Earths Curvature

[bushtuckerman]

It doesn't surprise me that there is great variability, when you imagine how little light has to bend in order to increase the distance you can see. 4.8km must be the purely geometrical distance at that altitude, given a perfect sphere.

povarian why tri-lobed?! sounds ominous.

I did watch a program once where it was suggested there was never any real belief by any majority of people that the earth was flat, and that this is a misnomer caused (in part) by looking at old religious maps drawn flat for convenience, and believing they must have gotten it wrong. In the same program it was also pointed out that a scientist (perhaps in the C18th??) decided it must be flat, since when he tried to measure the curvature of the earth using canals, he found he could see further than he ought to! of course he didn't know enough about optics to realise where he was going wrong.

 

[Pappa]

I did watch a program once where it was suggested there was never any real belief by any majority of people that the earth was flat, and that this is a misnomer caused (in part) by looking at old religious maps drawn flat for convenience, and believing they must have gotten it wrong. In the same program it was also pointed out that a scientist (perhaps in the C18th??) decided it must be flat, since when he tried to measure the curvature of the earth using canals, he found he could see further than he ought to! of course he didn't know enough about optics to realise where he was going wrong.

Stephen Jay Gould wrote an essay about it once too. He said that nobody who was anybody actually ever believed the world was flat, and only two or three minor scholars thought it was. Most educated people took it as read that the world was round and many uneducated plebes such as sailors just knew it was round from practical experience. He believed the arguements had been invented later. Also, he states that, contrary to popular myth, Columbus was never invloved in an arguement over the shape of the earth.

 

[Emma]

Refraction of light by the atmosphere has been known since the 17th century when Huygen, an amazing Dutch scientist, described it and drew excellent diagrams to explain it.
I also remember hearing that some apparent witch or sourceror or something similar was able to prove her ability as witch/sourceror by calling a city to float on the sea on the horizon. What she was actually doing was waiting for the right atmospheric conditions and going "look, see there you are" at a city on a bit of land that was normally below the horizon.
There are also 'ghostly' lights that wonder around Australia, I forget what they're called, but they're caused by atmospheric refraction of light, originally from campfires, but now recently including cars and houses. Apparently even if you know what they are, the behaviour of them is still highly disturbing, because they tend to follow you, rush at you, go high above you, dive down on top of you, hover in front of you, etc etc, and it's just caused by the air wobbling about a bit, like air does.

Anyway, some interesting stuff about the Solar system, off the top of my head:
On Neptune, and quite possibly Uranus, the hailstones are diamonds.
Several asteroids have orbiting moons, other asteroids. Example, Dactyl is a tiny asteroid orbiting Ida.
Titan has hydrocarbon (oil is made of hydrocarbons) seas and quite possibly rain as well.
Mars has the biggest mountain and volcano in the Solar System, Mount Olympus.
If you put a coke can on the surface of Venus it would be instantly crushed because of the pressure.
Some of the bigger asteroids have enough gravity for a person to be able to stand on them - but a slight twitch of your toe and you'd rocket off it and never get back.
Light has to travel so far that we are seeing stars that have been dead for millions of years - but we don't know which stars are dead.
Some of those stars that we don't know are dead might be black holes.
You can fit three Earths into Jupiter's Great Red Spot storm system, and at least one into Neptune's Great Dark Spot storm system.
People used to think that the Sun was a flaming ball of coal.
People used to think that Venus was just like Earth, with water and land and vegetation and everything.

And for any of them who think there is a physical backing behind astrology - the gravitational effect of a midwife's arm on a baby is several times greater than the gravitational effect of Jupiter on the baby.

 

[jdlenton]

the gravitational effect of a midwife's arm on a baby is several times greater than the gravitational effect of Jupiter on the baby.

Fantastic

James

 

[Povarian]

povarian why tri-lobed?! sounds ominous.

Not really ominous.

A section of a truely oblate spheroid is symmetrical above and below the radius of greatest eccentricity. Gravitational measurements (my knowledge is from the early 1980s, so may be out of date) showed that the Earth has more mass in lattitudes south of the equator, and this isn't evenly distributed, but occurs in three "bulges", hence tri-lobed. The mass distribution changes slowly with tectonic plate movement, with occasional sudden small changes with large earthquakes such are the one that caused the Asian Tsunami.

All in all, the variation from truely spherical are unimportant unless for some satellite applications.

I tried to find a web site that details this, but failed. The tri-lobed bit stuck in my mind after an interesting tutorial session with one of my professors while I was a student.

 

[Templar]

Hi Lithril,
found this web site which might help..

http://mintaka.sdsu.edu/GF/explain/atmos_refr/horizon.html

basicly it tells you how to work out the distance mathamaticly taking in factors like height etc.

I hope this helps

Karl

 

[bushtuckerman]

Not really ominous...The mass distribution changes slowly with tectonic plate movement, with occasional sudden small changes with large earthquakes such are the one that caused the Asian Tsunami...

thanks for the explanation