Manually working out rise/set times

Hey there folks,

It's raining and I'm bored so I thought I'd ask about something I've been pondering over.

I was trying to work out that if I knew where on Earth I was, and what time the Sun (or Moon, or anything really) rose and set - is there any way that I can roughly calculate when the object would rise and set at a different place on Earth, given that I knew its latitude and longitude?

For longitude I know that you get roughly the right answer if you just add 4 minutes for every degree you travel west, and subtract if you're going east. But is there an equally uncomplicated way of working out the differences in rise/set times caused by latitude?

I know I could just use Starry Night or whatever, but I'm just curious about how these things are calculated in the first place really. So if anyone can shed light on the latitude part it'd be most welcome!

Thanks.

Not easily. If you are interested in how these things work a great book is Astronomical Algorithms' by Jean Meeus or Practical Astronomy with a Calculator' by Peter Duffet-Smith. Both explain how to calculate these things but they are not the sort of calculations you would do in your head.

For rise and set times, the normal procedure would be (very roughly)

Calculate the geocentric RA and DEC of the object (or look these up) convert these to Altitude and Azimute co-ordinates (this is the bit where the Lat. and Long. come into play. You also need to calculate the Obliquity of the ecliptic, that is, the angle the axis of the earth presents to the ecliptic. You need to correct this for Nutation (wobble of the earths axis) and precession of RA co-ordinates. With the ability to convert RA/DEC into ALT/AZ you can then calculate the time when the ALT = 0 by iteration. (oh yeah then you also need to consider atmospheric refraction)

Most of this is easier than it actually sounds but definitely one to be done on your computer not in your head. I used to think spherical trigonometry was a bit of a b;ack art untilk I read Meeus and Duffet-Smith. Great books.