وفّر 50٪ من خلال الاشتراك السنوي في مجرة واحصل على تصفح لا محدود لأفضل محتوى عربي على الإنترنت.
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أشعة كهرومغناطيسية لا ترى بالعين المجردة تنبعث من الشمس بشكل طبيعي ومن بعض المصادر الاصطناعية الأخرى. تشغل الأشعة فوق البنفسجية جزءاً من الطيف الكهرومغناطيسي، وتتراوح أطوال موجاتها من 10 حتى 380 نانومتر؛ أي أقصر (ذات تردد أعلى) من الضوء المرئي وأطول من الأشعة السينية. ونظراً لطاقتها العالية فهي قادرة على كسر الروابط الكيميائية وتخريب الأنسجة الحية عند التعرض لها لفترات طويلة. وقد اكتُشفت على يد العالم الألماني يوهان فيلهلم ريتر عام 1801.
تمتص العديد من المواد الأشعة فوق البنفسجية مثل المعادن والنباتات والفطور والميكروبات والأحياء الدقيقة والمركبات الكيميائية غير العضوية. وبسبب هذا الامتصاص تنتقل الإلكترونات في المادة إلى مستوى طاقة أعلى، ثم تعود إلى مستوى طاقة أخفض في سلسلة من القفزات الصغيرة فتشع جزءاً من الطاقة التي امتصتها على شكل ضوء مرئي. ولذلك تدخل هذه المواد في صناعة الأصبغة المستخدمة في الإشارات الطرقية وسترات الأمان وغيرها للاستفادة من خاصية الإشعاع.
هناك العديد من المصادر الفضائية للأشعة فوق البنفسجية لذلك يتم الاستفادة منها في علم الفلك أيضاً؛ حيث تزود التلسكوبات الفضائية مثل تلسكوب هابل بأجهزة رصد علمية مخصصة لكشف هذه الأشعة. وعلى الرغم من أن التعرض لها لفترات طويلة قد يؤدي للإصابة بسرطان الجلد، إلا أنها تستخدم لعلاج بعض الأمراض الجلدية.
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