California Nebula

In long-exposure photographs, a familiar shape takes form among the stars: that of California. It is not a map, but a cloud of gas nearly 100 light-years long, about 1,000 light-years from us, in the constellation of Perseus.

It owes its red glow to a single star: Menkib, one of the hottest stars visible to the naked eye, tens of times more massive than the Sun. Its intense radiation excites the hydrogen in the cloud and makes it glow, a little like a neon tube.

In the sky, this cloud is huge, about five times the width of the full Moon. And yet it is so faint that you can barely see it, neither with the naked eye nor even through a telescope: only long photographic exposures bring it out.

This image is a mosaic of six panels, assembled one by one from Texas. One of the largest clouds in the sky, photographed piece by piece to capture it in full.