Like clouds floating overhead on a summer afternoon, celestial nebulae often take on shapes and names of well known earthly sights, objects, and even places.
There are, for example, the “Heart” Nebula, the “Ring” Nebula, the “Dumbbell” Nebula, the “North American” Nebula, and dozens of others.
But the California Nebula in the northern constellation Perseus is one of the most aptly-named emission nebula, bearing an uncanny resemblance to one of my favourite U.S. states. While this emission nebula is lovely in photographs, it’s quite faint and difficult to see visually. But the dark, dry skies of winter offer you a good chance to see this “stately” nebula with binoculars, and even your unaided eye.
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The California Nebula, NGC 1499 (from Palomar Observatories, Caltech).
The California Nebula, catalogued as NGC 1499, is a glowing cloud of hydrogen gas about 100 light years across. Like all emission nebulae, it’s lit up by a hot blue star, in this case, Menkib (xi Persei), one of the hottest and intrinsically brightest stars visible to the unaided eye. The nebula is close, by galactic standards… just 1,500 light years away in the Orion arm of the Milky Way, the same arm in which our sun lies. The nebula spans about 2.5 x 0.5 degrees… quite large. That means it’s better observed with binoculars than a telescope.
The glow of this cosmic cloud comes from hydrogen gas, which is pumped into a more energetic state by the blue and ultraviolet light from Menkib. When the hydrogen relaxes to a lower energy state, it emits red light at a characteristic wavelength of 656 nm. This is called “hydrogen alpha” light.
But the physical conditions inside the nebula result in strong emission of “hydrogen beta” light at 486 nm (blue-green); the same story applies to the Horsehead Nebula in Orion. That’s why keeners who want to see these two nebula often invest in a special “H-Beta” filter for their telescope. Though these filters aren’t good for much else.
You’ll find the California Nebula just north of Menkib in Perseus (see map below). It will fit into a wide-field of view of a fast telescope (use your lowest magnification). Binoculars are a better bet. A few people can even see this nebula visually. Wait for a night with dry air. And you’ll need dark sky… you have no chance of seeing this from the city.
NGC 1499 is just above the star Menkib in Perseus (lower left)
And if you’re into astrophotography, NGC 1499 makes a great target for longer exposures with a small telescope.