Golden age of Astronomy

The second half of the 20th century was truly a golden age for astronomy. Rapid advances in technology made it possible to build very large optical telescopes on the ground. By the early 21st century astronomers were using about a dozen telescopes with mirrors larger than 8 m (300 in) in diameter. Because it is much cheaper to build telescopes on the ground than in space, large ground-based telescopes with their ability to gather large amounts of light (think of a telescope as a bucket for collecting light; the bigger the bucket, the more light collected) are particularly valuable for studying the faintest objects. The most distant objects tend to be very faint, but they are very important for understanding the evolution of the universe. Since light takes a long time to reach us, the universe gives us a kind of time machine so that we can see what it was like when it was much younger than it is now. For the most distant objects observed so far, it took nearly 13 billion years for their light to reach Earth, so we are seeing them as they existed 13 billion years ago.

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