Feasible scientific explanations which are, nonetheless, wrong

[spudtater]

"The angle of the earth's axis changes from summer to winter. In the summer, the northern hemisphere is nearer the sun, while the southern hemisphere is further away. This difference in distance is what causes the temperature difference."

And if you did think that's how it works, consider this:

The moon revolves around the earth, it is said. However, the moon is a rather large satelite; it has one-eightieth of the mass of the earth. Now what actually happens is that both the moon and the earth revolve around the centre of mass of the earth-moon system.

Calculating the centre of mass can be done with GCSE-level physics; imagine you have a huge ruler, with the earth on one side and the moon on the other. Where would you have to put your finger in order to balance the system?¹ Well, you can work it out with moments; it is one-eightieth of the way from the centre of the earth to the centre of the moon, which turns out to be a point near the surface of the earth.

  _____
 /     \
(   .   )
 \_____/                                       (.)   
 =================================================
       /\

Fig. 1: The earth and the moon play on a see-saw. (Not entirely to scale)

So, let's contrast two situations. In situation A we have a full solar eclipse; the moon is directly in between the earth and the sun. In situation B we have a full lunar eclipse; the earth is directly in between the moon and the sun. Rotate the system in your head from situation A to situation B, bearing in mind where the centre of mass is. You should realise that in situation A, the earth is almost one earth-diameter further away from the sun than it is in situation B.

Situation A:    ( E )  (M)                    (             Sun             )

Situation B:  (M)  ( E )                      (             Sun             )

Fig. 2: Again, some errors in scale. Just use your imagination.

Now, days on which a solar eclipse occur are not especially colder than days on which a lunar eclipse occurs. We have to conclude that the distance from the earth to the sun just doesn't make that much difference to the temperature.

What does cause the temperature difference between summer and winter, then? Well, as I'm feeling both tired and evil, I shall not explain it right now. Rather, I'll leave you to ponder it. Mwahahahaha!!!

[1] Questions you might also want to ask, if you were in a sarcastic mood, are "where are you standing, then, in order to weild this mighty ruler?" and "why are the earth and the moon being 'pulled downwards' anyway? Which direction is down?" to which I will reply "stop being a smart-aleck", and probably give you extra homework.

Comments

[digitalraven]

Another question: Why is the moment of rotation in-line with the plane of the elliptic for this solar system?

Because I'm a smart arse and had to ask.

[galaxy-girl00.livejournal.com]

better watch he might give you lines!!!

[spudtater.livejournal.com]

I'd give him lines on his backside, if it weren't for those pesky anti-corporal-punishment laws!

[spudtater.livejournal.com]

Errr... not sure what you mean by a moment being in-line with something.

If you're asking why the moon is on the plane of the elliptic, well I know it isn't always there. But whenever we have a full solar or lunar eclipse, it will be. This is why I brought up these situations; because it simpilifies the situation to two dimensions rather than three. (Also, they just happen to be the points between which is the most difference in earth-sun distance.¹)

[1] I cannot prove this, but it is, in the same sense that Mt. Everest is, or that Alma Cogan isn't. Goodnight.   8^)

[galaxy-girl00.livejournal.com]

before reading that last line I was gonna say you sounded like a teacher =0)

[sigmonster.livejournal.com]

"Now, days on which a solar eclipse occur are not especially colder than days on which a lunar eclipse occurs. We have to conclude that the distance from the earth to the sun just doesn't make that much difference to the temperature."

Or we conclude that the oscillation of the earth-moon system about its center of mass every lunar month does give an oscillation in thermal *input*, but the thermal buffer is so big we don't notice; we only notice the larger annual oscillation. This gains plausibility as we recall the great big lag from longest day to (mean average) hottest day...

(Can I try? It's all about watts per square metre. Points normal to the solar ecliptic get lots, points further away get fewer, and which hemisphere benefits varies over the year. The tropics are exactly those points which are normal to the ecliptic at some time during the year. The arctic and antarctic are those areas in which watts per square metre per day hits zero at some time during the year.)

[spudtater.livejournal.com]

> [...] does give an oscillation in thermal *input*, but the thermal buffer is so big we don't notice

Foo. You're right, of course.

> [...] the great big lag from longest day to (mean average) hottest day...

Any idea how long this time difference is?
I always expected the longest day to also be the hottest, but now I come to think of it, it never is.

> [...] watts per square metre.

Bingo! Give that man a cookie.
Also contributing to the effect are:
1) More sunlight is absorbed by the atmosphere when it hits at a more acute angle.
2) The days are shorter and the nights are longer.

Here are some more pages, for people who don't understand phrases like "normal to the solar ecliptic":   8^)
http://www.scienceu.com/observatory/articles/seasons/seasons.html
http://www.loc.gov/rr/scitech/mysteries/seasons.html
http://www.msnbc.com/news/251727.asp

[sigmonster.livejournal.com]

>> [...] does give an oscillation in thermal *input*, but the thermal buffer is so big we don't notice

> Foo. You're right, of course.

For certain values of right - I think the change in thermal input is proportional to the (square of) monthly change in angle subtended by the sun, and that change is really rather small. It's also swamped by the eccentricity of the earth's orbit round the sun. (We're closest to the sun in January.)

OTOH, some full moons are 30% brighter than others - its luminosity is a square-of-distance twice over, earth-moon to sun and moon to earth, and the eccentricities in both systems are of order 0.1. The working is left as an exercise.

> I always expected the longest day to also be the hottest, but now I come to think of it, it never is.

I think the lag is about six weeks. The Met Office doesn't have it readily accesible in the form I want, but average June max., whole of the uk, 1971-2000, was 20.8 degress Celsius; August was 22.9.

Southern hemispere seasons are more moderate, because the buffer is bigger - more water and less land.

[f33b.livejournal.com]

It's all explained here, in nice simple terms.

[spudtater.livejournal.com]

Alas, I am brainwashed, indoctrinated, educated stupid and cannot comprehend Nature's Harmonic Simultaneous 4-Day Perpetual Time Cube Creation.

[neuralbuddha.livejournal.com]

"where are you standing, then, in order to weild this mighty ruler?"

Next to Archimedes and his lever, presumably.