> -----Original Message----- > From: tedd [mailto:tedd.sperling@xxxxxxxxx] > Sent: Friday, September 12, 2008 9:41 AM > To: Boyd, Todd M.; php-general@xxxxxxxxxxxxx > Subject: RE: Re: Google Maps Distance Between UK Postcodes > > At 3:54 PM -0500 9/11/08, Boyd, Todd M. wrote: > > > Considering that my other profession is Geophysicist, I'm kind of > up > >> on those sort of things. The Earth is an oblate spheroid and the > >> computation to include the curvature of the earth would be a bit > more > >> involved. > > > >---8<--- snip > > > >But it's also NOT an oblate spheroid! :) > > > >http://blogs.discovermagazine.com/badastronomy/2008/09/08/ten-things- > you > >-dont-know-about-the-earth/ > > Todd: > > LOL -- Discover magazine is hardly the definitive authority for > Geophysical terms. This is more an article written to make > controversial claims for laymen to ponder rather than to provide > anything of real substance for people who work in the Geophysical > field. It was hosted on www.badastronomy.com for the longest time. I don't believe he actually writes for Discover Magazine per se, but is rather hosting his astronomy blog on blogs.discovermagazine.com. And yes, you're right--it's absolutely not a dissertation or a professional lecture. It's mostly just a "fun" astronomy article. > Note, while the article claims that the Earth is NOT an oblate > spheroid, it does NOT provide a real alternative. However, it does > say "it would be smoother [billiard ball]" but it also claims that > "The Earth is more complicated than an oblate spheroid." So, which is > it? Is it as simple as a billiard ball or more complicated than an > oblate spheroid? Actually, the article claims both. As for his credentials--he's the JREF chairman now, and did work for several years on the Hubble telescope, I believe. :) I'm not saying the article was gospel, or that you were wrong. In fact, later in your reply, you go on to (mostly) agree with the article's author (though he didn't explain it quite as thoroughly as you have). I believe the article also mentions the scenario where "if the earth was 100% water," and goes on to talk about forces acting upon that water (moon, sun, rotation, etc). I believe he uses the term "geoid" in this scenario. > You see, it's one of those "Hit and run -- You can't prove me wrong > because I didn't say anything" articles. > > While technically the Earth isn't ANY standard/formal static size, an > oblate spheroid is a pretty good fit. > > Perhaps an example may be of assistance -- if the Earth was pure > water (a fluid medium having an equipotential surface) then its > surface could be described as a spheroid -- imagine a drop of water > in space without any external forces applied to it. > > If you introduce rotation, then the radius from the center of the > Earth to the equator (perpendicular to the axis of spin) expands and > the radius at the poles (axis of spin) reduces. As such, this surface > IS known and IS defined as an oblate spheroid -- and with respect to > Earth, this IS upon which the geodetic latitude determinations are > made. He makes the same claim. It sort of "flattens" as it spins. > Now, to be more exact in describing the Earth's surface, requires > more attention to detail. > > First, the Earth consists of more than just water and it's content > are not uniform with respect to distribution and density -- not to > mention numerous other physical properties (i.e., elasticity); > > Second, the Earth has rotational, orbital, and even processional > forces applied to it; > > Third, the Earth has external gravitational forces exerted on it from > the Sun, Moon, Planets, and et all; > > Considering all, the surface of the Earth becomes very complex to > compute, let alone to define for the general population. > > So, the problem of what term to use to define the surface of the > Earth really depends upon the audience you're addressing. If I were > talking to a group of preschoolers, I would use the term "Ball", but > if I was addressing a group of Geophysical Scientist, then I would > use the term "oblate spheroid." Incidentally, I have done both > successfully without objection. > > An "oblate spheroid" is good enough for me, but the author of the > article likes the term "Ball" -- each has their audience of believers. Nah, he just explains that the earth is SMOOTHER than a regulation-shaped billiard ball. Coupled with this was his explanation that it wouldn't be perfectly ROUND(/spherical) enough. ;) Either way, I'm no physicist or astronomer of any sort. I just thought it was an interesting read. He had written a few speculative articles about Hanny's Voorwerp a while back that I had stumbled upon, and I check his site every now and again to see if there's anything I can read to take my mind off work if I'm particularly frustrated/bored. Thought you might get a kick out of it, given your past (and present) experience. Peace, love, and flowers, Todd Boyd Web Programmer -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
