Author Topic: To go True or Magnetic  (Read 12390 times)

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Offline CW2274

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Re: To go True or Magnetic
« Reply #25 on: November 03, 2015, 05:25:48 PM »
The 4-Bears (weather Rock) corollary:

FUNCTIONALLY, this is *how* I determine(d) "true" north for my VP2:

1) SPRING EQUINOX - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.
2) SUMMER SOLSTICE - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.
3) AUTUMANL EQUINOX - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.
4) WINTER SOLSTICE - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.

The "straight Line" formed by the four rock locations "points" exactly NORTH - SOUTH.

Done four years ago, I "check" things every three months: "...shadow on rock? Yep...all's OK!" (wink,wink).
Ya but, that takes a whole year. Ain't gettin' no younger! :-|

Offline RPinCA

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Re: To go True or Magnetic
« Reply #26 on: January 18, 2016, 03:25:46 PM »
@CW2274, from another discussion I know you were with ATC, and you know I'm a GA pilot. We know that ATIS broadcasts surface winds using magnetic direction, as it corresponds to magnetic runway headings. Winds aloft are reported in geographic (true/celestial) units. I've seen conflicting information on the net regarding what we should use in a PWS. On my own, macht nichts, I'll know what I chose. But when I hook up to Wunderground (et al), I presume they would want all reporting stations in correspondence. Where I live, magnetic variation is 13.75, so the question seems relevant.

I know you chose magnetic, and I suspect your ATC background played a role in this. I tried finding the answer at Wunderground, but couldn't. Correction... I just found the answer, but I'll finish this post. I used a feature of Google search I've found helpful. My query was

wind direction magnetic or true/site=wunderground.com

The "site=xyz.com" makes a big difference in search results. I thought you might find this interesting, and hope you'll take it in a positive spirit. This is the link for the answer: http://help.wunderground.com/knowledgebase/articles/129054-how-is-wind-direction-referenced

"Wind direction is referenced to true north, not magnetic. The wind display has a marker located at the wind source, with a small arrow indicating the flow of the wind."

So, in the process of asking the question, I found the answer that seems important to this community. Whether or not you'll choose to leave the dark side is an open question.  ;)

Offline CW2274

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Re: To go True or Magnetic
« Reply #27 on: January 18, 2016, 05:46:14 PM »
@CW2274, from another discussion I know you were with ATC, and you know I'm a GA pilot. We know that ATIS broadcasts surface winds using magnetic direction, as it corresponds to magnetic runway headings. Winds aloft are reported in geographic (true/celestial) units. I've seen conflicting information on the net regarding what we should use in a PWS. On my own, macht nichts, I'll know what I chose. But when I hook up to Wunderground (et al), I presume they would want all reporting stations in correspondence. Where I live, magnetic variation is 13.75, so the question seems relevant.

I know you chose magnetic, and I suspect your ATC background played a role in this. I tried finding the answer at Wunderground, but couldn't. Correction... I just found the answer, but I'll finish this post. I used a feature of Google search I've found helpful. My query was

wind direction magnetic or true/site=wunderground.com

The "site=xyz.com" makes a big difference in search results. I thought you might find this interesting, and hope you'll take it in a positive spirit. This is the link for the answer: http://help.wunderground.com/knowledgebase/articles/129054-how-is-wind-direction-referenced

"Wind direction is referenced to true north, not magnetic. The wind display has a marker located at the wind source, with a small arrow indicating the flow of the wind."

So, in the process of asking the question, I found the answer that seems important to this community. Whether or not you'll choose to leave the dark side is an open question.  ;)
I find it somewhat laughable that WU says magnetic is not even a viable choice, but for their purposes, I guess not. Yes, I've chosen magnetic for my personal use, but 99% of the public uses true. Another thing, the arrow in the example is pointing the wrong way as the point should face where the wind is coming from, not going to. I noticed that my local TV station now does it backwards too.
I'll stick with magnetic as I like to compare with the neighboring airports, dark side and all. ;)

Offline RPinCA

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Re: To go True or Magnetic
« Reply #28 on: January 18, 2016, 06:03:11 PM »
Quote
Another thing, the arrow in the example is pointing the wrong way as the point should face where the wind is coming from, not going to.

I noticed this trend in display style, as well. I think you and I are "old school" and understand it points opposite of the way the wind is going (rewording intentional). I remember needing to learn this characteristic as a young man.

It appears we are entering a Least Common Denominator world, where it's simply easier to reach the broader public than it is to train the broader public. Intellectual "Collateral Damage" of the Internet Age. The practice is spreading, as you noticed. Even the Wunder Weather Station has an internal display screen that mimics the Wunderground style gauge, and it is a solid, well-designed product. The reasoning behind the WWS decision is sensible; the reasons behind the reasoning are not.

I'll admit with some chagrin, this subject had me imagining ways to make a mechanical wind vane that points with the wind. I think it is do-able, although I've not yet made a prototype. My guess is the traditional pointer is a historical consequence from the days of bows and arrows.

Offline CW2274

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Re: To go True or Magnetic
« Reply #29 on: January 18, 2016, 06:05:20 PM »
Quote
Another thing, the arrow in the example is pointing the wrong way as the point should face where the wind is coming from, not going to.

I noticed this trend in display style, as well. I think you and I are "old school" and understand it points opposite of the way the wind is going (rewording intentional). I remember needing to learn this characteristic as a young man.

It appears we are entering a Least Common Denominator world, where it's simply easier to reach the broader public than it is to train the broader public. Intellectual "Collateral Damage" of the Internet Age. The practice is spreading, as you noticed. Even the Wunder Weather Station has an internal display screen that mimics the Wunderground style gauge, and it is a solid, well-designed product. The reasoning behind the WWS decision is sensible; the reasons behind the reasoning are not.

I'll admit with some chagrin, this subject had me imagining ways to make a mechanical wind vane that points with the wind. I think it is do-able, although I've not yet made a prototype. My guess is the traditional pointer is a historical consequence from the days of bows and arrows.
Well put.

Offline Randall Kayfes

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Re: To go True or Magnetic
« Reply #30 on: February 01, 2022, 03:39:09 PM »
Just for kicks and I mean kicks - Polaris the North Star is Declination: +89 21' 42.44" So you can see that Polaris is about 18' from the Celestial North Pole which the earth's true north pole generally points to. Since Polaris is not on the Celestial Pole that means it circles it. So technically the Pole star aligns with the true north of the earth twice a day. Astronomers like me have to use Pole tables or programs to align our scopes with the celestial pole based on sighting and then offsetting Polaris. Also because of orbital and lunar considerations the true north pole of the earth can get ever so slightly out of alignment with the celestial pole as well. And Polaris is a double star, so which one do you use.

So, if you really want to be accurate...  :grin:   \:D/

(Just having fun - and remember don't trust atoms - they make up every little thing...)



Offline davidmc36

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Re: To go True or Magnetic
« Reply #31 on: February 01, 2022, 05:40:37 PM »
Well figured out why the station we moved yesterday anemometer wind direction was so far off. The phone app was off by 30+ degrees compared to real compass. Did several more calibrations with app twirling phone and it finally started agreeing with compass. Don't trust these apps on phones I guess. :sad: The reason I used it in first place, it had declination built-in when the gps is turned on.

Phone App. Ewwww! And the GPS will only help while moving.

If you have any desire to calibrate it to anything a 50 dollar compass can be a good piece of kit.

Offline box

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Re: To go True or Magnetic
« Reply #32 on: February 02, 2022, 05:32:25 AM »
 Mag variation in these parts is around 1degree west so to all intents and purposes can be ignored