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The Deepest Photo Ever Taken 218

Posted by timothy
from the whoah-dude-that's-deeeeep dept.
Astroturtle writes "Astronomers using the Hubble Space Telescope's powerful new Advanced Camera for Surveys (ACS) have taken the deepest visible-light image ever made of the sky. The 3.5-day (84-hour) exposure captures stars as faint as 31st magnitude, according to Tom M. Brown (Space Telescope Science Institute), who headed the eight-person team that took the picture."
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The Deepest Photo Ever Taken

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  • by MrP- (45616) * <> on Saturday May 10, 2003 @11:41PM (#5929003) Homepage
    I thought the Goatse man was the deepest photo ever taken. :P

    (Sorry, federal law requires that this joke be made.)
  • article (Score:3, Informative)

    by CowBovNeal (672450) on Saturday May 10, 2003 @11:42PM (#5929007) Homepage Journal
    May 7, 2003 | Astronomers using the Hubble Space Telescope's powerful new Advanced Camera for Surveys (ACS) have taken the deepest visible-light image ever made of the sky.

    The 3.5-day (84-hour) exposure captures stars as faint as 31st magnitude, according to Tom M. Brown (Space Telescope Science Institute), who headed the eight-person team that took the picture. This is a little more than 1 magnitude (2.5 times) fainter than the epochal Hubble Deep Fields, which were made with the Hubble's Wide Field and Planetary Camera 2. It is 6 billion times fainter than what can be seen with the naked eye.

    Brown and his colleagues chose to point at a spot 1 southeast of M31, the Great Andromeda Galaxy, in order to get a census of faint stars populating M31's outer halo. The full ACS image is about 3.1 arcminutes square, the size of a sand grain held at arm's length against the sky. The ACS magnifies this small field into a vast panorama of some 300,000 stars and thousands of faint background galaxies. At M31's distance of 2.5 million light-years, the faintest of the stars are slightly less luminous than our Sun. A large fraction of the most distant galaxies appear patchy and irregular, testimony to the collisions and mergers in the early universe that built up the familiar galaxies we see closer around us today.

    Most of the stars in the image indeed proved to be in M31's halo, judging from their colors and brightnesses. Moreover, they show a surprisingly wide range of estimated ages -- from 6 to 13 billion years, compared to 11 to 13 billion years for our Milky Way's halo stars. Perhaps M31 has captured and torn apart younger dwarf galaxies than our Milky Way has done. Or perhaps M31 underwent a massive, disruptive merger with a single large galaxy billions of years ago; in this scenario some of M31's younger disk stars could have been flung into its halo. Or maybe some combination of these events triggered waves of star formation in regions that ended up in M31's outer fringes.

    The image was made in two colors: near-infrared and "visual" (a band spanning the part of the spectrum running from yellow through green). The renditions displayed here were crafted to resemble true-color views by interpolating from these two colors. These vignettes each show only about 1 percent of the ACS image. The full image is available from the Hubble Telescope's press site at various qualities and sizes (up to 128 megabytes), along with more highlights and a finder chart showing its relation to M31.

    Plans are afoot for an even deeper "Ultra-Deep Field," which will use ACS for longer exposures in four colors and go slightly fainter still.
  • 3.5 Day Exposure? (Score:5, Interesting)

    by Anonymous Canard (594978) on Saturday May 10, 2003 @11:46PM (#5929023)
    Imagine a Beowulf... um. Seriously, how do you cope with reciprocity failure in a 3.5 day exposure. I would have thought that stray heat or electron flow would turn the whole image to static with such a long exposure. HST must consist of unfathomably cool (literally and figuratively) electronics.
  • by HotNeedleOfInquiry (598897) on Saturday May 10, 2003 @11:48PM (#5929034)
    Just how many photons they detected for the faintest star.
    • I haven't read the article, but I do have a degree in astrophysics, so I can guide you in how to calculate it.

      There are a few different ways of measuring magnitude (apparent, bolometric, etc). Bolometric is essentially the integral over all wavelengths. I'm guessing they didn't do a real bolometric measurement, but I could be wrong.

