Parents' Notes for Unit 5: The Babylonians, the Egyptians, and Naked Eye Astronomy

Preparation

Below are notes on the main points of each assignment.

• History Web Lecture: The level of detail in ancient astronomical observations is often surprising to us, but when we realize how important these observations were for timekeeping and time-stamping purposes, we can see why these cultures went to great lengths to make their observations as accurate as possible. The photos show artifacts from the actual periods we are discussing to drive home the realization that ancient astronomers were "doing science" in the sense of recording and comparing their observations, often across centuries and very different cultures.

• Science Web Lecture: This lecture concentrates on the motions of planets and methods of tracking them against the background sky using the modern celestial coordinate system. Think of this as an "explosion" of the earth's latitude-longitude system into space. The celestial North Pole is directly above the earth's north pole. The celestial equator is directly above the earth's equator. By using the celestial equator system, we can plot the position of planets against the background stars without ambiguity and make possible comparison of observations over long periods of time.

• Mastery Exercise: A major part of the Mastery Exercise involves reading the star map. You may need to print the map off so that your student can examine it carefully.
  • As with earth maps, celestial north (the point above the north pole of earth) is to the top and celestial south is to the bottom, but this map uses curved coordinate lines to preserve the constellations as they may actually be observed.
  • The white line through the middle is the horizon. The compass points will help you orient the map to the sky at 9pm in mid-October (the moon will change positions, but the other planets and the constellations should be the same for nights near October 15).
  • The map was generated for Seattle. People south of the middle US may see some of the stars that appear below the horizon line.
  • The celestial equator is the curved red line with the "hours" marked on it. These go from right to left because, if you are facing south in the northern hemisphere to observe them, the planets (most of the time), sun and moon move from right to left against the background stars. Hours of right ascension are just a way of measuring points in the sky, like latitude and longitude on earth. They are related to hours of time, because the sky rotates about one hour of RA in one hour of earth time. This relationship is NOT exact because of the earth's motion around the sun.
  • The whole thing rotates from left to right each night as the earth turns.
  • The green curved line is the path the sun follows during the year. Help the student see that the sun is "on" the celestial equator at 0 hours right ascension (RA) and at 12 hours RA: these are the spring and autumn equinoxes. It is furtherest north at 6hrs RA, in June and furthest south at 18 hours RA (in December).
  • The constellations are drawn but not labeled on the map—my experience is that this gets too confusing.

• Discussion: The discussion will focus on using coordinate systems to identify locations in the sky, both for the astronomical information and as a skills-development project in reading maps and graphical information.

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