Crosswords0 min ago
Incredible But True.
Around the 4th of July each year the Earth is furthest from the Sun despite the hottest period in the UK
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"At the age of 10 almost 74 years ago I saw, in the Scottish Museum in Edinburgh what I can best describe as a giant plumb ball suspended from the dome high above the the floor.The ball had a conical pointer a short distance above a graded pattern on the floor.I could hardly believe I was looking,at first hand,the tilt of the earth shown graphically on the grid calibrated in degrees."
- I have never seen the pendulum either in Edinburgh or at the London Science Museum, but they do sound pretty impressive.
"Many thanks for your various replies.Some good and some less so.
It was my intention to stimulate opinion"
-D'oh. Such an equivocal response. I dislike the mystery. Whose posts were good, which posts were less so?
"it certainly achieved that however,I now ask the most intriguing question of all.How did it all begin and in such an orderly fashion?"
- How did all of what begin, and what is proceeding in an orderly fashion.What do you think it the most likely answer to your question?
- I have never seen the pendulum either in Edinburgh or at the London Science Museum, but they do sound pretty impressive.
"Many thanks for your various replies.Some good and some less so.
It was my intention to stimulate opinion"
-D'oh. Such an equivocal response. I dislike the mystery. Whose posts were good, which posts were less so?
"it certainly achieved that however,I now ask the most intriguing question of all.How did it all begin and in such an orderly fashion?"
- How did all of what begin, and what is proceeding in an orderly fashion.What do you think it the most likely answer to your question?
Zacs-Master
So the earth spins faster the further from the sun?
21:09 Fri 19th Jul 2013
The Earth's distance from the Sun has very little direct effect on the rotational speed of the Earth (although climate changes over the year do have a slight effect on the speed of rotation). The Earth does however take a bit longer to rotate with respect to the Sun when it is closer because it is also orbiting the Sun at a faster rate in the same direction as it rotates on its axis.
So the earth spins faster the further from the sun?
21:09 Fri 19th Jul 2013
The Earth's distance from the Sun has very little direct effect on the rotational speed of the Earth (although climate changes over the year do have a slight effect on the speed of rotation). The Earth does however take a bit longer to rotate with respect to the Sun when it is closer because it is also orbiting the Sun at a faster rate in the same direction as it rotates on its axis.
The time required for the Earth to rotate once around with respect to the Sun, is determined by its mostly uniform rate of rotation around its axis in combination with the variable speed of its orbit around the Sun at different points along it's elliptical orbit. A closer orbit translates to a faster orbital speed.
Elliptical orbits? You want Kepler's laws of motion. The radius of the ellipse changes in length but "sweeps out equal areas in equal measures of time".
Based on inverse square law, if you increase distance from sun by 3.4% then you reduce theoretical received sunlight intensity by 1/{1.034^2} which comes to 93.5% (of December intensity, for Northern hemisphere).
I find it an intriguing idea that Southern hemisphere summer might be shorter in duration than in the north* as the earth speeds up in its orbit around the sun but, perhaps, being at its closest approach to the sun in that segment of the orbit makes up any shortfall in heat intake for the hemisphere as a whole?
Or does it? Maybe an assymetrical heating of the planet is responsible for one or more global weather mechanisms?
*Thinking again, surely the gap between equinoxes is still 6 months in the southern hemisphere? Equal areas rule again.
Elsewhere, I found: -
"London is at latitude 52 deg N.
At 21 june, at noon the Sun will be at a maximum angle of 90-52+23.5 = 61.5 degrees.
On 21 December, at noon the Sun will be at a minimum noon angle of 90-52-23.5 = 14.5 degrees."
I can't do justice to the mathematics but we can all shine a torch against a wall and watch what happens to the illuminated area when you tilt the angle of the beam: fixed intensity spread over a larger area = reduced intensity per unit area.
Is the reduction as simple as sin(angle)? I don't know but, for what it's worth, if the noon sun at 90deg=100% intensity then sun at 61.5deg would be 87.8% and sun at 14.5 deg would be 25%.
You'd need a spreadsheet to do it justice but you don't need that to tell you that ~18 hours of daylight in summer means it'll be hot and ~6 hours sunlight in winter mean it will be cold. ...at least theoretically, in the middle of a continental land mass. Britain is a special case, the effects of being surrounded by sea, the Gulf Stream, the wobbly Jet Stream, as we are frequently reminded by the Met Office folk.
