Tag: H alpha

Purple shag Sun

By Phil Plait | November 1, 2012 10:05 am

The great astrophotographer Andre van der Hoeven sent me a shot he took of the Sun a few days ago. Looks like either Barney or the Grape Nehi folks paid it a visit:

[Click to envioletenate.]

Pretty cool. First, of course, the purple color is not real. It’s just the color Andre chose for this picture when he processed it. Second, he used an Hα filter, which lets through a very narrow slice of light (actually in the red part of the spectrum). This color is emitted by warm hydrogen, and is preferentially under the influence of the Sun’s magnetism. You can see arching prominences – huge towers of gas – off the edge of the Sun. The long stringy bits on the face of the Sun are called filaments, and are actually the exact same thing as prominences! Prominences are filaments we see from the side, instead of looking down on them. The terminology is a holdover from when astronomers first started observing the Sun, and we’re kinda stuck with it.

Also, Andre inverted the picture, so what looks black is actually very bright, and what looks bright is very dark. Those bright white blotches? Sunspots. For some reason, our brains can pick out detail better that way, and it also gives an eerie 3D sense to the image. He made a close-up mosaic of his pictures, too, which is actually a bit creepy. It’ll keep the Halloween spirit going for another day, at least!

Image credit: Andre van der Hoeven, used by permission.

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CATEGORIZED UNDER: Astronomy, Pretty pictures

The delicate tendrils of a solar dragon

By Phil Plait | September 2, 2011 7:00 am

Alan Friedman is an "amateur" astronomer who takes astonishing images of the Sun. You may remember his picture of our star that was so cool I chose it as one of my Top 14 Pictures of 2010.

He’s still snapping away, and on August 17th took this lovely picture of a prominence erupting from the Sun’s surface:

[Click to enfilamentate.]

Isn’t that gorgeous? A prominence is a towering arc of material lifted off the Sun’s surface by intense magnetic fields. To give you an idea of how strong the magnetic forces are, a prominence can have a mass upwards of a hundred billion tons, and be cranked up thousands of kilometers off the Sun’s surface… despite the crushing gravity of nearly 30 times that of Earth’s!

And some people call the Sun "average". Ha!

Alan takes these images with a pretty nice ‘scope equipped with a filter that blocks all the light from the Sun except for a narrow slice of color preferentially emitted by warm hydrogen. He then inverts the image of the solar disk (but not anything on the limb or outside it), which is an old astronomy trick to make contrast more obvious to the eye.

This image is part of a much larger one showing much more of the solar edge, including another magnificent prominence. Amusingly (to me at least), when I saw the picture above, my first thought is that it looked like a sitting dragon, facing to the right, sniffing a fish floating in front of it (and given that I’m at Dragon*Con right now, I love this imagery even more). Then I realized it also looks like a dragon facing to the left, head down on the Sun’s edge, like it’s ready to pounce! I’d suggest staying out of its way; after all, this dragon would be about 150,000 km long: well over 10 times the size of the Earth.

Do you see it as a dragon too? Funny how once our minds latch onto a picture like that, it’s hard to not see it that way!

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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

The Sun roils over Mexico

By Phil Plait | August 23, 2011 6:00 am

Yesterday, "amateur" astronomer César Cantú took an amazing mosaic image of the Sun, showing our star boiling and writhing under its own dynamic forces:

[Click to unGdwarfenate.]

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 (H alpha).

The gas on the Sun’s surface emitting Hα 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.

Amazingly, this picture (which is really a mosaic of six separate shots) was taken using a telescope with only a 90 mm (3.5 inch) lens. The Coronado 90 mm telescope is a favorite of sidewalk astronomers, since it shows the Sun in amazing detail, but is totally safe to look through since it blocks almost all the Sun’s light. It’s common to see them at planetaria and museums, set up where passers-by can get a quick glimpse of the Sun. For most, it’s the first time they ever see the might and power of a star only 150 million kilometers away.

And if you want a sense of scale here, in the picture above the Sun is about 450 pixels across. On the same scale, our entire planet Earth would be only about 4 pixels across.

Just in case you were feeling big and important today.

Credit: Image used by permission of César Cantú.

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CATEGORIZED UNDER: Astronomy, Pretty pictures

The boiling, erupting Sun

By Phil Plait | October 28, 2010 7:00 am

I keep thinking there’s nothing new under the Sun– or on it. With SOHO, and SDO, and a thousand other telescopes pointed at it, it would take something pretty freaking cool to surprise me.

