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Space Science

Light Echoes Solve Mystery of Tycho's Supernova 98

Ponca City, We love you writes "Powerful telescopes in Hawaii and Spain are using 'light echoes' from the original supernova explosion that have bounced off dust in the surrounding interstellar clouds to identify the precise type of supernova that Tycho Brahe saw 436 years ago. Although the echoed light from Tycho's supernova is around 20 billion times fainter than the original light observed in 1572, the team took identical images of the sky a few months apart and then digitally subtracted one from the other to find evidence for several sets of light echoes rippling across patches of dust in the northern Milky Way. 'Using light echoes in supernova remnants is time-travelling in a way, in that it allows us to go back hundreds of years to observe the first light from a supernova event. We got to relive a significant historical moment and see it as the famed astronomer Tycho Brahe did hundreds of years ago,' said Tomonori Usuda, of the Subaru Telescope in Hawaii. Tycho's original observations were particularly important as he immediately concluded that the new star, visible even by day, could not be closer than the Moon challenging the Aristotelian view of the cosmos, widely accepted since ancient times, which held that the sky beyond the Moon never changed."
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Light Echoes Solve Mystery of Tycho's Supernova

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  • by suso ( 153703 ) * on Friday December 05, 2008 @10:05AM (#26002159) Homepage Journal

    That is really cool. Like some kind of galactic diff.

    • That seems like it opens up a completely new view of the universe from the past if I understand correctly. They can diff images in all directions and identify unknown supernova events in the past?
  • Tycho! (Score:1, Funny)

    by gmccon ( 179305 )
    Did anyone else know that web comics predated the Internet? Tycho Brahe has been keeping it real for hundreds of years!
  • by Tx ( 96709 )

    "Light echoes?" Is there something wrong with the word "reflections" now? Hmm, let me just check my light echo in the mirror..yep, still pretty.

    Amazing work though, from my laymans perspective it seems incredible that they can get usable data in this way.

    • Re:Light echoes? (Score:5, Insightful)

      by Vellmont ( 569020 ) on Friday December 05, 2008 @10:19AM (#26002311) Homepage

      Is there something wrong with the word "reflections" now?

      In human experience, a reflection is instantaneous, where an echo appears after a period of time. Thus echo is more descriptive to layman (remember them?). You know and I know that a reflection isn't instantaneous, it's just not generally perceptible to our eyes like an echo is perceptible to our ears.

    • Re:Light echoes? (Score:5, Interesting)

      by Sockatume ( 732728 ) on Friday December 05, 2008 @10:24AM (#26002357)
      "Echoes" evokes the idea that the light from the star first reaches us directly, then a delayed reflection of that light reaches us afterwards. "Reflections" are colloquially assumed to be instantaneous. I think it's a neat bit of semantics, really.
      • by Yvan256 ( 722131 ) on Friday December 05, 2008 @10:44AM (#26002559) Homepage Journal

        HA-ha! You like semantics! /Nelson Muntz

      • Reflections are not instantaneous. (Yes, I'm annoying...but correct.)
        • Re: (Score:2, Insightful)

          by osu-neko ( 2604 )
          True. Actually, the real difference between the meaning of the word "reflection" and "echo" lies on in the delay but in the repeat. An echo is a reflection that is perceiving after one has already perceived the same thing the first time. So, although you see the gun fire and a second later here the report, that first hearing of the report is not an echo. But when you then hear the same report reflected off of the wall behind the guy firing the starting pistol, that is an echo. Since we saw the original
          • I understood that echo was a useful term in this context, but I couldn't figure out why it was better than reflection. You, sir, have expressed what I could not quite put my finger on.

            You're proof that the int3rpipes is more than just trolls, flamewars, and idgits...thanks!

        • by Lijemo ( 740145 )

          Thats why he said "are colloquially assumed to be instantaneous" instead of "are instantaneous"

          • That's a cop-out. See previous response to my comment for the correct interpretation of the semantics. (btw, osu-neko ftw!)

            Why do I say it's a cop-out? Because it can be applied to any bad definition with equally valid results. For instance, I now assert that the poster to whom you refer "is colloquially assumed to be wrong" as support for my response. See? Meaningless.

    • Re: (Score:3, Interesting)

      by nschubach ( 922175 )

      That's alright, I'm still trying to figure out which way is 'North' in space... Does North always point to the magnetic pole of Earth even on Mars? Has someone studied the Milky Way and determined that there's a magnetic ring perpendicular to the dish?

