Tag: Sun

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

Look! Up in the sky! It’s…it’s… it’s an amazing optics display

By Phil Plait | November 1, 2012 7:00 am

It’s funny what tiny little ice crystals can do. Floating high in the air, suspended by air currents, they hang there… and then a ray of sunshine enters them. The light gets bent due to complicated physics, the interplay of that beam of light passing from air to a solid crystal and out again. But once that beam leaves, the sky can light up with a wizard’s pattern of colors and shapes. And if you’re very, very lucky, you’ll see something that you’ll remember the rest of your life.

Something like this:

Holy diffractionation! [Click to heliocanesenate.]

Mind you, this picture is real. David Hathaway – appropriately enough, a solar physicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama – took it using a wide-angle lens to get the whole thing. It’s a High Dynamic Range shot, meaning he combined pictures with 3 different exposure times to see both faint and bright things simultaneously. He took the shot on October 30, 2012.

Everything you’re seeing here is pretty well understood: they all have a name and a specific set of circumstances under which you can see them.

The Sun is the bright blob near the horizon. It’s circled by the 22° halo, a fairly common optical effect in the winter; I see dozens every season. On either side of the Sun are parhelia, nicknamed sundogs. Those are the teardrop-shaped rainbows. Sometimes, as seen here, these stretch out into long streamers called parhelic circles. They are parallel to the horizon but in this wide-angle shot the shape is distorted, bending them up.

Directly above the Sun, dipping down to touch the halo (the math term for this is osculating, which means kissing) is a gull-wing curve called the tangent arc. Above it, connecting the "wings", is the Parry arc.

As an aside, I’ve seen tangent arcs only twice in my entire life. One was at a University of Virginia football game in the winter when the Sun was setting. It was so bright and looked so much like a V that I joked that it was a sign we’d win the game. Georgia Tech trounced us. So much for divination using signs in the sky.

Above the tangent and Parry arcs is a faint rainbow (well, it’s not caused by raindrops, but it’s broken up into colors and has the familiar rainbow-shape) called the Parry supralateral. Faint and off to the right, nicking the supralateral, is a tightly-curved rainbow called the Parry infralateral.

Amazingly, there are still two more to go! The upside-down rainbow at the top is called a circumzenithal arc, because it’s centered on the zenith, the point directly above your head.

Finally, the last thing I can see is a very faint white vertical oval on either side of the the 22° halo and going off the top of the frame, past the circumzenithal arc. That’s the heliac arc, something I’d never even heard of before looking it up here. That’s a new one for me.

Amazing, aren’t they? And get this: there are lots more kinds of phenomena like this, and they’re all caused by ice crystals in the air! The crystals have different shapes – some are flat, some barrel-shaped, so they bend light differently, and their orientation to us causes all these fantastic displays.

By coincidence, just a few days ago BABloggee Joe DePasquale (who works at the Harvard Smithsonian Center for Astrophysics) also saw an aamazing display. Here’s one of the shots he sent me:

Wow. You can see a lot of the same features as in David Hathaway’s picture, too (in fact, Joe made a diagram so you can see what’s what). BABloggee Alan French let me know that there’s a fine gallery of them on Flickr, too.

It’s possible some of this was due to ex-Hurricane Sandy getting moisture high in the atmosphere where it could freeze into crystals. But I’ll note again that I have seen many of these same haloes myself. Most are not rare at all, and all you need to do is keep your eye on the sky. Seriously, one of the first things I do on any day where there are high clouds is look near (not at!) the Sun and see if there’s anything to be seen.

Usually there isn’t. But sometimes, just sometimes, you get that amazing display that makes all the fruitless searching totally worth it.

Look up! There’s a whole Universe out there. And some of the coolest stuff is really close to home, literally just over your head.

Image credits: David Hathaway; Joe dePasquale, used by permission. Tip o’ the Snell’s Law to SpaceWeather.com and to Elwood Herring for pointing it out to me.


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CATEGORIZED UNDER: Cool stuff, Pretty pictures, Top Post

Oh, snap! Another X-class flare from the Sun

By Phil Plait | October 23, 2012 11:59 am

Yesterday, an active region on the sun – basically, a collection of magnetically active sunspots – popped off a series of flares that were actually fairly energetic. NASA’s Solar Dynamics Observatory caught the action in this video:

Neat! These shots were in the ultraviolet, where flares are easier to spot.

Sunspots are where the Sun’s complex magnetic field pokes through the surface. The field lines store ridiculous amounts of energy (did you see my BAFact for today?), and allow plasma – superheated, ionized gas – to flow along them. Think of these field lines like a pillowcase full of tightly wound springs. If one of them snaps – which can happen if they get too close to each other, for example, or when the churning surface of the Sun ratchets up the tension in the field lines beyond their capacity to restrain themselves – it blasts out its energy, which then snaps other lines, which release their energy, and so on. You get a cascade of explosions, resulting in a solar flare.

