Thanks to AnsuGisalas for linking to A* in a discussion thread on this TechRepublic article; it was something of a non sequitur, but I'll take it. :D
The recent string of posts on telescopes and the 1893 World's Fair and all that actually started, my notes just reminded me, with a post from mid-last-week on the then-mysterious event in May 1999 dubbed The Day the Solar Wind Disappeared. In that post I mentioned that later research suggested the almost complete shut-off of the solar wind in Earth's direction was due to active regions on the Sun's surface choking off the coronal hole through which the solar wind would otherwise have been issuing, and went on to explain that "active regions" are just areas on the Sun's surface where something is happening, aside from just the usual solar currents of heat and magnetism, and gave an example of sunspots as one such type of region.
But there are other types of active regions--and ones that make for much cooler pictures, too. For instance, a solar prominence is an extension of relatively cool plasma above the Sun's surface (and those "filaments" in the sunspot picture in the earlier article were types of solar prominences too, just viewed top-down so you couldn't really tell they were above the surface); some of them get really big, like this one seen from Skylab in 1973, which was called one of the largest ever recorded:
And a coronal hole is more or less what it sounds like, I guess; these cooler, depressed areas of the surface are filled with much lower density plasma, and the solar wind comes tearing out of them along open magnetic field lines--"open" because they head out into space without looping back to the Sun's surface, which is why the solar wind can escape from those spots. Here's half of a STEREO image of one (that dark spot in the middle-ish; there are also some at the poles, but this isn't a great view of them), taken with its Extreme Ultraviolet Imager:
The twin STEREO probes and the SDO are nifty space instruments; I've talked about them before here (with more big Sun images). Here's a massive coronal hole stretching across the top half of the Sun, as seen on February 1-3 of this year by SOHO in extreme ultraviolet:
Not to be left out, there's also the ESA/NASA SOHO probe, which has taken some nifty extreme ultraviolet photos of solar-wind-borne plumes that extend out of large coronal holes that usually inhabit the Sun's poles:
Thanks to webcomics.biz (and the reader(s) who submitted my comic?) for listing A*, even giving it a little capsule review, and making a custom banner thingy for it. Neat! And they've also got an entry for my weekend fairy tale comic, The Princess and the Giant, so double-yay! :D
Well I talked up the current wave of fancy solar probes like STEREO, SOHO, and the SDO yesterday, but it was actually the old Skylab space station that verified the existence of coronal holes back in the '70s with orbital X-ray telescopes; Skylab's studies of the Sun in X-ray and ultraviolet frequencies, as well as others, provided a real breakthrough in solar research. Skylab didn't do so bad getting its own photos of those plumes from polar coronal holes, for instance:
Skylab studied plenty of active regions, too; here's a nice X-ray photo from Skylab showing emissions from magnetic loops in the corona: "the seat of intense magnetic fields, where X-rays escape from heated gas trapped in magnetic loops that connect points of opposite polarity":
I've been a fan of Winsor McCay's fantastic old (1905-1914) Little Nemo in Slumberland newspaper comic strip for a while now, and yesterday I finally got around to watching the 1989 anime adaptation, which, although it involved such luminaries as Ray Bradbury and Moebius in the concepting and writing phases, has really as little to do with the original comic as could be. The characterization is all wrong (the princess is horribly snooty, for instance, and Nemo has been given a Disney-esque flying squirrel companion ;P), and the story is bad. So why am I embedding a YouTube playlist of the full movie?
Well I don't know. It had a tortured production, but it is at least animated well--by the Japanese studio that had just finished animating a rather better movie, Akira. Little Nemo was in fact the first anime with a nationwide theatrical release in the United States (but Akira was the first I saw).
(By the way I just recently added a "playlistembed" tag for embedding YouTube playlists on the A* forum. :D)
Well I've been talking about discoveries made by Skylab in recent posts, but I've never actually dedicated a post to Skylab itself (ie a post in which I summarize Wikipedia's Skylab entry for myself :p), so maybe it's due!
Oh first though I have to remind you, fair reader, about my weekend fairy tale comic, The Princess and the Giant, which updates Sundays, this weekend being no exception. So look forward to a new page of that, and if you need catching up, here's a link/preview to/of last week's page:
After the Apollo program succeeded in landing men on the Moon in the late 60's, NASA knew they'd have to find something else to do with the people and hardware that had been put to work in Apollo. One thing they came up with was using the workhorses of the Apollo program, the mighty Saturn V rockets, as carriers of space station components that would be designed to fit neatly into the shell of one of the rocket's sections; this type of scheme actually went back to ideas that German scientist and "father of American space flight" and all that, Wernher von Braun, had submitted as far back as 1959. A station based on this type of scheme was developed, and the result, Skylab, launched into Earth orbit on a modified Saturn V rocket in 1973.
