Off Topic

Beagle · Post by **Beagle** » Mon Mar 19, 2007 1:30 pm

Makes sense but this is not my cup o' tea. Gotta leave for a short.

Post by **Minimalist** » Mon Mar 19, 2007 1:32 pm

I heard someone suggest on the news the other day that from time to time the earth's orbit can become more or less elliptical.

Forum Monk · Post by **Forum Monk** » Mon Mar 19, 2007 1:39 pm

Knowing a little about astronomy, I can tell you for cetain it has nothing to do with tilt of the earth or the eccentricy of the earth's orbit. If what they are seeing is 'real', atmospheric refraction or some other atmospheric phenomenon is the most likely cause. It is definately not astronomical.

Digit · Post by **Digit** » Mon Mar 19, 2007 1:41 pm

That's correct Min, the actual track through space is actually like a homeward bound drunk as the track is influenced by the other planets.
In addition, taking the orbit to be parabolic with the sun at one foci, the parabola itself precesses. In the case of Mercury the precession is rapid enough to show in one life time.

Post by **Minimalist** » Mon Mar 19, 2007 1:44 pm

I like your analogy, though.

Beagle · Post by **Beagle** » Mon Mar 19, 2007 1:48 pm

Forum Monk wrote:Knowing a little about astronomy, I can tell you for cetain it has nothing to do with tilt of the earth or the eccentricy of the earth's orbit. If what they are seeing is 'real', atmospheric refraction or some other atmospheric phenomenon is the most likely cause. It is definately not astronomical.

I'm glad you know some astronomy Monk. We run into the need for that alot. Especially archeoastronomy.

Digit · Post by **Digit** » Mon Mar 19, 2007 1:50 pm

The only way a change in refraction would shorten the dark period and cause the rising point to change is by either increasing the apparent diameter of the sun or by bending the light rays more Monk. If it were dust or gas for example there should also be an absorption change and with that a change in colour.

Forum Monk · Post by **Forum Monk** » Mon Mar 19, 2007 2:06 pm

About the earths orbit, the drunken sailor or whatever, analogy is true but the movements and wobbles are very tiny and only make a difference at the sub-arcsecond level with respect to observational astronomy. The movement is actually an ellipse with the sun at one focus point. Comets move in parabolic orbits. I don't know much about this orbital precession you refer to. There is another precession, which results in the shifting of the vernal equinox.

Atmospheric refraction is not affected much by dust, though dust will scatter the light. It is affected by the amount of atmosphere the light must pass through, always more near the horizon than at zenith; the relative humidity; and the temperature.

They'll probably link it to global warming.

Digit · Post by **Digit** » Mon Mar 19, 2007 4:19 pm

Sorry Monk, confusion this end, yes of course it's an elipse.
The precession I think is best explained this way.
Assume a line passing through both foci for Mercury and pointing directly at a fixed star, if you then plotted its swing on each side of the Sun the distances would be equal.
On the next orbit the shape is still an elipse but the line is now no longer pointing at the star but has moved to one side, and on the next orbit the line is still further displaced so the orbit is itself rotating relative to the Sun, but the foci remain the same relative to each other.
All planets do it but most take a long time to do it.
How much dust or aerosols is needed to modify refraction and difraction I know not, but this much I can say. I live on the coast and the air is much cleaner, in relative terms, than in industrial areas and the effect of that difference are very noticable I can assure you.

Forum Monk · Post by **Forum Monk** » Mon Mar 19, 2007 5:13 pm

Well done Digit.
You're speaking of what is called perihelion precession which is caused by the fact the center of mass for the solar system (the barycenter) is offset from the sun, and so the sun also rotates about it. The effect is quite small, roughly 1/2 an arcsecond or less per year and is slightly different for each planet.

Digit · Post by **Digit** » Mon Mar 19, 2007 5:21 pm

If it is increased refraction Monk, as suggested in the article, I wonder why it hasn't been noticed in the Antarctic, after all, there's a permanent research station there.

Beagle · Post by **Beagle** » Tue Mar 20, 2007 5:14 pm

http://www.spiegel.de/international/0,1 ... 80,00.html

Everyone loves Knut. The three-month-old polar bear born in one of Berlin's zoos has become a star in the German capital and has won hearts the world over. Indeed, the exact date of his first public appearance -- likely to be made later this week -- is the subject of almost as much anticipation as the details of Britney Spears Alcoholics Anonymous love affair. It's impossible not to love the little guy, right?

Well, not quite. Animal rights activists, as SPIEGEL reported Monday, aren't so enthralled with the polar bear baby. They are concerned that Knut, who is being raised by human hand after his mother rejected him, is in danger of losing touch with the bear necessities. Some would like to see him dead.

This is incredible! Some animal rights activists want to have a polar bear cub destroyed. Because it was bottle fed!
From the John Hawks website.

Post by **Minimalist** » Tue Mar 20, 2007 6:33 pm

Because it was bottle fed!

Maybe they are afraid it will grow up "spoiled?"

Digit · Post by **Digit** » Wed Mar 21, 2007 4:10 am

This is typical Beag of the ARAs mentality.
Years ago some one in the UK who was fighting against slavery was accused of disliking blacks, he replied, quite rightly, that 'you don't have like Negroes to see that slavery is wrong'.
The same seems to apply to the ARAs, they get Fox hunting stopped without stopping Foxes from being shot, snared or poisened, and try to stop Deer from being culled so that now we have got to cull 500000 of them, and stop Badgers from being culled so now the cull will have to be even larger.
They argument? It's not natural, some have even suggested that starvation should be allowed to run its course as it is 'natures way', and many of them couldn't tell a Stoat from a Weasel if it didn't have a label on it.
They will soon be telling me that they've asked that Bear cub!

Forum Monk · Post by **Forum Monk** » Wed Mar 21, 2007 4:54 am

The answer is simple.
You need to reintroduce packs of ravenous wolves. The only natural pedator to many of these mammals. Then let nature run its course. Of course you will have to get rid of the domestic sheep and cows, since they upset the balance by giving the wolves something easy to eat.

There - problem solved.