山中求救訊號

Hong Kong Hiking Web: 民間搜索隊 CountrySide Volunteer Search Team: 山中求救訊號
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   By MKSJ on Sunday, December 18, 2011 - 1:02 pm:  Edit Posted From: 219.77.85.106

While this is already 2 years old, it is nonetheless appropriate to raise 2 technical points here which may be of some importance.

Tecnical Point I:

When the Party-In-Distress blows the whistle 3 blasts :
1. the 1st Blast catches the attention of the Rescue Party.
2. the 2nd Blast permits the Rescue Party to identify the direction from which the sound is coming from.
3. the 3rd Blast permit reconfirmation/refinement of the Direction.

Technical Point II :

Assumig that the parties are 1 Km apart and it take 12 minutes to hike overthere.

1. the 2 Blasts by the Party-In-Distress will act as refinements to the Direction-of-the-Hike.

Question : how often should the Rescue Party send One-Blast requests during the 12 minutes.

   By Jackwabbit (Jackwabbit) on Tuesday, December 06, 2011 - 5:41 pm:  Edit Posted From: 116.49.115.40

我用Storm Whistle, 吾夠氣都可以吹到耳聾.
這個論題幾乎兩歲大了.如果讀者有些混淆, 可以返回「山中求救訊號」 的第一個post:
Archive through 2010/3/15 --> December 12, 2009, 吹3次或吹6次的討論 :-))

   By MKSJ on Monday, December 05, 2011 - 10:27 pm:  Edit Posted From: 219.73.56.35

Bought a Fox 40 pealess whistle yesterday. ( made in Canada )

Instructions on back of package reads :

INTERNATIONAL WHISTLE CODE
One blast : "Where are you?"
Two blasts : "Come to me."
Three blasts : "I need help!"

If you hear any of these signals, respond with one blast. Each blast should last 3 seconds.

   By Jackwabbit (Jackwabbit) on Wednesday, November 30, 2011 - 11:08 am:  Edit Posted From: 116.48.109.203

香港通訊業聯會「50222遠足留蹤服務」
http://www.the-sun.on.cc/cnt/news/20111130/00407_088.html

   By Jackwabbit (Jackwabbit) on Wednesday, November 09, 2011 - 4:33 pm:  Edit Posted From: 116.48.119.29

請讀者不要誤會,雖然我認為對野外急救有興趣的香港醫生的醫學知識和技術水準好高,
但我認為他們對野外 soft skills 的經驗始終是一個未知之數。
附上是Dr. Paul S. Auerbach 寫的blogs,主題是有關其它兩個醫生對野外風險觀
點和求生心態的分析。

The Concept of Risk:
http://www.healthline.com/health-blogs/outdoor-medicine/concept-of-risk

Concepts of Emotion and Survival:
http://www.healthline.com/health-blogs/outdoor-medicine/emotion-and-survival

心水清的朋友已經留意到下列"Wilderness Communication" 的作者是一個護士和高
級救護員... 其實我的 subtext 是香港的野外急救 / 醫學是否可以 think and do outside the (traditional) box?

   By Jackwabbit (Jackwabbit) on Sunday, October 30, 2011 - 5:10 pm:  Edit Posted From: 116.48.49.122

"Wilderness Communication"
http://www.wemjournal.org/article/S1080-6032(11)00132-3/fulltext#sec6
http://download.journals.elsevierhealth.com/pdfs/journals/1080-6032/PIIS1080603211001323.pdf

雖然是有關美國的資料, 在香港只可以用來作為參考.
文中有提到任何電子儀器都可以壞, 所以要 "Back to Basics": 攜帶哨子, 信號鏡, 和一個可靠的生火方法. 讀者又可以留意一下作者背景不是一個專業的電子工程師而是是一個護士和高級救護員 (paramedic)...

   By Jackwabbit (Jackwabbit) on Saturday, February 12, 2011 - 11:53 am:  Edit Posted From: 218.250.105.250

大家可以留意下友隊朋友寫的文章:
http://www.doyouhike.net/group/19049/1/474543,0,0,0.html

   By Jackwabbit (Jackwabbit) on Wednesday, January 05, 2011 - 1:24 pm:  Edit Posted From: 116.48.49.7

LIGHTNING – THE BEAUTY AND THE BEAST
http://wildernessmedicinenewsletter.wordpress.com/category/survival/

From SOLO Wilderness Medicine Newsletter.

