# the shape of the earth? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [February 25, 2010, 6:25am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371 "2010-02-25T06:25:40Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [February 26, 2010, 9:07pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/41 "2010-02-26T21:07:07Z")
**ivan astikov** said: > [@](#): > > Still, say we put a marker on the ocean bed either side of a subduction zone, measured the distance and then 100 years later, went back and measured them again; would we expect them to be the same distance apart exactly? How long a time span would we need to know for definite whether the distance is changing, or not? The tectonic plates are moving at a rate of millimeters per year. These are measured using GPS satellites or lasers and satellites. [http://oceanlink.island.net/SOLE/tectonics/WCDA.html](http://oceanlink.island.net/SOLE/tectonics/WCDA.html) [http://www.eece.maine.edu/research/gk12/Plate\_Tectonics.htm](http://www.eece.maine.edu/research/gk12/Plate_Tectonics.htm) ---
**Author:** ![dropzone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dropzone/32/7515_2.png) [@dropzone](https://boards.straightdope.com/u/dropzone)\ **Post date:** [February 27, 2010, 5:39am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/42 "2010-02-27T05:39:02Z")
> [@miriam\_hassan](#): > > The shape of the earth is spherical-like a ball..is this true or is it only a scientific guess? > > The reason im saying this is because, the earth has almost always been viewed from a lense- a convex lense mostly. Is it possible that the shape of the earth only appears round because as the light rays pass through the lense they bend at a certain angle and the image that forms is a result of this ‘bending’. Can it be possible that if the Earth is viewed from a “special” lense, in which light rays can be bent differently, will this show a different shape of the earth from the space? Madame, kindly ignore all the above answers, as you have stepped into a nest of vipers. 😉 What you describe is possible, but scientists made the adjustments long before they could observe it; and they figured out, because of how rotation can drag forward the midsections of planets and people, the major diameter of an ellipsoid Earth was slightly more than the minor diameter of the similarly ellipsoid Earth. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [March 2, 2010, 12:17am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/43 "2010-03-02T00:17:15Z")
> [@Todderbob](#): > > It wasn’t “measured,” but IIRC (and I’m not sure I do) there was an ancient Egyptian, pre-dating the Greek empire, who had a theory of a heliocentric universe and had the circumference of the Earth down quite close, but I can’t find more information about that. > On the other hand, [Aristarchus of Samos](http://en.wikipedia.org/wiki/Aristarchus_of_Samos#Precession) measured the length of a year very accurately (circa 230 BC). > > What I did find, however, was the record of [Eratosthenes](http://en.wikipedia.org/wiki/Eratosthenes), whose story matches the one that I recalled from earlier (which I think I must’ve conflated with one of the Muslim world, my bad), which had an error rate of only about 5 or 10 percent. Is that accurate enough to qualify? Actually, [Eratosthenes’](http://en.wikipedia.org/wiki/Eratosthenes#Eratosthenes.27_measurement_of_the_earth.27s_circumference) measurement may well have differed from our current best estimates by less than 1%. [Aristarchus](http://en.wikipedia.org/wiki/Aristarchus_of_Samos) is probably also the “Egyptian” you are thinking of who proposed a heliocentric universe. Almost certainly, however, he did not take this view for what we would consider good scientific reasons. Neither the instruments nor the mathematical tools that provided the evidence for heliocentrism in the 17th century were available in his time. Both Eratosthenes and Aristarchus were associated with the Library of Alexandria (Eratosthenes was chief librarian), but neither was born in Egypt. They belonged to the Greek speaking, cosmopolitan Hellenistic culture established there in the wake of the conquests of Alexander the Great, not to the much older Egypt of the pharaohs and pyramids. ---
**Author:** ![luce\_gilmore](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@luce\_gilmore](https://boards.straightdope.com/u/luce_gilmore)\ **Post date:** [March 2, 2010, 12:15pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/44 "2010-03-02T12:15:10Z")
The reason the ancient Greeks concluded that the Earth was round was because, when the Earth’s shadow passed over the Moon during a lunar eclipse, the shadow’s edge was always circular, no matter what time of day the eclipse occurred. (Lunar eclipses do not have to happen at night.) The only shape whose shadow is circular from all directions is a sphere. QED. I do not know how the Greeks knew that lunar eclipses were caused by the Earth’s shadow, but it is the kind of plausible conclusion that naturally arises when you have been doing naked-eye astronomy for centuries, as both the Egyptians and the Mesopotamians had been doing. ---
**Author:** ![Powers](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Powers](https://boards.straightdope.com/u/Powers)\ **Post date:** [March 2, 2010, 3:04pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/45 "2010-03-02T15:04:11Z")
> [@luce\_gilmore](#): > > (Lunar eclipses do not have to happen at night.) A lunar eclipse occurs when the moon passes into the Earth’s shadow. Nighttime is defined as the period in which the particular portion of the Earth you’re on is in shadow. I’m not clear on how you could see a shadowed moon from the daytime side of the Earth. Powers &8^] ---
