I don’t get a chance very often to combine two previous posts, but I was thinking recently about planetary nebulae — winds of gas blown off by dying stars — and remembered my very favorite one in the whole sky, Abell 39:

[Click to ennebulenate.]

Isn’t that awesome? It’s like it’s right out of Star Trek. I’ve written about the giant haloes surrounding some planetary nebulae before, and also about why some objects look like smoke rings. In a (nut)shell, as a star like the Sun begins its long, slow path to dying, it expands into a red giant and blows off a thick wind of matter. This material expands spherically in most cases, streaming off in all directions into space and forming what’s called a giant outer halo.

In most planetaries (like the famous Cat’s Eye nebula, and the less famous but also cool NGC 6826) the outer halo slams into material floating in interstellar space, causing it to get all clumpy or form a bright rim as the surrounding matter gets plowed up. But the ...