Wikipedia:Featured picture candidates/Marine sextant

Marine sextant

The animation illustrates the use of a marine sextant at sea, for measuring the altitude of the Sun above the horizon. This information, coupled with the knowledge of the exact time and the position of the Sun in the celestial sphere at the moment of the observation, allows the determination of a line of position, with an accuracy of about 1-2 nautical miles

Reason

This is a revised version of an animation already nominated in WP:FPC. I believe it helps to better understand the basic principle of the instrument and illustrates cleary its use in celestial navigation. The picture file contains a detailed explanation of the numbered frames.

Articles this image appears in

Sextant, celestial navigation

Creator

Joaquim Alves Gaspar

• Support as nominator — Alvesgaspar 17:36, 7 April 2007 (UTC)
• Comment is there a way to avoid artifact when WikiMedia thumbnails it? gren グレン 18:08, 7 April 2007 (UTC)
• Support per Commons discussion. ~ trialsanderrors 20:08, 7 April 2007 (UTC)
• Support. Shame about the artifacts in the thumbnail but very good quality and useful for the article(s). Diliff | (Talk) (Contribs) 16:38, 8 April 2007 (UTC)
• Support Very informative Jellocube27 21:29, 8 April 2007 (UTC)
• Support Much improved! Just one suggestion, there is actually one last step: 5) read the elevation from the index bar. You might have the measurement "40°" circled briefly. It would make clear the purpose of the device. --Bridgecross 02:38, 9 April 2007 (UTC)
• Support. Perfect! I never knew how to use one of those things, and after just looking at the thumbnail image for a couple loops, it makes sense. — BRIAN0918 • 2007-04-09 13:26Z
• Question: Would you really see the sun as a full circle? Wouldn't it just be a half-circle? — BRIAN0918 • 2007-04-09 13:28Z
  • Answer - Yes, a full circle whose size depends on the telescope in use. On the left part of the horizon mirror, which is in fact a transparent glass, the sun's image is dimmer because the reflectivity of the glass is lower. In practise, our eyes seem to melt both images. Alvesgaspar 13:51, 9 April 2007 (UTC)
• Support: Very good picture, but would it be possible to smoothen up the animation?  ~Steptrip 15:49, 9 April 2007 (UTC)
  • Yes, it is possible but I don't have the time right now. I'll have to go back to the (Corel) drawing board and double the number of frames. - Alvesgaspar 20:54, 9 April 2007 (UTC)
• Info - Brian0918 question made be realize the animation had a mistake: the white boundary line between the glass (left) and the mirror (right) should also rotate. It is fixed now. Alvesgaspar 18:40, 9 April 2007 (UTC)
• Support - Instantly explains the means of operation. — BillC ^talk 23:16, 9 April 2007 (UTC)
• Support TomStar81 (Talk) 05:08, 10 April 2007 (UTC)
• Weak oppose. Much improved, indeed, but I still don't like the simple "squishing" of the instrument when it is tilted. There really should be some perspective in that part of the animation. --Janke | Talk 06:05, 10 April 2007 (UTC)
• Support as I did on commons ! Blieusong 20:10, 10 April 2007 (UTC)
• Support very useful to understand an instrument everybody knows, but few know how to use. Moravice 16:52, 11 April 2007 (UTC)
• Support clearly explains everything :-D --Penubag 08:28, 13 April 2007 (UTC)penubag

Promoted Image:Using sextant swing.gif --trialsanderrors 04:57, 15 April 2007 (UTC)