   By saikunger on Sunday, December 26, 2010 - 8:54 am:  Edit Posted From: 182.152.211.198

"My understanding here is that if you hold your hands together, this will create a circuit-conduit for electricity to pass thru. And the electric-pulses thus created might stop your heart. "

no la

雷擊電流經過身體連接大地和帶電荷的雲團 ... hold hand togehter 如和被電擊能致停心跳有關也只能說是如雷擊右肩就有一個circuit是經左手去去左肩經在左邊的心臟才落地 ... 電流過心令心停跳

但如左肩被雷擊?

also stand on one leg 這說法有點意思 ... 是和step voltage 跨步電壓有關

不在這談step voltage 了自己上網去查吧

說這麼多因為我是出泥行的也是吃電燈佬這行飯

   By MKSJ on Saturday, December 25, 2010 - 10:14 pm:  Edit Posted From: 219.78.210.153

Also at dinner was a Hiker who just finished a hiking trip around Si-On, China.

His comment on the Standing-On-One-Leg is this :

1. You should also not hold your hands together.
2. This will reduce the chance of Cardiac Arrest.
oxoxoxoxoxoxo
My understanding here is that if you hold your hands together, this will create a circuit-conduit for electricity to pass thru. And the electric-pulses thus created might stop your heart.

Any medical grounds on this / comments ?

   By MKSJ on Saturday, December 25, 2010 - 10:05 pm:  Edit Posted From: 219.78.210.153

Had dinner with a UC Berkeley Professor ( Atmospheric Science ) , back in September.

Talked about the recent Lighting-Strikes in Hong Kong, some 5,000 or more lighting-strikes within a few hours.

The general agreement here is that Atmospheric Electricity can be much stronger at times nowadays.
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Spoke with the Professor about counting to FIVE after a Lighting-Strike :

1. If you can hear the Thunder within the Count of 5, then precautionary actions, including standing on one leg, etc. should be taken immediately.

The professor said - At Least 10 .
oxoxoxoxoxoxox
I take this to mean that Atmsopheric Electricity can be stonger nowadays and you still have a chance of getting struck by lighting even farther away , Count-Of-Ten instead of Count-Of-Five.

Any comments/ info from Jackwabbit is much appreciated.

   By Jackwabbit (Jackwabbit) on Monday, November 01, 2010 - 2:57 pm:  Edit Posted From: 116.48.108.134

先前在這裡講過:
"STOP KISS"的領導策略 : Saturday, April 03, 2010
求救書和撤退流程: Saturday, August 21, 2010
現在結合一下"STOP KISS" 和「求生重點的次序」:

yourpic.jpg

請多多指教.

   By 盲拳小子 on Friday, October 01, 2010 - 1:30 pm:  Edit Posted From: 202.126.218.6

之前的 message at 2010-9-02 at 2:27 p.m. 有個錯誤 on the Optics Refraction Formula , 現更正 :

The Optics Refraction Formula :
[ Sine of the Angle of Refraction ] = [ Refractive Index between the 2 media ] x [ Sine of the Angle of Incidence ]

Correction now made .
oxoxoxoxoxoxo
沒有 touch Optics 好幾十年 D o野記得唔清楚 大部份已交番晒比老師 真是不該
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所以 [ 老人家 ] 網友曾說過 世事難料。

其實 盲拳小子的師承都算幾靚 :
1. Mathematics 方面 有 Dr. Eugenio Calabi , 教過 Calculus I , Calculus II 和 Number Theory .
2. Physics 方面 有 Dr. Fay Ajzenberg-Selove , 教過 Optics / Uncertainty Principle 等等
3. Physics 方面 有Dr. Bob Schrieffer , 教過 Quantum Mechanics / etc. .

Dr. Calabi 是 Calabi-Yau Manifold 的原創者 相信物理/數學界的網友都會對此有點印象
Dr. Ajzenberg-Selove 是 2007 National Medal of Science 的 Laureate .
Dr. Robert ( Bob ) L. Schrieffer 是 1971 Nobel Prize Laureate in Physics.