**Author:** ![luce\_gilmore](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@luce\_gilmore](https://boards.straightdope.com/u/luce_gilmore)\ **Post date:** [March 2, 2010, 5:09pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/46 "2010-03-02T17:09:53Z")
> [@Powers](#): > > A lunar eclipse occurs when the moon passes into the Earth’s shadow. Nighttime is defined as the period in which the particular portion of the Earth you’re on is in shadow. I’m not clear on how you could see a shadowed moon from the daytime side of the Earth. > Powers &8^] Atmospheric refraction means that the moon is actually about one degree BELOW the horizon when it appears ON the horizon. Likewise the sun. The particular event I recall happened shortly after the death of Princess Diana, when the moon actually rose (as seen from the UK) in eclipse, at sunset. Pure geometry would require the full moon to be directly opposite the sun, but in practice the two can be visible at the same time (about 178 degrees apart), owing to refraction. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [March 2, 2010, 5:32pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/47 "2010-03-02T17:32:43Z")
The important point is that the lunar eclipse can happen with the Moon in very different locations relative to the Earth. As a counter-example, you couldn’t say the Moon is spherical just because it always looks round to us, since we always see it from pretty much the same direction (maybe it’s conical in the back, shaped like a big ice cream cone). ---
**Author:** ![miriam\_hassan](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@miriam\_hassan](https://boards.straightdope.com/u/miriam_hassan)\ **Post date:** [March 5, 2010, 7:00am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/48 "2010-03-05T07:00:46Z")
no no, thays not the way i mean it…you see, the box is an object, made of solid surface, but the earth- apart from the matter which is the earth’s surface, is actually comprised of gases. and gases have no shape-right…so because the earth is spinning at a great speed , it appears as if its round…but lets say if it were to stop, would it appear a round object? you see, if u look at a spinning box, it appears nearly round…how can u tell until it stops that it wasnt round?(considering u havent seen the static box b4) ---
**Author:** ![miriam\_hassan](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@miriam\_hassan](https://boards.straightdope.com/u/miriam_hassan)\ **Post date:** [March 5, 2010, 7:31am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/49 "2010-03-05T07:31:51Z")
> [@Irishman](#): > > Take a camera. It uses a convex lens. Take a picture of a box (you know, a thing with lots of right angled corners). Does the picture look like a sphere? no no, thays not the way i mean it..you see, the box is an object, made of solid surface, but the earth- apart from the matter which is the earth’s surface, is actually comprised of gases. and gases have no shape-right..so because the earth is spinning at a great speed , it appears as if its round..but lets say if it were to stop, would it appear a round object? you see, if u look at a spinning box, it appears nearly round..how can u tell until it stops that it wasnt round?(considering u havent seen the static box b4) ---
**Author:** ![Todderbob](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@Todderbob](https://boards.straightdope.com/u/Todderbob)\ **Post date:** [March 5, 2010, 8:48am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/50 "2010-03-05T08:48:32Z")
> [@miriam\_hassan](#): > > no no, thays not the way i mean it..you see, the box is an object, made of solid surface, but the earth- apart from the matter which is the earth’s surface, is actually comprised of gases. and gases have no shape-right..so because the earth is spinning at a great speed , it appears as if its round..but lets say if it were to stop, would it appear a round object? > you see, if u look at a spinning box, it appears nearly round..how can u tell until it stops that it wasnt round?(considering u havent seen the static box b4) To the naked eye, a box spinning sufficiently fast might appear to lack corners. The Earth does not spin sufficiently fast to appear that way from space to the naked eye, much less satellites which take pictures at the fractions of a second level. The Earth spins at a speed equal to, if you took an orange and rotated it so one side faced you every 24 hours. While the actual speed it spins on the surface is faster, that’s only because it’s much larger… it rotational speed is really quite slow. As for gasses having no shape – that’s not entirely true. Gasses behave in a predictable manner, you just can’t see them. They behave in the same manner that the water or any other liquid does. They sink to the bottom, until they hit something denser than they are. ---