Flares can be pretty small, or hugely huge. Scientists categorize them by the amount of X-ray energy released, so we have low-energy C class, medium M class, and yikesingly X class. This flare from yesterday just edged into X class territory, so it was decent, but not too bad. Happily it was on the edge of the Sun, and the blast was directed away from Earth, so it’s not expected to affect us. For further reassurance, there have been 14 previous flares since this new sunspot cycle began a couple of years ago, and we’re still here.

However, as the Sun spins, this active region is rotating toward us. If it stays active, we could see some interesting events from it that can cause aurorae on Earth. The odds of anything bad happening – power outages, or loss of satellites, for example – are low, but not entirely zero. I personally am not too worried about it, but it’s always good to keep our eyes on our nearest star. It can pack quite a punch, and we’re still a year or so away from the peak of the current sunspot cycle.

Image credit: NASA/SDO


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CATEGORIZED UNDER: Uncategorized

The raw power of the Sun

By Phil Plait | October 19, 2012 11:00 am

Early this morning, while you were sleeping, or working, or reading Twitter, the Sun had different plans: it erupted, blasting an immense tower of plasma upward off its surface:

[Click to enheliosenate.]

This image was taken by NASA’s Solar Dynamic Observatory at 08:15 UTC this morning. The scale of it is staggering. The Sun is 1.4 million kilometers across – 860,000 miles – so this plume was at least 400,000 km long. Going back through the images, it had been brewing for hours, but really got its start around 05:00, meaning it erupted upwards at well over 100,000 km per hour. That’s fast enough to cross the face of our planet in less than 8 minutes.

By the way, did I mention the total mass of such a prominence is billions of tons? And the Sun does this kind of thing all the time.

We’re in no real danger from an eruption like this, especially this one: it’s on the Sun’s limb, so it was heading away from us. But these events can trigger storms like coronal mass ejections, where billions of tons of material is sent hurtling across the solar system at mind-crushing speeds. Those can interact with our magnetic field, creating havoc with our satellites and causing power outages.

But that’s why we keep an eye – many eyes, in fact – on our Sun. Never forget: our Sun is a star, with all the power and fury that implies. The better we understand it, the better we can protect ourselves from it when it gets angry.

Image credit: NASA/SDO. Tip o’ the welder’s glasses to Camilla SDO.


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MORE ABOUT: prominence, SDO, solar storm, Sun

STEREO catches an eruptive prominence

By Phil Plait | October 15, 2012 12:27 pm

Via Jenny Winder on Google+ I saw this way cool video of an eruptive prominence on the Sun: a towering arc of plasma held aloft by the Sun’s magnetic fields. Sometimes these field lines are unstable, and the plasma can blast away from the Sun and out into space:

This video was taken by one of NASA’s twin STEREO spacecraft; a pair of probes with one orbiting well ahead and the other behind the Earth. They stare at the Sun, literally giving us an angle on it we can’t get from our planet. Specifically this was from the STEREO Ahead spacecraft, and combines an ultraviolet view of the Sun itself together with a visible light portion that shows the Sun’s outer atmosphere, called the corona.

You can see the prominence form, rise up, and then erupt away into space over the course of one day, on October 6-7, 2012. Sometimes this material rains back down to the surface, and sometimes it escapes entirely. When it does the latter, it can flow outward, impact the Earth, and cause a geomagnetic storm. Usually those do us no harm, though if they get big they can disrupt satellites and potentially cause power outages. More likely they just create gorgeous aurorae which can be photographed from the ground.

It’s actually rather amazing how many space-based eyes we have on the Sun and the amount of data they send back. The Sun is a feisty beast, and getting feistier as we approach the maximum part of its magnetic cycle. The more we observe it, the more we learn, and learning is always good.


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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

The August solar eruption, in HD video!

By Phil Plait | September 28, 2012 6:56 am

In August, the Sun erupted in an epic explosion: a towering arc of material blasted off the surface and into space. The images of it were incredible enough, but the folks at NASA/Goddard Space Flight Center put together an astonishing high-def video of the eruption as seen by the Solar Dynamics Observatory, the Solar Terrestrial Relations Observatory (or STEREO), and the Solar Heliospheric Observatory (SOHO):

Yowza. Set it to hi-res and make it full screen. Try not to drool.

They have more images, videos, and higher-resolution stuff on the GSFC Multimedia site. You really want to go there and take a look.

Our Sun is gorgeous, and dangerous, and amazing. These pictures and videos are more than just beautiful; they are telling us about the mechanisms and processes occurring both on the surface and inside our nearest star. Given the impact this can have on Earth, the more we know, the better.