為什麼會有個緣份和幾位世界級 ( world-class ) 的教授交往 真是考起 想了很久也想不通。

   By 隨風 on Friday, September 10, 2010 - 5:36 pm:  Edit Posted From: 116.49.109.63

So much for the Cell Phone abuse:

"Cell phones can save a life in Olympic National Park wilderness -- but please don't call for a copter ride"
http://www.peninsuladailynews.com/article/20100905/news/309059993/cell-phones-can-save-a-life-in-olympic-national-park-wilderness

   By Nite Hiker on Tuesday, September 07, 2010 - 9:50 pm:  Edit Posted From: 180.219.4.205

Anyone had use this GPS program:

http://www.it18.com/index.html

   By 盲拳小子 on Thursday, September 02, 2010 - 2:45 pm:  Edit Posted From: 202.82.82.238

Tracking via Hourly Intervals 是用當日的 [ 日中天 ] Sun’s Transit ( ST ) 的時刻為依歸 , 即用 :
>> Sun’s Transit Time ,
>> Sun’s Transit Time + / - one hour ,
>> Sun’s Transit Time + / - two hours ,
>> Sun’s Transit Time + / - three hours ,
>> etc.

   By 盲拳小子 on Thursday, September 02, 2010 - 2:35 pm:  Edit Posted From: 202.82.82.238

現 upload [ 春分 ] 的圖 :
mkssunve.jpg

   By 盲拳小子 on Thursday, September 02, 2010 - 2:33 pm:  Edit Posted From: 202.126.218.6

現 upload [ 夏至 ] 的圖 :
mkssunss.jpg

   By 盲拳小子 on Thursday, September 02, 2010 - 2:31 pm:  Edit Posted From: 202.126.218.6

現 upload [ 秋分 ] 的圖 :
mkssunae.jpg

   By 盲拳小子 on Thursday, September 02, 2010 - 2:29 pm:  Edit Posted From: 202.126.218.6

現 upload [ 冬至 ] 的圖 :
mkssunws.jpg

   By 盲拳小子 on Thursday, September 02, 2010 - 2:27 pm:  Edit Posted From: 202.82.82.238

圖已畫好 但 盲拳小子 的 Data Set 和 天文台 的數據有少少 discrepancies , 也有需要談一談三個項目 , so that we all know what the differences are .
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項目一 日出的時刻

在地面用肉眼去看太陽 會見到一個 Sun Disk ( 太陽餅 ) , 而不是一個小圓點 因為太陽的體積大

先計算出 [ Center of Sun Disk ] 和 [ Edge of Sun Disk ] 的 Sustained Angle to the naked eye , 用 :
1. Sun’s Radius 是 1,392,000 Km ;
2. Earth-Sun Distance 是 149, 597,887.5 Km ( 中位數 ) .
用 arctangent 算出 [ Sustained Angle ] 為 [ 0.5331 degrees ] .

估計天文台會用 { First Ray of Sun-Light } 為日出的時刻 , 即在 [ 水平線 ] 看到 [ 第一線陽光 ] 的時刻 :
1. 這 [ 第一線陽光 ] 是由 Sun Disk 的 Top Edge 射出 ,
2. Center of Sun Disk 在這一刻仍是在水平線以下約 [ 0.5331 degrees ] 位置

盲拳小子 會用 { 旭日初升 } 為日出的時刻 , 即在 [ 水平線以上 ] 看到 [ 半個太陽 ] 的時刻 :
1. 這時 Center of Sun Disk 會剛剛在 [ 水平線 ] 位置

For 2010-6-21 夏至 , { First Ray of Sun-Light } 和 { 旭日初升 } 的差距時間估計約為 4分鐘 .
This is unlikely to make a difference significant enough for our purpose-at-hand .

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項目二 陽光的方向 is assumed parallel

This done for calculation convenience and is an approximation .

For analysis purposes , 先 identify 兩組 Sun Ray :
>> 第一組 Sun Ray 由 [ Center of Sun Disk ] 射向 [ Center of Earth ]
>> 第二組 Sun Ray 由 [ Center of Sun Disk ] 射向 [ North Pole of Earth ]

兩組的方向 ( direction of propagation ) 有 slight difference , 用 :
1. Radius of Earth ( Polar-to-Pole Direction ) 是 6356.8 Km ;
2. [ Center of Sun Disk ] 至 [ Center of Earth ] 的 Distance 是 148,205,887.5 Km .
( 即 [ Earth-Sun Distance ) 減 [ Radius of Sun ] )
用 arctangent 算出 [ Differential Angle ] between the directions of 兩組 Sun Rays 為 [ 0.0025 degrees ] .