It ran into trouble right away, though: during launch, wind resistance tore off the station's micrometeoroid shield, damaging the tie-downs holding one of the station's solar panel arrays, and an exhaust plume from a separation rocket fired during one of the later stages of the launch sequence hit the partially deployed solar panel, effectively destroying it. The station made it into orbit, but without its shield, which had also been intended to reflect away some of the heat of the Sun, the interior temperature rose to an uninhabitable 126 degrees F. And the accident in which the shield was lost had not only led to the destruction of one of the solar arrays, but had also caused the other solar array to be stuck pinned to the side of the station, so the overheated station also had a significant power deficit.
The heating was the most immediate problem, as the station would soon get so hot that its plastic insulation would melt, filling the interior with poisonous gas. NASA scrambled and launched a repair mission just eleven days later. Flying around the station in an Apollo Command/Service Module, this is what the three-man crew of the repair mission saw:
^ The torn cables and tubing sticking out on the left side show where the shield had been torn away, exposing that large copper-colored surface. And you can see the jammed solar array on the right-hand side.
To fix the overheating problem, the crew of this repair mission deployed a gold "parasol" over the area originally intended to have been covered by the shield; you can see it in the first photo in this post, toward the bottom of the fuselage; you can also see there the solar array that was pinned now fully deployed (a second spacewalk two weeks later freed it, and finally got sufficient electricity flowing through the station), and (I think) the vacant spot on the other side of the fuselage where the other array would have been, had it not torn off during launch.
With the station habitable again, that crew was able to spend a few weeks engaged in research experiments, including the first detailed observations of the Sun with Skylab's instruments (more on that in the post linked at the top of this article!). In all they spent 28 days in space, which was a record for the time. Two more crews would work in Skylab over the next seven months, each setting a new record for time in space: 59 days for the second crew, and 84 for the third.
By Apollo standards, Skylab's interior was pretty plush. They had a full-sized shower, seen enjoyed here by a member of the second crew
(^ That image is from NASA's Great Images in NASA gallery; I posted some of my favorites from it on the A* forum some time ago--check 'em out, there's great stuff in there.)
Eventually though the crews found showering, drying, and vacuuming away the excess water in zero gravity rather difficult, and settled for just using damp washcloths instead. There's also an interesting note in the Wikipedia article that crews found bending and sitting in zero gravity puts an uncomfortable strain on stomach muscles--without gravity, you have to use your abdominal muscles to stay bent over... So in space, sitting is how you get really chiseled abs, maybe. Or maybe you just get really sore. Here's a mockup of the Skylab dining area from a Smithsonian exhibit; I guess the manikin isn't quite in a full sitting position:
Here's a 1972 NASA diagram of what it was supposedly all going to look like when inhabited; you can see that the big telescope is in the X-shaped solar array, that Apollo CSMs would dock at that end, and that yep, there would have been the second side solar array opposite the first, if it hadn't been torn off during launch (the "APPOLLO" typo is also fun :D--ooh, rocket science!):
Skylab had launched in May 1973, and after those three manned missions, by February 1974, NASA felt that the station, over a year old, was getting too old to be safe for habitation--which seems like a quaint notion nowadays since we're used to say the International Space Station staying up there for years and years, but such was the feeling at the time. But with the Space Shuttle due to be ready in '79, subsequent studies concluded, by '78, that the station, now abandoned for four years, should still be inhabitable ("It still had 180 man-days of water and 420 man-days of oxygen, and astronauts could refill both; the station could hold up to about 600 to 700 man-days of drinkable water and 420 man-days of food"), and a gyroscope that had failed in the interim should be repairable; furthermore, the last crew on the station had boosted the station to an orbit 6.8 miles (10.9 km) higher, which was supposed to keep the station at a relatively stable orbit until at least the early 1980's. Shuttle missions could refurbish the station, and boost it to an even higher orbit, further extending its operational life.
