You guys are unbelieveable! I've had the martian analemma & EOT question for a long time but never asked it for fear that you'd think I was a bit crazy. I thought who would even go to the trouble to calculate it since there's not a big market for sundials on Mars. I'm delighted that someone else has had the same question and even has a picture of one!
Understanding why analemma and EOT curves take the shape that they do is a question that we have all struggled with. In fact, is is in the top ten of the FAQs that I recieved. I've always thought that if you compare the factors which determine the curve for two different planets, then it would be a lot easier to see how each factor affects the curve's shape. Now I know the shape of the EOT curve is determined by the earth's axis inclination and the eccentricity of its orbit. Which of these two factors cause the two big humps and the two small humps of the curve? The analemma's shape is simply the EOT values plotted against the solar declination. Right? Which of these factors causes the figure eight? Why is one lobe bigger than the other? Why is the analemma slightly off center vertically? Why doesn't Mars also have a figure eight analemma? I'm sure there are many people who'd like answers to these questions myself included. I have my own theories but I'm not sure that they are correct. Thanks for dealing with my flood of questions this week. John Carmichael Tucson Arizona is>Hello, > > The March '82 Sky&Tel article, "The Analemmas of the Planets", is an >interesting piece, I scanned a portion of my copy and posted the image >of the Martian Analemma at the following URL. > >ftp://ftp.gcstudio.com/pub/sundial/marseot.jpg > > As Robert mentions it has a teardrop shape, this I believe is due to >the fact that the eccentricity component currently dominates over the >figure-eight shape of the planet's obliquity component. If I'm not >mistaken, I believe Earth's Analemma had such a shape (teardrop) some >95,000 years ago. > > BTW, the article also illustrates a "human" Analemmatic Dial with an >Analemma implemented for EoT correction, the dial is in Tucson Arizona >at the Flandrau Planetarium. > >Best, > >Luke > > >R.H. van Gent wrote: >> >> John Carmichael wrote: >> >> > I usually don't write two different letters to the list on the same day, but >> > could'nt resist the following question in view of today's landing on Mars. >> > >> > What would the martian analemma and Equation of Time look like? >> >> Martian and other non-terrestrial analemmas were discussed in: >> >> David A. Harvey, "The Analemmas of the Planets", Sky & >> Telescope, vol. 63 (1982), 237-239. >> >> The Martian analemma is rather simple compared with the terrestrial case and >> resembles an asymmetrical droplet. >> >> Even more boring are the elliptical analemmas of Mercury, Venus and Jupiter. >> >> 8-shaped analemmas such as the terrestrial case are found on Saturn, Uranus, >> Neptune and Pluto. That of Saturn barely manages to form an 8 and those of >> Uranus and Pluto exhibit large north-south spans of 164 and even 180 degrees. >> >> These calculations were based on the planetary rotation parameters as they were >> known at that time and can probably be improved somewhat for the outermost >> planets as better determinations have become available. >> >> Also have a look at: >> >> http://www.analemma.com/ >> >> ================================================================ >> * Robert H. van Gent * Tel/Fax: 00-31-30-2720269 * >> * Zaagmolenkade 50 * E-mail: [EMAIL PROTECTED] * >> * 3515 AE Utrecht * Home page (under construction): * >> * The Netherlands * http://www.fys.ruu.nl/~vgent/ * >> ================================================================ > >