The difference here is very small and we can assume that [ all Sun-Rays approaching Earth ] are parallel in direction , for our purpose-at-hand .
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項目三 日光的折射 ( Refraction of Sun Rays thru the Atmosphere )

陽光的折射 基本上會用到 Physics 裡 Refraction formula for OPTICS :
>> [ Angle of Refraction ] = [ Refraction Index for the 2 media ] x [ Angle of Incidence ]

以 2010-12-21 [ 冬至 ] 為例 太陽在 [日中天 ] 時刻的 [ 仰角 ] should be based on :
1. TILT of the Earth’s Rotation Axis at [ 23.5 degrees ] , full effect on this day ;
2. The Latitude of Hong Kong being [ 22.3 degrees North ] .

[ 45.8 degrees ] = [ 23.5 degrees ] + [ 22.3 degrees ]
初部估計當日 [ 日中天 ] 的仰角 Azimuth 為 [ 44.2 degrees ] ( = 90.0 degrees minus 45.8 degrees )

而 Hong Kong Observatory Almanac 2010 的數值為 [ 44 degrees ] .
It would seem that the [ Refraction thru the Atmosphere ] effect for this specific time is less than [ 1.0 degree ] .

在 盲拳小子 的圖裡 , [ Sun Ray Refraction ] effects are ignored , but we should all keep-in-mind that the error here may be a few [ degrees ] , both in the Azimuth (仰角 ) and Direction (方向 ) of the Sun Ray .

   By 盲拳小子 on Tuesday, August 31, 2010 - 9:53 pm:  Edit Posted From: 202.126.218.6

之後的 [ 太陽位置圖 ] 會以這圖為依歸
mkstrial.jpg

Any comments at this point is kindly appreciated .

   By 盲拳小子 on Tuesday, August 31, 2010 - 9:02 pm:  Edit Posted From: 202.82.82.238

之前的 message 2010-8-31 at 8:46 p.m. 又有失誤
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THIS IS WRONG ( 錯誤 ) :
i.e. : [ Direction of Earth’s Rotation Axis ] is given by :
minus [ cos 23.5 degrees ] x [ U-Direction Unit-Vector ]
plus [ sin 23.5 degrees ] x [ Z-Direction Unit-Vector ]
oxoxoxoxoxoxo
THIS IS RIGHT (正確 ) :
i.e. : [ Direction of Earth’s Rotation Axis ] is given by :
minus [ sin 23.5 degrees ] x [ U-Direction Unit-Vector ]
plus [ cos 23.5 degrees ] x [ Z-Direction Unit-Vector ]
xxxxxxxxx
一時手快 sine 和 cosine 掉轉o左 , Sorry !

   By 盲拳小子 on Tuesday, August 31, 2010 - 8:51 pm:  Edit Posted From: 202.126.218.6

Summarizing , 2 questions here :
1. 日中天的時刻 可否用中位數 12:23 hrs . ?
2. 若用 12:23 hrs. , plus-or-minus variation 約是 15 minutes , 太陽的位置會有多大轉變 ?

   By 盲拳小子 on Tuesday, August 31, 2010 - 8:46 pm:  Edit Posted From: 202.82.82.238

這裡 也談一談 FACTOR THREE -- TILT OF THE EARTH’s ROTATION AXIS
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mkstilti.jpg
基本上 , Earth’s Rotation around the Sun :
1. 用上圖的 [ X-Axis ] 和 [ Y-Axis ] 為依歸 ,
2. 更 set up [ Z-Axis ] perpendicular to the [ X-Y Plane ] . ( coming-out-of-the-page , so-to speak ) .

在 Tilt of the Earth’s Rotation Axis 方面 ,
1. 用上圖的 [ U-Axis ] 和 [ V-Axis ] 為依歸 ,
2. 而 [ Z-Axis ] is also perpendicular to the [ U-V Plane ] .

i.e. : [ Direction of Earth’s Rotation Axis ] is given by :
minus [ cos 23.5 degrees ] x [ U-Direction Unit-Vector ]
plus [ sin 23.5 degrees ] x [ Z-Direction Unit-Vector ]

And that is to say : [ the Earth’s Rotation Axis ] is tilted via an angle of 23.5 degrees in the [ U-Z Plane ] .