But the Space Shuttle was delayed (the first Shuttle wouldn't launch until 1981), and then it became clear that the station's orbit would not last as long as had been forecast; ironically enough, an unexpected increase in solar activity--that field in which Skylab research had played such a key role--caused increase heating of the upper atmosphere, and thus higher drag on the station, causing it to slow--and thus fall. This increased solar cycle had been predicted in 1976 by the National Oceanic and Atmospheric Administration, but NASA had apparently ignored this, and instead had used what one NOAA scientist called an "inaccurate model" for predicting the solar weather and its effects. And even by late 1977, NORAD was able to predict that the station would re-enter the atmosphere in mid-1979.
NASA had been working on a booster system Shuttles would have attached to the station to boost it to a higher orbit, but it wasn't quite complete, even if they had been able to get some rocket missions ready to take it up to the station. There was nothing for it: Skylab was going to come down, and an international media frenzy began, with bets on where and when it would fall, and contests to be the first to recover pieces. Skylab re-entered the atmosphere on July 11, 1979. NASA tried to aim it for a spot in the ocean off South Africa, but their calculation of how fast it would burn during re-entry was off by 4%, and so pieces instead landed in Australia (NASA had also predicted that the chances of debris hitting a human being were "only" 1 in 152); some debris landed in the Shire of Esperance in western Australia (you know, it had never really occurred to me to consider that there are "shires" outside of Tolkien, such has been my isolation in shire-less regions of the US of A), who in retaliation fined the United States $400 for littering, which of course our government did not deign to pay--but finally in 2009 an American radio host "raised the funds from his morning show listeners and paid the fine on behalf of NASA." Aw.
The author of the webcomic Calamities of Nature has been doing a weekly science blog update, and as he seems actually to keep up regularly with goings on, I have a recent post of his to thank for pointing out that Hubble discovered a fourth moon of Pluto--or scientists using Hubble did, anyway. Currently known by clunky temporary designations--S/2011 P 1, or "P4"--it is a tiny moon with an estimated diameter of "8 to 21 miles (13 to 34 km)," which is a fair deal smaller than Pluto's two other small moons, Nix and Hydra (20 miles (32 km) and 70 miles (113 km) across, respectively), and way smaller than Pluto's largest moon, Charon, which is 648 miles (1,043 km) across (and not really all that much smaller than Pluto itself, which has a diameter of about 2,300 kilometers; in fact, Pluto/Charon qualifies as a binary system, since their mutual center of gravity is above the surface of Pluto--some astronomers, apparently, even call the pair a "double dwarf planet"; another interesting Pluto/Charon factoid is that they're both tidally locked to each other--the same part of the surface of each is always facing the other).
Here are a couple of Hubble's recent shots of the system, in which P4 could be seen:
Hubble was actually being used to look for any rings that might exist around Pluto, and the long exposures it was taking for that allowed the tiny P4 to be visible in the resulting images.
Well! It isn't every day a new moon is discovered in our solar system; and this discovery adds a bit more spice to the New Horizons mission, which is expected to reach Pluto in 2015. Will even more moons be discovered?
Surprisingly, there is no real precise definition of what qualifies as a moon. Wikipedia says: "Every body with an identified orbit, some as small as a kilometer across, has been identified as a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets." So currently the title "moon" is a bit arbitrary; I would hope, though, that if New Horizons finds, say, meter-sized rocks going around in the Pluto dwarf system, they don't call those "moons"; I mean, you've got to draw the line *somewhere*, right? The line has tended to shift around, though; Wikipedia also says
As of July 2009, 336 bodies are formally classified as moons. They include 168 orbiting six of the eight planets, seven orbiting three of the three dwarf planets, 104 asteroid moons, and 58 satellites of Trans-Neptunian objects, some of which will likely turn out to be dwarf planets. Some 150 additional small bodies were observed within rings of Saturn, but they were not tracked long enough to establish orbits. Planets around other stars are likely to have natural satellites as well, although none have yet been observed.
That's a lot of moons already, and with better observation of who knows how many scads of Trans-Neptunian and so on objects there are floating around way out in the far reaches of our solar system, well, some day we may really be up to our ears in moons if something isn't done!
I noticed in an AP article that the Dawn probe now orbiting the giant asteroid Vesta in the Solar System's asteroid belt has sent back more detailed photos. NASA says that Dawn will begin close (1,700 mile distant) orbits of the asteroid for scientific study on the 11th of this month; it will approach as close as 110 miles in its year-long study of the possible dwarf planet.
