| This chart shows the position of the true
sun in the sky throughout the year. The y–axis on the chart represents
the declination of the sun in the sky for one year, going from –23.26°
in the winter to +23.26° in the summer. The x–axis represents the difference
in time from what your watch reads to the actual position of the sun in
the sky.
The listing of actual daily declinations is found at this site: DECLINATIONS This chart also demonstrates why even though the longest day of the year is around June 21st, the latest sunset occurs a few days after that. At the top of the chart we can see there is more lateral motion of the sun than motion downwards. In other words, when your watch reads that the sun should have set, the true sun will have drifted slightly to the east (up). The opposite effect occurs in the winter. While the shortest day of the year is around December 21st, the latest sunrise does not occur until several days after that. The speed of the true sun on the ecliptic now reflects its elliptical orbit around the sun, moving faster in January and slower in July. Have you ever looked at a rise and set time chart of the sun and noticed that in the summer the earliest sunrise and latest sunset do not occur on the longest day of the year? Or that in the winter the latest sunrise and earliest sunset do not occur on the shortest day of the year? This phenomenon is directly related to the shape of the analemma. Altitude is the angle up from the horizon. Zero degrees altitude means exactly on your local horizon, and 90 degrees is "straight up". Hence, "directly underfoot" is -90 degrees altitude. Azimuth is the angle along the horizon, with zero degrees corresponding to North, and increasing in a clockwise fashion. Thus, 90 degrees is East, 180 degrees is South, and 270 degrees is West. Using these two angles, one can describe the apparent position of an object (such as the Sun at a given time). The altitude and azimuth values are for the center of the apparent disk of the Sun or Moon. The listing of daily sunrise and sunset
times is found at: Sunrise/Sunset
Times
Not a part of this project, but interesting, some sunrise/sunset diagrams. Anchorage,
Alaska
If the software had
been installed, you would have created these diagrams!
|
3.
Describe in your own words the dilemma of the analemma.
When
during the year is the sun "fast" and "slow"?
Go
look around http://www.analemma.com
and then come back and
put
into your own words what causes these variations shown on the Analemma.
I
would like a long typed paragraph please!