      • Re:Light echoes? (Score:5, Informative)

        by mrsquid0 ( 1335303 ) on Friday December 05, 2008 @11:08AM (#26002815) Homepage

        North in the sky is defined to be the point directly above the Earth North Pole of rotation. The northern half of the sky is the part of the sky between the celestial equator and the north celestial pole. For a planet north is defined using the right hand rule of rotation. Curl the fingers of your right hand. That is the direction of the planet's rotation. Stick out your right thumb. That is the direction of the planet's north pole. The same rule applies to Galactic north. Just apply the rotation rule to the Galaxy. Once you get outside the Galaxy supergalactic coordinates are used, which are defined here: [].

      • That's alright, I'm still trying to figure out which way is 'North' in space... Does North always point to the magnetic pole of Earth even on Mars? Has someone studied the Milky Way and determined that there's a magnetic ring perpendicular to the dish?

        Don't forget that geographic North and magnetic North aren't the same thing. The concept of North predates any knowledge of magnetism, that just turned out to be a convenient way to figure out which direction North was once the lodestone was discovered (but n

  • R.I.P. Monument Builders

  • by Anonymous Coward on Friday December 05, 2008 @10:18AM (#26002305)
    Here's a link [] to the supernova in question. Also, here's Brahe [] himself. Remember that all his observations were naked-eye - pre telescopes.
    • by UdoKeir ( 239957 )
      Tycho Brahe had a nose [] made of silver and gold.

      And his friend had copper knickers.
    • I'm still trying to figure out what contribution this "discovery" (reenactment?) brings. It's neat they can use this light echo technique to reconstruct a supernova, and it's nice they can now definitively classify Tycho's supernova, but everything else seems to be already known. Even the technique they used to do it doesn't seem new. Is there some new contribution to astronomy here or are they just showing off?
  • by mangu ( 126918 ) on Friday December 05, 2008 @10:22AM (#26002345)

    This could be used to determine distances very precisely. If we know when that light was emitted and we know the speed of light, then we can calculate with great precision the distance from the star to the reflecting dust cloud.

    • Re: (Score:3, Insightful)

      This could be used to determine distances very precisely. If we know when that light was emitted and we know the speed of light, then we can calculate with great precision the distance from the star to the reflecting dust cloud.

      You also have to account for any differences between the earth-star distance and the earth-cloud distance, but it's still the largest ever radar system.

      • Re: (Score:3, Interesting)

        by mangu ( 126918 )

        You also have to account for any differences between the earth-star distance and the earth-cloud distance

        One could start by assuming that the points which are being illuminated now and have the biggest angular separation from the star are at the same distance from earth as the star. Those points form a circle with a 436 light-year radius. The size of that circle as seen from earth will give you the distance to the star.

        I'm assuming that there is enough dust everywhere in space to return a detectable reflect

      • You also have to account for any differences between the earth-star distance and the earth-cloud distance, but it's still the largest ever radar system.

        If they're light echoes, shouldn't it be sonar?

    • Re: (Score:3, Informative)

      by halcyon1234 ( 834388 )

      Although... if we know when that light was emitted, then we know the distance to the supernova already. There's four pieces of information that could be known. If we know two of them, we can map out the Earth/Supernova/Cloud system:

      1. The distance from Earth to the Supernova at the time of the supernova event (equal to the time it took for light from the supernova to reach Earth)
      2. The distance from the supernova to the reflecting cloud (equal to the time it took for the light from the supernova to reach the cl
  • by Doc Ruby ( 173196 ) on Friday December 05, 2008 @10:30AM (#26002419) Homepage Journal

    When can we point our telescopes at an object hundreds or thousands of lightyears distant, and pick up the light reflected back at us that previously traveled from Earth to that object, then reassemble it into images? Images of the Earth's past, twice as old as the lightyear distance of the object?

    We could look at an object 1000 lightyears distant for reflections of Jesus being crucified. Search among objects 250-600 lightyears distant for reflections of people arriving in the "Americas" on ships before Columbus. 176ly distant objects could show us images of Newton getting hit by a falling apple.

    Finally a use for the combined computing power of all Earth's computers.

    • by glaswegian ( 803339 ) on Friday December 05, 2008 @11:01AM (#26002731)
      We would need monumentally large telescopes for this. The largest optical telescope on earth, the Keck, has a diameter of 10m. Using the Rayleigh Criterion [], we can calculate the minimum resolvable detail at a given distance. For example, we can resolve details on the surface of the moon (in the visible) that are around ~20 meters across. If you want to resolve an apple falling on somebodies head you need ~10 cm resolution. So to see this happening on the moon we would need a telescope with a primary mirror ~ 2.6 km across. To see the same thing echoed back from a dust cloud near the closest star to our sun (4 ly * 2), you would need a telescope with a primary ~ 7e+10 m across or around half the distance between the earth and the sun. Not to mention that the signal would be very weak and completely lost in noise.
      • by frieko ( 855745 )
        This wouldn't do anything to improve SNR, but two ordinary telescopes 7e+10 m apart have the same resolving power as one giant one.
      • by Doc Ruby ( 173196 ) on Friday December 05, 2008 @12:29PM (#26003825) Homepage Journal

        A telescope array [] acting as an interferometer doesn't need to be a single large sensor like that. We can orbit the array with separations of 1E13, just beyond Neptune. That would give us resolution of something like 5.8E-20 arcseconds. The radius of that regular polygon with 10cm sides is about 7E21m, or about 740,000 light years. Which would show light that left Earth about 1.48 million years ago. Orbital arrays much closer to Earth are sufficient for looking for apples only 175ly away.