      Anyway, the relationship between intensity (I) and apparent magnitude (m) is

      m = -[19 + (2.5).log(I)]

      Intensity is in units of power/area, such as W/m^2 or ergs/cm^2 (cg

      • by Anonymous Coward
        How can you, having studied astronomy, having an understanding of the vastness of space, still participate in such worthless endeavors as racism? How can you consider that important, worthwhile, or right?
      • MOD PARENT DOWN. (Score:2, Informative)

        by Anonymous Coward
        Moderators: Please don't encourage this guy in any way, even if this comment of his may very well contribute to the technical discussion.

        He doesn't deserve positive karma until he learns some respect. When he learns to treat people of all colors as he wishes to be treated himself, then perhaps he can contribute to the discussion in a worthwhile manner.

        What goes around, comes around. Paranoid delusions about people of other races (sexes / political and religious beliefs) are so 1700's and have no place in
      • by supernova87a (532540) <> on Sunday May 11, 2003 @10:28AM (#5930617)
        Ok, here's the calculation for you curious types, regarding how many photons arrived from the faintest star in the picture:

        Let's suppose that the picture was taken in the "V" filter. I just happen to have the number of photons per second per meter squared that arrive from a star of 20th magnitude: 86.157. (taken from here []).

        So the faintest stars in this picture are 31st magnitude? That's 11 mags fainter than 20, which by the handy old formula

        mag1-mag2 = -2.5 * log(flux1/flux2)

        which means that the 30th magnitude star puts out about 4x10^(-5) times as much flux.

        Using the reference star's flux from above, this means that 0.0034299 photons per second per meter squared arrived at Hubble. The exposure was 84 hours, and the area of Hubble is (2.5m)^2*pi, so tada:

        The total number of photons in the picture from the faintest star is: 20365.83

        Still not too shabby. They probably could have found even fainter stuff.
      • I think this guy may be an example of a freak-whore. I noticed that $$$$$exygal, the ultimate fan-whore, is in his freaks list. Oh, the irony.....
    • by Liquid Tip (672473) on Sunday May 11, 2003 @01:04AM (#5929277) Homepage
      The best way is to download the processed HST images and see what the count rate is for a faint star. Then multiply by the gain (in the header of the image) which will give you the number of photons detected. A way to guestimate the number of photons is to compare the flux of the faintest star with the Sun. At the Earth's distance the Sun has a flux of 1.36x10^6 erg s-1 cm-2 and the apparent mag of the sun is V=-26.8. If we assume that we have a star with V=31 mag (the 50% completeness level is V=30.7 mag) then the flux recieved from the star is given by: F2/F1 = 100^((m1-m2)/5) where F1 and m1 are the flux and magnitude of the sun and F2 and m1 refer to the star. This gives 1.03x10^-17 erg s-1 cm-2. Convert the ergs into photons by the de Broglie frequency (E=hv) where we assume that a V-band photon has a wavelength of 550nm or a frequency of 5*10^14 s-1. Thus, each photon carries 3.61x10^-12 ergs which gives a rate of 2.85x10^-6 photons s-1 cm-2. So a 3.5 day exposure is 302400 secs and HST has an aperature of 240 cm so we get about 50000 photons at the entrance of the telescope. Remember.. detection of these sources means having a low background so that these photons are not lost in noise! I should also point out that HST does not leave the shutter open continuously for 3.5Hs, instead it takes a series of short exposures that are co-added. I hope this helps (and doesn't freak people out!)
  • What fstop was that?
  • by d-rock (113041) on Saturday May 10, 2003 @11:52PM (#5929059) Homepage
    3.4 day exposure? Even for a space-based platform, that has to be really stable to produce a good image. Does anyone out there have any info on how they maneuver the telescope to keep it pointing at the same point while minimizing shifts in the field?

    • While I'm no expert, I believe the answer is simply "gyroscopes". Very good ones, I'm sure. Also, they use reference stars to correct the gyroscopes when they drift.
    • by deathcow (455995) on Sunday May 11, 2003 @12:06AM (#5929102)
      Many spacecraft have small jets that push them into different positions in space. Hubble has no jets because the exhaust gas from jets could damage its delicate mirrors. Instead, Hubble uses momentum to move.

      When Hubble needs to move to a new target, engineers on Earth radio a signal to the HST flight computer. The flight computer then activates the Reaction Wheels.

