The Universe is a big place... and it's getting bigger every day.
The Universe originated approximately 13.7 billion years ago as a hot, nearly uniform gas, and has been expanding ever since. It was always assumed that expansion was slowing, with the tug of gravity applying the brakes. But shortly before the end of the 20th century astronomers got a big surprise: the Universe was not slowing down, it was speeding up. We live in an accelerating Universe.
Very little is known about this accelerated expansion, and even less about its cause. The SuperNova Acceleration Probe, or SNAP, is designed to shed light on this mystery. SNAP will use precise measurements of exploding stars called supernovae, as well as the subtle distortion of the light from distant galaxies, to measure the expansion history of the Universe. The details of this history may reveal the origin of the cosmic acceleration. SNAP will investigate over one thousand square degrees of sky — more than 5000 times the size of the full Moon! — with a 500 megapixel camera.