Well then. Surprise!


Holy solar retinopathy! That’s the Sun?

Yup. But this is not a space-based image from some bazillion dollar observatory! This phenomenal picture was taken by astrophotographer Alan Friedman with this relatively small (but very, very nice) ‘scope. He shot it on October 20th, and it shows our nearest star in the light of hydrogen, specifically what astronomers call Hα (H-alpha). I’ll get to that in a sec…

In this picture you can see sunspots, giant convection cells, and the gas that follows magnetic loops piercing the Sun’s surface. When we see them against the Sun’s surface they’re called filaments, and when they arc against the background sky on the edge of the Sun’s disk they’re called prominences.

The image he took is amazingly high-resolution! He has two closeups, one of the filament and sunspot near the edge of the disk on the left, and the other of prominences leaping up off the edge and silhouetted against the sky:

Read More

CATEGORIZED UNDER: Astronomy, illusion, Pretty pictures

Found: 90% of the distant Universe

By Phil Plait | March 24, 2010 12:01 pm

This is fascinating news: 90% of the distant Universe was thought to be missing, but it was recently found. And what’s weird is, it was found to be in the red. Quite literally.

[Note: before you ask, this has nothing to do with dark matter. See below!]


First, a bit of background. Galaxies are filled with hydrogen gas, and that gas is a major component of the clouds that collapse to form stars. When that happens, the hot stars ionize the gas: the flood of ultraviolet light strips the electron away from the proton, freeing both. If the electron gets near the proton again, they can recombine. Because of quantum mechanics, the electron can only exists in certain energy states, which are a bit like steps in a staircase. You can jump from the third step down to the second, but there is no second-and-a-halfth step.

So it is with electrons. It used to be taught that this levels were like orbits, but that’s not a great analogy; the staircase is better. So if the electron is on the second level and drops to the first, it gives off energy in the form of light (just like when you step down you lose a bit of energy too, and it takes energy to go up a step). For the 2 to 1 step in hydrogen, the photon emitted is in the ultraviolet, and has a special name: Lyman alpha.

Ionized hydrogen gas clouds tend to blast out lots of Lyman alpha. This makes it a good way to search for distant star forming regions; just look for that wonderful wavelength of light associated with the 2 – 1 transition of hydrogen.

As it happens, we know that when the Universe was young, about a quarter the age it is now, star formation was going on at a much higher rate on average than it does now. So astronomers figured, hey, why not do searches for distant galaxies using Lyman alpha? They should pump it out, and make them easy to see.

So they looked. And to their surprise, they only found about 10% of the galaxies they predicted they should!

Uh oh.

This has been a problem for some time. But it’s not anymore: a recent experiment by astronomers shows that the galaxies are there, but they’re hidden!

What they did is look in one part of the sky, using the GOODS South field (part of which is pictured above), trying to find Lyman alpha emitting galaxies. Then they looked at the same region, but looked instead for H alpha, the line emitted when an electron jumps down from the third energy level to the second. And guess what they found: tons of galaxies!

The problem, they surmised, is that the galaxies are actually there and emitting Lyman alpha. But before that ultraviolet light can get out of one of those galaxies, it gets reabsorbed by gas inside the galaxy itself. We never see it.

But H alpha can more easily escape the galaxies once it’s produced. For one thing, it’s red light, and that can penetrate the gas and dust better than the ultraviolet Lyman alpha light can. There are other more complicated reasons as well, but the point is, the galaxies were simply hidden from us before, but not anymore. By extrapolating their results, it looks like they found 90% of the distant Universe!

I’ll note: this has nothing to do with dark matter. As it happens, 90% of the matter in the Universe is in a form that emits no light, but affects other matter through gravity. We know it exists, and you can find out why here. We know it exists locally, in nearby galaxies and clusters of galaxies, too. This new result doesn’t affect that, since the now un-hidden galaxies are very far away, like many billions of light years away. They can’t possibly affect nearby galaxies, so they don’t account for dark matter.

I love this study. It’s a great application of simple logic, though it wasn’t so simple to do: they had to use a lot of time on a monster 8 meter telescope to do it! But they were able to answer a question that has been around for some time, and it really does look like they’ve solved it.

And, as always, it makes me wonder what else is lurking out there in space, hidden but for a leap of logic and technology that will allow us to unveil it. Science is all about thinking around problems, and peeking into dusty corners. Sometimes the most interesting things are found there… including, in this case, the vast majority of the Universe!

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

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