1 Astronomy: Universe at a Glance, Ch. 1a What you see depends on from where you observe: Ancients lived in a very dark world at night compared to us today, and the sky was magnificent and enticing. Sometimes observed from deep holes in the ground to block out as much excess star light as possible. The retinas in our eyes always adjust to the ambient light. Built observatory edifices like: Stonehenge, Machu Picchu, and many other places around the world. Used to mark the seasons and healing Mayan Chichen Itza: At equinox sunset shadow moves down the steps and ends at the snake s head India: many sites for astronomical measurements Early native American Anasazi sites: The pyramids and other sites in ancient Egypt
2 Almost everything that astronomy deals with involves time: Gazing into the night sky is like using a time machine, looking into the past. Light travels at a speed of 300,000 km/ second (equivalent to seven (7) times around Earth per second). Distance is often, conveniently, described in light-seconds, -minutes, -hours, -years, which represent the time it takes light to travel in these units of time. Earth to Moon = 1.2 sec Sun to: Mercury Venus Earth Mars 3.22 minutes 6.01 minutes 8.32 minutes 12.7 minutes Inner terrestrial planets Jupiter Saturn Uranus Neptune Pluto 43.3 minutes 1.32 hours 2.66 hours Outer gaseous planets 4.16 hours 5 hours Farthest comets 14 hours Edge of solar system Proxima Centauri (nearest star) Orion Nebula 4.3 years 1,500 years Milky Way center 26,000 years Stars and galaxies Andromeda Galaxy Very distant galaxies Early universe 2.36 million years BILLIONS of years up to 14 billion years Discover cosmos by studying the electromagnetic radiation that comes from objects in space. All objects (planets, moon, stars, galaxies, us, everything) exist in space under the influence of
3 When an object is moving past Earth its (instantaneous) velocity it tangent to the to the surface. But, due to gravity s pull it is also falling. The resulting motion is an ORBIT that is elliptical (possibly circular) By being in FREEFALL the object is weightless, just like when skydiving or in a falling elevator. Here is an interesting thought (only speculation): When early people were attracted to the magnificence ns mystery of the night sky, one of the major events of life, they also noticed that they can not touch or each it (being held to Earth by gravity). It is easy to fall to the ground but impossible to get to the heavens So one can speculate that within the development of religion people might that: Up in the sky, on the clouds, or in space HEAVEN exist. Difficult to enter. Under earth among the volcanic fire and brimstone is HELL. Easy to fall, easy to be trapped. Professional astronomers (about 10,000 globally) Use huge telescopes on high mountains Use rocket and satellites probes sent near and far away Use unmanned balloons Perhaps may NOT know the constellations Amateur astronomers (a few million to hundreds of millions) Usually know the constellations, as a guide for observations Monitor the brightness of variable stars Discover asteroids, comets, and exploding stars Join the search for planets orbiting the Sun Ancients: About 4,000 stars can be seen by the naked eye. Gave names to the constellations, especially Egyptians, Greeks, early Arab, Chinese, India, all other societies but--- end result today dominated by global political events, like the colonial period--- Told stories and made mythology based on these constellations Engaged in astrology Sailed the oceans without a compass, by watching the stars, and knowing the winds and currents Noticed brightness, color and other characteristics.
4 They wondered as the wandered: Planets versus stars: The word planet means, wandering in Greek. Ancients noticed that some planets have a noticeable retrograde motion (going backwards sometimes. Planets do not twinkle like stars, because stars are point sources and planets not. The twinkling is an atmospheric effect of a distant point source. We can sometime see the shape and size of planets, but stars are always points, even with powerful telescopes. Naming stars and constellations: Depends upon the society (like ink blot test). Once named can become a part of society mythology. The ancient Babylonians, and later the Greeks (as recorded by Ptolemy), established most of the northern constellations in international use today. When European explorers (during the colonial period) mapped the stars of the southern skies, European and American astronomers proposed new constellations for that region, as well as ones to fill gaps between the traditional constellations. Not all of these proposals caught on, but in 1922, the International Astronomical Union(IAU) adopted the modern list of 88 constellations. After this, precise boundaries were drawn for each constellation, so that every point in the sky belonged to exactly one constellation. Many stars have the same names given by the Egyptians, Greeks and Romans. TODAY are (by convention) divided into 88 constellations, which contain ALL spherical space around Earth.
5 THE STARS THAT WE CAN SEE by naked eyes are our neighbors in the Milky Way galaxy and/or VERY BRIGHT distant ones!! All stars APPEAR to be same distance from us, because of the huge distances. This as an illusion. We need clever ways to determine these distances. (Remember that our two eyes see distance by parallax. When distance is very great, parallax looses its sensitivity!!) For more recent history, see the sections regarding the great scientists, like Galileo, Newton, Einstein and so forth----- Access my expanded article about the Scientific Method on the Main Page of this site!!