      Reaction wheels are heavy fly wheels that spin. As they spin, the momentum from their motion causes the telescope to move. There are four Reaction Wheels. By spinning each one at a certain speed and in a certain direction, engineers can point the telescop e anywhere they want.
      • by neurostar (578917) <neurostar.privon@com> on Sunday May 11, 2003 @12:23AM (#5929163)

        As they spin, the momentum from their motion causes the telescope to move.

        Well, it's techincally a litter different than that. The wheels don't actually cause hubble to translate within a plane. Instead they rotate hubble. By turning the spinning wheels, a torque is exerted on hubble, causing it to rotate.

      • by d-rock (113041) on Sunday May 11, 2003 @12:36AM (#5929200) Homepage

        Interesting. I was actually thinking more along the lines of automatic compensation, but I hadn't even thought about gyroscopes vs. impulse jets. I poked around a little on the hubble site for the instrumentation and flight computer and I found the handbooks for the instruments at this site []. Appearently, the gyroscopes are used for coarse motion detection and the FGS uses constellational guidance. The manuals actually make a pretty interesting read.

        On a side note, a constellational guidance is related to how head mount displays like UNC's HiBall [] work.

      • Many spacecraft have small jets that push them into different positions in space. Hubble has no jets because the exhaust gas from jets could damage its delicate mirrors.

        Another reason that gyros are used is much more practical: fuel storage limitations. For a satellite that is to be in orbit for years and will be constantly redirected, the fuel required for something like that would be many times the mass of the satellite, and thus impossible to put into orbit.
    • by LMCBoy (185365) on Sunday May 11, 2003 @01:03AM (#5929271) Homepage Journal
      3.4 days is the effective exposure time, from stacking many shorter exposures. If HST integrated for 3.4 days without reading out the CCD, the entire chip would be saturated with cosmic rays, not to mention the fact that the Earth is typically in the way for half the orbit(*), limiting individual exposure times to about an hour or so.

      (*) except for a small patch of sky called the CVZ: continuously visible zone

      BTW, if you're keeping score at home, 30th magnitude is 1 trillion times fainter than the human eye can see!

      [*shameless plug* Tom Brown is using my thesis code to analyze these data :) ]
    • by supernova87a (532540) <> on Sunday May 11, 2003 @10:37AM (#5930648)
      The Hubble has an instrument called the Fine Guidance Sensor (FGS) package. Given two stars that are bright enough near the sky location of your desired target, Hubble will be able to guide to within sub-pixel accuracy for as long as you like.

      If only one star is available, guiding is still possible, but the field may slowly rotate, since one star only provides one of the two needed pointing constraints (of position and orientation).

      A big project in preparation for Hubble was the creation of the Hubble Guide Star catalog, exactly for this purpose -- to make sure that given what people would want to observe, there would always be enough guide stars within an acceptable distance!

      for more information, see here [] if you're interested! If you're ambitious, you can even read the instrument handbooks for yourself: here []
  • by bertok (226922) on Sunday May 11, 2003 @12:05AM (#5929097)
    Direct link to the full-resolution JPEG. (~4.9MB) a/formats/full_jpg.jpg []
  • by SILIZIUMM (241333) on Sunday May 11, 2003 @12:06AM (#5929101) Homepage
    See also the press release [] with tons of photos. Enjoy your new wallpaper ! :)
  • (Score:5, Informative)

    by zaneIO (606505) on Sunday May 11, 2003 @12:07AM (#5929104)
    Here is a link to a higher resolution image. []
  • by jeffrey1681 (148195) on Sunday May 11, 2003 @12:15AM (#5929136)
    The image is not actually a single exposure of 3.5 days in duration, but is actually made from 250 separate exposures taken from Dec. 2 to Jan. 11, 2003. The total exposure time was 3.5 days.

    For those who are interested, the original hubble press release is located here [].