**Author:** ![Powers](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Powers](https://boards.straightdope.com/u/Powers)\ **Post date:** [March 5, 2010, 3:20pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/51 "2010-03-05T15:20:24Z")
> [@miriam\_hassan](#): > > no no, thays not the way i mean it..you see, the box is an object, made of solid surface, but the earth- apart from the matter which is the earth’s surface, is actually comprised of gases. and gases have no shape-right..so because the earth is spinning at a great speed , it appears as if its round..but lets say if it were to stop, would it appear a round object? > you see, if u look at a spinning box, it appears nearly round..how can u tell until it stops that it wasnt round?(considering u havent seen the static box b4) I think you’re having us on. Why did you bring up lenses and light refraction in your initial post if you really were talking about this, which has nothing to do with lenses at all? Powers &8^] ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [March 5, 2010, 4:32pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/52 "2010-03-05T16:32:18Z")
**miriam hassan** said: > [@](#): > > you see, if u look at a spinning box, it appears nearly round..how can u tell until it stops that it wasnt round?(considering u havent seen the static box b4) If you move around the box at the same speed the box is spinning, the box will look like it is sitting still (and the surroundings will look all funky). We have seen the Earth from objects moving around the Earth at the same speed the Earth is moving: cameras on Geosynchronous satellites. Ergo, we have effectively seen the Earth sitting still and not spinning. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [March 5, 2010, 4:39pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/53 "2010-03-05T16:39:55Z")
> [@miriam\_hassan](#): > > no no, thays not the way i mean it..you see, the box is an object, made of solid surface, but the earth- apart from the matter which is the earth’s surface, is actually comprised of gases. and gases have no shape-right..so because the earth is spinning at a great speed , it appears as if its round..but lets say if it were to stop, would it appear a round object? > you see, if u look at a spinning box, it appears nearly round..how can u tell until it stops that it wasnt round?(considering u havent seen the static box b4) Wait, the earth is comprised of gases except for the surface? You can’t possibly mean that. First, if the earth were a balloon filled with gases except for the skin covering it, it would look exactly like a solid sphere looks. And we know that the earth isn’t filled with gases. It’s filled with solids, except the center which is a liquid, but a liquid at such pressures that it holds up the solid packed masses above it perfectly well. But even if you’re just expressing yourself in some weird way, your question comes down to: do the transparent gases that form a thin coating around the earth affect the way it looks from space? That answer again has to be no. There are huge numbers of reasons for this, but the simplest is obvious. Gravity. Gravity will pull any mass as large as the earth into a sphere over time. The earth is very close, within a percent or so of a perfect sphere. There is a bulge at the equator because of the spinning you mention, and some minor bumps and depths along the surface due to slow-term plate tectonics, but these hardly matter. There cannot possibly be corners or sharp edges. Gravity would reduce them to rubble. We can see this with every other planet and planetoid that we study. Even the larger asteroids are spherical. The presence or absence of an atmosphere doesn’t matter. We can’t see into the depths of Jupiter or Saturn but since they’re way more massive than the earth is, we know to a certainly that their interiors are spherical. The earth isn’t spinning very fast at all, as astronauts who look down at it can see for themselves. There are astronomical bodies which do spin incredibly fast, like pulsars. But any competent scientist would be able to tell from the pattern of light and other electromagnetic radiation given off whether it was coming from a sphere or some other object. There would be no possible way to hide this. You can’t seriously be trying to ask whether the earth is box-shaped, can you? Could you try sharing what your question really is about? ---
**Author:** ![miriam\_hassan](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@miriam\_hassan](https://boards.straightdope.com/u/miriam_hassan)\ **Post date:** [March 8, 2010, 8:05am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/54 "2010-03-08T08:05:06Z")
> [@miriam\_hassan](#): > > The shape of the earth is spherical-like a ball..is this true or is it only a scientific guess? > > The reason im saying this is because, the earth has almost always been viewed from a lense- a convex lense mostly. Is it possible that the shape of the earth only appears round because as the light rays pass through the lense they bend at a certain angle and the image that forms is a result of this ‘bending’. Can it be possible that if the Earth is viewed from a “special” lense, in which light rays can be bent differently, will this show a different shape of the earth from the space? this was my question..viewing from a lense is only one reasoning, the rest, i want to find out. the box comparison was in answer to a question, not my analogy.. ---
