Talk:Figure of the Earth

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Geodesy[edit]

This text is taken from chapter 1 of the public domain resource Geodesy for the Layman at http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/TR80003A.HTM#ZZ0 -- please Wikify as necessary. —Preceding unsigned comment added by The Anome (talkcontribs) 10:19, 25 May 2003

I've been reading Gordon Lauf's Geodesy and Map Projections and some of the information is different. e.g. he has Krassowsky with a major semi axis of 6,378,295 rather than the 6,378,245m quoted here, and a reciprocal flattening of 298.4 rather than the 298.3 quoted here.

Also an issue which particularly concerns me is Lauf's suggestion that in general "the geodesic has an infinite number of windings on the spherical earth", oscillating between a given latitude north and south. WHilst this may be true "in general", I would infer that there are particular examples where this is not the case and relatively short periodicitites of return can be found. Harry Potter.

article name[edit]

Since figure of the earth is an expression, shouldn't the name if this article be Figure of the earth? Kingturtle 03:12, 13 Dec 2003 (UTC)

I believe the 245.0, 298.3 values to be the correct ones. 85.76.129.149 20:27, 28 Feb 2005 (UTC)

I don't understand the title. Why isn't it called "Shape and size of the Earth"? This would be a more normal English expression. Borock (talk) 13:21, 1 December 2009 (UTC)
We must use the term most often used in the references, which is "figure of the Earth". This figure is indeed its shape and size. — Joe Kress (talk) 19:32, 1 December 2009 (UTC)
Cool. You learn something every day. Which is one reason to visit WP. :-) Borock (talk) 05:07, 15 December 2009 (UTC)

from PNA/Geology[edit]

  • Figure of the Earth - This has been lifted from a public domain web page [1]. No problem there, but it refers to a number of non-existent diagrams. These could probably be borrowed from the same source, but they are of poor quality. --Heron 17:01, 27 Nov 2004 (UTC)

The actual figure of the earth[edit]

The article describes many ways of approximating the shape of the earth, but other than the triaxial bit or the pear shape thing, the article doesn't mention what the figure of the earth is to any appreciable degree. Where are the relative high and low points of the geoid. —Preceding unsigned comment added by 71.102.144.27 (talkcontribs) 03:00, 14 March 2007

According to NASA (http://www.nasa.gov/worldbook/earth_worldbook.html) the earth is pear-shaped. ig 12.110.164.222 (talk) 21:49, 10 December 2010 (UTC)

Deflection of the vertical[edit]

"The angle between the plumb line which is perpendicular to the geoid (sometimes called "the vertical") and the perpendicular to the ellipsoid (sometimes called "the ellipsoidal normal") is defined as the deflection of the vertical."

But what is the sign convention? I believe the deflection is the angle from the vertical to the ellipsoid normal. Right? Jrvz (talk) 20:41, 19 October 2010 (UTC)

The reference direction is usually the ellipsoidal normal, hence from the ellipsoidal normal to the plumb line. In addition, the deflection of the vertical relative to the ellipsoidal normal has a north-south component ξ and an east-west component η, where north and east are positive. See Geodesy pages 218–219. — Joe Kress (talk) 08:35, 20 October 2010 (UTC)

CopyVio - Geoid[edit]

The Geoid section appears to have been copied verbatim from "Geodesy for the Layman". Item 3 of that document's Foreword says "[this document] contains no copyrighted material...". Is that enough to make this copy/paste OK? Even if the copy/paste is OK, we should acknowledge the source.

A Google search for the phrase "The geoid is a surface along which the gravity potential is everywhere equal" will find other instances, and it's not obvious which is the original. 203.176.108.99 (talk) 06:02, 11 October 2012 (UTC)

"Geodesy for the Layman" should certainly be cited. Documents prepared by employees of the US federal government are in the public domain. Sometimes the federal government published documents that contain copyrighted work prepared by others, used by permission. But the statement "[this document] contains no copyrighted material..." seems to mean that it was prepared only by federal employees in this case.
I don't think a single sentence, "The geoid is a surface..." is a copyright problem, so I think we can leave it alone unless we can establish that it was first published outside of Wikipedia. Jc3s5h (talk) 12:48, 11 October 2012 (UTC)

Flat Earth[edit]

Who knew; the Earth really is flat!JoelDick (talk) 13:22, 26 May 2014 (UTC)