因為 [ U-V Axis ] 和 [ X-Y Axis ] 兩組並不吻合 所以會有更多 variation in 日中天的時刻
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其實盲拳小子 does not fully understand all the issues here . More time is needed .

但 Hong Kong Observatory Almanac 的 Page 34 有提及 可以作參考

   By 盲拳小子 on Tuesday, August 31, 2010 - 8:42 pm:  Edit Posted From: 202.82.82.238

圖有失誤 這圖才對:
mkstrant.jpg

   By 盲拳小子 on Tuesday, August 31, 2010 - 8:38 pm:  Edit Posted From: 202.126.218.6

這裡 也談一談 FACTOR TWO -- EARTH’s ORIBT AROUND THE SUN
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首先 要談一談怎樣計算出 [ 日中天 至 日中天 的 Elapsed Time ] , i.e. : time elapsed in-between consecutive Sun's Transits .

基本上 地球的自轉速度很穩定 是 :
>> 每 23小時 56分 4.100秒旋轉 360 degrees .
>> This works out to [ 15.0411 degrees per hour ] .
xxxxxxxx
mkstrans.jpg
假設某一天的 [日中天 ] , EARTH 在軌道中的位置是圖中的 [ Position A ] :
1. 23小時 56分 4.100秒 之後 EARTH 已自轉了 360 degrees , 並已在軌道上移動至 [ Position B ] .
2. 但 [ Position B ] 並非 [ 日中天 ] , 要繼續 [ 移動 ] 和 [ 自轉 ] 多些少到 [ Position C ] 才是 [日中天 ] 位置

Basically , [ 日中天 至 日中天 的 Elapsed Time ] 的長短 是視乎於 [ 地球環繞著太陽運行的速度 ] .
i.e . [ Time-Elapsed in-between consecutive Sun’s Transits ] is dependent on the [ angle-sweeping velocity of the Earth in its orbit around the Sun ] .
oxoxoxoxoxoxo
於是 用 Kepler’s Laws 計算出 :
1. [ 日中天 至 日中天 的 Elapsed Time ] at Perihelion ( Jan 3 近位 ) 是 24小時 0分 8.0751呀秒
2. [ 日中天 至 日中天 的 Elapsed Time ] at Aphelion ( Jul 4 遠位 ) 是 23小時 59分 52.2574秒

i.e. plus or minus roughly 8 second from the mean [ 24-hours-day ] .

由於 difference 是 cumulative , [ 日中天的時刻 ] 會在中位數兩邊 fluctuate .

   By 盲拳小子 on Tuesday, August 31, 2010 - 8:34 pm:  Edit Posted From: 202.82.82.238

這裡 先談一談 FACTOR ONE -- STANDARDIZED TIME ZONES

基本上 Longitude / Meridian 的 [ 零度位置 ( Zero degrees Position ) ] 是在 London , i.e. :
>> the [ Zero Degrees Longitude / Meridian ] passes thru the Greenwich Observatory in London .

而 Standardized Time Zone :
1. 是將 [ 360 degrees ] 分為 24個 Time Zone 即每個 Time Zone covers an Longitudinal Area of 15 degrees .
2. 香港所屬的 Time Zone 是由 [ 112.5 degrees East ] 至 [ 127.5 degrees East ] 這一個 Time Zone .
3. 這一個 Time Zone 的中位位置是 [ 120.0 degrees East ] .
oxoxoxoxoxoxo
基本上 太陽的 [ 直射位置 ] 會向西移動 [ 15 degrees Longitude-wise ] per hour , 即 7.5 degrees every half-an-hour .

假設在某一天的 [ 12:00 hrs. Hong Kong Time ] , 太陽的 [ 直射位置 ] 是在 [ 120.0 degrees East ] 這一條 子午線 ( meridian ) /經線 ( longitude ) ; 粗略地估計 :
>> [ 12: 10 hrs. Hong Kong Time ] 太陽的 [ 直射位置 ] 會是在 [ 117.5 degrees East ] 這一條 子午線 ( meridian ) /經線 ( longitude ) 之上
>> [ 12: 20 hrs. Hong Kong Time ] 太陽的 [ 直射位置 ] 會是在 [ 115.0 degrees East ] 這一條 子午線 ( meridian ) /經線 ( longitude ) 之上
>> [ 12:30 hrs. Hong Kong Time ] 太陽的 [ 直射位置 ] 會是在 [ 112.5 degrees East ] 這一條子午線 ( meridian ) /經線 ( longitude ) 之上