        The signal to noise is of course extremely high ("astronomical"). That's why I mentioned the combined computing power of all the world's computers. We're gonna need a bigger boat, but that's a good sea to sail her on, to catch this shark :).

        • by Kagura ( 843695 )
          Can somebody please explain why this is? I understand the difference between total collecting area and actual resolving power, but I'm missing something fundamental. It doesn't seem like two telescopes linked by interferometry should increase the resolution just because they are separated by a large distance. To me, I can only imagine an increase in resolution because the total collecting area is increased, but not due to their separation.

          My question is, why does separating two telescopes by distance gre
          • You can look into aperature synthesis [], which is the technique at work.

            • by Kagura ( 843695 )
              Thanks, but I read the page and a couple others, but still didn't get my answer. :( I don't see how separating two telescopes and connecting them by interferometry increases the resolution so dramatically.
              • You're getting double the information by using two telescopes. Most of the info is redundant. But there is phase info, available to the "phased array", in what you're getting. The interferometry is the method of extracting the phase info. The phase info isn't redundant between the two telescopes. So that extra info is an increase over the single telescope's. The extra info is the increased resolution.

        • Re: (Score:3, Insightful)

          by Urkki ( 668283 )

          It's not just computing power. We'd actually need to catch enough reflected photons that originated from the Earth, so we'd have anything at all to process.

          I think it would be a problem even if there was no other light except what we want to observe, ie. there would be no external noise.

          Also, the "mirror" isn't a flat plane, so we'd get a bunch of "Earth photons" that originatead at different times, reflected at different times, and then arrive at our telescope at the same time.

          To get anything useful, we'd

          • The flatness of the surface isn't really a problem, because the photons that arrived a little later (by speed of light, the distance of the "roughness") are going to be extremely similar to the ones that arrived at the time of the first photons reaching the closer parts of the roughness. In fact what helps us is our tolerance of a somewhat soft focus. Since our resolution is 10cm, which light travels in 3.33564095E-10 seconds, our probably much longer exposure (to collect photons) means our focus is not goi

        • by jagdish ( 981925 )
          Its funny how in this economic climate the meanings of the words economical and astronomical have interchanged.
      • by geekoid ( 135745 )

        Just put the image in photoshop and zoom way in~ duh I see t on TV all the time

    • Jack McDevitt had a similar idea in one of his books. The protagonist is a historian's assistant. One of the ideas was to use faster than light travel to intercept old radio and video broadcasts to recover some history. I believer it was mentioned in Seeker [] but I may be wrong. The characters got sidetracked by something else so never got past the idea stage.
      • I didn't know about McDevitt's version of this idea. I thought of it when thinking through "faster than light travel" applications, when I realized that reflected light "bends space" back to the source, which is effectively time travel. I was helping build a digital camera out of a lot of cutting edge DSP for noise reduction and feature enhancement, including some efforts at reversing the effects of air turbulence confusing light paths to the sensor. It occurred to me that similar processing, but more advan

    • Re: (Score:2, Interesting)

      This would definitely not work. There is no imaging (no lens, or pinhole) at work. What you are proposing is analogous to sitting in a dark room with white walls with the television on: you will see areas of color on the wall, but you will be unable to deduce from these reflections what the picture on the TV looks like (beyond getting the average color of the TV picture). Of course, if the wall were a mirror, you could do it, but walls are diffuse reflectors, which means that, at each point on the wall,
      • That's where the reverse ray tracing comes in :).

        There are probably plenty of distant objects with little to no intervening matter. And then there's probably distant objects that have intervening matter that collimates light, either optically or gravitationally.

  • by Aladrin ( 926209 ) on Friday December 05, 2008 @10:31AM (#26002429)

    I'm amazed that he was able to observe that and figure out that the common concept of the sky was wrong at the time. I can't imagine how much thought must have gone into something like that.

    • by Aliks ( 530618 ) on Friday December 05, 2008 @11:00AM (#26002713)

      Well he had already done a lot of work on parallax measurements for astronomical objects. So when the supernova appeared, and showed no parallax against the moon . . . he was on pretty firm ground stating that the moon was closer to earth than the supernova.

