NASA's Touch the Invisible Sky Audio Podcasts NASA/Chandra X-ray Center

The galaxy pair NGC 4038 and NGC 4039 is commonly referred to as the Antennae Galaxies because their distorted streamer-like spiral arms look like insect antennae. Initially two separate spiral galaxies, gravity drew NGC 4038 and 4039 together in a titanic collision.

Imagine that you could only hear sound from the middle three keys on a piano and were asked to name a song, or were only allowed to touch one petal of a plant, and were asked to name the flower. The universe revealed to us by optical telescopes is immense and breathtaking, but it is not even half the story.

Four hundred years ago, the famous astronomer Johannes Kepler (best known as the discoverer of the laws of planetary motion), was startled by the sudden appearance of a "nova" of "new star" in the western sky, rivaling the brilliance of the nearby planets. Although the nova was new to the night sky, the event was actually the death of an old star, now called a supernova.

Galaxies are collections of millions to billions of stars gravitationally bound together. Galaxies come in different shapes and sizes, and fall into three broad categories: spiral (shaped like a pinwheel), elliptical (like a ball, sometimes round and sometimes squashed) and irregular, with no obvious shape or structure. Our own Milky Way galaxy is a spiral.

Of the estimated three hundred billion stars in our galaxy, Eta Carinae may well be the biggest and brightest of them all. Weighing in at 150 times the mass of our Sun, it is five million times as luminous!

A supernova is the dramatic end of a supergiant star's life. The Crab Nebula is the remnant of a powerful supernova which was visible from Earth in the year 1054. This supernova was so bright that it could be seen in the daytime sky for 23 days, and it was documented by astronomers throughout the Far East. The Crab Nebula is found in the constellation of Taurus and got its name because its outer shape roughly resembles a Crab's pincer.