香港的 Longitude 通常用 114.16 degrees East , 因此估計 :
1. 香港的 [ 日中天 ] 時刻 會是在 [ 120.00 degrees East ] 的 [ 日中天 ] 時刻之後 [ 23分20秒 ] 的時刻

在這方面 Hong Kong Observatory Almanac 2009 / 2010 的 Page 34 也有較詳盡的解釋
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由於 [ 120 degrees East ] 是這一個 Time Zone 的中間位置 平均 [日中天 ] 時刻會是 [ 12:00:00 hrs. Hong Kong Time ] ( Standardized Time Zone ) :
1. 可以考慮用 [ 12時23分20秒 ] 為香港的 [ 日中天 ] 時刻的 [ 中位數 ]

   By 盲拳小子 on Tuesday, August 31, 2010 - 8:29 pm:  Edit Posted From: 202.82.82.238

An issue that needs to be looked at , first , is that :
>> the [ Sun’s Transit Time ] does vary from-day-to-day .
即 : [ 日中天 ] 的時刻每天都會有變動
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先列出數據 for the YEAR 2010 : ( based on the Hong Kong Observatory Almanac )
1. Feb 9 至 Feb 14 -- 日中天 ( Sun’s Transit ) 的時刻是 12: 38 hrs.
2. Oct 25 至 Nov 12 -- 日中天 ( Sun’s Transit ) 的時刻是 12: 07 hrs.
3. 其餘日子 -- 日中天 ( Sun’s Transit ) 的時刻是在 12:07 hrs. 和 12: 38 hrs. 時段間的某一個時刻

Variation Gap 約為 31分鐘 ( 12:38 hrs minus 12:07 hrs. = 31 minutes )

And this arises from 3 Factors : ( to be discussed , next )
FACTOR ONE -- STANDRADIZED TIME ZONES
FACTOR TWO -- EARTH’s ELLIPTIC ORBIT AROUND THE SUN
FACTOR THREE -- TILT OF THE EARTH’S ROTATION AXIS

   By 盲拳小子 on Tuesday, August 31, 2010 - 8:25 pm:  Edit Posted From: 202.82.82.238

這裡 先列出之後會用到的數據 , for reference .

SUN :
>> Diameter of Sun 約是 1,390,000 Km .

EARTH :
>> Equatorial Radius 約是 6,378.1 Km .
>> Polar Radius 約是 6,356.8 Km .
>> Mean Radius 約是 6,371.0 Km .

EARTH’s elliptic orbit around the Sun ( 地球的軌道是隨圓形的 ) :
>> Perihelion -- Sun-Earth 的距離約是 147,098,074 Km .
( Perihelion -- Earth 最接近太陽的時刻 , around Jan 3 )

>> Aphelion -- Sun-Earth 的距離約是 154,097,701 Km .
( Aphelion -- Earth 最遠離太陽的時刻 , around July 4 )

>> Eccentricity of Ellipse = 0.001671123
>> Period -- 365.256363 Solar Days ( 1 Solar Day = 24.00 hours )
>> Average Speed -- 29.78 Km/s .
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The primary purpose here is for error-tracking purposes :
1. If an error / mistake is found at a later stage , we need to find out whether it arose from the discrepancies in the Base Data presented here or otherwise from an improper / crude calculation method / procedure that may need further refinement .

   By 盲拳小子 on Tuesday, August 31, 2010 - 6:12 pm:  Edit Posted From: 202.126.218.6

Correction on last message :
中間一段應是 :

因此 在 [ 春分 ] 至 [ 秋分 ] 這一段時間 , for Beijing :
1. 日出在 [ 東至東北方 ] ,
2. 日中天在 [ 南方 ] ,
3. 日落在 [ 西至西北方 ] .

Error now corrected .

