September 12, 2011
-last time we discussed archaeoastronomy, how there are sites that show these civilizations understood
some form of relationship to the sun, today we’ll discuss how they were able to determine these things
and how much astronomy they were actually able to comprehend
The Sun’s Daily Cycle
1 . due to Earth’s 24-hour eastward-spin around its polar axis, the Sun moves westward across the sky; it
rises in the east, reaches its highest point at noon, then sets in the west
2. N-hemisphere: Sun is mostly seen on the South side of the sky, reaching due (exact) South at noon
3. S-hemisphere: Sun is mostly seen on the North side of the sky, reaching due North at noon.
The Sun’s Annual Cycle
Fall and Spring Equinox (~Sept 23, ~Mar 21): Sun rises due E and sets due W, spending equal time above
and below the horizon (equal day and night). (Equinox: Latin for “equal night”) on other days of year it’s
a little bit off east when it rises, and a little bit off west.
2. Winter Solstice (~Dec 23): Sun rises and sets at its southernmost position, traversing a short, low arc
in sky (shortest day of the year and lowest noon sun) (Solstice: Latin for “solar standstill”).
-causes day to be shorter, arc is significantly lower than on the day of the equino