The scale of things

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Raging clouds, near and very, very far
Bad Astronomy | July 22nd, 2012 6:30 AM

I know, right? This ridiculously amazing picture … was taken by Randy Halverson of DakotaLapse.com, whose photos have been featured here on the BABlog many times…. He took this one on the evening of July 19, 2012 as part of a time lapse he’s making. The vast Milky Way galaxy glows above the red clouds illuminated by town lights from below. And on the horizon a storm rages, eruptions of lightning strikes captured in this 15 second exposure.

Funny – the Milky Way looks a bit like a cloud there, but instead of countless droplets of water held up in our air, it’s composed of hundreds of billions of stars suspended in space by their orbital motion around the galactic center. We can see only a few thousand stars with our naked eyes, and they’re all very close, most within a hundred light years of Earth. But the Milky Way is a thousand times bigger than that, and the glow we see is actually the blended light of far more stars than there are people on Earth.

And yet in this shot even that mighty power is reduced to a faint smear compared to the electric discharge of a nearby storm. The raw energy released in a bolt of lightning is staggering, but it’s essentially nothing compared to a galaxy’s worth of stars. It’s only their terrible, terrible distance that dims them.

As you juggle the events that happen in your daily life, remember this photograph. It’s easy to get distracted by smaller flashy things that are nearby, and forget about much bigger issues if they’re far enough removed. It’s a thought worth holding close.

Photo credit: Randy Halverson, used by permission.

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An astronomer has produced a single image of the moon that you can adjust the scale by zooming in and out, and pan to see the moon’s surface—up close and personal. The single image is actually composed of 166 separate sub-images.
I don’t say too often, “Amazing.”

Links in original.

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Pow! ZOOM! To the Moon! | Phil Plait
Bad Astronomy | 26AUG12, 6:56 AM

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If you need a little extra dollop of awesome in your day, then try zooming in and flying over the surface of the Moon, care of astronomer Pete Lawrence’s incredible mosaic of our nearest cosmic neighbor:

[ Must click to see the image/picture. ]

Click the button on the lower right that makes the picture expand to fit the browser, then zoom in and out using the + and - buttons. Click and drag to fly around. Make vrooom vroom noises.

Make sure you zoom in all the way and then cruise over the terminator, the day/night line. Trust me.

This ridiculously cool image is composed of 166 separate sub-images taken over the course of just 45 minutes on August 10, 2012. He used a Celestron 14" with a video camera. Get this: each of the 166 sub-images is actually made up of 1000 separate video frames, which are stacked and processed to pick out the best bits of each one, resulting in a single high-quality frame. So he really took 166,000 images!

That’s so cool. I love what digital cameras have done for astronomy.

Pete’s images of the sky are amazing; check them out at digitalsky.org, and you can keep up with him on Twitter.

He also sent me this shot he took in 2009 showing the Moon in three different phases; you must click it to see it full size. It’s pretty impressive.

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The Scale of Things | Spaceweather dot com, 28AUG12

For the past few days, amateur astronomers have been monitoring a big cloud of plasma hovering above the sun’s eastern horizon. How big is it? Göran Strand of Frösön, Sweden, superposed the Earth and moon on a picture he took yesterday to show the scale of things:



“It was an amazing view through my binoviewer,” says Strand. “I placed the Earth and moon at their correct separation: 384,400 km apart. This is one big prominence.”

The cloud is held aloft by solar magnetic fields. If those fields become unstable then the cloud could collapse, hitting the stellar surface and producing a Hyder flare. Amateur astronomers with backyard solar telescopes are encouraged to monitor developments.

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NASA’s WISE Survey Uncovers Millions of Black Holes
— Press Release | 29AUG12

With its all-sky infrared survey, NASA’s Wide-field Infrared Survey Explorer, or WISE, has identified millions of quasar candidates. Quasars are supermassive black holes with masses millions to billions times greater than our sun. The black holes “feed” off surrounding gas and dust, pulling the material onto them. As the material falls in on the black hole, it becomes extremely hot and extremely bright. This image zooms in on one small region of the WISE sky, covering an area about three times larger than the moon. The WISE quasar candidates are highlighted with yellow circles.