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CATEGORIZED UNDER: Astronomy, Pretty pictures

Why is the Sun so round?

By Phil Plait | September 12, 2012 7:00 am


[NOTE: When I originally wrote this, I made a mistake - I said the Sun was 30 arcseconds across, when it's actually 30 arcminutes. For some reason, that number got stuck in my brain, and the math I did was based on the incorrect number! I have corrected the math in the text below. Usually I keep the original mistake in an article (striking through the text) along with the correction - that's my way of admitting mistakes. But given that this is math, I was afraid that might look a bit confusing, so instead I'll note my brain hiccup here, and keep the math clean by simply fixing it. However, this does change the analogy I used in the text comparing the Sun to a basketball, so in that case I struck through the text and added the correct analogy. I know, it sounds confusing, but it'll be clear when you read the article. My apologies for this!]

A new study has been published that seems very simple yet has some very interesting repercussions: it shows the Sun is the most spherical natural object ever measured.

Measuring the Sun’s diameter is actually rather difficult. For one thing, observations from the ground have to deal with our atmosphere which warbles and waves above us, distorting images of astronomical objects. To get past that, the researchers used a camera on NASA’s Solar Dynamics Observatory, which orbits high above the Earth. The camera is very stable, and gets past a lot of the problems of measurement uncertainty.

Another problem is that the Sun doesn’t have a solid surface. It’s not like a planet – and even that can be tough to measure. Since the Sun is gaseous, it just kind of fades away with height, so if you try to get too precise you find a lot of wiggle room in the size. In fact, the largest variation the researchers found in the solar diameter was due to intrinsic roughness of the Sun’s limb – in other words, on very small scales the Sun isn’t smooth.

Still, there are ways around that. The point here isn’t necessarily to find the actual size, but the ratio of the diameter of the Sun through the poles (up and down, if you like) to the diameter through the equator. That tells you how spherical the Sun is.

What I would expect is that the Sun is slightly larger through the equator than through the poles, because it spins. That creates a centrifugal force, which is 0 at the poles and maximized at the equator. Most planets are slightly squished due to this, with Saturn – the least dense and fastest spinning planet, with a day just over 10 hours long – having a pole to equator ratio of about 90%. It’s noticeably flattened, even looking through a relatively small telescope.

The Sun spins much more slowly, about once a month. That means the centrifugal force at its equator isn’t much, but it should be enough to measure. So the scientists went and measured it.

And what they found is that the polar and equatorial diameters are almost exactly the same. In fact, they found that the equatorial diameter is 5 milliarcseconds wider than the polar diameter. An arcsecond is a measure of the size of an object on the sky (1° = 60 arcminutes = 3600 arcseconds), and the Sun is about 30 arcminutes (1800 arcseconds) across. In other words the equatorial diameter is only 0.0003% wider than the polar diameter!

The Sun is a 99.9997% perfect sphere. Hmmm.

Put another way, if you shrank the Sun to the size of a basketball, the equatorial diameter would be wider than the polar one by about 0.4 microns – the width of a human hair less than the size of an average bacterium! That’s actually pretty cool.

Read More

CATEGORIZED UNDER: Astronomy, Cool stuff

A HUGE solar filament erupts into space

By Phil Plait | September 10, 2012 11:45 am

On August 31, the Sun threw a major tantrum. It started with a vast arc of material towering over its surface, a stream of plasma flowing between two sunspots. Sometimes these collapse back down to the Sun’s surface, but this one exploded, blasting hundreds of millions of tons of material out into space.

SDO captured this ridiculously awesome picture of the arc just before it erupted:

Holy solar hissy fit! [Click to enfilamentenate.]

This picture is a combination of two images, both in the extreme ultraviolet part of the spectrum (30.4 and 17.1 nanometers, to be specific), where magnetic activity is easy to spot. The bright spot to the upper left is a sunspot, which are normally dark in optical light, but shine brightly in the UV. The filament, as the arch is called, is so big it’s hard to comprehend: it was something like 300,000 kilometers (nearly 200,000 miles) across! That’s nearly enough to extend from the Earth to the Moon.

Having a hard time picturing that? Yeah, me too. Happily, NASA provided an image with the Earth for comparison. Yegads. And there are more images of the event on the NASA/Goddard Flickr page.

Stephen Ramsden is an astronomer who runs the Charlie Bates Solar Astronomy Project, and he saw it while at Dragon*Con! I was at D*C but totally missed this, but he got a very cool picture too. As you can see in this picture, it was erupting when he caught it. I’m kicking myself to have missed the solar observing at the con, and next year I’ll be sure to take a look. I’d hate to miss something like this again!

