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WonderScience fact

The Sun is white. Its light mixes all the colours of the rainbow, and seen from space, or high in a clear sky, it shines white. It looks yellow, orange or red only when it is low, because its light then crosses more air, which scatters away part of the blue.

Astronomy

Science

The story behind the card

Sunlight contains every visible wavelength in fairly balanced amounts, which our eyes read as white; its output actually peaks in the green part of the spectrum. Air molecules scatter short, blue wavelengths far more than red ones, an effect named after the physicist Lord Rayleigh. That scattered blue light is what makes the sky blue. Astronomers do class the Sun as a G-type star, loosely called a 'yellow dwarf', but the label reflects its surface temperature of about 5,500 °C, not the colour we see. Cultures picture it differently too: the Sun on Japan's flag is red.

Türkçe oku
Güneş aslında beyazdır. Işığı gökkuşağının bütün renklerini bir arada taşır; uzaydan bakıldığında ya da açık havada gökyüzünün yükseklerindeyken beyaz görünür. Sarı, turuncu ya da kırmızı görünmesi ancak alçaldığında olur: Işığı o zaman daha kalın bir hava tabakasından geçer ve hava mavinin bir kısmını saçar.

Güneş ışığı görünür tayfın bütün dalga boylarını birbirine yakın oranlarda içerir, gözümüz de bu karışımı beyaz algılar; ışığın en yoğun olduğu bölge aslında tayfın yeşil kısmıdır. Havadaki moleküller kısa dalga boylu mavi ışığı kırmızıdan çok daha fazla saçar. Fizikçi Lord Rayleigh'in adıyla anılan bu olguya Rayleigh saçılması denir; gökyüzünü mavi gösteren de saçılan bu ışıktır. Gökbilimciler Güneş'i G tipi bir yıldız olarak sınıflandırır ve bu tür yıldızlara halk arasında “sarı cüce” de denir. Ama bu sınıf, gördüğümüz rengi değil, yaklaşık 5.500 °C'lik yüzey sıcaklığını anlatır. Güneş'in rengi kültürden kültüre de değişir: Japonya bayrağındaki Güneş kırmızıdır.

Sources and further reading

Background reading: Sunlight
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George Orwell used the phrase “cold war” in 1945, and the American journalist Walter Lippmann made it popular in 1947. Because nuclear weapons made open war between the superpowers too dangerous, the rivalry spread into other arenas. After the Soviet Union launched the Sputnik satellite in 1957, the United States passed the National Defense Education Act of 1958 to fund science, maths and language teaching. In 1959, at an American exhibition in Moscow, Vice-President Richard Nixon and the Soviet leader Nikita Khrushchev argued about capitalism and communism in a model kitchen, an exchange remembered as the Kitchen Debate. In 1972 in Reykjavík, the American Bobby Fischer beat the Soviet champion Boris Spassky for the world chess title. The Olympics were boycotted in turn: the United States and many allies stayed away from Moscow in 1980, and most of the Soviet bloc from Los Angeles in 1984.

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