(Click to enlarge. Via.)
Check out this gorgeous mosaic of the Sun by César CantÃº. The All Glowing Orb is a sexy specimen in general, but it’s looking exceptionally swank in CantÃº’s work. So what exactly are we looking at here?
That hardly looks like the Sun, does it? That’s because he used a filter that blocks all the light we see except for a very narrow slice of color in the red part of the spectrum. That filter lets through only light from warm hydrogen, at just the right temperature to allow the electrons in the hydrogen atoms to drop from the third energy level to the second. You can picture the electron in an atom like it’s on a staircase, and only allowed (by quantum mechanics) to sit on a step, or move from one to the other. It takes energy to move it up a step, and gives off energy when it moves down. When it jumps down from the third to the second, it emits a photon – a particle of light – at a wavelength of 656.3 nanometers, and astronomers call this light HÎ± (H alpha).
The gas on the Sun’s surface emitting HÎ± is under furious stirring due to magnetic fields and other forces, and you can see that in the twisted, roiling appearance in this photo. I particularly like the dark arc just left of center: that’s a filament, an eruption of gas off the surface. It’s about 150,000 kilometers (90,000 miles) long! It’s a bit cooler than the surface material, so it’s darker, and we see it in silhouette. When those happen on the limb of the Sun they’re called prominences, and you can see several of those in this picture too.