The universe can fool you. Objects that look like they’re close together can be a good distance apart. And it can take a lot of time and effort to figure that out. An example is the Cocoon Nebula. It’s a glowing cloud of gas and dust in Cygnus, the swan. It’s half way up the northeastern sky at nightfall, below Deneb, the bright star that marks the swan’s tail. The nebula is part of a larger complex of gas and dust known as IC 5146. After the Cocoon, its most prominent feature is a dark nebula — a long ribbon of gas and dust. It absorbs the light of the stars behind it, so it looks black. It extends away from the Cocoon like a long tail. Over the decades, astronomers have come up with many estimates for the distance to the complex — from about 1400 to more than three thousand light-years. And they’ve assumed that the Cocoon and the dark nebula were at the same distance. But a study a couple of years ago came up with a new finding. Using a space telescope that produces highly accurate d
