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

[ShelleyAnn]

Assuming I want to add my chlorine after the sun has "gone down"...exactly when can I call it "evening" and add my chlorine? I have my pump on a timer to conserve energy but it seems that I'm always going out in the dark to add chlorine and then have to turn the pump on for a couple more hours to mix. I was out at 6pm yesterday and wondered to myself, "hey, isn't the sun down enough to not degrade my chlorine"? I'm kinda using that timing of it's late enough in the day so you don't need to slather the sun screen on. Does it work the same way for chlorine? Doing it earlier while it's still light out would also help in the testing department as I will be able to see the darn vial color with natural light.

Shelley

[Pam and Jim]

I like the question- don't know the answer.
I'll be watching to see what they say...

[halds]

I think if you asking for a specific time, there is no answer. The sun begins to go down immediately after high noon, and ends is when the sun sets. Anything in between is a graded level of UV exposure.... you have to decide what you are happy to accommodate with you schedule. I just wait until after dinner, but I leave my pump run until we go to bed.

[aquarium]

Heh,

I just adjusted the timer on our pump to give me more time in the evening to add bleach and test. We have a steep hill behind our house to the west, so I consider the sun to be 'down' when the pool is in the shade of the hill.

TW

[CarlD]

Well, there's sundown, then there's twilight, then there's naval twilight...

The issue of sunlight is the UV rays break down chlorine so having it work at night means one less thing to affect the chlorine. When the UV exposure passes, then it's ok.

[waterbear]

If you are an orthodox jew it is the time it goes down in Israel! (actually some truth in this!)

[Henry3]

And the Moslem definition:
"dark" is traditionally defined as "when you cannot distinguish between a black thread and a white thread".

[sailork]

I bought a second set of trippers for my intermatic timer. I have it run several hours in the morning after sunrise, and then I have it run two hours in the late evening. That way the pool doesn't go as long between circulations. Right now it kicks on just before 10 so I can run out there and dump some bleach in before the Daily Show. The nice thing is that the timer will turn it off for me so I don't accidentally leave it run all night.

As far as your question is concerned as the sun begins to set there is so little light (compared to noon) reaching your pool that it would probably make no difference at all if you added the chlorine then. It has to do with the amount of atmosphere the light has to travel through and the incident angle on your pool. I only add mine so late because thats when the trippers are set.

[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.