    The site includes the image in a variety of different formats, including a 123 MB tiff file.
    • It is doubly misleading. In a single exposure, the SNR increases as the exposure time. On the other hand, when you combine multiple images, you get noise from each image. Thus signal increases linearly and noise increases as a square root of the number of images combined. If all (250) images had identical exposure time, the resulting image has 16 times less SNR than a single image of 3.5 days exposure. This is the worst case and in this case, it is equivalent of about 5 hours exposure. So effectively, they
  • by Anonymous Coward
    Aristotle writes: "Philosophers using the Bubble Head Telescope's powerful new Advanced Cognition for Sophistry (ACS) have taken the deepest thought ever thunk. The 3.5-day (84-hour) idea captures notions as powerful as 31 SBU (Silent Bob Units), according to Plato (The Platonic Academy), who headed the eight-person team that contemplated the thought."
  • Streaks (Score:2, Insightful)

    by stratjakt (596332)
    If you look at the image, there are some odd streaks that go from red to blue (or blue to red).

    I'm just curious here, what are they? I thought maybe it could be a bit of space debris that whizzed in front of the camera, but with an exposure of 3.4 days, the streak would go from one side or another.

    What moves that far in 3.4 days? A comet? A meteor? A star?

    And that big bright cluster in the lower bottom, what's that? It looks pretty close galaxy-wise.

    It's a neat pic for sure, a little blurry, which
    • Re:Streaks (Score:3, Interesting)

      by localghost (659616)
      If you look at the image, there are some odd streaks that go from red to blue (or blue to red).
      I'm just curious here, what are they? I thought maybe it could be a bit of space debris that whizzed in front of the camera, but with an exposure of 3.4 days, the streak would go from one side or another.

      The streaks are probably something that moved, though some of them seem brighter in the center, which would indicate it was oscillating. I'm not exactly sure. Anything could move any distance in 3.4 days.

      And t
      • Actually, if you read the article, that globular cluster is actually one of M31's clusters. The brightest globulars around M31 are about 13th magnitude, so they are visible in amateur telescopes (although they look like faint stars).

        It does show impressively how good the resolution of the photograph is.
        • The article was slashdotted, so I just guessed from pictures. It was hard to tell, but it looked like it was in front of the galaxy. I know nothing about astronomy, though.
    • Re:Streaks (Score:5, Informative)

      by Liquid Tip (672473) on Sunday May 11, 2003 @01:15AM (#5929311) Homepage
      The "streaks" centering on stars are diffration spikes from the secondary mirror support. The colour alternates as different wavelenghts cause different diffration spacings.

      The big bright cluster is actually a member of Andromedae (M31). Very impressive! The appearance of fuzziness is because the CCD oversamples the resolution of the telescope - which is necessary for good photometry - if you want it "sharp" then just bin the pixels by 2x2 or 3x3 or whatever looks best!
  • by Jerf (17166) on Sunday May 11, 2003 @12:31AM (#5929185) Journal
    Something I've wondered for a while... what's up with the points coming off the stars? I've always accepted it when I see it with my own eyes because I don't expect my own eyes to be optically perfect, so I always thought it was distortion, but looking at the full image [] I see that the brightest stars once again have points coming off of them in four directions. Typically they are directly up, down, left, and right, but in that image, they appear to be about five to ten degrees off that.

    The biggest example I see is about 3/4s of the way to the right and about 1/5 of the way down on the image, where there is a huge-looking star.

    Why four points? Why do we see them even when the star itself is not in the picture (look on the top border for examples, like the one almost directly in the middle)? I guess I would expect that if the light source is too bright the spread would be in a circular formation and simply blur the star, not blur it in just those four directions so much stronger then the rest.

    Is it just QM at play? If so, why it is almost always directly up, down, left, and right, instead of random and perhaps even changing over time directions (which probably would get right back to simply looking blurred)? Detector flaws?
    • by Anonymous Coward on Sunday May 11, 2003 @12:43AM (#5929224)
      Modern optical/IR/UV telescopes typically have a large primary mirror, which reflects light back to a smaller secondary, which reflects the light through a small hole in the primary to the detectors. The secondary is supported by little rods. It is diffraction of light by those supports which cause stars to have distorted shapes.

      (Astronomers understand the diffraction issues very well... it's usually not a problem; it just looks weird.)

