edmund Halley discovered, by comparing accurate modern and historical star charts, that stars move slowly in different directions in the sky. Scientists recently spotted a small, red star moving across the sky rapidly enough that they could determine its recent path. Turns out that about 70,000 years ago, it passed through our Oort Cloud. Read more HERE.
• Such events are thought to the main producers of Oort-Cloud comets, more commonly called long-period comets. Two recent long-period comets were Hyakutake (1996) and Hale-Bopp (1997). Both were very bright because they were probably making their first trips to the inner Solar System. Did you see them? Read more about long-period comets HERE.
• Did you see Comet West in 1975? At its brightest, it was possible for astronomers to study it in daylight. Like many long-period comets, its orbit is not stable, and could range from 250,000 to one million years. Now that's a long-period comet! As it approached the sun, it broke up into at least four large pieces, giving further uncertainty to its future movements.
Additional Readings
• There is no longer any living person who has walked on the Moon. Read more HERE.
• Poem: "Astronomy", by A.E. Houseman. Read it HERE. What is the poem about? Do you know your astronomy well enough to understand all of it? What does astronomy do for the poem?
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