Image credit: NASA/JPL-Caltech/UCLA

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WISE Media Teleconference
— 29AUG12

NASA hosted a news teleconference at 10 a.m. PDT (1 p.m. EDT), Wednesday, Aug. 29, to announce new discoveries from its Wide-field Infrared Survey Explorer (WISE). The discoveries are related to the distant universe, including supermassive black holes and rare galaxies.

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^ Unmasking Giant Black Holes | Goddard Space Flight Center

YOUTUBE NOTES. From the NASA Swift team, watch full screen 1080p! Most large galaxies contain a giant central black hole. In an active galaxy, matter falling toward the supermassive black hole powers high-energy emissions so intense that two classes of active galaxies, quasars and blazars, rank as the most luminous objects in the universe.

Thick clouds of dust and gas near the central black hole screens out ultraviolet, optical and low-energy (or soft) X-ray light. Although there are many different types of active galaxy, astronomers explain the different observed properties based on how the galaxy angles into our line of sight. We view the brightest ones nearly face on, but as the angle increases, the surrounding ring of gas and dust absorbs increasing amounts of the black hole’s emissions.

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Temba, his spiral arms wide | Phil Plait
Bad Astronomy | September 3rd, 2012 7:02 AM

Lying roughly 50 million light years from Earth is the magnificent spiral galaxy NGC 5033. Although that distance is a soul-crushing 500 quintillion kilometers, it’s actually relatively close by on the cosmic scale. Close enough that a lot of detail can be seen in the galaxy… and it also makes for a stunner of a picture:

Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

This shot was taken by friend-of-the-BA-blog Adam Block using the 0.8 meter Schulman Telescope on Mount Lemmon in Arizona. It’s a whopping 13 hour exposure taken in near-true color.

It’s amazing what you can see in just this picture if you know what to look for. The spiral arms of the galaxy are fairly open, which is common enough, but the outer ones stick out a bit more than you might expect. The nucleus is very small and bright, more so than I’d expect for a typical spiral as well. Both of those things led me to expect this is an active galaxy, and that turns out to be the case.

Every big galaxy – ours included – has a supermassive black hole in the center. The Milky Way’s is 4 million times the mass of our Sun! In some galaxies, like ours, happily, the black hole is just sitting there. But in some there is gas actively falling into the hole. It spirals around and forms a very hot and very large disk, which glows fiercely as the matter is heated to temperatures of millions of degrees. The disk can blast out light from radio waves up to X-rays, and we say that the galaxy is "active".

A quick search of the literature didn’t turn up any measurements for the mass of black hole in NGC 5033, but it does confirm that it’s an active galaxy. Interestingly, the black hole is not located in the exact center of the galaxy! That’s very unusual, and indicates that NGC 5033 recently merged with another galaxy, probably a smaller one. It’s a cannibal! But then, most big galaxies are. It’s how they get big… and you’re living inside a big one, so there you go.

This may explain the wide arms on the galaxy as well; a collision and merger can distort the shape of the galaxy. Also, check out all the pink blobs along the arms: those are sites of furious star formation, the hot energetic massive young stars lighting up the gas around them. That also is common after a big collision.

Finally, one more nifty thing. You can see long ribbons of dark dust festooning the galaxy in the inner region. Dust absorbs light from stars behind it. But see how the dust looks like it’s only on one side of the galaxy, the half in the picture below the center? That’s an illusion, sortof. In reality there’s dust orbiting all around the center. However, there are stars above and below the disk of the galaxy, and the ones between us and the far side fill in the darkness a little bit, so the dust is less apparent. I’ve written about this before, and it does happen in quite a few spirals. Click the links in the Related Posts section below to see more gorgeous galaxies with this feature.