Based on the images so far, scientists have been surprised by the variety of features on the asteroid's surface, most notably a series of deep grooves along the equator, and a series of three old craters informally called "Snowman" due to their arrangement; you can see them on the left here, with some other grooves visible above them--this is from about 3,200 miles (5,200 kilometers) away (keep in mind that Vesta averages about 530 km--330 miles--across):
In other Solar System exploration news, the Juno spacecraft will launch on Friday for Jupiter. When it reaches the gas giant in 2016, it will conduct a detailed study of the planet's magnetosphere, among other things; Jupiter's magnetosphere should be a good one to study, because unlike a rocky planet like Earth, where a good deal of the magnetosphere is hidden from view inside the planet, with a gas giant like Jupiter the right instruments can see through the gas to study the magnetosphere right down to the center, or thereabouts (it should also be able to tell for sure if Jupiter *has* a rocky center)--also, Jupiter's magnetosphere is over twenty times stronger than Earth's. One question that it is hoped Juno will answer is whether Jupiter's magnetosphere is generated by compressed hydrogen gas inside the planet, where the pressure is so intense that it squeezes electrons off the hydrogen molecules, allowing the gas to conduct electricity, or by hydrogen even farther down, near the core, where the pressure becomes so strong that it compresses the gas down to a liquid called metallic hydrogen. Here's a NASA chart showing the types of hydrogen, along with other elements, in the gas giants:
As you know, in my spare time I while away the hours googling my own stuff, and in the process of doing that this past weekend I found some nice people who've linked to A* in recent months, so now I'm going to thank them. :D A* was on someone's poll for Webcomic of the Year :o, so thanks to whoever that was--how exciting! Thanks to Mark Linimon for including A* on his favorite comics list. And thanks to Samuel John Klein and his ZehnKatzen Times site for the very interesting article analyzing the dramatic power of black and white in the context of A* and The Twilight Zone. :)
Wed Aug 03, 2011 1:17 am
Joined: Sat Aug 07, 2010 8:18 am Posts: 71
Vesta shows the same kind of grooving that we can see on Phobos. This has to be caused by very low-velocity collisions, with ejecta and smaller orbiting thingies rolling over the surface to leave tracks. On Phobos at least one track of an irregularly-shaped chunk that bounced and skipped. On Vesta the rotation must have been a factor. In the asteroid belt there are probably lots of minimal collisions like this.
__________________________________________________________________ Last year I had a calendar from Sky & Telescope with that fantastic pic of Phobos. Plenty of time to stare at it and wonder how those grooves came to be. Also that big crater is strange. Not like it was hit with something really solid, but more like a clumpy aggregate of slush and small pieces. Out there things may never become rock-hard from accumulating but instead be in stages of porosity or light compaction- there's just not enough gravity to stick things together with authority (not counting the big chunks from the breakup of the planet that might have occupied that orbit)... anyway, the hit on Phobos must have broken up and swept over in loose chunks leaving all those mysterious trails and that discoloration where it popped like a bag of powder. This could have even happened when Phobos was still an asteroid, before some orbital excursion brought it too close to Mars. With the entire asteroid ring more or less at the same rate and direction of motion except for the slight differences in relative velocity and spin for each unique mass there's probably lots of bumping and grinding going on in slow motion. Like billiards, or New York taxis!
Last edited by Glennnnn on Wed Aug 03, 2011 7:16 pm, edited 1 time in total.
Black hole news! Data from the Chandra X-ray telescope has been used to come up with the first evidence for hot gas falling into a black hole. The galaxy in which this was observed was NGC 3115, a relatively nearby galaxy at 32 million light years from Earth. This composite image of the galaxy shows blue Chandra X-ray data over a visible light image obtained by the ESO's Very Large Telescope:
The X-ray emissions come from binary stars, and hot interstellar gas; researchers observed that the temperature of the interstellar gas, which they can calculate based on the amount of X-ray energy it emits, begins a marked increase within about 700 light years of the galaxy's center; they think this heating can only be due to the gas being compressed as it is pulled inward by the supermassive black hole at the center. That 700 light year distance is thus NGC 3115's Bondi radius, named after the "Anglo-Austrian mathematician and cosmologist" Hermann Bondi.
A Bondi radius of that size confirms that NGC 3115's central supermassive black hole must contain about 2 billion solar masses, which I think was the approximate value first assigned to it when the hole was discovered back in 1992. That makes it the nearest billion-solar-mass-class black hole to Earth; the supermassive black hole A*, at the center of our own galaxy, boasts only about 4 million solar masses--1/500th the size of NGC 3115's! (Remember though that we already know of larger ones: M87's has been measured at about 6.6 billion solar masses, and the one at the center of OJ 287 *might* be about 18 billion solar masses.)
