This is such a blindingly obvious question it must have been covered, but I can’t find it. Here goes:
The US (and doubtless the rest of the world) is divided into time zones, 15 degrees wide, give or take some wanderings to follow state lines, etc. At just one meridian in that 15 degrees the sun is directly in the south at noon.
Where is that meridian? in the middle of that roughly 15-degree zone, perhaps?
(And, of lesser interest at the moment, do the time zones follow generally on lines evenly divisible by 15 degrees, or are some extra large at the expense of others?)
It’s more or less at evenly spaced intervals, except for national boundaries.
Meridians go up and down, north to south, like the sections of an orange. How could the sun be “in the south at noon” on an up-and-down line? Are you perhaps thinking of a side-to-side east-west boundary, like the Arctic Circle, marking how far north you are?
Anytime you’re farther north than the equator, during winter in the Northern Hemisphere the sun is going to be more in the south at noon. The further north you go, along whatever meridian, the more southerly the sun will appear.
I believe what he is asking is where inside the time zone solar noon corresponds with the time zone’s noon. Solar noon occurs when the sun is directly overhead, or due south in the sky (in the middle of its east to west journey.)
This page explains it pretty well. The standard meridian for any given time zone is where solar noon occurs at local noon. So in Greenwich, England, solar noon is at exactly 12:00 Greenwich time.
When the sun is directly toward the south (or in the Southern Hemisphere, directly toward the north), that is called “local noon”. Local noon occurs at the same time everywhere on a given meridian, regardless of latitude. The meridians where local noon and noon by the clock coincide occur at longitudes 0°, 15°, 30°, etc., E and W. So the standard meridian for Eastern Standard Time is 75°W longitude (which happens to be near Philadelphia). Generally the statutory time zones coincide approximately with a 15° wide area centered on these lines so that local noon and noon by the clock differ by no more than a half hour (except during daylight saving time). There are some exceptions. Nome, Alaska is about two hours off from what it should be because it has been decided that it is important to have most of the state in one time zone.
Well, Bibliophage you were one of the first guys on this board to bust me but I can’t help but jump up here and add a cents worth.
Local noon hardly ever occurs at 12:00 P.M. at the standard meridian. The Sun’s travel along the ecliptic varies for two reasons and both of those contribute to a variation in solar transit time. There is eccentricity of orbit, and inclination of axis.
Even at the standard meridian the Sun rarely passes over at 12:00 at noon. I’m thinking of a word…
Actual analemma photographs are one of the rarest and, in my opinion, neatest photographs taken. They show something that most people don’t even notice to exist, but that has been observed for thousands of years. Plus, you have to admit that analemma is high on the list of naughty-sounding-when-mispronounced astronomical terms, somewhere near Uranus.
Anyway, for the original question: ideally, the center meridian of that 15 degree swath of earth would have ‘high noon’ be due south four times a year, during the solstices and the other ones… googles… the eqinoxes. The solstices would be the top and bottom of the analemma, and the equinoxes would be the crossing point.
Of course, the timezones are laid out as much by political boundaries as by where they physically should be. There are probably latitudes in timezones that don’t contain the ‘high noon meridian’, if you were to give it a name.
Ideally, either the whole planet would have one timezone, or every degree (or minute of a degree, or second of tthe minute) would have it’s own timezone, each one 4 minutes (or four seconds, or one fifteeth of a second) different.
Ben
Go find a phtograph of an analemma, it’s cool. Each one represents the devotion of a camera for most of a year and, at minimum, seven exposures. The maximum would be ~365 exposures, which I’ve never seen. It’d be really nifty, perhaps I’ll have to do it.
Should’ve googled some more. The analemma.com diagram shows that the analemma is skewed–the crossing points do not occur at the soltices (most northerly or southerly) or equinoxes.
And here I thought that I was the only one to think that a photo showing a real sky manifestation of an analemma was fabulous. I saw mine in the SciAm Library’s book Earth and Sun.
But to the point. The solstices DO occur at the extreme North and South points of the analemma, and the equinoxes occur at the halfway points (North to South) of said same. If that is what y’all were saying anyway count this as an affirmation…
