Part 2: A history of astronomy with respect to ancient civilizations and cultures, and the progenitors of science and empirical skepticism.
These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:
01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences
Astronomy in Prehistory
Transcript: Humans has been anatomically modern for about 40 or 50,000 years. If you can imagine what life would have been like 30 or 40,000 years ago for hunter-gatherers somewhere in Europe or Africa or the plains of Asia, you can realize that the sky must have been important to them. The first use of astronomy was not in the modern, scientific sense. Astronomy and the stars and the sky were a fundamental part of people's lives. The sky was a map, a clock, a calendar, a source of myth and legend, and more. If you lived in those times you would have needed to know the motion of the sun to be able to go on a journey, a hunting journey, to be able to return before dark. Nobody ever stayed out before dark in the time before electricity and lights. If you were living and subsisting off natural vegetation and fruits and berries you would need to be able to keep track of the seasons to know where your food supply was or follow the migrating herds, so you needed to use the sky as a calendar. If you were navigating on the open ocean, as many tribes in Polynesian areas or tropical areas of the Earth did, you would need to use the sky as a map for navigation. Cultures over thousands of years have been able to travel thousands of miles in small boats by their knowledge of the sky as a map. For these reasons and more the sky has been important to cultures throughout the centuries. In fact, it is unfortunately only in the modern age that people have become detached from the night sky because so many of us live in cities.
Motions in the Sky
Transcript: What would you observe if you looked at the sky for a year from somewhere in the Northern hemisphere? You'd notice that the stars rose in the east and set in the West and appeared to move about a fixed point in the Northern sky. You'd notice that the Sun, the Moon, and the planets all traverse the same strip of the sky. You'd notice that the stars rise and set slightly earlier everyday and that the constellations move through the entire sky in the course of a year. You'd notice that the Sun during the summer rises slightly North of due-East, and the day is longer than twelve hours. In the winter you'd notice the Sun rising South of due-East, and the day is shorter than twelve hours. You'd notice the constellations rising in the East and setting in the West and always preserving a fixed pattern with respect to each other. You’d notice the regular pattern of the Lunar phases repeating every 28 or 29 days. You’d notice the rare phenomena of eclipses and the fact that Solar eclipses are much rarer than Lunar eclipses, and neither occurs every month. And you would notice that some of the planets follow irregular motions with the fixed constellations. All of this you would notice by careful, naked-eye observations over the course of the year.
Transcript: The constellations of the night sky are among the oldest human artifacts. For thousands of years humans have been noticing patterns and using them to navigate, or to keep track of the sky, or to tell myths and legends. There are 104 constellations in the modern sky. Some of them are extremely old. There is evidence that Ursa Major, the great bear, which includes the asterism of the Big Dipper, dates back to at least 10,000 years. Asian tribes named this constellation, and knowledge of this constellation traveled from Asia through to Europe and to North America. The thirteen original, and then twelve, constellations where the sun, moon, and planets travel, were divided into the Zodiac, the circle of animals. Those are the familiar twelve constellations of the star signs. But in general, the constellations are a rich source of human history as myths and legends have been posited in the constellations for many, many years. The constellations don't look like the things they are supposed to represent; you have to use your imagination. Remember, the constellations were used as shorthand by people who depended on the night sky for their very existence.
Transcript: The patterns and motions of the stars in the night sky can be used for navigation. In the Northern Hemisphere the stars all appear to move about a fixed point in the sky called the Northern Celestial Pole. There happens to be a fairly bright star in this direction called Polaris. The elevation of Polaris above the horizon gives your latitude on the Earth’s surface. For thousands of years navigators have been able to use the motions and patterns in the night sky to navigate. Islanders in small boats in the South Pacific were able to travel distances of several thousand miles with an accuracy of fifty or sixty miles purely using the motions and patterns of the night sky.
Transcript: The celestial sphere is an imaginary sphere surrounding the Earth onto which are projected the objects of the night sky. There are several fixed points on the celestial sphere that are important. The Zenith is the point directly over your head. The Nadir is the point directly below your feet. The line drawn across the sky that represents the highest elevation of the sun or any other object as it traverses the sky is called the Meridian. The sun rises through to its highest point and then starts setting as it passes the Meridian. The other important points are to define two angles anywhere on the celestial sphere that give uniquely the position of any star or object. Altitude and Azimuth are two angles that can do this. Altitude is the angle with reference to the horizon, and Azimuth is the angle along the horizon. Astronomers use a different coordinate system based on Right Ascension and Declination. The other important track on the sky is the Ecliptic, the path traveled by the sun. This is also the region of the sky within which you will see the motions of the moon and the planets.
Transcript: The apparent motions of the stars in the night sky depend on your position on the Earth’s surface. At a northern temperate latitude, the stars rise in the east and set in the west, and they travel on slanting paths across the sky. The north celestial pole sits in the northern sky and the elevation of the pole, or the bright star Polaris, is the same as your latitude on the Earth’s surface. Some stars are visible throughout the night as they orbit the north celestial pole; they are called circumpolar stars. If you were positioned at the Earth’s equator, stars would appear to rise directly out of the east and set directly into the west. The north celestial pole would be down on the horizon. That represents the region around which the stars are rotating in the night sky. If you moved to the pole of the Earth, the north pole of the Earth, the north celestial pole would be directly overhead; imagine yourself standing on the top of a spinning top staring upwards. All of the stars would be circumpolar; those near the horizon would be orbiting parallel to the horizon, and all stars would appear to circuit around the north celestial pole, or the star Polaris, which would be directly above your head.