The "Geeks" will love this...when does the sun go down?

[giroup01]

exactly when can I call it "evening" and add my chlorine?

Sunrise and sunset times for your location at: http://aa.usno.navy.mil/data/docs/RS_OneYear.html

[KurtV]

Here are the geeky nautical definitions of the three twilights.

Civil Twilight: Begins in the morning and end in the evening when the center of the sun is 6 degrees below the horizon. Illumination is sufficient to distinguish terrestial objects, horizon is well defined and bright stars are visible under good atmospherics (so long as there isn't too much moonlight or artificial illumination).

Nautical Twilight: Begins in the morning and ends in the evening when the center of the sun is 12 degrees below the horizon. At the beginning or end of nautical twilight, with good atmospherics and in the absence of other illumination, general outlines of ground objects may be distinguishable, but detailed outdoor operations are not possible and the horizon is indistinct.


Astronomical Twilight: Begins in the morning and ends in the evening when the center of the Sun is 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening sunlight doesn't contribute to illumination. Sun illumination is almost imperceptible for some time after the beginning of morning astronomical twilight and before the end of evening astronomical twilight.



If you want to know exactly when the sun sets in your location you have to know your elevation and acount for the atmospheric refraction and even then your local apparent sunset can be affected by large geological formations such as mountains.




I'm really not that much of a pedant myself, I just add bleach anytime after the sun is below the tree line.

[medvampire]

Is there really a best time of day to dump bleach in? My scedule forces me to dump in around 8 in the morning when I get home from work. Is this gonna be a problem?
I dump in just enough to get the FC to 4 and start my pump and run it untill 7 pm and leave it off at night to help prevent heat loss. The kids dont jump in till around 1 or 2 in the afternoon to allow for circulation of the bleach (and them to get their lazy kisters out of bed).
If I add muratic acid, I have them wait untill 5 or 6 pm, do a quick ph check, and then dive in.
Thanks to the board I am learning you dont have to be anal but just watchfull.
Later
Steve

[waterbear]

ideally the best time would be in the evening so the sun has the least effect on it and it can work all night to sanitize but,IMHO, it is more important to test and add it on a regular schedule as you are doing so I think you are fine.

[medvampire]

Thats kinda what I thought so I will just keep doing what I am doing cause it seems to be working.

Thanks
Steve

[halds]

We leave our opaque solar cover on whenever we are not using the pool. It is very noticeable how much longer the chlorine level stays within range doing this. Im sure it also helps to inhibit algae. So far this summer I average 1-2 gallon of bleach a week for 30,000 gal IG pool. (without heavy swimmer load)


Hal