I.   Astronomy of the Earth's Motion in Space

    An algebra-based overview of elementary and (mostly) pre-telescope astronomy, for personal study, also for middle school (some), high school (mostly) and beginning college. Starting with the apparent motions of the Sun and stars on the celestial sphere, it explains the seasons of the year, latitude and longitude, time zones and universal time, and the basics of navigation.

    Next calendars are described--Julian and Gregorian, Metonic (esp. Jewish), Moslem, Persian and even Maya.

    After that the site tells how the spherical shape of the Earth was recognized and measured, leading to the formula for the distance of the horizon, the concept of parallax and the ways the ancient Greeks estimated the distance of the Moon. The Greeks also tried to derive the distance of the Sun, starting the road to heliocentric theory, with roles by Ptolemy, Copernicus, Galileo and Kepler. The section ends with a fairly detailed discussion of Kepler's laws and planetary orbits, which serves as a bridge to the next section, on Newtonian Mechanics.

    Interspersed with the above are three web pages on the Moon (which may also be tied to the Greek calculations of the Moon's distance) and one on the precession of the equinoxes, connected to the Milankovitch theory of ice ages.

1. Stargazers and Skywatchers
 1a.    The Celestial Sphere
 1b.    Finding the Pole Star
2. The Path of the Sun, the Ecliptic
 2a.    Building a Sundial
3. Seasons of the Year
 3a. The Angle of the Sun's Rays
4.   The Moon: the Distant View
 4a.    The Moon: A Closer Look
 4b.   Optional:  Libration of the Moon
5. Latitude and Longitude
 5a.   Navigation
 5b.   The Cross-Staff
 5c.    Coordinates
6. The Calendar
 6a.    The Jewish Calendar   (optional)
7. Precession
8. The Round Earth and Christopher Columbus
 8a.     Distance to the Horizon
 8b.     Parallax
 8c.     How Distant is the Moon?--1
 8d.     How Distant is the Moon?--2
    The central role of the Sun
 9a.    Aristarchus: Is Earth Revolving around the Sun?
 9b.    The Earth's Shadow
 9c.    Copernicus, Galileo, and the Discovery of the Solar System
10. Kepler and his Laws
 10a.   The Scale of the Solar System
11. Graphs and Ellipses
 11a.    Ellipses and Kepler's First Law
12. Kepler's Second Law
 12a.   More on Kepler's Second Law
 12b.   How Orbital Motion is Calculated

Optional: The 2004 Transit of Venus
 12c.     Halley's Method of Deriving the AU
 12d.     The displacement D of the track of Venus
 12e.     Deriving the Astronomical Unit