      - A friendly neighborhood astrophysicist
    • Almost all modern optical/IR/X-ray telescopes use a CCD to capture the light that is incident on the telescope. Each pixel in the CCD can hold a certain number of electrons (which are produced when a photon hits the pixel). When that number is exceeded, usually through too many photons hitting the same pixel as in this case, the electrons spill over into the surrounding pixels. This is called blooming and produces the spikes that you see in the image. So basically, the spikes mean that the star is overe
    • by fmaxwell (249001) on Sunday May 11, 2003 @01:28AM (#5929350) Homepage Journal
      Something I've wondered for a while... what's up with the points coming off the stars?

      As was mentioned in another post, those are diffraction spikes from the supports for the secondary mirror.

      Newtonian reflectors [] and classical Cassegrain [] telescopes support their secondary mirror with "spiders" that produce diffraction spikes. There have been various efforts over the years to eliminate these from that type of telescope. One method is to seal the tube with an optical flat (a flat piece of optical glass) which supports the mirror. The trade-offs include longer times for the scopes to reach temperature equilibrium, distortion from imperfections in the optical figure of the flat, and slight light loss. Other attempts have included the use of spiders with curved support arms [], which reduce or eliminates spikes at the cost of slightly degraded overall image contrast.

      Other telescope types, such as refractors [], Maksutovs [], Schmidt-Cassegrains [], and Yolo reflectors [] have no diffraction spikes, but they are all more optically complex (Yolos, for instance, require toroidal mirrors) and are more difficult to produce as a result. Refractors have the added problem of chromatic abberation, which is the fringing of color on the edge of bright objects. Various complex, multi-element objectives have been developed to reduce, or even practically eliminate, this problem. The problems are optical complexity, cost, and light loss. Figuring a 3-element objective lens for a refractor means grinding six optical surfaces with precise curves. Compare that to a Newtonian which has a single parabolic primary mirror and a flat optical secondary.

      There are many other telescope types than the few popular types I mentioned here and each have their proponents. Most designs that have survived the test of time can be made to perform well, but each has trade-offs.
      • Aren't the diffraction spikes a predictable optical effect based on the star's brightness? Why isn't the effect corrected out of the image in postprocessing?

        I suspect that they leave them in because it looks dramatic and romantic for press releases. :)

        • Aren't the diffraction spikes a predictable optical effect based on the star's brightness? Why isn't the effect corrected out of the image in postprocessing?

          Subtracting data from scientific images is not a good idea. What if there is a dimmer star hidden in a diffraction spike? The next image of that section of sky is unlikely to be taken by a scope with diffraction spikes rotated relative to the former. Then, suddenly, they show a star that was "missing" on the post-processed image. At the very least
          • The next image of that section of sky is unlikely to be taken by a scope with diffraction spikes rotated relative to the former.

            Oops! I meant to say "likely" rather than "unlikely." Sorry for any confusion that may have caused.
    • They're artifacts caused by the supports for the secondary mirror.

      You know when you're watching a movie, if the lens points close to the sun, you see a sequence of little polygons move across the field? That's the image of the actual aperture being reflected off the many glass/glass and glass/air surfaces in the lens. (Modern lenses are complex, and are made of many "simple" lenses stacked together.)

      Since the secondary mirror is in the "opening" of the telescope, it needs to be supported. The supports c

    • Why four points? Why do we see them even when the star itself is not in the picture (look on the top border for examples, like the one almost directly in the middle)?

      No quantum mechanics, just plain ol' classical optics. Those are diffraction patterns. Crosses are the Fourier transform of a square, so I assume their aperature stop is a square.


  • Very impressed... (Score:3, Insightful)

    by Dynedain (141758) <slashdot2 AT anthonymclin DOT com> on Sunday May 11, 2003 @12:31AM (#5929186) Homepage
    I know there are countless galaxies out there...but they are so far away, I was extremely surprised at how many galaxies I could see in the big 4MB JPEG.
    • Re:Very impressed... (Score:5, Interesting)

      by LMCBoy (185365) on Sunday May 11, 2003 @01:33AM (#5929367) Homepage Journal
      Actually, the really unique thing about this image is the stellar populations. The stars you see in the image are almost all in the Andromeda galaxy (aka M 31), seen here [].

