Expert: Tom Whiting - 8/29/2010

Question
What is the best way to illustrate in a diagram the eastern horizon going from northeast to southeast? Also, where on the diagram would the rising point of the sun be for the following: summer solstice, winter solstice, vernal equinox, and autumnal equinox? I am just beginning to learn about these out of curiosity of learning something outside my comfort zone, and the websites I have visited in my search for knowledge have not made me understand the concept very well. I am unsure as to where the suns rising points would be on each of these 4 occasions when on the eastern horizon. Thank you very much in advance!

Answer
Hi Sandy,
Depends on how complicated you want this to be... the ultimate answer involves some trigonometry, which is not my speciality. But as a general rule, if you live between 0 and 40 degrees north latitude, the sun rises almost exactly due east at the equinoxes, and at it's northernmost point on the eastern horizon at the June solstice, and at it's southernmost point on the eastern horizon at the December solstice.
The equator is the easiest example... sunrise is due east at the equinoxes, and 23.5 degrees north and south of due east at the respective solstices... the amount of tilt of the Earth's axis from the vertical.
Naturally the farther north you are, say up in mid-Canada, then the rising point at the June solstice is much farther North on the horizon, until you get to (and above) the Arctic Circle, where the sun doesn't rise or set at all (or just once during the year), but just circles around the sky at the June solstice, and doesn't rise at all at the December solstice. And the reverse is true for the far southern hemisphere.  The actual values of these numbers (in degrees north or south) depends on your exact latitude, and as I said, involves some trig.  But I am not a math major. So I just try to keep it simple... for us astronomy majors. Let the math people calculate the exact values and positions, as us observational astronomers don't normally need them because we really don't care where the sun rises. All we want is the amount and times of total darkness available to us on any given date. (You can't see the starry sky in the daylight).  Hope this helps,  
Clear Skies,
Tom Whiting
Erie, PA