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Forum Index : Solar : ’Noon’ or ’Midday’?
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| neil0mac Senior Member  Joined: 26/12/2009 Location: AustraliaPosts: 210 |
For the solar purists (and the pedantics?) 'Noon' and 'Midday' "ain't necessarily the same thing". 
Noon occurs at 12 P.M. Midday is halfway between sunrise and sunset - and can vary by as much as six and a bit minutes - the blue line). If you promise to meet someone at midday and they arrive a minute or two either side of noon and then leave promptly, they may be there before (or after) you, and neither will see the other. OK. So it's one of those useless facts you come across when doing research. (BTW, the chart is for Gunnedah NSW at 30 deg. 50 minutes South.) And the blue dots are so you don't have to remember how ays there are in the 12 months of the year. |
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| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Yep Long shadow time Bob Foolin Around |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=neil0mac]six and a bit minutes I have a dumb question: What's a "bit"? I see it used all over the place and it's high time I knew what folks are talking about. 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
I have a dumb question: What's a "bit"? I see it used all over the place and it's high time I knew what folks are talking about.
. . . . . Mac In this case Mac, it's more than six and less than seven. But if you're on the equator it's exactly 6 and 'nothing' as well as at the poles where 'midday last all day for weeks ats a time - and then you don't have one at all ('winter time'!) Alternatively it's a fair amount less than 'a lot'. In between those extremes it varies. See http://www.usno.navy.mil/USNO/astronomical-applications/data -services/rs-one-year-us for both US(A) and international data to make your own 'bits' if applicable. |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Mac, A BIT is what you drill a hole with. A BIT is a expression for a small amount...a little bit of apple pie A BIT is a smaller fraction of what makes up a BYTE in data with electronics ...8 bits make a byte A BIT is was the misses gives you if you are lucky......I have a headache means no bit today. A BIT is what goes in the horses mouth...part of a bridal. A BIT explains Oz hair loss with emails....bit by bit going bald. Bit is past tense of bite. So yes it is used everywhere. Pete. Sometimes it just works |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Pete That's a good BIT of an explanation but I think Mack meant Noon unless I'm wrong which is more than possible as it happens more than a BIT of the time. Hi Mack If its NOON that's the problem that's when the shadow of a stick stuck in the ground vertically is the longest, this is caused because we have average time zones for setting the clock but if we aren't at the set point of the time zone then the time is wrong for where we are, so NOON isn't 12 o'clock. Clear is as clear as a BIT of Mud. All the best Bob Foolin Around |
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| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Don't you mean 'shortest'? E.g. on the equator there is no shadow at all at 'mid-day'. Just for record, the data I based the graph on is from the 150th meridian, used for setting the EST time zone down under, which isn't out by 'much' - which in this case, is probably less than 'bit'. |
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Tim_the_bloke Senior Member Joined: 15/11/2009 Location: AustraliaPosts: 105 |
I am not a "pedantic". I am a pedant.  |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Neil You got me mate I thought one thing and wrote another, you are exactly right. All the best Bob Foolin Around |
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Loomberah Regular Member  Joined: 11/06/2008 Location: AustraliaPosts: 43 |
 Actually, its over 15 minutes, and is known as the Equation of Time. It's the difference between midday 12pm and solar noon (ignoring daylight savings), and varies over the year due to the Earth's elliptical orbit and the obliquity of the ecliptic.
At this time of year, the difference is relatively small. There are also offsets to apply for people who dont live on a standard time zone meridian... although Neil is quite close to one 
Read all about it here: Wikipedia page Loomberah weather +solar&UV, astronomy, photography, organic farm |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I have to ask Neil0mac, which calendar was used to prepare the first graph. My calendar has May with 31 days, but your graph shows only 30. Is this an Excel thing? Maybe Gunnedah has a different calendar. As you are talking about pedantic, maybe this is an appropriate point to add. Gordon. become more energy aware |
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| Loomberah Regular Member Joined: 11/06/2008 Location: AustraliaPosts: 43 |
They take a day off May and add it to August around those parts Loomberah weather +solar&UV, astronomy, photography, organic farm |
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| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Gordon 1, 'May'be that was an 'august' occasion? Gordon2, I did notice a 364 day 'year' but wasn't fussed enough to chase the discrepency! The info came from ... http://www.usno.navy.mil/USNO/astronomical-applications/data -services/rs-one-year-world ... ... imported into Excel and 'massaged'. Anyone seriously chasing an extra watt or two would probably only make some gain by adjusting their system for the times the year where midday varies by more than 6 minutes (first and third quarters of the year), as 10 degs. off perpendicular has no appreciable loss of irradiation collection. |
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| Loomberah Regular Member Joined: 11/06/2008 Location: AustraliaPosts: 43 |
In a fixed system pointing North there is no gain to be made by making any adjustments, the sun still follows the same path across the sky and is highest when due North, the time on your clock makes no difference whatsoever! With a brightest part of the sky tracker, the local clock is also irrelevant. Loomberah weather +solar&UV, astronomy, photography, organic farm |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I agree with Loomberah I have been biting my tongue here over all this need for plotting the sun across the year and think its a waste of good energy and just being pedantic, that at the end of it, it will make 2/5 of F---ALL differance. If the sun was a 100 meters away maybe it be worth considering. There is a time the classroom needs to step out into the field and do some real experiments because theory dont always equal fact. The other thing is something needs to run all this and short of a nassa computer its just a pipe dream, as 4096 bytes of program space in a micro just aint going to cut it. Pete. Sometimes it just works |
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