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enquiringman
2006-Aug-21, 04:05 PM
Folks, I'm no astronomer or scientist but would like to ask a question that's been bugging me. Due to earths eliptical (hope spelling ok!) orbit it follows that twice a year the earth reaches its closest point to the sun. Which hemisphere would be enjoying their summer at these points and is the average temperature higher than a summer experienced at earth's furthest point from the sun (given the same latitude and discounting land mass and altitude)? Please explain in laymans terms if possible. Thankyou all.

Nowhere Man
2006-Aug-21, 04:13 PM
Look up aphelion and perihelion in a good encyclopedia. Also look up ellipses and orbits (hint: The Sun is not at the center of the Earth's orbit).

Fred

enquiringman
2006-Aug-21, 04:17 PM
Thanks for furnishing me with the correct terms. Doesn't really answer my question though? Or does it? mmmmmmmmm

Jason Thompson
2006-Aug-21, 04:20 PM
Due to earths eliptical (hope spelling ok!) orbit it follows that twice a year the earth reaches its closest point to the sun.

The sun is not at the centre of the eliptical orbit, as your statement suggests you think, it is at one of the foci. What this means in layman's terms is that the Earth makes a single close approach in one orbit. The closest approach happens in January, and the Earth reaches its furthest from the sun in July.

enquiringman
2006-Aug-21, 04:26 PM
Jason, thanks, an explanation on the orbital path even I can understand. I take it then that the southern hemisphere should enjoy higher average temparatures in their summer as the earth is closer to the sun?

enquiringman
2006-Aug-21, 04:34 PM
I suppose what I'm trying to ask is what impact distance to the sun has on temperature?

enquiringman
2006-Aug-21, 04:36 PM
In the context of the original question please!!

Tim Thompson
2006-Aug-21, 05:07 PM
The variable distance from the sun has no short term impact on weather, and no measureable consequences that I know of on temperature records. Whether or not the summer is warmer or colder in one hemisphere or the other is dominated by the tilt of Earth's axis, which determines the angle of incidence for sunlight. The distribution of oceans and land mass, and the rotation of Earth (which determines trade winds), are also more important to seasonal temperature.

Over very long periods of time (tens of thousands of years), the changing distance from Earth to Sol does affect climate trends (Milankovitch cycles (http://aa.usno.navy.mil/faq/docs/seasons_orbit.html), Milankovitch Cycles and Glaciation (http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm)).

Thomas(believer)
2006-Aug-21, 05:14 PM
Also, even though the Earth’s distance to the sun varies as Earth moves between the apsides of its elliptical orbit, these variations are not the cause of the seasons.[1] Besides axial tilt, other factors contribute to seasonal temperature changes. Orbital eccentricity can influence temperatures, but on Earth, this effect is small and is more than counteracted by other factors; research shows that the Earth as a whole is actually a few degrees warmer when farther from the sun.[2] Mars however experiences wide temperature variations and violent dust storms every year at perihelion.[3]

A quote from this (http://en.wikipedia.org/wiki/Season) wikipedia link and think gives an answer to your question.

Roy Batty
2006-Aug-21, 06:47 PM
The BA also explains it rather well here (http://www.badastronomy.com/bad/misc/seasons.html).

Wolverine
2006-Aug-22, 01:10 AM
The BA also explains it rather well here (http://www.badastronomy.com/bad/misc/seasons.html).

Indeed. More on the subject here (http://curious.astro.cornell.edu/question.php?number=331), as well.

PhantomWolf
2006-Aug-22, 03:51 AM
I take it then that the southern hemisphere should enjoy higher average temparatures in their summer as the earth is closer to the sun?

You'd think that wouldn't you, but not really. The main reason being that the southern hemisphere doesn't have as much land mass. As you go inland, because you are surrounded by rocks, you tend to get a condition where hots are hotter and colds are colder (hence why the centre of the US has 6 feet of snow in winter and molten pavement in summer ;)) while much of the southern hemisphere is relatively close to the coastline and so cooled by the oceans. Obvious exceptions tend to be Southern Africa and the midle of Australia.

Ken G
2006-Aug-22, 04:55 AM
The BA also explains it rather well here (http://www.badastronomy.com/bad/misc/seasons.html).

Here's a quote from that link:


The distance of the Earth to the Sun is a smaller effect yet, but it does exist! So the Southern Hemisphere gets slightly hotter summers and slightly colder winters than the North. But only by a couple of degrees, and only on average.

