Is there a computer program that can predict when the sun sets on any date?

Question

Is there a computer program that can predict the exact time the sun will set from any location on earth at any date? I understand that elevation and whether the horizon is "distorted" by, say, a mountain plays a role. But if the computer program just uses a perfect sphere for the Earth but can predict the actual movement of the Earth in space in relation to the sun I would already be very impressed. If this is hard to model then how big (in seconds) are the expected inaccuracies.

Answer 1

Actually, the professional programs use an ellipsoid for the Earth, not a sphere.  They also include a factor for the atmospheric bending of light (assuming an average atmosphere).  

Hills and mountains on the horizon are practically impossible to include -- the program would need to access a data base of every hill, valley, mountain, and cliff in the world; its not worth the effort.  (And what if you are in the shadow of a building?)  Just add in an amount for your personal location, knowing that the sun moves 1/4 degree per minute.  So if that mountain range to the west seems to be 5 degrees high, then sunset will be 20 minutes early.

Predicting the orbit of the Earth is not hard these days, if you use the data already computed for you.  For maximum accuracy, you could use the JPL DE405 ephemeris data.

Predicting the rotation of the Earth is a bit harder, because it is irregular.  However, the length of the day changes by only 1 or 2 milliseconds a year, so you could assume a constant value and even after 100 years you would be off by only 37 seconds maximum.

When you add in all the sources of error (mainly the atmosphere), it is very hard to get the time of sunset / sunrise within 1 minute.  In the area of the arctic circle, the programs are sometimes (rarely) off by 20 minutes!

Answer 2

You can get rise and set times for the sun and moon to the nearest minute for you ZIP code at Weather Underground, and many other weather forecast pages.

Answer 3

i use xephem

Answer 4

Yes, the US NAVY has the most accurate system and has posted it on the web:

http://aa.usno.navy.mil/data/docs/RS_One...

Answer 5

I don`t know about a computer program, but there`s this:

http://bodmas.org/astronomy/riset.html  and

http://aa.usno.navy.mil/data/docs/RS_One...

Answer 6

you should buy starry night program ..

you chose where you are in the world and it will show you where planets are every night .

starryy night is awesome ! you won't be sorry that you bought it . i was thinking of the cost too and after i bought it ...wow was the money worth it!!!

i look online to see when eclipses are going to happen ...time , date and place on earth, punch it in my program and wantch it on there.

if i'm going out to look at the night sky i can see in the daytime what will be out and even print off a star map that show's me were things are too look at.

i can see what time the moon will rise tonight and what pase it is .

when jupiter will come into view and where . for any planet

even has awesome astronomy news links on it.

i see when the sun will go down so i know when the stars will be out each day