Based on inverse square law, if you increase distance from sun by 3.4% then you reduce theoretical received sunlight intensity by 1/{1.034^2} which comes to 93.5% (of December intensity, for Northern hemisphere).
I find it an intriguing idea that Southern hemisphere summer might be shorter in duration than in the north* as the earth speeds up in its orbit around the sun but, perhaps, being at its closest approach to the sun in that segment of the orbit makes up any shortfall in heat intake for the hemisphere as a whole?
Or does it? Maybe an assymetrical heating of the planet is responsible for one or more global weather mechanisms?
*Thinking again, surely the gap between equinoxes is still 6 months in the southern hemisphere? Equal areas rule again.
Elsewhere, I found: -
"London is at latitude 52 deg N.
At 21 june, at noon the Sun will be at a maximum angle of 90-52+23.5 = 61.5 degrees.
On 21 December, at noon the Sun will be at a minimum noon angle of 90-52-23.5 = 14.5 degrees."
I can't do justice to the mathematics but we can all shine a torch against a wall and watch what happens to the illuminated area when you tilt the angle of the beam: fixed intensity spread over a larger area = reduced intensity per unit area.
Is the reduction as simple as sin(angle)? I don't know but, for what it's worth, if the noon sun at 90deg=100% intensity then sun at 61.5deg would be 87.8% and sun at 14.5 deg would be 25%.
You'd need a spreadsheet to do it justice but you don't need that to tell you that ~18 hours of daylight in summer means it'll be hot and ~6 hours sunlight in winter mean it will be cold. ...at least theoretically, in the middle of a continental land mass. Britain is a special case, the effects of being surrounded by sea, the Gulf Stream, the wobbly Jet Stream, as we are frequently reminded by the Met Office folk.
The equinoxes are skewed towards perigee because the Earth's orbital speed is greater during perihelion, the Earth spending less time on that side of the Sun.
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Hi mibn,
That particular Wiki paragraph has two [citation needed] labels on it and, imho, is dubious.
By my calculations, 22-31 December is 10 days. 10 +31 +28 (non leap year) +31, +30 +31 + 22 (22nd June) = 183 days.
The other half of the year being 182 days, obviously. By 'skewed towards' did you actually mean 'different by 1 day'?
That particular Wiki paragraph has two [citation needed] labels on it and, imho, is dubious.
By my calculations, 22-31 December is 10 days. 10 +31 +28 (non leap year) +31, +30 +31 + 22 (22nd June) = 183 days.
The other half of the year being 182 days, obviously. By 'skewed towards' did you actually mean 'different by 1 day'?
Hi mibn,
I knew there was something ultra-basic I was overlooking. Solstices are easy to remember (always either 21st/22nd). No-one really marks the equinoxes, so it's less a matter of me forgetting than one of never having memorised them to begin with. ;-)
Co-incidentally, I edited something out of my last post, for the sake of brevity, dealing with one point at a time etc. It was the thing about the rates of change of sunrise and sunset times being uneven between longest day and shortest night. Unavoidably, the shifting times meet in the middle and give us an equinox.
Having accepted your point about a different length of summer in southern hemisphere, can we quantify how much shorter, seeing as how I reckoned the solar intensity is up to 7% greater for them, at perihelion?
I knew there was something ultra-basic I was overlooking. Solstices are easy to remember (always either 21st/22nd). No-one really marks the equinoxes, so it's less a matter of me forgetting than one of never having memorised them to begin with. ;-)
Co-incidentally, I edited something out of my last post, for the sake of brevity, dealing with one point at a time etc. It was the thing about the rates of change of sunrise and sunset times being uneven between longest day and shortest night. Unavoidably, the shifting times meet in the middle and give us an equinox.
Having accepted your point about a different length of summer in southern hemisphere, can we quantify how much shorter, seeing as how I reckoned the solar intensity is up to 7% greater for them, at perihelion?
I suspect that for a Keplerian orbit, time precisely compensates for distance so that over the course of one year Northern and Southern Hemispheres receive equal illumination from the Sun regardless of any fixed degree or direction of axial tilt. Current axial tilt and alignment would tend towards briefer but more intense Summers for the Southern Hemisphere, albeit moderated by other factors influencing planet-wide climate. I will happily consider any thoughts or information supporting or refuting my suspicions.
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