Are clocks set so that noon matches solar noon in the middle of a time zone at aphelion (or perihelion)? I.e., when does the eq. of time give zero correction? Bill -----Original Message----- From: math-fun-bounces@mailman.xmission.com [mailto:math-fun-bounces@mailman.xmission.com] On Behalf Of Robert Munafo Sent: Saturday, December 11, 2010 12:16 PM To: math-fun Subject: Re: [math-fun] Analemma Looks like you got the calculation pretty close. An expert on the subject[1] says that the equation of time on Mars varies from +40 minutes to -50 minutes relative to the mean. Here is a plot: http://www.giss.nasa.gov/research/briefs/allison_02/analemma.GIF and the page that talks about it: http://www.giss.nasa.gov/research/briefs/allison_02/ and a nice photo on the Mars surface with multiple Sun images added in to show what it looks like compared to the horizon: http://apod.nasa.gov/apod/ap061230.html Note those Mars Sun images are a little smaller than the Sun that we see from Earth. So the analemma is actually a bit smaller than it might appear if you are taking the size of the Sun's disc as the scale cue. - Robert [1] Allison, M. 1997. Accurate analytic representations of solar time and season on Mars with applications to the Pathfinder/Surveyor missions. Geophysical Research Letters 24(16) pages 1967-1970. (97GL01950) PDF here: http://pubs.giss.nasa.gov/docs/1997/1997_Allison.pdf On Fri, Dec 10, 2010 at 15:25, Joshua Zucker <joshua.zucker@gmail.com>wrote:
My rough calculation based on what I quickly looked up of Mars's orbit eccentricity suggests that solar noon won't be off from clock noon by more than an hour.
-----Original Message-----
A puzzle for the computationally minded ... The orbit of Mars is much more elliptical than Earth's. So the analemma effect is much stronger. On the Earth, we simply use mean solar time in our daily affairs, and ignore the slight difference between clock noon and local physical noon. The difference is only +- ten minutes or so, and is swamped by the effect of time-zone quantization. (Never mind daylight savings.)
The puzzle: Could future Mars colonists ignore the analemma? The day length is about 24:40, so the natural thing to do is simply live by the longer day. Most of us could use an extra forty minutes a day. But would the Martians sometimes find the sun rising at (clock) midnight?
-- Robert Munafo -- mrob.com Follow me at: mrob27.wordpress.com - twitter.com/mrob_27 - youtube.com/user/mrob143 - rilybot.blogspot.com _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun