#### scott_sieger

Just an observation that may open some discussion on just how fragile the earths condition is.

When we look at the changes in seasons from winter to summer we know that this is caused by the angle of axis of the planet as it orbits the sun ( am I correct in say ing this).

So in summer for the northen hemisphere the northern hemisphere is closer to the sun by let us say approximately half the earths radius in distance ( closer to the sun than in winter).

When considering the distances to the sun in total this amount of change is so insignificant to the distance overall to the sun.

So

Distance to sun equals 149,500,000ks

Radius as a percentage of distance to sun = 0.0004251505%

IF one assumes hypothetically the planets obit reduces, say, by the radius again.

radius as a percentage of the distance to the sun would =0.0004251685%

so to move the planet 6356 ks closer to the sun as happens with our seasons would see an overall
change of 0.00000018% difference in the relationship with the overall distance.

The observation is this.

For a change of distance to the sun of less than .00000018% we see an increase in temperature of a hypothetical 25 degrees celsius

.00000018% change in radial orbit = 25 degrees C.

Assuming we move the planet only the radius distance again, only 6356ks closser to the sun.

we would see a > 50 degree change in the average global temperature.

I am sure someone out there can do the maths so much better I am absolutely hopeless at it is shown above.

But the object of this post is that the gain in temperature by such a small amount of orbital change shows just how fradgile our existence on earth is.

If the orbit where to change Just 0.00000018% either increase or decrease in distance (R) life would more or less cease to exist on this planet. Hypothetically.

what do you think?

Might be a good maths excersise to do it properly.

I am assuming here for instance

1. that seasonal change requires a 6356 k difference. ( I know this figure is excessive)

2. That the heat from the sun can be linea in nature as one gets closer to the sun ( it may be more exponential)( this to is probably wrong)
3. That i am assuming stuff I have no idea about.

I don't for a moment consider this observation to be new I am sure it has all been observed before.

Related Other Physics Topics News on Phys.org

#### chroot

Staff Emeritus
Gold Member
The largest reason why summer is hotter than winter is because the Sun is up for more hours of the day, and is higher in the sky. When the Sun is directly overhead, its light travels through less of the atmosphere, and thus more of it hits the ground.

Try integrating the flux received on the ground over 24 hour periods in summer and winter if you'd really like to understand the seasons. Hint: it's quite a bit larger an effect than your 42 ten-thousands of a percent due only to the distance between the surface of the Earth and Sun.

Point of fact, the Earth's orbit is not a circle, it's an ellipse. The difference between its aphelion and perhelion is much larger than a half Earth-radius.

- Warren

#### Jonathan

Given that the angle of tilt is about 23.5 degrees and that 6356km is indeed the correct radius, the distance differential at geometric north pole is given by:
2r*sin(23.5)
which is about 5070km. The percent of total distance is then:
(5070*100)/149500000
which is:
.003390567%
Of the total distance. This is as much as I know how to do at this point, but like Chroot, I don't think it is as unstable as this rudimentary calculation seems to say.

#### scott_sieger

Choot,
Thanks for taking the time to reply,

But you say
The largest reason why summer is hotter than winter is because the Sun is up for more hours of the day, and is higher in the sky. When the Sun is directly overhead, its light travels through less of the atmosphere, and thus more of it hits the ground.
And i ask what is the reason the sun is more higher in it's zenith in the first place? Or is this a silly question?
also a .00000018% gain would apply to the entire orbit and not jsut a bit of it. so at the lowest orbit on the track would be also reduced.

And of course there are many many deriviations involved. THis I am not debating. Nor am I postulating a theory, just an observation regards the distance fradgility.

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#### chroot

Staff Emeritus
Gold Member
Originally posted by scott_sieger
And i ask what is the reason the sun is more higher in it's zenith in the first place?
Because of the earth's 28.5 degree rotational axis tilt relative to its orbital plane.

- Warren

#### scott_sieger

so in summer the tilt brings that part or side of the planet closer to the sun....yes?

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#### scott_sieger

sorry ...I mean hemisphere

#### chroot

Staff Emeritus
Gold Member
Originally posted by scott_sieger
so in summer the tilt brings that part or side of the planet closer to the sun....yes?
The tilt means that for half the year, the sun is up longer and higher in the sky than the average of twelve, and opposite for the other twelve. The northern hemisphere experiences summer while the southern hemisphere experiences winter, and vice versa.

