(25.0K)
| On a clear, moonless night, far from city lights, you can see a pale band of
light spangled with stars stretching across the sky (fig. 15.1). The ancient
Hindus thought this shimmering river of light in the heavens was the source
of the sacred river Ganges. To the ancient Greeks, this dim celestial glow looked
like milk spilt across the night sky, and so they called it the Milky Way. In
the seventeenth century, Galileo showed that the Milky Way is millions of stars
too dim to be seen as individual points of light. Now, in the twenty-first century,
we know that these stars, along with our Sun, form a huge, slowly revolving
disk--our galaxy. The word galaxy itself comes from the ancient Greeks and their
word for "milk"galactos. Thus, "Milky Way" is both the
name of the band of light across the night sky and the name of our galaxy. A view of the Milky Way on a clear, dark night is one of nature's finest
spectacles. Superposed on the dim background glow are most of the bright stars
and star clusters that we can see, which all belong to our galaxy. Here and
there, however, dark blotches interrupt the glowing backdrop of stars, as you
can see in figure 15.2. Ancient Incan astronomers observing the Milky Way from
their temple observatories in the Andes gave these dark areas names, just as
peoples of the classical world named the star groups. Today, we know the dark
regions are clouds of dust and gas that give birth to new stars, as we discussed
in chapter 13. |