The same amount of daylight hours.....

When you think the poles get 24 hours of sun in summer and then no sun in winter....

I tried to google this but couldn't find and answer.

I think the answer is yes with exception of shadows.

Except for some East Coast states. They have daylight savings which gives them an extra hour of daylight. Or does daylight 'savings' mean they are saving an hour hour of daylight meaning they then have an extra hour of darkness. I'm so confused.

The expression 'daylight' needs a fairly rigid definition here. There are atmospheric phenomena such as "white nights" that may skew the insolation equilibrium. Also, Earth is not near perfectly round ball, it is squashed at the poles, so, theoretically, they get somewhat less exposure.

Well today here on the tropic of Capricorn we got exactly 12 hours of sunlight as it's the autumn equinox today. Reciprocally it's the Spring equinox in the northern hemisphere. From tomorrow our Daylight hours will now be getting less than 12 hours per day. Of course the daylight hours have been getting shorter since the summer solstice on the 21st of December when in the southern hemisphere you receive the max amount of daylight hours - the further south you are from the equator the greater this amount is but is indirectly proportional to the amount you receive once the earth has done half an orbit around the sun - this is when the winter solstice occurs (21 June).

Here's a solar chart for perth - these are a very useful tool for designing buildings and are incredibly accurate. e.g. if you look at the 21 March sun path and draw a line from the centre out to say where it touches the outer circle that is the bearing at either sunrise (exactly due east) or sunset (exactly due west) with the total sunlight hours being 12 (6am to 6pm). it also gives you the sun's altitude in the sky e.g. at 11 oclock today the sun was at approx 27degrees East of North at an horizontal altitude of 55deg . You can actually see just how large the spread is from Summer sunrise/sunset position to winter sunrise/sunset position respectively.

These diagrams are specific for latitude so I cannot use Perth's one for say Darwin.


Argh hang on you're in Victoria on daylight saving so you get an extra hour of sunlight each day

No they don't. The one simple answer is refraction. The poles will never have the same amount of light as the tropics because of the way light bends through the atmosphere.

Aren't we talking about the same number of light HOURS. Not intensity (refraction) or how hot it is (closer to sun at equator). Hours.


I say not quite, as it is not a sphere.
(Oblate spheroid, if anyone cares)

But so damn close we may as well call it equal

From Wiki

The naive expectation is that, for every place on Earth, the Sun will appear to be above the horizon for exactly half the time. Thus, for a standard year consisting of 8760 hours, apparent maximal daytime duration would be 4380 hours. However, there are physical and astronomical effects which change that picture. Namely, atmospheric refraction allows the Sun to be still visible even when it physically sets below the horizon line. For that reason, average daytime (disregarding cloud effects) is longest in polar areas, where the apparent Sun spends the most time around the horizon. Places on the Arctic Circle have the longest total annual daytime of 4647 hours, while the North Pole receives 4575. Because of elliptic nature of the Earth's orbit, the Southern Hemisphere is not symmetrical: Antarctic Circle at 4530 hours receives 5 days less of sunshine than its antipodes. The Equator has the total daytime of 4422 hours per year.[2]

It does then go on to talk about definitions and measurements in a practical sense using sunshine hours as oppose to sunlight hours - using a device called, wait for it........ a sunshine recorder- to take into account visible sunlight due refraction and other bits and pieces. But I think on strict terms based on Sandfoots original question, this is the answer.


I was surprised that the poles got more sunlight on average then the equator...

^^^ very interesting.

I also liked the bits about how often it is sunny


Since sunshine duration depends chiefly on concentration of clouds and fog in the observed area, locations with arid climate naturally correlate with high sunshine duration values, and, conversely, lowest values of sunshine duration are encountered in areas with wet, west-coast oceanic climate.

The two areas with highest sunshine duration in the World, measured as annual average, are southwestern United States (Arizona and Nevada) and northeastern Africa (Egypt, Sudan and Chad).[4] The city claiming the title of the sunniest in the World is Yuma, Arizona, with over 4,000 hours (90% of time) of bright sunshine annually.[4][5] The sunniest month in the World is May in the base of Eureka in the far north of Canada, which receives 16.5 hours of bright sun daily

evlPanda said..



Everywhere has 12 hours of sunlight today.


Everywhere has the same amount of sunlight each year. The angle differs, as does the weather, and you won't get any sunlight if you live down a mine, but everywhere gets the same amount of sun in the sky each year.

I've given you a green thumb to cancel out the red one Evil. Of course everyone gets 12 hours today. The original question was geometric, everyone knows the earth is perfectly round and the sun is a point source at infinity. If you reckon you only got 11hrs 58mins today you're living down a mineshaft with apostrophe man.

Sandfoot said..
... as we live on a near perfectly round ball.
Cheers.

No we don't!! We live on an oblate spheroid, or even more accurately, a geoid. "Near perfectly round" it most definitely ain't!

^^^ didn't I say whaaaaay back that it is an oblate spheroid, but the difference from a sphere is negligable.
Geez people, switch on




Now Notwal if you are going to bring up 'surface roughness', that affects circumference, which means gravity varies, and light will bend................

Poodle said..

RiffRaff said..



No

No.

Or in WA...

"yeaahh, nahhh"

evlPanda said..

Ian K said..

evlPanda said..







Everywhere has 12 hours of sunlight today.




Everywhere has the same amount of sunlight each year. The angle differs, as does the weather, and you won't get any sunlight if you live down a mine, but everywhere gets the same amount of sun in the sky each year.

I've given you a green thumb to cancel out the red one Evil. Of course everyone gets 12 hours today. The original question was geometric, everyone knows the earth is perfectly round and the sun is a point source at infinity. If you reckon you only got 11hrs 58mins today you're living down a mineshaft with apostrophe man.

And now you had two red thumbs?The original question was...

Does every point on earth receive the same amount of daylight hours?

If it's not a trick question involving mountain ranges, mine shafts and clouds then the answer is a simple "Yes".

___

While on the topic of spheres I saw a great analogy on how to understand if space is curved or flat.

The sum of the angles that make up a triangle always add to 180 degrees.

However, if you make a large enough triangle on the surface of the earth that's not the case.

From the North Pole draw a line straight down to the equator.

Then turn left 90 degreesGo around the equator 1/4 of the way around the Earth.

Turn left 90 degrees.Go all the way back up to the North Pole.

You have 3x 90 degree angles.

The Earth therefore is not flat. I thought this was kinda cool : \

No they don't. Refraction causes light to bend. I was wrong with what i previously said before as the poles actually get more light due to refraction not the other way around. this is the amount of day light, I'm not talking about the intensity of light. refraction means that the sun may be over the horison however because the atmoshere makes light bend, you will still be able to see the sun. if light wasn't effected by the atmoshere (refraction) then the answer to the question would be yes. Understand? this is another reason why the moon is large when you see it just over the horizon and also the reason why the sun appears to set very quickly compared the usual speed it moves across the sky.

Toph said..
this is the linken.wikipedia.org/wiki/Sunshine_duration

did everyone miss this???