Kenapa Langit Nampak Biru, Tapi Senja Jingga?

Pandang langit tengah hari: warnanya biru. Tunggu matahari hampir terbenam: warna yang sama boleh bertukar jingga dan merah. Matahari tidak menukar warna lampunya secara tiba-tiba. Perjalanan cahaya melalui atmosfera yang berubah apabila matahari rendah.

Cahaya matahari mengandungi pelbagai warna. Setiap warna mempunyai panjang gelombang berbeza. Molekul kecil di atmosfera, terutamanya nitrogen dan oksigen, menyerakkan cahaya biru lebih kuat berbanding merah. “Serakan” bermaksud cahaya berubah arah selepas berinteraksi dengan molekul udara.

Pada siang hari, cahaya biru yang diserakkan dari banyak arah sampai ke mata kita, lalu langit kelihatan biru. Ketika matahari dekat ufuk, cahaya terus daripadanya merentasi laluan atmosfera yang lebih panjang. Lebih banyak cahaya biru tersebar keluar daripada laluan itu, sementara lebih banyak jingga dan merah terus sampai ke mata. Debu, asap, awan dan keadaan udara boleh mengubah warna yang kita lihat.

Cuba demo di bawah: gerakkan matahari dari tengah hari ke ufuk dan perhatikan ilustrasi cahaya serta warna langit. Ia menunjukkan idea serakan secara ringkas, bukan ramalan warna langit sebenar. Jangan pandang matahari secara terus untuk menguji perubahan itu; lihat langit di sekelilingnya sahaja.

Jadi langit biru dan senja merah ialah dua hasil daripada cahaya yang sama, tetapi melalui laluan yang berbeza di atmosfera.

Look at the sky at midday: it is blue. Wait until the Sun is near the horizon: that same sky may turn orange and red. The Sun does not suddenly change the color of its lamp. What changes is the path sunlight takes through the atmosphere when the Sun is low.

Sunlight contains many colors, each with a different wavelength. Small molecules in the atmosphere, especially nitrogen and oxygen, scatter blue light more strongly than red light. “Scattering” means light changes direction after interacting with air molecules.

During the day, blue light scattered from many directions reaches our eyes, so the sky looks blue. When the Sun is near the horizon, its direct light travels through a longer path in the atmosphere. More blue light is scattered out of that path while more orange and red light continues toward our eyes. Dust, smoke, clouds, and air conditions can change the colors we see.

Try the demo below: move the Sun from midday toward the horizon and watch the illustrated light and sky color change. It shows the idea of scattering; it is not a forecast of the real sky. Do not look directly at the Sun to test this—look at the surrounding sky instead.

The blue daytime sky and a red sunset are two results of the same sunlight taking different paths through the atmosphere.