17. Objects don't actually "have colour". Rather, our eyes see the light waves reflecting off objects around us.
18. As UV light is outside of the "visible spectrum", UV waves are invisible to the human eye. But not to lots of other mammals, insects and birds. Humans are trichromats meaning that we can only see three colour wavelengths: blue, green, red. Birds on the other hand are tetrachromats, meaning they see four wavelengths: blue, green, red, and UV. This allows them to see the world more vividly than us!
19. Gamma-ray bursts were discovered serendipitously in the late 1960's by U.S. military satellites which were on the lookout for Soviet nuclear testing in violation of international treaties. The satellites carried gamma-ray detectors since nuclear explosions produce gamma-rays. They did not find any violations of the nuclear treaty, but they did discover bright bursts of gamma rays from beyond the solar system.
20. In the 1960's a startling discovery was made quite by accident. A pair of scientists at Bell Laboratories detected background noise using a special low noise antenna. The scientists soon realized they had discovered the cosmic microwave background radiation. This radiation, which fills the entire Universe, is thought to be leftover radiation from the Big Bang, or the time when the universe began.