مشاهدة : 1041
لأول مرة منذ 360 عاما.. تطابق الشمالين الحقيقي والمغناطيسي
بالنسبة لأي شخص يقف على "خط الطول الأول" في المرصد الملكي في غرينيتش، جنوبي العاصمة البريطانية لندن، يحمل بوصلة سيعرف أن الشمال الحقيقي للأرض لا يتوافق مع الشمال المغناطيسي لها.
فالشمال المغناطيسي في حالة تغير دائم، وذلك بسبب الغلاف المغناطيسي المتجول للأرض، أما الشمال الحقيقي فهو النهاية الشمالية القصوى لمحور الأرض.
ولهذا السبب لم يحدث أن تطابق كل من الشمال الحقيقي والشمال المغناطيسي منذ قرون، لكن هذا الحال سيختلف الشهر المقبل، إذ ولأول مرة منذ 360 عاما، سيحدث تطابق واصطفاف للشمالين الحقيقي والمغناطيسي.
وهذا التطابق والاصطفاف بالنسبة إلى المستكشفين التقليديين في لندن والمناطق المحيطة بها، يعني أنه لن تكون هناك حاجة إلى إجراء تعديلات على قراءات البوصلة للتمييز بين الشمال الحقيقي والشمال المغناطيسي المتأرجح إلى الشرق دائما.
ويعد هذا الأمر حدث نادر للغاية، فهو لم يحدث من قبل أن يتم بناء مرصد غرينيتش في العام 1676، بحسب ما ذكرت صحيفة "تليغراف" البريطانية.
وفي الواقع، عندما تم تحديد "خط الطول الأول" (برايم ميريديان) عام 1884، كان يشير إلى خط وهمي بين القطبين الشمالي والجنوبي، وكان الشمال المغناطيسي آنذاك يميل بحوالي 25 درجة إلى الغرب، وهو واحد من أكبر التناقضات بين الشمالين في مئات السنين.
ومن المعروف أن الزاوية التي تصنعها إبرة البوصلة بين الشمال الحقيقي والشمال المغناطيسي تسمى "الانحراف"، وعلى مدى مئات السنوات القليلة الماضية كان الانحراف في بريطانيا سالبا، مما يعني أن جميع إبر البوصلة كانت تشير إلى الغرب من الشمال الحقيقي.
ويقول الخبراء إن خط الانحراف الصفري، الذي يطلق عليه اسم "خط اللا انحراف"، يتحرك غربا بمعدل حوالي 20 كيلومترا سنويا.
وقال عالم المغنطيسية الأرضية في هيئة المسح الجيولوجي البريطانية سياران بيجان "في وقت ما من شهر سبتمبر، سيتطابق خط اللاانحراف مع خط الطول في غرينتش.. وهذه هي المرة الأولى منذ إنشاء المرصد التي تتزامن وتتوافق فيها أنظمة الإحداثيات الجغرافية مع الجغرافية المغناطيسية في هذا الموقع".
وأضاف بيجان أن هذه الظاهرة "ستستمر في بريطانيا على مدار 15 إلى 20 عاما، بحلول عام 2040، ثم من المحتمل أن تبدأ بالانحراف شرقي الشمال الحقيقي".
ومع ذلك، فإن اجتماع الشمال المغناطيسي والشمال الحقيقي وتطابقهما لن يكون له أي تأثير على الحياة اليومية.
يشار إلى أن خط غرينيتش مقياس زمني يعتمد على دوران الأرض حول نفسها في يوم واحد بالاعتماد على خط الطول الذي يمر بالمعهد الملكي الفلكي البريطاني في بلدة غرينيتش في بريطانيا، والذي أعتمد نقطة مرجعية للتوقيت في العام 1883، واعتمد بوصفه الخط صفر.
أما القطب الشمالي المغناطيسي فهو نقطة على سطح الأرض تقع في نصف الأرض الشمالي ويكون عندها اتجاه الحقل المغناطيسي الأرضي عموديا باتجاه الأسفل، وتقع هذه المنطقة بالقرب من القطب الشمالي الجغرافي، وهي غير ثابتة في مكانها وتتحرك مع مرور الوقت بسبب حدوث تغيرات مغناطيسية في الغلاف الخارجي للأرض.
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