      M 31 is 2.2 million light-years away. This is the galaxy that Hubble originally resolved into stars, thereby settling the Shapley-Curtis debate [] on the true scale of the Universe. However, the stars Hubble saw were the very brightest supergiants in M 31. In this HST image, we see stars 2 magnitudes fainter than the ancient main-sequence turn-off; i.e., stars which are intrinsically fainter than our Sun! This lets us learn a lot about the ages and chemical composition of M 31's halo stars, which turn out to be quite different from the stars in our halo (our halo is entirely composed of ancient, metal-poor stars; M 31's halo contains stars that are only 6 Gyr old, and much more metal-rich than our halo).

      I heard Tom Brown give a talk on this work last week; very cool stuff.
  • by jkauzlar (596349) on Sunday May 11, 2003 @12:38AM (#5929210) Homepage
    desktop background ever created :) Its sure worth the effort, however!
  • by Anonymous Coward
    I just thought about how detailed the full size pic is, and how to appreciate that without a poster printer. I'd like to see something similar to osx's default screensavers (with the softly zooming pictures of trees/beach, etc) and have it use this picture.

    I'd like to see it zoom in to the picture, while also changing x/y of the camera on a spline (etc). And each time choose a different starting point, and make it's speed adjustable.

    All of those high-res pics are beautiful! maybe i'm 'a gonna dust off the
  • by glrotate (300695) on Sunday May 11, 2003 @12:45AM (#5929234) Homepage
    The grandeur of such an image almost forces one to reasses their place in the world. To think that the area in the photograph is equivalent to the area covered by a grain of sand at arms length is mindnumbing. The universe is unbelieveably amazing.
  • "Your Web browser appears to be set to block cookies. requires a cookie file, though you may visit the site without supplying any personal information, rendering the cookie anonymous. If you believe you reached this page in error, try clicking one of the links below to access our site."
  • ...and I can't even find my keys!

  • Will be about 20 billion light years, since we think the universe is about 20 billion years old.

    For an interesting article, see: ID =000F1EDD-B48A-1E90-8EA5809EC5880000

    On parallel universes. Very interesting reading. If you're at a university, you will be able to browse the site's archives and access the nice PDF version of the article (which has the pictures supersized to full-page size).
    • I believe the current estimates are 13.5 or 14 billion years, and have been for a couple of years.
      • by dh003i (203189)
        I hadn't bothered to look for the latest figures.

        Of course, my statement was oversimplistic. If we survie another 1 billion years, then the furthest object we'd be able to resolve would be 14.5-15 billion light years away.

        Anyways, the article on parallel universes is very interesting. Somewhere out there, there's a universe where I'm dictator of the world! ;-)
    • by LMCBoy (185365) on Sunday May 11, 2003 @01:47AM (#5929407) Homepage Journal
      You're right, if you take deepest image to mean "image of most distant objects" instead of "faintest objects". However, the Universe is 13.7 Gyr old, not 20 Gyr.

      Here's your deepest image then: _ilc_64 0.jpg

      That's from the recent WMAP mission, which mapped the cosmic microwave background in exquisite detail, pinpointing the age of the Universe (and many other cosmological parameters) to high precision. You're looking at an all-sky image of the Universe as it looked when it was 100,000 years old, and became transparent for the first time. IOW, you are literally seeing the fires of creation.

  • And to think any one of those smaller stars could have a planet orbiting it.. with its own culture and civilization and technology. Wow...
  • Damn, (Score:5, Funny)

    by fireman sam (662213) on Sunday May 11, 2003 @01:08AM (#5929293) Homepage Journal
    I'd hate to have to hold my finger on the button for that long without shaking the camera.

    *This is a lame joke*
  • So I dl'd the huge tiff. Awesomeness. But I cant quite see that Galaxy...

    Long, Long ago, far, far away ...

    Rifed with Intergaltic Civil War.

    Sorry, I mean Gentrification.

    I guess 25 Million (?) light years just isnt enough ;(
    • Re:A Galaxy ... (Score:3, Interesting)

      Don't forget, this is only 3.1 arcminutes^2 of the sky. that's the size of a grain of sand held at arms-length against the sky, according to the article. That leaves a ton of sky still unseen.