So the effect asked about in the OP is actually not negligible-- seasons are slightly more moderate in the northern hemisphere, all else being equal. That all else is not necessarily equal was explained well by PhantomWolf.

tony873004
2006-Aug-22, 09:36 AM
Also, Milankovitch Cycles are a key player over long periods of time. Earth's eccentricity is constantly changing. Sometimes it is nearly circular. Other times it is 3x what it is today. At 3x, the difference between perigee and apogee is a much more significant player in the seasons.

The direction of the Earth's tilt rotates in a 26,000 year cycle. As was already mentioned, the Southern Hemisphere has less land mass, and that helps keep things a bit cooler in their summer even though they are closer to the Sun. But in 13,000 years, the Northern Hemisphere, with its large land masses will be at perihelion during its summer. And when that happens when Earth's eccentricity is 3x today's value it can become quite toasty.

Google for Milankovitch Cycles. It's very interesting.

enquiringman
2006-Aug-22, 10:18 AM
I thank every one of you for your informative answers and taking the time to reply to me - I have learned a great deal more than I had bargained for and hopefully some of you have too. It has resulted in me needing to ask just a couple of more questions before we close off and move on to the moon poll (promise!).
As clearly the distance does make a difference;
1/ What are the actual distances involved?
2/ Can we measure the "strength" of sunlight at a given latitude (thereby discounting angle of incidence) in both the southern and northern hemisphere. (electrical charge produced by solar panel per hour? no doubt you guys will know of a better way)
We could therefor model the likely degree of "toasting" in Tony's excellent answer and help my understanding of our orbits effect on climate. Perhaps it might even impact on our calculations for the likelihood of life on other planets (just threw that in to try and appeal - don't go there please!)Appreciate if we could stick to the effects of the sun and distance and not meander into the average specific latent heat capacity of land and water mass, ocean currents etc - Thanks again everyone.

max8166
2006-Aug-22, 10:22 AM
Can you not measure the power of the sunlight in Watts per cubic meter? I thought that this would change in a predictable way (1/distance ^2) so you could get an exact number for the hemisphere.

enquiringman
2006-Aug-22, 10:53 AM
Max, thanks for the reply. Would it not be easier to measure in Watts per square meter? With regards to the original question posted this would impact on solar energy ie the specific output of panels at a given latitude would differ if sited in the northern or southern hemispheres due to the distance from the sun. For large installations this could be significant and if so would require specifying. I'm wondering also if this may impact on the incidence of skin cancer in Australia (no this is not a joke by the way!)? Thanks to previous answers I now know that the sun is closer to Australia during their summer.

neilzero
2006-Aug-22, 05:30 PM
If I recal correctly the Earth is more than 2 million miles closer to the sun on about Jan 3d each year, so the southern hemisphere should have warmer winters and cooler summers. Since data does not support this, the land/ocean layout apparently cancels the 5? degrees k difference we should measure. Neil

antoniseb
2006-Aug-22, 05:45 PM
If I recal correctly the Earth is more than 2 million miles closer to the sun on about Jan 3d each year, so the southern hemisphere should have warmer winters and cooler summers.

Oops, January is summer in the Southern Hemisphere. So the Southern hemisphere should have more extreme seasons were it not for the moderating influence of the larger fraction of ocean on the Southern surface.

The South Pole has more extreme weather than the North Pole, but that's not really a fair comparison because the South pole is higher elevation and on land, and the North Pole is at sea level and on the ocean.

grant hutchison
2006-Aug-22, 06:04 PM
If I recal correctly the Earth is more than 2 million miles closer to the sun on about Jan 3d each year, so the southern hemisphere should have warmer winters and cooler summers. Since data does not support this, the land/ocean layout apparently cancels the 5? degrees k difference we should measure. NeilThat'd be warmer summers and colder winters, since the southern hemisphere is having its summer during January.
Incoming solar radiation is about 7% greater on Jan 3 than it is on Jul 4, so we'd expect the climate to be more extreme in the southern hemisphere. But, as PhantomWolf has already indicated, the southern hemisphere is about 81% water by surface area, to be contrasted with a figure of 61% in the north. The water provides a thermal buffer for the southern hemisphere, absorbing energy in summer and releasing it in winter, so it turns out that average southern summer (January) temperatures are actually lower than average northern summer (July) temperatures.
But in 11,000 years' time, perihelion will occur during the northern summer, and so there should be noticeable seasonal extremes in the north, compared to the south.

Grant Hutchison

Wolverine
2006-Aug-23, 05:34 AM
Note: enquiringman had originally devoted his thread to two separate topics, a) elliptical orbit & the seasons, and b) whether or not we've landed on the Moon, with a poll included for the latter. The Questions & Answers section is the proper place for the first, while Conspiracy Theories is the appropriate venue for the latter. I've split the topic into two threads; the Apollo discussion is now located here (http://www.bautforum.com/showthread.php?t=45942).