Expert: Courtney Seligman - 1/3/2010

Question
I am a sculptor and I have this idea for a kinetic sculpture that the top needs to be under the sun at all time so the effect that I am trying to achieve takes place. so my idea is to create a base with a mechanism that will rotate at the same speed of the sun so the sculpture is under the sun at all times. Now since this sculpture will be taken to several shows around the country I need to adjust the position of this base according to the time of the day when the sculpture is put on the exhibition. So, my question to you what is the speed or how lon does the sun take to describe the arch between east and west. I hope I make sense with this description.
Thank you
Alfonso

Answer
If I understand your idea, the lower part of your sculpture will rotate to the "east" as the Earth does, but you want the Sun to remain directly above it, essentially immobile. That would require the rotating part of the sculpture to move to the east at the same rate that the Sun moves westward across the real sky.

That time is, on the average, 24 hours (in fact, that's essentially how we define 24 hours -- the average time for the Sun to move once around the local sky, during the course of the year). The portion of the time that the Sun remains above the horizon varies during the seasons, from less than 9 hours during winter to more than 15 hours during summer (for most of the lower 48 states), depending upon the location. But that doesn't change the overall motion of the Sun along its diurnal (daily) path, which is always 24 hours, give or take a few seconds.

If I have misunderstood what you're trying to achieve, send a more detailed discussion of your goal, and I'll try to give you an answer more suited to your purpose.