# Need to Know time

1. Jul 19, 2011

### facenian

Hello, I need to know time of sunset and sunrise for every day of the year. Is there any free software that can give such information in a sistematic way?

2. Jul 19, 2011

### Janus

Staff Emeritus
3. Jul 19, 2011

### facenian

thank you, it will be very helpfull!

4. Jul 19, 2011

### mp3car

also, this site is available.. it generates a very basic table that can be imported into excel (there are even instructions for doing so on the page). You can start with a city location or you can use lat/lon and reference time zone...

http://aa.usno.navy.mil/data/docs/RS_OneYear.php

If you want to do something neat with the data, make an additional column in excel for the length of daylight (just use formulas in excel to calculate it). Then plot the length of daylight for a period of 1 year. You will see a sinusoidal plot (unless you live directly on the equator). The minimum value of the y-axis would be 0 hours of daylight and the maximum would be 24 hours of daylight. The 12 hour line on the y-axis would be the "zero crossing" of the plot, with crossings occurring on the equinoxes. The peak is the summer solstice, and the trough/valley would be the winter solstice. The amplitude of this plot would increase as you move towards the poles... If you plot it like this, you can really see why some times of the year, the days seem to get a lot longer/shorter with just one passing day (when the plot has a high slope, like March/September, when daylight in the mid-latitudes of the US gets about 2m:30s longer/shorter), while other times of the year the length of daylight barely changes from one day to the next (like in June and December when the slope of the plot is almost zero and the length of daylight changes by only a second or two with each passing day).

5. Jul 20, 2011