科學圖說

雪山上的銀河拱橋
(Milky Way over Snow Mountain)

銀河在中國古代又稱天河、銀漢、星河、星漢、雲漢，是由無數暗星、數千億顆恆星和較暗塵埃的光所成。夏冬季所見銀河有不同的景觀，北半球的夏季能夠看到最為壯麗的銀河，但這些都不是銀河系的全貌，而僅是銀河系的一部分。銀河系總質量大約是太陽質量的6千億至3兆倍，直徑約10萬光年。自古以來，氣勢磅礡的銀河就是人們十分注意觀察和研究的物件。古人不知道銀河是什麼，把銀河想像為天上的河流。著名的神話故事牛郎織女鵲橋相會，這鵲橋就是鋪設在這天河之上。

The Milky Way appears as a haze of light comprised of countless faint stars, hundreds of billions of bright stars and gases. In summer and winter, it takes on different appearances. In summer, the
Milky Way is most majestic in the Northern Hemisphere. This is not the
whole galaxy, only a part. The Milky Way’s total mass is from about 600 billion to 3 trillion times the mass of our sun, with a diameter of 100,000 light years. Since ancient times, people have observed and studied the Milky Way. The ancient Chinese imagined it as a river flowing in the heavens. There is a tale of the Cowherd and the Weaver Girl, banished to opposite sides of the Milky Way, who meet once a year when magpies form a bridge over this “heavenly river”.