Astronomy Picture of the Day

Explanation: Welcome to millennium three. During millennium two, humanity continually redefined its concept of "Universe": first as spheres centred on the Earth, in mid-millennium as the Solar System, a few centuries ago as the Galaxy, and within the last century as the matter emanating from the Big Bang. During millennium three humanity may hope to discover alien life, to understand the geometry and composition of our present concept of Universe, and even to travel through this Universe. Whatever our accomplishments, humanity will surely find adventure and discovery in the space above and beyond, and possibly define the surrounding Universe in ways and colours we cannot yet imagine by the threshold of millennium four.