It’s funny how much information you can squeeze from a single picture! You have to be careful and not over-interpret it, and of course a lot of the things I’ve written here wouldn’t have been known without other observations of NGC 5033 using different telescopes and different methods in different types of light.

But even just one picture can tell you a lot. And in my opinion – and I tend to be right about these kinds of things – the wave of beauty that flows over you when looking at this picture is only enhanced by knowing more about the galaxy itself… and is boosted in no small way by the fact that we can know these things.

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[hanshan]

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... In some galaxies, like ours, happily, the black hole is just sitting there. (...)

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… and you’re living inside a big one, so there you go. ...


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...You have to be careful and not over-interpret it, ...


... boosted in no small way by the fact that we can know these things.


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^^^

Thanks, hanshan.
I just love that we can know these things.

[brainpanhandler]

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Why is the Sun so round? | Phil Plait
Bad Astronomy | September 12th, 2012 7:00 AM

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 arcseconds across. In other words the equatorial diameter is only 0.02% wider than the polar diameter!

The Sun is a 99.98% 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 the width of a human hair. That’s actually pretty cool.

Read the rest of this entry »

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In the comment space directly above, there is an error in the third paragraph from the bottom in Why is the Sun so round? posted at Bad Astronomy. Phil Plait has rewritten that paragraph with an additional revision in another, so I decided to keep things simple by putting the article as it is today below his introduction. Links in original.

[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!]

Why is the Sun so round?

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.

What this almost certainly means is that the assumptions people make about the Sun aren’t quite on the ball*. One assumption is that the Sun is a big ball of gas, and the only forces on it are gravity, pressure, and centrifugal force. The physics of those aren’t too hard to work out, but up until now predict a slightly squashed Sun. So something else must be going on.

One obvious thing is the Sun’s ridiculously complicated magnetic field. The gas inside the Sun is hot, and the atoms making it up have their electrons stripped off. That makes them ions (and the gas is then called a plasma), which are affected by magnetic fields. It’s possible that the strength of the magnetism inside the Sun acts like a sort of tension, stiffening the Sun, so it doesn’t bulge out at the equator as much as expected (or at all).

Also, since the Sun isn’t solid, it doesn’t spin as one. Parts of it rotate faster than other parts; it spins once every 25 days at the equator, but every 35 days at the poles. It’s possible that this isn’t constant with depth (plasma under the surface may spin at different rates than stuff at the surface) and that could affect this as well.

Most interestingly to me is that the scientists determined the Sun’s size doesn’t change with time, including the 11 year solar cycle. The Sun’s overall magnetic field fluctuates with time, weakening and strengthening on an 11 year cycle (which is why we’re seeing more sunspots now; we’re approaching solar max). If the Sun’s shape were being restricted by interior magnetic fields, you might expect the size to change slightly with the cycle as well. The scientists who did this study have ruled that out.

So what’s going on? Hard to say. We do actually have a very good understanding of the solar interior due to advances in physics over the past century or so – models have been tested very carefully and what we have now works extremely well… up to a point. What will happen next is that different models will be tested to see which ones can match observations, then more predictions will be made, and then more and better observations will be done to test those predictions. Some models will survive this trial, and our understanding will have grown.

This issue of the Sun’s sphericity strikes me as a fluctuation on what we know. It doesn’t mean everything we thought we knew is wrong, just that there’s more to know about the Sun.

And that, of course, is why science is so much fun! It never ends, and there’s always something new and interesting to discover.

Image credit: Thierry Legault

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* HAHAHAHAHAHA! Get it?

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I LOVE THIS.

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The subtlety of cosmic violence | Phil Plait
Bad Astronomy | September 14th, 2012 6:30 AM

One of the most amazing things I can think of can be stated simply:
some stars explode.

That’s incredible. An entire star, millions of kilometers across and massing octillions of tons, can go supernova, tearing itself to shreds. The explosion is so huge that it releases more energy in a few months than our Sun will over its entire lifetime.

