The celestial unicorn isn’t much to look at. Monoceros fills a void between the bright constellations Orion, Gemini, and Canis Major and Canis Minor. Yet you need dark skies to see even a smattering of stars in that region. And none of them represents the horn of the unicorn. But there is an object that resembles a horn right about where the horn should be. It’s faint, though, so it shows up only in long-exposure photographs.
The Cone Nebula is at the edge of NGC 2264, a complex of young stars and giant, billowing clouds of gas and dust. Ultraviolet energy from the young stars sets the hydrogen gas in the clouds aglow. That makes much of the region shine reddish pink.
But the complex also includes clouds of colder gas and dust. Those clouds form dark streamers and blobs against the colorful background. The Cone Nebula is the most prominent, with its narrow end pointing toward the center of NGC 2264.
The nebula spans about seven light-years. That’s almost twice the distance from the Sun to its closest neighbor stars.
A hot, bright young star close to the Cone is ripping away material from its top. Yet the gas and dust deep inside the cone may remain dense and cold enough to give birth to new stars. If it does, then one day the energy from these stars will erode the cone from the inside — stripping away the unicorn’s faint “horn.”
We’ll talk about another nebula in the unicorn tomorrow.