Winter in Northern Hemisphere
 

:rolleyes:
Now that we are in the winter season we would expect the sun to be furtherest away from Earth.
The Truth is that today Jan 3rd the sun reaches its perihelion which means its is closest to the Earth. This seems to be a bit of a paradox.
Read on and you will get the answer why this is so.

[url]http://www.space.com/spacewatch/301206_happy_perihelion.html[/url]

Mally :coffee:

[QUOTE=mfgoode;95223]:rolleyes:
Now that we are in the winter season we would expect the sun to be furtherest away from Earth.
The Truth is that today Jan 3rd the sun reaches its perihelion which means its is closest to the Earth. This seems to be a bit of a paradox.
Read on and you will get the answer why this is so.

[url]http://www.space.com/spacewatch/301206_happy_perihelion.html[/url]

Mally :coffee:[/QUOTE]In what way is it a paradox? Unless a planet's perihelion occurs precisely at one of its equinoctes, one hemisphere will always have its perihelion on the winter side of the equinoctes. Even if that occurs, precession will ensure that it doesn't happen very often.

If the planet doesn't have an axial tilt, it doesn't have seasons anyway.


Paul

Equinox.
 

:rolleyes:
My dear Paul, there is no such word in my dictionary as 'equinoctes'.
Do you mean equinox?
I said it was a BIT of a paradox. In winter we would expect the sun to be fartherest away from the Earth. On the contrary it is closest.
I agree with you that it is due to the tilt of the earth's axis which causes the seasons and not the distance of earth from the sun.
Mally :coffee:

Precession
 

[QUOTE=xilman;95224]In what way is it a paradox?
Even if that occurs, precession will ensure that it doesn't happen very often.

If the planet doesn't have an axial tilt, it doesn't have seasons anyway.


Paul[/QUOTE]

It happens only twice a year on 21st. March and 21st. Sept

Mally. :coffee:

[QUOTE=mfgoode;95226]:rolleyes:
My dear Paul, there is no such word in my dictionary as 'equinoctes'.
Do you mean equinox?
I said it was a BIT of a paradox. In winter we would expect the sun to be fartherest away from the Earth. On the contrary it is closest.
I agree with you that it is due to the tilt of the earth's axis which causes the seasons and not the distance of earth from the sun.
Mally :coffee:[/QUOTE]Equinox is a Latin noun ("equal night"), so the plural is?

I still don't see it as anything of a paradox. In the southern hemisphere perihelion occurs near mid-summer. So what?


Paul

[QUOTE=mfgoode;95227]It happens only twice a year on 21st. March and 21st. Sept

Mally. :coffee:[/QUOTE]If you read my posting more clearly, you will see that I was referring to a planet for which perihelion occurs precisely at an equinox. It is [b]that[/b] situation which occurs only very rarely. I do not know when the the earth's perihelion next passes an equinox but it must be a long time hence. The drift of the longitude of perihelion for the earth is measured in arc-seconds per millenium, and perihelion is almost 90 degrees from the northern vernal equinox...

Paul

[QUOTE=mfgoode;95226]I agree with you that it is due to the tilt of the earth's axis which causes the seasons and not the distance of earth from the sun.[/QUOTE]The axial tilt causes most of the temperature variations over the year, it is true.

However, the orbital eccentricity is significant and solar heating is several percent greater at perihelion than at aphelion. This effect is very easily measurable.


Paul

thanks for info
 

Does this explain warmer than normal even up north, or is this an annual
occurence?I would expect the latter.Are we exceptionally close this year?
Warning:Relative to sun, what's clockwise?I would suggest shying away from this in the same argument, unless your a Nasa or space analyst, whereby it
might be crucial. We have the conventions in math and science, but one hell of a job, in going from flushing the toilet to 'the speed' of light'.
Has anyone ever categorized all of this, or is it still in the making? These
'torques' going on all over the place, and critical incidence points.

[QUOTE=xilman;95233]The axial tilt causes most of the temperature variations over the year, it is true.

However, the orbital eccentricity is significant and solar heating is several percent greater at perihelion than at aphelion. This effect is very easily measurable.


Paul[/QUOTE]

:smile:

Quote:"solar heating is several percent greater at perihelion than at aphelion."

That is exactly the paradox as athough the heating is supposed to be more at perihlion yet it is winter!

The heating effect is not depending on the distance away or near the sun as at those astronomical distances the effects though measureable are insignificant.

What really matters is the angle of incidence of the suns rays which is important. At 0* to the normal (i.e. head on vertical) it is hottest. At any other angle it is multiplied or resolved by cosine of the angle. Taking it to the extreme if a ray skims the earth at 90* to the normal ( i.e. tangential to the earths surface) the heating effect is zero.

We come across this every day when at noonday due to head on rays it is warmest.

Mally :coffee:

warmer than normal!
 

[QUOTE=David John Hill Jr;95247]Does this explain warmer than normal even up north, or is this an annual
occurence?I would expect the latter.Are we exceptionally close this year?
Warning:Relative to sun, what's clockwise?I would suggest shying away from this in the same argument, unless your a Nasa or space analyst, whereby it
might be crucial. We have the conventions in math and science, but one hell of a job, in going from flushing the toilet to 'the speed' of light'.
Has anyone ever categorized all of this, or is it still in the making? These
'torques' going on all over the place, and critical incidence points.[/QUOTE]

:smile:

My advice: stick to maths and keep astronomy as a hobby

Mally :coffee:

[QUOTE=mfgoode;95298]That is exactly the paradox as athough the heating is supposed to be more at perihlion yet it is winter![/QUOTE]As I've said repeatedly, and yet you seem not to have paid any attention: at the moment it is only winter in the northern hemisphere. It's summer in the southern hemisphere and it's just after perihelion. There the earth is closer to the sun and it is hotter than at aphelion. Where's the paradox?

Anyway, the heating is undoubtedly more at perihelion. The earth recieves almost 10% more heating at perhelion than at aphelion. The effect on the earth's climate is quite marked. The northern winter is much warmer and shorter than the southern winter, entirely due to the fact that perihelion lies close to the boreal mid-winter. The northern summer is correspondingly cooler and longer than the southern summer


Paul