For his non-profit Charlie Bates Solar Astronomy Project, Stephen takes solar telescopes across his region and uses them to teach people (including kids!) about the Sun and its effect on us. I’ll note he accepts donations to help him do this. Hint hint.

Finally, I’ll add that this amazing solar eruption traveled outward at about 1500 kilometers per second (900 miles/second) and nicked the Earth’s magnetic field on September 3, sparking aurorae in extreme latitudes. This had little real impact on us, but I gently remind you the Sun is still not at its peak. It’ll reach the max of its cycle next year sometime, and the biggest flares and other storms tend to happen a few months after the peak. It’s hard to say if this will do any damage – loss of satellites and power blackouts are possible, though no direct harm to humans on Earth can happen – but we’ll see. The most likely outcome is aurorae, so keep your browser tuned to the NOAA Space Weather Prediction Center and SpaceWeather. If we do get aurorae, those are great places to let you know.

Images credit: NASA/GSFC/SDO; Stephen Ramsden


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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: filament, SDO, solar storm, Sun

Awesomely blemished inverted solar beauty

By Phil Plait | September 2, 2012 7:01 am

Alan Friedman’s photos are no stranger to this blog; I’ve posted a lot of his amazing pictures of the Sun (See Related Posts, below). So many, in fact, that one needs to be surpassingly cool to add to the lineup.

So, yeah:

[Click to ensolarnate.]

Yegads. He took this on July 29, 2012. Because the image is inverted – dark things appear bright, and vice-versa – sunspots are intense white patches, bright plages appear dark, and towering filaments are whitish-gray.

Note how the Sun’s face gets darker toward the center and brighter toward the edge – meaning in reality the center is bright and the edge dimmer. This is called limb-darkening (the opposite of limb-brightening seen in some gas clouds), and occurs because gas around the Sun absorbs its light. We look through more of it near the edge than toward the center, so there’s less light coming from the limb of the Sun.

I’ll note that only the face of the Sun is inverted, though. Everything outside that is normal, so the leaping prominences of gas on the edge are bright, as they should be. That might be a bit confusing, but it does make for a dramatic picture.

And given how volatile our local star, you don’t have to go very far to get drama out of it.

Image credit: Alan Friedman


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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

BAFact Math: The Sun is 12 *trillion* times brighter than the faintest star you can see

By Phil Plait | August 28, 2012 10:00 am

[BAFacts are short, tweetable astronomy/space facts that I post every day. On some occasions, they wind up needing a bit of a mathematical explanation. The math is pretty easy, and it adds a lot of coolness, which I'm passing on to you! You're welcome.]


Today’s BAFact: The Sun is 12 trillion times brighter than the faintest star you can see with your naked eye.

In yesterday’s BAFact, I showed how the Sun is about 400,000 times brighter than the full Moon – and I showed my math. That’s an amazing brightness difference, but while I was writing it I had to wonder: how much brighter is the Sun than the faintest star you can see?

The faintest stars visible to the naked eye have a magnitude of about 6. This depends on lots of stuff, like how dark the sky is, how good your eyesight is, and so on. Some people with excellent vision can see stars down to magnitude 7, and there are reports of a few extraordinary people who can see even fainter. But on a dark night, the average person can just barely see 6th magnitude stars.

Let’s use that number then. All we have to do is plug that into the equation I gave yesterday (and remembering that the Sun has a magnitude of -26.7):

Brightness ratio = 2.512(6 – (-26.7)) = 2.51232.7 = 12 trillion

Yegads! That’s 12,000,000,000,000 times brighter!

Now, to be fair, that’s not really the brightness range your eyes can detect. You can’t look right at the Sun easily or comfortably; it’s simply too bright. So the range of brightness your eye can see is probably smaller.

We can put a lower limit on it easily enough using the Moon. The Moon is the second brightest object in the sky, and we know we can look at that easily enough, so let’s do that math (the Moon’s magnitude is -12.7 when it’s full):

Brightness ratio = 2.512(6 – (-12.7)) = 2.51218.7 = 30 million

Wow. So you can comfortably see objects over a brightness range of 30 million. That’s impressive! The eye is a pretty cool little machine.

As an aside, your eye isn’t linear; it’s logarithmic (in reality, it’s more complicated than this, and I’m simplifying, but close enough). In other words, a star giving off twice as much light doesn’t look twice as bright as another. The way your eye responds to light squeezes down the scale, making it easier to see fainter and brighter objects at the same time.

So how faint do objects get? Ah, that’ll be tomorrow’s BAFact. Stay tuned!


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CATEGORIZED UNDER: Astronomy, BAFacts
MORE ABOUT: magnitudes, Moon, star, Sun
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