I'll take a stab at this as I'm the first to reply, apparently; but others will correct me if I've got it wrong, I'm sure. We have to be brave enough to try explanations at the risk of being wrong so we can learn, eh?
If the earth orbited in a perfect circle (no ellipse) then there would be no vertical values to the EOT; the EOT would be flat and the analemma would collapse to a straight vertical line. The horizontal displacements correspond to the amounts the earth has rotated "too much" or "too little" (compared to its mean motion) because of its elliptical path. If the earth orbited without any axial tilt, then there would be no north-south motion of the sun; it would rise at the same place relative to the horizon each day, and the analemma would collapse to a flat horizontal line. The vertical displacements correspond to the amount the sun appears to be above or below the celestial equator, which is a direct result of our axial tilt. That is why the analemma is exactly twice as tall as the earth's axial tilt. (Summer + 23.5 degrees, winter -23.5 degrees, depending on your hemisphere) Therefore, if the earth travelled in a perfect circle with no axial tilt, the analemma would collapse to a point, and all simple equatorial dials would be perfectly accurate, all the time. Jeff Adkins John Carmichael wrote: > Hello again: > > In light of Luke's very clear and informative explanation of how a planet's > orbit and the inclination of its axis affect the shape of the analemma and > EOT curves, what would the analemma look like if the orbit were a perfect > circle and there was no tilt to the axis? Would the analemma be a straight > vertical line, a point, or would it simply disappear? > And would the EOT curve turn into a horizontal line with a value of zero? > > Thanks again, > > John Carmichael -- =-=-=-=-=-=-=-=-=-=-=-=-= [EMAIL PROTECTED] Jeff Adkins Location: 38.00 N, 121.81 W CA, USA, Earth, Sol III