- Warren

#### scott_sieger

The overall reason for me to ask these question is That I am Hypothetically attempting to understand what would happen if the ice on the south pole melted due to global warming. What affect this might have on our orbit and tilt thus rotation.

#### chroot

Staff Emeritus
Gold Member
Originally posted by scott_sieger
The overall reason for me to ask these question is That I am Hypothetically attempting to understand what would happen if the ice on the south pole melted due to global warming. What affect this might have on our orbit and tilt thus rotation.

If the south pole were somehow to melt, it would have no effect at all on either the rotation or the orbit of the planet.

Here's a link for you: http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Seasons.shtml

- Warren

#### Jonathan

Chroot is right, the sun does get higher in the sky during summer than in winter. When it is higher it goes through less atmosphere, which is why it is easier to look at the sun at dawn or dusk than noon. We know that the brightness of the sun is proportional to the inverse square of the distance, so assuming the earth's orbit is circular and has a radius of 149,500,000km and assuming that the earth and sun are points, then the average brightness is proportional to 1/(149,500,000^2) and the increased brightness in summer is proportional to 1/((149,500,000-5,070)^2) or 1/(149,494,930^2). The difference of those then is 1/(149,500,000^2)-1/(149,494,930^2), which is 3.034844684*10^(-21). This proves that the effect is really small, and so is more likely due to the height of of the sun.
EDIT: One should note that because the earth's orbit is an ellipse, the earth's center probably changes distance from the sun far more than 5,070km, so there is no way the distance differential due to the tilt has any noticable effect on the climate at all.

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#### Jonathan

Man! You alway get a post in edgewise! Okay, because ice and water have different densities and water spreads over a surface while ice doesn't, the melting poles could have an affect on the earth's rotation through redistribution of mass and therefore an attempted change in angular momentum, which will increase or decrease the planet's rotation, but I don't know how much. I don't think it'll have too big an affect on the orbit though.

#### scott_sieger

Guys,

I am not trying to despute that the sun is higher in summer.

I am not debating why we experience heating of the atmosphere.

All i am attempting to discuss is if the planet were to move just

.00339% closer to the sun we would all cook....

the .oo339% figure as Jonathan has calculated is the radial shift towards the sun by the hemisphere.

OK forget the way the maths is approached and focuss on the question of a change in orbit of only let's just pull a figure.

...say....0.005%

#### scott_sieger

Line of quest

I want to find out the efects of global warming.
The biggest impact i feel would be ice melt down on the poles

To do this I need to determine just how fradgile our planets life support systems are.

If the planets orbit is extremely important to this fact then obviously melting of the ice would be also important.

Hence the question about any deviation in orbit relative to temperature changes caused by global warming.

So I guess this leads to the question:

Am I right in my hypothesis that if the planets rotation, wobble, and orbit are affected even in a very small way we have a significant problem on our hands.

#### chroot

Staff Emeritus
Gold Member
Originally posted by scott_sieger
.00339% closer to the sun we would all cook....
Uh, no.

- Warren

#### scott_sieger

Choot,

How close do we need to go to the sun before we cook?

#### chroot

Staff Emeritus
Gold Member
Originally posted by scott_sieger
To do this I need to determine just how fradgile our planets life support systems are.
Life on this planet has survived some six mass extinction events, including a massive asteroid or comet impact. It has withstood repeated and prolonged ice ages. It has withstood the accumulation of atmospheric oxygen, a substance which was chemically toxic to many primitive organisms. Life on this planet is by and large EXTREMELY robust.

Melting of the polar ice caps would cause ocean waterlines to rise, making some places uninhabitable. Would it destroy all life on earth? Hardly.

We, as a modern species, have experienced very little of the wide variety of climates to which the earth has historically subjected our ancestors.

- Warren

#### syano

Hi Scott,

If the bottom line of what you are asking is “how fragile is the Earth’s distance from the Sun?” For a simple answer, I would say we would have to determine what “fragile” means and the discussion would likely be kicked to the Philosophy or Theory Development forums.

However, I do believe if the Earth’s orbit fell closer to the sun there would be measurable effects. And at a critical point the effects would be catastrophic (as far as the human race goes.)

But I disagree with how you led up to there being a possibility that the Earth shortens its orbital distance with the Sun…

In your original post you mention the reason for Earth’s seasons are due to its rotation on its axis…Then you mentioned how the northern hemisphere will be closer to the Sun in the summer than it was in the winter…And then you lead on with some formulas and end by asking how fragile Earth’s orbital distance is to the Sun.

The fallacy I see in that statement is how you link Earth’s rotation with how close Earth’s orbit is to the Sun.

