Equinox?

Badly Shaved Monkey

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Badly Shaved Monkey
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According to this morning's weather forecast, today is the astronomical equinox defined by the "Sun crossing the equator". Why, therefore,is my sunrise to sunset interval already 12h13m?
 
Badly Shaved Monkey said:
According to this morning's weather forecast, today is the astronomical equinox defined by the "Sun crossing the equator". Why, therefore,is my sunrise to sunset interval already 12h13m?
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Wiki gives two reasons for this:

1) The sun is not a point source of light, but a disk (*), with an angular size of 31 to 32 arc minutes (depending on the actual distance, which varies because the earth's orbit is an ellipse). It will take indeed 12 hours from the time that the first spot on the edge of the sun disk rises above the horizon at sunrise to drop below the horizon around sunset, but then the rest of the sun disk still has to disappear.

(*) a disk as seen in the sky, lest anyone think I really think it's not (roughly) a sphere.

2) Atmospheric refraction of the sunlight actually causes the first sunlight to be seen before any point of the sun disk is above the horizon. And likewise, it will cause the last sun light to still be seen a bit after the whole sun disk has disappeared below the horizon.
 
Badly Shaved Monkey said:
According to this morning's weather forecast, today is the astronomical equinox defined by the "Sun crossing the equator". Why, therefore,is my sunrise to sunset interval already 12h13m?
Click to expand...

That 13 minutes is how much the day got longer because we use Daylight Savings Time.
 
Foo phil

Thank you for posting the video - I didn't know that!! It sounds as if there might be a series of videos under the general heading of 'stay curious', so I shall investigate.
 
foophil said:
Found a great YouTube video explaining why day and night aren't equal on the equinox:

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Nice video.

From ca 1:40min onwards, it shows a picture of earth's orbit divided into four "quadrants" between the equinoxes and solstices, and argues that the time between the vernal equinox and summer solstice (i.e. spring), and the time between summer solstice and autumnal equinox (i.e., summer) is longer than those on the winter side.

Kepler already had discovered this with his second law: a planet sweeps equal areas (of the ellipse of its orbit) in equal times. Newton later proved this from his theory of gravity to be true. You can clearly see the areas on the summer side being larger than those on the winter side. The picture, of course, is exaggerated for effect, the earth's orbit is not nearly as eccentric.

However, this effect is incumbent on the aphelion (the point where the earth is farthest away from the sun) being in the summer. These days, it varies between 3 and 6 July. And because the earth has a precession with a period of ca. 26,000 years, in 13,000 years time the aphelion will be close to the winter solstice and the autumn and winter will actually be longer.
 
Excuses, excuses... I read that relativity is breaking down, this is the first sign.
 
Mojo said:
They're published in The Times.
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:D No, how are they determined? In other words, how is the transition from day to night defined? I was suggesting that it's not defined as the diameter of the sun coinciding with the horizon and that is indeed one effect. Another is atmospheric refraction near the horizon and a third is the ellipticity of the orbit as others have written
 
The topic seems to be in a twilight zone :p.

The twilight begins in the evening or ends in the morning when the centre of the the solar disk is fifty minutes of arch bellow the horizon. That adds a minimum of almost 7 minutes to our days -in case the sun's apparent path follows the gradient of the Earth-. At my latitude -almost 35°- more than one minute is added.

Badly Shaved Monkey informs he has some six minutes added to that so, what's "its" location? Britain?

foophil said:
Found a great YouTube video explaining why day and night aren't equal on the equinox:

Click to expand...

Nicely crafted intelligent yet easy videos. I enjoyed "the twelve days of evolution". A must for those who live within a one mile radius of a crazy creationist.
 
aleCcowaN said:
That adds a minimum of almost 7 minutes to our days -in case the sun's apparent path follows the gradient of the Earth-. At my latitude -almost 35°- more than one minute is added.

Badly Shaved Monkey informs he has some six minutes added to that so, what's "its" location? Britain?
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Do you mean a minimum of 7 mins is added and at your latitude another minute is added? And my UK latitude adds 6.
 
Badly Shaved Monkey said:
Do you mean a minimum of 7 mins is added and at your latitude another minute is added? And my UK latitude adds 6.
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Yes. I was checking today's day length in my country -still in summer daylight saving time-:

Buenos Aires (about 35°) ---> 6:56 to 19:04 (12 h 8 m)
La Quiaca (about 23°, next to the Tropic of Capricorn) ---> 7:26 to 19:32 (12 h 6 m)
Ushuaia (about 55° ---> the same England-Scotland's borders) ---> 7:35 to 19:45 (12 h 10m)
Esperanza (about 63° ---> about Trondheim's) ---> 6:48 to 19 (12 h 12m)

In Amundsen-Scott (90°) they just got half sun out all day around. A few days ago they were in a twilight.
 
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hecd2 said:
No, how are they determined?
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Expanding on Mojo's explanation that they're published in The Times: Rupert Murdoch, who owns The Times, determines the times of sunrise and sunset, and the sun complies. Simples really.
 
ddt said:
Expanding on Mojo's explanation that they're published in The Times: Rupert Murdoch, who owns The Times, determines the times of sunrise and sunset, and the sun complies. Simples really.
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Rupe owns The Sun as well as The Times. The Sun has always complied to his demands.
 
That 13 minutes is how much the day got longer because we use Daylight Savings Time.

DST deals in hours, not minutes. And it's Daylight Saving Time.
 
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SusanB-M1 said:
Foo phil

Thank you for posting the video - I didn't know that!! It sounds as if there might be a series of videos under the general heading of 'stay curious', so I shall investigate.
Click to expand...
The Youtube series is called "It's okay to be smart". It's pretty good.
 
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