Day length - rule of twelfths?

[Twister_Ken]

Guess we all know the rule of twelfths applied to tides. Does it also apply to increasing/decreasing day length - i.e hardly any alteration in June or December, and seemingly losing minutes of daylight per day at the mo?

 

[sarabande]

in the midst of this site, is the full story of daylight length.

http://www.analemma.com/SunGraph/index.html


With pictures of the daylight hours / nautica / astronomical twilight.

 

[iangrant]

Time on your hands?

cor blimey a struggle to log back in to this lot, and there you are still.

hope you are all well and enjoying the ever earlier sunsets.

 

[Danny Jo]

Guess we all know the rule of twelfths applied to tides. Does it also apply to increasing/decreasing day length - i.e hardly any alteration in June or December, and seemingly losing minutes of daylight per day at the mo?

Yup, variation in day length describes the same sine wave as tidal height.

I once asked one of my kids (more mathematically savvy than me) why sine waves crop up so often in nature. The answer went something like: because it describes circular motion (i.e. the motion of a point rotating on the circumference of a circle).

Rotation of the earth on its axis (tides); rotation of the earth around the sun (day length).

 

[bedouin]

I think you will find that Sunrise/Sunset fit closer to the "rule of 12ths" than tides do.

 

[Twister_Ken]

Hi Ian, and welcome back.

Still playing ducks and drakes with Wightlink?

 

[iangrant]

ducks and drakes

Ken thanks for the welcome back.

happily the iow ferries don't get into chichester harbour where the pink anchor ribbon has decreed the bar our limit of navigation.

with cooler weather and a few passes earned i may just get out there jousting wi' the b#ggers again soon, most possibly the weekend after next.

 

[AngusMcDoon]

Guess we all know the rule of twelfths applied to tides. Does it also apply to increasing/decreasing day length - i.e hardly any alteration in June or December, and seemingly losing minutes of daylight per day at the mo?

The rule of twelfths applies as an approximation to anything that is sinusoidal or nearly so. So not just tides and daylight hours, but yer pistons' speed in yer engine when you are motoring into a lumpy head sea, those head sea waves that are slowing you down, how much yer wobbly bits wobble when you've just gone over aforementioned waves, and so on.

 

[Chris_Robb]

Guess we all know the rule of twelfths applied to tides. Does it also apply to increasing/decreasing day length - i.e hardly any alteration in June or December, and seemingly losing minutes of daylight per day at the mo?

I would have thought that was the case.

However yesterday you would have ben caught out badly if you had used it at half tide to determine how much further the water would go out!

 

[gordmac]

Engine piston movement isn't sinusoidal.

 

[AngusMcDoon]

Engine piston movement isn't sinusoidal.

I know it isn't truly sinusoidal, but it's pretty close. I did say approximate. Daily tide curves aren't true sinusoid either.

 

[Chris_Robb]

I know it isn't truly sinusoidal, but it's pretty close. I did say approximate. Daily tide curves aren't true sinusoid either.

Perhaps more like a bell curve???