  • Mirror of full JPG (Score:5, Informative)

    by idiot900 (166952) on Sunday May 11, 2003 @01:24AM (#5929335)
    [] bl e/full_jpg.jpg

    is a mirror of the full JPEG - about 5M. Enjoy.
  • Big Picture... (Score:5, Interesting)

    by HobbitGod42 (568144) on Sunday May 11, 2003 @01:30AM (#5929355) Homepage
    Does anyone know if there is a BitTorrent file out for the 128mb TIFF? the nasa servers are a bit slow and I feel my hardware cycles and bandwidth could be of use...
  • by Nintendork (411169) on Sunday May 11, 2003 @01:35AM (#5929372) Homepage
    This is the official site [] where the photos are.


  • by Beautyon (214567) on Sunday May 11, 2003 @05:52AM (#5930002) Homepage
    The most intersting thing about these images now is the fact that they are not blurred:

    This Nature [] article describes how....hmmm I had better quote:

    "As a beam of starlight hops towards us through countless Planck times, its speed varies. This would smear the beam out so that different parts arrive at different times and distort our picture of where it came from. The longer the journey, the bigger the smear."

    So that means that these deep Hubble photographs should all get more blurry the deeper you look and not razor sharp like we have come to love.

    Its a fascinating problem!
    • I've read that paper, and there's a major problem - they do the calculation in the direction of propogation, but then try to use the result in the transverse direction. You can't do that. No one's done the calculation in the transverse direction, so we still don't know what the theoretical prediction should be.

      • Dimes will get you dollars that the "theoretical prediction" is EXACTLY what we're seeing. Otherwise, it's not much of a theory, is it, and there's not much mileage in telling your thesis advisors that they've been smoking crack for twenty years.

        "But wait!" you say. "Perhaps the graduate student in question would come up with a NEW and IMPROVED theory!" Right. In which case, her "theoretical prediction" would be EXACTLY what we're seeing, right? =)
    • Wouldn't that simply cause 'Temporal Blur' .. so that if something was moving it would appear blurred. Most of what we see is moving so slow (from our point of view) that it may as well be static - so we'd never notice a bit of temporal smear.


      NOTE: I don't know what I'm talking about :)
  • Hey pr0n [],

    Looks like your site has some opposition!!!!

    Props to you, dude!!
  • by ortholattice (175065) on Sunday May 11, 2003 @08:26AM (#5930292)
    The article says 300,000 stars were captured in 3.1 arcminutes. Let's see, assuming uniform distribution of them:

    a = angle subtended by capture (radians) = 2*pi*3.1/(360*60) = .000901
    b = area of capture on a sphere of radius 1 =approx= a^2 = .0000008118
    c = fraction of entire sphere = b/(4*pi) = .0000000646
    d = number of visible stars in entire sky = 300000/c = 4,643,000,000,000

    So that means almost 5 trillion stars are visible by Hubble in the entire sky. That's a lot of stars to catalog. (Assuming I didn't err like they did in the $97 trillion RIAA calculation... someone pls double check and flame me if appropriate.)

    • Afraid I don't quite agree with your detective work, there :)

      Your mistake is the assumption that this image is representative of the entire sky's stellar density. HST was pointed near the Andromeda Galaxy for this image; almost all of the stars you are seeing are in the Andromeda Galaxy. Most points on the sky will have a much lower density of stars. See, for example, the Hubble Deep Field [], which was purposely pointed at an "empty" region of sky, and which contains only a handful of stars.
    • They pointed the HST at an area of sky 1 degree southwest of the Andromeda galaxy, M31. They wanted to take a census of stars in the halo of M31. So the number of faint stars/sq.arc.min. in this region of the sky is likely to be higher than in other areas. Even though the Milky Way also has an halo of stars that extends in all directions, and so faint stars would be expected to be seen by Hubble if it pointed in any direction, M31's halo of stars would be concentrated in the area of M31 and cause a local
  • Someone above mentioned 31st magnitude is a trillion times dimmer than what the human eye can see. And someone else mentioned that the faintest star in the image was made with about 20,000 photons captured over 3.5 days.

    Something seems strange. I remember hearing that the human eye can discern a single photon, as from radioactive breakdown in a wristwatch face. I found something to back that up here [] and here [] (actually apparently single photons are discarded as noise; 2 or three are better).

    So by my c

The trouble with opportunity is that it always comes disguised as hard work. -- Herbert V. Prochnow