   By 盲拳小子 on Tuesday, August 31, 2010 - 5:57 pm:  Edit Posted From: 202.126.218.6

Replying Mailliw’s message on 2010-8-31 at 3:29 p.m. :

以中國曆法和 Astrophysics 計算 [ 日出在正東 ] 和 [ 日落在正西 ] 都只會在 [ 春分 ] 和 [ 秋分 ] 這兩天出現
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北京的 Latitude 約是 39.9 degrees North :
1. [ 春分 ] 至 [夏至 ] 這一段時間 日出的方向會由 [ 正東 ] 移動位置至 近乎[東北方向 ]
2. [ 夏至 ] 至 [ 秋分] 這一段時間 日出的方向會由 近乎[ 東北方向 ] 移動位置至 [正東 ]
3. [ 春分 ] 至 [夏至 ] 這一段時間 日落的方向會由 [正西 ] 移動位置至 近乎[ 西北方向 ]
4. [ 夏至 ] 至 [ 秋分] 這一段時間 日落的方向會由 近乎[ 西北方向 ] 移動位置至 [正西 ]

因此 在 [ 春分 ] 至 [ 秋分 ] 這一段時間 , for Beijing :
1. 日出在 [ 東至東北方 ] ,
2. 日中天在 [ 南方 ] ,
3. 日落在 [ 西北方 ] .
所以 :
4. 上午的某一時約刻 太陽在 [ 正東 ] ,
5. 下午的某一時約刻 太陽在 [ 正西 ] .

The point here being that [ 用太陽位置來定東南西北四個方向 ] 在 Temperate Zone 可以考慮 , but more details are needed .
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But at the current moment , we shall concentrate on Hong Kong first , as this is more useful locally here .

   By mailliw on Tuesday, August 31, 2010 - 3:36 pm:  Edit Posted From: 219.76.248.199

盲拳小子說:「也估計在夏至 June 22 這天 香港會出現這樣的情況 : 3. 正午時分 太陽在北方 ( shining directly onto the Tropic Of Cancer at 23.5 degrees North ) 」

精細地說來:在頭頂向北移1.5度。
在一般日常情下,是否算是「正午時分 太陽在北方」?或是,更像似在頭頂?

   By mailliw on Tuesday, August 31, 2010 - 3:29 pm:  Edit Posted From: 219.76.248.199

以下資料可能出錯,是嗎?

在北京 一年 365 / 366天都會出現這樣的情況 :
1. 日出時分 太陽在正東方 or thereabouts 升起
2. 日落時分 太陽在正西方 or thereabouts 落山

   By 盲拳小子 on Friday, August 27, 2010 - 2:16 pm:  Edit Posted From: 202.82.82.238

[ 愚見 ] 網友 -- 現階段無需要花太多時間去 digest the information , 因為稍後會有個較詳盡的分析和 presentation :
1. 會有 2010 春分/夏至/秋分/冬至 這四天的 [ 太陽方向圖 ] , on an hourly basis or thereabouts.

圖會用 [ 2-D 東南西北 ] 和 [ 3-D Isometric View ] 為 presentation 的基礎
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但要先談一談 [ 日中天 ] 的時刻的問題 , next , 為再來的一系列圖作準備 .

   By 隨風 on Thursday, August 26, 2010 - 2:31 pm:  Edit Posted From: 112.118.39.40

One can use the shadow of a vertical instead of looking directly into the sun.

This way, even at noon, the shadow points to the opposite direction for the most part of the year. Only at time when the sun is directly overhead, then the shadow is useless. See the post by "盲拳小子":

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TOPIC THREE ---Sun is directly above Hong Kong at Noon 太陽在香港的 [ 頭殼頂 ]

For the YEAR 2009 , the 2 ( nearest ) days are :
>> June 3 at 12: 21 hrs.
>> July 9 at 12: 29 hrs.

For the YEAR 2010 , the 2 ( nearest ) days are :
>> June 3 at 12: 21 hrs.
>> July 10 at 12: 29 hrs.

Hence, for days around June 3rd and July 10th each year, the shadow is difficult to see, or even no shadow at all!

   By paaserby on Thursday, August 26, 2010 - 11:05 am:  Edit Posted From: 158.132.243.10

如果沒有儀器輔助,加上長時間觀測,
基本上太陽位於正午時份,是極其難於靠目測法評估東南西北的.
但當太陽越接水平線時,越易於用之評估方向.

   By 愚見 on Wednesday, August 25, 2010 - 8:23 pm:  Edit Posted From: 112.118.201.209

Very informative. Thank you, 盲拳兄.

It will certainly take me some time to digest.


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