**Author:** ![miriam\_hassan](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@miriam\_hassan](https://boards.straightdope.com/u/miriam_hassan)\ **Post date:** [March 8, 2010, 8:16am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/55 "2010-03-08T08:16:56Z")
> [@Powers](#): > > I think you’re having us on. Why did you bring up lenses and light refraction in your initial post if you really were talking about this, which has nothing to do with lenses at all? > Powers &8^] no, im not bringing u on..the question is about the shape of the earth, why it appears round, can it be a scientific guess, and how strong are the supporting theories, why do you believe what you see?( i mean if u wear concave lenses, ur brain will register things upside down, then what is reality-upside down or downside up?) the box thing was only in answer to a question. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [March 8, 2010, 4:34pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/56 "2010-03-08T16:34:21Z")
miriam, we’ve answered your question. Gravity means the Earth is spherical. As already stated, rock cannot withstand the stress and will flow like liquid. The difference in height between Mt. Everest (highest elevation) and the Marianas Trench (lowest elevation) is ~20 km. The mean radius of Earth is 6371 km. That means the surface irregularities of mountains vs ocean bottoms amount to ~0.3% of the Earth’s radius. That’s smoother than a billiard ball. Plus, oceans fill in a good part of the lower bits, making it appear even smoother, ~ 0.14% of the Earth’s radius. Satellites in geosynchronous orbit are moving at exactly the same rotational speed as the Earth, so do not have any visual distortion from rotation. They show a spherical Earth. Photos of Earth taken by astronauts from the Moon show a spherical Earth. Pictures of Earth taken by space probes going to other planets show a spherical Earth. There is nothing in any of that to question that the Earth is a slightly oblate spheroid with a surface roughening. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [March 8, 2010, 5:31pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/57 "2010-03-08T17:31:52Z")
Not to mention that the Arctic and Antarctic circles are smaller than the Tropics of Cancer and Capricorn, which are smaller than the Equator, but the Equator is almost exactly the size of all the great circles of longitude. And not to mention that you can see further in every direction from the tops of mountains and tall buildings. And that you can see all the stars making circles around the two poles from anywhere on Earth, including from the poles, themselves. And any surveyor knows that quadrangles on the Earth do not follow the laws of plane geometry. If you lay out an area of ten miles running straight east-west, ten miles running straight north from the two ends, and then another line running straight east-west at the top, the top line will be smaller than ten miles in the northern hemisphere, and longer than ten miles in the southern hemisphere. Or, if, on the other hand, you lay out a triangle on the earth, the angles will always add up to more than 180˚, and the bigger the triangle, the larger the sum. Every Single Time. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [March 8, 2010, 6:03pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/58 "2010-03-08T18:03:08Z")
> [@Irishman](#): > > The difference in height between Mt. Everest (highest elevation) and the Marianas Trench (lowest elevation) is ~20 km. The mean radius of Earth is 6371 km. That means the surface irregularities of mountains vs ocean bottoms amount to ~0.3% of the Earth’s radius. That’s smoother than a billiard ball. I know this fact gets repeated by multiple people, but it’s not actually true. Or, more presicely, it conflates different measurements. The tolerance number for a pool ball this factoid refers to is +/- 0.005" on a 2.250" diameter. Problem is, that’s the _diametral tolerance,_ or the amount that the nominal diameter is allowed to deviate from 2.250". Irregularities are covered by “surface roughness” (for localized irregularities like Mount Everest) or “sphericity” (for bulk distortions of the ball shape). The surface finish of a pool ball is clearly far, far better than +/- 0.005" and I suspect the sphericity is too. ---
**Author:** ![miriam\_hassan](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@miriam\_hassan](https://boards.straightdope.com/u/miriam_hassan)\ **Post date:** [March 9, 2010, 4:42am UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/59 "2010-03-09T04:42:44Z")
so the reason why the earth is roughly round, as i understand it, is that the matter which makes up the earth is pulled towards the centre for all directions due to earth’s gravity and perhaps the centripetal force created due to the spin of the earth that adds up in the same direction… ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [March 9, 2010, 3:18pm UTC](https://boards.straightdope.com/t/the-shape-of-the-earth/530371/60 "2010-03-09T15:18:41Z")
> [@miriam\_hassan](#): > > so the reason why the earth is roughly round, as i understand it, is that the matter which makes up the earth is pulled towards the centre for all directions due to earth’s gravity and perhaps the centripetal force created due to the spin of the earth that adds up in the same direction.. Close; you’re right that gravity pulls the Earth into a sphere. The spin of the Earth makes it bulge slightly at the equator and be squished slightly at the poles. The technical term is “[oblate spheroid](http://en.wikipedia.org/wiki/Oblate_spheroid)”. In the second picture there, the minor axis corresponds to the Earths axis. (But the Earth isn’t nearly that squished. Drawn to scale, you wouldn’t see it.) [Previous page](https://boards.straightdope.com/t/the-shape-of-the-earth/530371.md?page=2)