Talk:Horizon

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Contents 1 Refraction 2 Unheadered stuff 3 Added gemoetrical horizon 4 Mushroom cloud 5 Metric? 6 Mental Calculation 7 Etymology 8 Curvature of the horizon

[edit] Refraction

I added brief mention at the end of the fact that the actual visual horizon is a little further than the calculation in the article would suggest, because of refraction.

Actually, I would like to have changed the nomenclature completely here, but I didn't feel like taking the time to redraw the picture. The word "visual horizon" ought to include the effect of refraction, while "geometric horizon" is the horizon for a spherical planet, but without the effect of atmosphere. I don't know of a phrase meaning "where the horizon would be if the Earth were a plane," but "geometrical horizon" isn't it.

[edit] Unheadered stuff

so why is it purple then?

I came to this page to see if it said anything about why the sky (during a clear day) gets grayer as it gets closer to the horizon. If anyone has a good treatment or link, that would be swell. Jake 00:02, 19 Aug 2004 (UTC)

Maybe this would be better treated on sky since that is where they talk a little about the color? Jake

See airmass or extinction (astronomy) for an explanation of this phenomenon. --Lasunncty 00:18, 29 January 2006 (UTC)

[edit] Added gemoetrical horizon

I added the part about perspective drawing and the "geometrical horizon". In a way, it is similar to the description of "astronomical horizon". However, astronomical horizon was described as a plane, while I believe the horizon is alway a line. Note that it compares the astronomical horizon to the true horizon (one being lower than the other), even though one is described as a line and one as a plane. It seems like this could use some clean up to clarify this distinction.

Robbrown 21:06, 29 January 2006 (UTC)

[edit] Mushroom cloud

Why does the horizon picture look like it has a mushroom cloud in the background? User:fresheneesz

[edit] Metric?

How about a formula using miles. Why is there only formulas using the lame metric system?

   How about performing a simple conversion you lazy person
   Graemec2 13:13, 13 November 2006 (UTC)

[edit] Mental Calculation

What if you do not have a calculator? Naval officers often use a thumb rule calculation that you can do in your head, that is:

The distance to the horizon in miles is equal to the square root of the height of eye in feet, multiplied by 1.1.

It usually suffices to choose a height of eye that is a square of a round number, like 4, 9, 16, 25, 36, etc. If in a small boat or looking through a periscope, assume a height of eye of 4 feet, the square root of 4 is 2, multiply by 1.1 to get the distance to the horizon of 2.2 miles. If you are on a larger boat, use 9 feet [3.3 miles], a bigger boat, 16 feet [4.4 miles], and so on. If your height if eye is mid-way between 9 and 16 feet, the distance would be half way between 4.4 and 5.5 miles, say 5 miles.

The distance provided by this thumb rule is roughly 10 percent shorter than the exact distance. That accuracy is usually quite sufficient for an eye-ball approximation of a ship or lighthouse that far away.

24.15.3.112 18:22, 24 February 2007 (UTC)tvbanfield

[edit] Etymology

The Zeitgeist Movie^[1] says that Horizon is a contraction of Horus-is-risen, in the sense that the horizon is from where the god of the sky rises. Is there anything in this or are they talking crap?

Straussian 14:38, 2 July 2007 (UTC)

The OED indicates that horizon comes from the Old French orizonte. The relation between horus and the word horizon is wishful coincidence. Horizon is related to the word meaning limit in greek. This word was accepted into Latin to designate a limit of time "hora" and space "horison." The word horison was in latin long before english existed. Horison cannot come from an english contraction because it was a word already. The sentance "Horus is risin" in latin would be "Horus oriras" or "Horus orirbas" depending on tense of the statement (latin may be off). So a contraction of the statement would sound nothing like Horison. The same film makes the assertion that we get our word sunset from the egyptian god set. This is just as bogus as set comes from the germanic languages and more specifically the old English sitten, derived from setten. —Preceding unsigned comment added by 131.107.0.73 (talk) 21:16, 6 September 2007 (UTC)

That's what I thought. The film does indeed seem to contain a lot of wishful etymologies. Thank you for clearing that up. Straussian 11:54, 13 November 2007 (UTC)

[edit] Curvature of the horizon

I am bit a confused about the formula for the curvature of the horizon. Are you sure this section is correct? I am a complete novice to such calculations, but I am interested in space flight so I wanted to do some quick calculations and encountered some problems...

I agree on the part, that in 10 km altitude, the curvature is 0.056. Since the curvature is the reciprocal of the angular radius in radians, this results in 1/0.056 rad = 17,84 rad = 17,84 * 180/PI degrees = 1022 degrees as angular radius.

In 2640 km altitude the curvature is 1. The angular radius then is 1/1 rad = 1 * 180/PI degrees = 57,28 degrees as angular radius. But as far as I understand the text in the section says it should be 45 degrees!?!?

Most probably I am getting something wrong, but it would be great if someone could comment on that.

I am also bit clueless about how to handle "angular radius" since I have not found a clear definition here in Wikipedia. Is there a figure somewhere that explains this concept? Maybe that would make clear where my fault is.

Thanks! Chris