And yet, when seen from a distance, supernovae can produce structures of astonishing subtlety and beauty. About 11,000 years ago, a star over 800 light years away exploded in the constellation Vela, producing an expanding gas cloud. Here is one small part of that nebula:


^ Image credit: ESO

That gorgeous structure is NGC 2736, also called the Pencil Nebula, part of the much larger Vela supernova remnant. This picture was taken using the 2.2 meter MPG/ESO telescope in Chile. As the debris from the titanic explosion expands, it rams into the interstellar gas surrounding it. That compresses the gas, and drives a shock wave through it. A shock wave occurs when an object moves at supersonic speed through some other material – although the gas in space is thin, in some places it’s thick enough that atoms and molecules in it do collide. It’s still a thin vacuum by our standards, but physics will not be denied.

Think of it this way: imagine two people standing a few meters apart, holding a rope between them. One of them snaps their end up and down sharply. A wave is created which moves down the rope, and a second or so later the other person feels the tug. The information that the first person moved the rope took some amount of time to travel down the rope in the form of that wave.

Sound is similar, in that it’s a compression wave. When something happens to make a sound – like a tree falling in a forest – it compresses the air, and that compression moves outward at (duh) the speed of sound. It’s a way of transmitting information from one spot to another.

But now imagine something moving faster than sound. Instead of hearing the sound first, the supersonic object would actually travel past you before its sound would. Because you didn’t hear anything first, that event would surprise you, right? You might even be… shocked.

Hence the term shock wave.

And that’s what’s happening in NGC 2736. The gas from the supernova is expanding far faster than sound in the surrounding gas, so the gas is shocked. It gets hugely compressed, and forms those thin filaments and ribbons. You see this a lot in space where one thing is slamming into another (see Related Posts below). The energy of the shock wave heats up the gas, which then glows, and from a safe distance we see it as a thread of light, finely detailed and structured.

They say that in space, no one can hear you scream… but in reality, if you pick the right place and scream hard enough, you can make yourself heard across thousands of years in time, and trillions of kilometers in space.

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Related Posts:

- Revealing the Veil
- The beating heart of W5
- A dying star with the wind in its hair
- The cold, thin, glorious line of star birth

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Sound is similar, in that it’s a compression wave. When something happens to make a sound – like a tree falling in a forest – it compresses the air, and that compression moves outward at (duh) the speed of sound. It’s a way of transmitting information from one spot to another.

But now imagine something moving faster than sound. Instead of hearing the sound first, the supersonic object would actually travel past you before its sound would. Because you didn’t hear anything first, that event would surprise you, right? You might even be… shocked.





...you can make yourself heard across thousands of years in time, and trillions of kilometers in space.



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Re Brain Cell Universe:

The Topographic Man is revealed.

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Thanks, hanshan. Since I don’t know the works of either Mr. Brunner or Mr. Constantine, I think, from a personal point of interest with regard to the scale of things, the more scientifically specific would be cosmological ideas expressed in an excerpt that I’ve personally transcribed from David Deutsch’s TED talk. The only thing is, and it’s not surprising, Deutsch didn’t include shock or sound waves, or vibrations ftm, in his hypotheses. However, when I first heard Deutsch’s talk, I don’t think I could’ve been more excitedly dazed for days.
The excerpt begins approx 07.45.


^ David Deutsch | TED JULY2005

“…The brain contains an accurate, working model of the quasar; not just a superficial image of it—though it contains that as well—but an explanatory model embodying the same mathematical relationship, and the same causal structure. That is knowledge.

“And, if that weren’t amazing enough, the faithfulness with which the one structure resembles the other is increasing with time. That is the growth of knowledge.

“So the laws of physics have this special property: that physical objects, as unlike each other as they could possibly be, can nevertheless embody the same mathematical and causal structure, and to do it more, and more so over time.…”

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