From the sound of his Wikipedia article, Bondi was a pretty interesting fellow. An Austrian, his prowess in mathematics took him to Cambridge in 1937, at the tender age of 18, allowing him to escape the persecution of Jews in his native country--but then, once World War II broke out, he was interned on the Isle of Man and in Canada--due to his Austrian nationality, I guess. But he went on to become a lecturer in mathematics at Cambridge, and a British subject.
And for a time, Bondi contended with the Big Bang: before the discovery of cosmic background radiation in 1964 thrust the Big Bang theory, which predicted such radiation, to the forefront, the Steady State theory developed in 1948 by Bondi, Fred Hoyle, and Thomas Gold held some sway as the scientific explanation of the universe. Einstein's general relativity had shown in 1916 that a static universe was impossible, and Edwin Hubble had shown in 1929 that the universe was expanding; the Steady State theory tried to reconcile these observations with a belief in an eternal, essentially unchanging universe--a belief Einstein had shared before Hubble's breakthrough--by positing that matter is continually created as the universe expands, keeping the average density of matter in the universe steady over time. This sounds goofy to us now, but it was tantalizingly difficult to disprove for a while, since, as Wikipedia says, "the amount required is low and not directly detectable: roughly one solar mass of baryons per cubic megaparsec per year or roughly one hydrogen atom per cubic meter per billion years, with roughly five times as much dark matter." Needless to say, the Steady State theory has long been discredited; fortunately for black hole fans, Bondi would go on to much more scientifically grounded theories. :)
The galaxy I was talking about yesterday, NGC 3115, in which hot gas has for the first time been observed falling into a black hole (and a 2-billion-solar-mass supermassive one, at that), is a lenticular galaxy; lenticular galaxies are disc-shaped like spiral galaxies such as our own Milky Way, but don't have clearly defined spiral arms; they also tend to be brighter and to have larger central bulges than spiral galaxies. Since they don't have the spiral star formation areas of a spiral galaxy, they have less ongoing star formation, and tend to consist of older, redder stars. There have been theories that lenticular galaxies are old spiral galaxies whose arms--the primary star-forming regions--have used up all their gas in star formation; however, the greater brightness and larger central bulge of lenticulars suggest that there is more to their formation than just fading from a spiral. Another theory is that they're the result of a galactic collision or merger that sucked the gas away from the original spiral arms, but the bulge and the types of stars they contain don't make them an easy fit for that model, either.
I've mentioned a lenticular galaxy before, which also happens to be the largest known galaxy in the universe: IC 1101 weighs in at about 100 trillion solar masses--our spiral Milky Way galaxy, by comparison, has 0.25 trillion. So those lenticulars must be doing something right. I've got a couple pictures of IC 1101 in the post I made about it in February.
IC 1101 may be a bit bland-looking for all its size, but don't let that make you think that all lenticular galaxies are dull. For instance, the lack of spiral arms makes the bands of dust in NGC 2787 (a barred lenticular galaxy about 24 million light years away) stand out in rather impressive fashion, as captured by Hubble in 1999:
The Cartwheel pretty definitely *is* the result of a galactic collision--probably with one of the two smaller galaxies to its left, or a third candidate galaxy not in the frame, which would have passed through the center of the larger galaxy. The collision produced two waves of intense star formation, now visible as an inner orange ring and outer blue ring; the outer ring is about 1.5 times the size of the Milky Way. But for some real fireworks, lets look at it in a composite of different wavelengths:
image by NASA/JPL-Caltech/P. N. Appleton (SSC/Caltech) (source)
^ That's blue for ultraviolet (from NASA's 2003 Galaxy Evolution Explorer satellite, or "GALEX"), green for visible light (from Hubble), red for infrared (from Spitzer), and purple for X-ray (from Chandra). For our purposes, the pink areas around the outside of the Cartwheel are the most interesting: those are areas of both high ultraviolet and X-ray emission, likely being generated by material being sucked off binary companion stars by stellar black holes. The blue ultraviolet of the outer wheel as a whole suggests that that intense star-forming region is creating large stars, 5-20 times the mass of the Sun. The orange center is visible and infrared emissions from the second wave of star formation; the green areas are older, less massive stars, whose primary emission is in the visible spectrum.