Re: Where would you have to be standing on the Earth for it to appear that the

Fred,
you ask a great question! Let me make sure I understand your question, though, then I'll try to answer it.

You are wondering where on the earth you could stand, where as the Sun set, it would appear to drop from the zenith (the point in the sky right over your head) straight down to the western horizon?

OK, assuming that is what you are asking, then the answer gets a little complicated. It's complicated, because it depends on what time of year it is! As you have probably read, the Earth is tilted on its axis. That means that as we go around the Sun in our orbit---one full turn every year---the Sun appears to move north and south in a big cycle in Earth's sky as the seasons change. In fact, it's this apparent motion that's the real cause of our seasons on Earth, but that's another topic. :)

Anyway, because the Sun's apparent position is tied to Earth's seasons, let's pick a particular time of year, and I'll try to answer your question finally!

Let's say it is right around March 20. This date is special, because it is the official beginning of Spring in the northern hemisphere, and of Autumn in the southern hemisphere. On this date, if you were standing at the equator, the Sun would appear to rise due East of where you were standing, pass right overhead (through the Zenith), and then set again due West. Also, any stars in the night sky which happened to be at the same north-south position as the Sun (astronomers call this north-south position declination) would also appear to rise due East in the evening, pass overhead, then set due West!

(Naturally, stars further north of or south of this line in the sky, would appear to travel in arcs rather than straight lines. There's no place on Earth where all the stars would rise in the same place!)

And by the way, six months later on September 23, as Fall is beginning in the North and Spring is starting Down Under, an Equatorial observer would have the same experience as in March!

The Earth is tilted about 23 degrees. This means that at the start of Summer (June 21 this year), someone living near latitude 23 degrees North on the Earth (say, a skywatcher in Cuba, Mexico, or just north of the Hawaiian Islands) would get to see the Sun travel in this direct East-West path. Meanwhile, someone at latitude 23 degrees South would get to see this same show on the official start of southern Summer, December 22! :)

I hope this has helped you a little bit; it can be tough imagin- ing the whole complex dance that the Sun and stars make as they seem to wheel around the sky every night throughout the year!

Take care,
Lew Gramer