Two Crosses

The night sky features two great crosses -- one in the northern hemisphere, and the other in the south.

The Northern Cross is another name for Cygnus, the swan, which sails high overhead on summer evenings.

It’s a noteworthy constellation for several reasons. For one thing, it hosts the bright star Deneb. This white supergiant is one of the most impressive stars in our region of the galaxy. It’s so far away that astronomers don’t know its exact distance. Yet it’s still easily visible to the eye alone, standing at the top of the cross.

And when we look at Cygnus, we’re looking down the spiral arm that contains our own solar system, so we see lots of amazing celestial objects -- bright clouds like the North American Nebula, and even black holes. In fact, Cygnus is home to the first black hole ever found, Cygnus X-1.

The southern sky also has a cross. But Crux isn’t nearly as big as Cygnus. In fact, Crux is the smallest of the 88 constellations.

No matter, though, because Crux is brilliant, boasting four prominent stars. And it also has a well-known dark feature: a cloud of light-absorbing dust known as the Coalsack Nebula, which is only a few hundred light-years away.

The Southern Cross has one fault, though: It’s so far south that most of us in the United States can’t see it. Still, the Northern Cross is quite prominent at this time of year, and it really does resemble both a cross and a swan -- a beautiful feature of the summer sky.

Script by Ken Croswell