California (Nebula) Dreamin’

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Nov 24, 2014
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Rogelio Bernal Andreo is an astrophotographer … but saying that is like calling a world-class chef a “cook.” Andreo is a master, one of those people who can tease photons out of the sky and then turn them into works of art that nearly defy description.

For example, here is his mosaic of the sky showing two stunning objects: the California nebula, and the magnificent Pleiades star cluster:

Holy. Haleakala. Yes, you really really want to download the fully embiggened version of that, because it’ll freeze your brain with its beauty and scope.

It’s hard to know where to even start with this! So let’s take it one at a time. On the left is the ruddy glow of the California nebula, officially called NGC 1499. It’s a vast cloud of gas and dust stretching several dozen light-years in length, which is huge on anyone’s scale. It’s part of a large cloud of gas that long ago condensed to form baby stars. But don’t be fooled by the adjective; these are very, very ill-tempered babies indeed. Take a closer look:

See that bright star just to the right of the gas, inside that arc of gas? That is Xi Persei, also called Menkib. It’s a beast, a monster 30 times the mass of the Sun, and blasting out light at a hair-raising 250,000 times the rate the Sun does. That’s so much radiation that we think that’s what’s setting the nebula aglow. Remember, that gas cloud is more than 400 trillion kilometers long, and it’s being lit up by a single star. The star and cloud are something like 1,000 light-years from Earth, yet the star is visible to the unaided eye. From that distance, you’d need a decent telescope to see the Sun at all.

The nebula is named because of how much it looks like its eponymous state, and I have to agree, it’s a good match (too bad it’s not nearer to the North America nebula). The ribbons and filaments you see inside the cloud are due to shock waves inside the gas, where waves of material slam into slower stuff, compressing it. The gas is expanding because long ago, several of the massive stars born from it lived out their lives and exploded as supernova, dumping huge amounts of energy in to the gas and causing it to rush away. The California nebula is only one segment, one arc of a far larger shell of gas that we cannot see because it has no nearby powerhouse stars illuminating it.

On the right of Bernal’s magnificent mosaic is the famed Pleiades cluster—the Seven Sisters—a collection of youngish stars all formed from a single cloud of gas and dust. The cluster is very roughly 400 light-years away (much closer to us than the California nebula), big enough and bright enough to be seen with the naked eye. In fact, a lot of people mistake them for the Little Dipper!

Deep, high-resolution pictures of the stars show them lighting up diaphanous sheets of material around them. Years ago, it was thought this was the material from which the stars formed, and that always bugged me. The cluster is about 100 million years old, which is way too old to still be surrounded by its birth cocoon. And, it turns out, that intuition is correct: that material belongs to an entirely different cloud of dust, and it just so happens the cluster is passing through it right now! Bernal’s photo makes this more clear; there are vast swaths of dust littering that whole part of the sky.

I have to point out the difference in color between the Pleiades and the California nebula. In the latter case, the gas in the nebula is being excited by ultraviolet light from Xi Persei. These photons hit the hydrogen atoms in the gas and are absorbed by the electrons in the atoms. The electrons dump that extra energy by emitting light, predominantly in the red part of the spectrum.

In the case of the Pleiades, the light is coming from dust near the stars that’s reflecting the starlight. The stars are blue, so the reflected light is blue, too. Because of this, we call the California nebula an emission nebula, while the Pleiades dust is a reflection nebula. The physics of this is actually pretty neat, and if you want to read more I have a detailed (and hopefully clear) description in an article about a gorgeous nebula that is both reflecting and emitting light. You really want to see (and read) that.

And do you want to know another amazing thing about this picture? Take a look at the Pleiades again in the big version of the full mosaic. See the diamond of four bright stars, just above the fifth star? On the sky, the full Moon is just about the same size as that diamond (this is shown in the zoomed picture above for clarity).

Now take a step back, and look at this full mosaic again. The whole thing is a staggering 18° across, 35 times the width of the full Moon! How much of the sky is that? Stand up, and hold your arm out in front you. Bend your wrist in, so you’re looking at the palm of your hand and your fingers: If you held your hand like that up to the sky, it would be cover about the same amount of real estate as Bernal’s photo. Wow.

Bernal’s work is simply phenomenal. You really need to peruse his site; everything there is a masterwork. (I’m a big fan of his portrait of the Big Dipper, for example.) Many are for sale, too.

And one final note: Years ago, I picked his “Orion from Head to Toe” as the best astrophoto for 2010. I cannot stress enough how much you want to click that link. To put this in perspective, I have seen thousands of astrophotographs over my life, and that Orion picture is one of my favorites of all time.

As usual, I have to smile wryly when I hear people try to distinguish art from science. The Universe is both, folks. You may try to tear them apart, but you cannot, for the artistry of the Universe is forever intertwined with how it works. They drive each other; the science is why the art is beautiful, and the art is one of the reasons we pursue the science.