Just because the northern hemisphere is closer to the Sun it does not mean the Earth is closer to the Sun. You cant really “tilt” a ball…Earth’s axis is an imaginary line used to describe how Earth rotates.

Back to the original question… “Is the Earth’s distance from the Sun ‘fragile’”… I would say it is.

S

#### russ_watters

Mentor
Originally posted by syano
But I disagree with how you led up to there being a possibility that the Earth shortens its orbital distance with the Sun…

In your original post you mention the reason for Earth’s seasons are due to its rotation on its axis…Then you mentioned how the northern hemisphere will be closer to the Sun in the summer than it was in the winter…And then you lead on with some formulas and end by asking how fragile Earth’s orbital distance is to the Sun.
Just a clarification, but the Earth's orbit is an ellipse, not a perfect circle, so the orbital distance most certainly does vary. Perihelion (closest point of approach) is around January 2nd and the orbital distance varies by about 2%.

#### scott_sieger

Russ,

Actually you have a very valid point. I should have explain the use of the tilt as a way of dtermining temperature gain the closer we get to the sun.

The reasoning is as follows

The seasons come to be because of the tilt of the axis as the planet rotates. In summer the tilt is such that the hemisphere in question is closer to the sun. the planet being a sphere means that there is no appreciable change in obit.

However if one confines the distance change with in the sphere then one can calculate a distance within the sphere that could be extended to the radius of the orbit hypothetically.

I assumed that this would be known and have made this mistake before.

The planet of course doenot change it's orbit or it's tilt for that matter (true?) the relationship of the tilt to the sun changes however as the planet orbits.
so therefore within the sphere of the earth there is a distance variation that I am using to equate or show how fradgile the planet is with regards to any hyperthetical change in orbit.

Russ.

To have said this all properly in your language what should I have written?

Your help on this would be appreciated. I am obviously not doing a good job of it.

#### hypnagogue

Staff Emeritus
Gold Member
scott, maybe I'm misunderstanding you, but it still seems as if you are thinking of the seasonal climate changes of the Earth as a function of orbital distance from the sun. But in fact seasonal climate changes arise as a function of the angle at which the sun's rays strike the Earth. During summer the rays are more direct, and during winter they are more glancing. Orbital distance really has nothing to do with this effect of seasonal climate changes. In fact, if I'm not mistaken, during the winter months of North America the Earth is actually closer to the sun than during the summer months.

#### Rog

Originally posted by scott_sieger
Guys,

I am not trying to despute that the sun is higher in summer.

I am not debating why we experience heating of the atmosphere.

All i am attempting to discuss is if the planet were to move just

.00339% closer to the sun we would all cook....

the .oo339% figure as Jonathan has calculated is the radial shift towards the sun by the hemisphere.

OK forget the way the maths is approached and focuss on the question of a change in orbit of only let's just pull a figure.

...say....0.005%
It should be noted that the distance we are from the Sun only has a marginal effect on the variant temperature on earth if this wasnt true then our elliptical orbit would see us drift from boiliing to freezing conditions on a planet wide scale. It predominently has to do with the atmosphere and its absorbtion and reflective abilities in relation to the amount of energy we receive from the sun. This is why the greenhouse effect will have much deeper implications in the short term then any slight (and I mean slight) deviation in the earths orbit.

#### Artman

What I think everyone is trying to say is that it is our angle in relation to the sun, not distance that makes the most difference in our seasonal variations. I believe that we are actually closer to the sun in the Northern hemisphere in the winter than we are in the summer,
http://www.exploratorium.edu/exhibit_services/exhibits/s/summer_sun.html [Broken]
so this seems to bear out what has been said.

I believe that conditions for CIVILIZATION, as we know it, are fairly fragile. However, if the axis of the earth should change and the south pole melts, a new south pole will form elsewhere. Life in New York City or Mexico City or Tokyo, etc. may change. Cities come and go as food supplies, services etc come and go. But it will begin again elsewhere. And life in general, as chroot said, is VERY hardy.

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#### scott_sieger

Thanks every one,

My appologies to Choot

Hey

No bigger fool than an old fool.

#### chroot

Staff Emeritus
Gold Member
Originally posted by scott_sieger
My appologies to Choot
Why apologies to me? Although I can be a pain in the ass sometimes, I really am only here because I like helping people understand things (and coming to understand new things, too).

You asked a simple question, and hopefully now you understand the concepts better. That's why we're all here.

- Warren

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