This was yesterday's
APOD, and I was interested to know what it could be. Turns out it's a map of microwave energy... the microwave energy of the universe.
No...
really!!!
Quote:
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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 strange thing about the noise was that it was coming from every direction and did not seem to vary in intensity much at all. If this static were from something on our world, like radio transmissions from a nearby airport control tower, it would only come from one direction, not everywhere. The scientists soon realized they had discovered the cosmic microwave background radiation. This radiation, which fills the entire Universe, is believed to be a clue to it's beginning, something known as the Big Bang.
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So, what this is above, is a detailed map of cosmic radiation energy, coming at us in teeny tiny amounts from all over. And using the map of this radiation, cosmologists figure they can tell that the universe is 13.7 billion years old (accurate to 1%). Also, the universe is composed of 73 percent dark energy, 23 percent cold dark matter, and 4 percent atoms. Also, the first stars ignited 200 million years after the Big Bang. And, the universe will always be expanding. (!)
How can they tell? Dunno, I don't have the full explanation.