      More details in Wikipedia.

    • Re: (Score:1, Offtopic)

      by dkleinsc ( 563838 )

      And even more amazing is that a guy that smart didn't know when to empty his bladder.

      This has been a message from the Tasteless Jokes Department.

    • Not actually true, Tycho Brahe's model of the solar system was very similar(geometrically) to Ptolemy(earth in the center) and Copernicus(sun in the center). He put the earth in the center, the sun and the moon were orbiting around the earh while the other planets where orbiting around the sun.

      The real breakthrough came from Johannes Kepler( who was working with Brahe and later on was using Brahe's observations) who went away from using circular orbits, and to a certain extent discovering gravity. You can r

      • by Aladrin ( 926209 )

        The 'common concept' I refer to is that the night sky's background is static, as was mentioned in the summary. I'd have been even more impressed if he'd figured out the Earth wasn't the center of the universe at the same time.

    • Re: (Score:3, Insightful)

      by lawpoop ( 604919 )
      It is laudable, but I wonder how much doubt there was going on at the time. For instance, the Greeks knew that the Earth was round, but there was common conception that the Earth was flat -- I'm not talking about what educated people thought, but what the commoners thought. European scholars studied classical literature ( back then it was just "literature" I guess ), and they were exposed to ideas from the Greeks and the Muslims, who helped transmit the Greek texts. So they got exposed to a lot of different
  • Tycho: I saw a light in the sky that looks like an exploding star.
    Scientific community: We don't believe you until we can see it ourselves. Neh!
    • Re: (Score:2, Informative)

      by mrsquid0 ( 1335303 )

      Actually, the scientific community of the time (such that it was) was mostly convinced by Tycho's observations.

  • by Tastecicles ( 1153671 ) on Friday December 05, 2008 @10:56AM (#26002683)

    ...continues to bring surprises like this. I'm just wondering if this is the same method we astronomers use to detect local masses such as transneptunian planets (or "Plutoids", if you will) or asteroids or -gulp!- Near Earth Objects such as the Saturn V Stage discovered and misidentified as a natural coorbiting body a couple years ago? Could light ripples be detected and identified on a pair of plates of the same patch of sky taken a year apart?

  • I hate those expressions! That implies that the original light was faint. But faint compared to what? Why not just say that it was 1/x-th the brightness of the original event's visible light? The echos/reflections are relative to the original, in terms of what makes the story interesting. Both the original event and the reflections are found on some hard scale of luminosity, but that's not referenced... so why the awkward, un-anchored, and thus meaningless reference? Grrrr. 20 billion times fainter than the
    • by TheThiefMaster ( 992038 ) on Friday December 05, 2008 @11:34AM (#26003095)

      xxx times less than yyy == yyy/xxx.
      It's common language these days, learn it!

      • xxx times less than yyy == yyy/xxx.
        It's common language these days, learn it!

        He wasn't asking how to express it, he was asking them to include YYY if you are going to call something XXX times fainter than YYY so that he has some clue as to the starting point.

        This object is 100 times lighter than object B. That doesn't tell you much since object B could be a gnat, a basketball, or a galaxy.

        • I got a +5 already, so it doesn't matter :) /joking

          But seriously, if something is 20 billion times fainter it's going to be barely visible, regardless of how bright the original is.

          It's also more impressive journalism to use "20 billion times fainter" than "1.3 candles" or some other actual measurement.

          • Re: (Score:3, Interesting)

            But seriously, if something is 20 billion times fainter it's going to be barely visible, regardless of how bright the original is.

            Our sun is ~20 billion times fainter than it will be when it supernovas. And seems to be bright enough to light up the world nicely. OP is right, it would be nice to know how bright the original was.

            • sorry, pal, Sol is just too small to supernova. It's short by about 1.4 solar masses. What'll likely happen is it'll burn out of hydrogen, start burning helium and contract, then when it starts to burn heavier elements (lithium, beryllium, through carbon, nitrogen, oxygen...) the outer shell of helium will cool and expand out to the orbit of Venus and possibly Earth. By this time the core'll be burning even heavier elements, but due to the size of the sun it won't even reach the iron cycle - the photosphere

              • Re: (Score:3, Funny)

                by ScentCone ( 795499 )
                Another few million years and Sol will just be a lump of cold nuclear waste.

                Hey, don't sugar-coat it, OK?
    • by Quirkz ( 1206400 )
      Well, the article does say the original object was "brighter than Venus" so that's a start. Also, considering these were naked eye observations, it's not even possible to have a precise brightness value for the original. That of course means the 20 billion number probably is more of a guess than a precise number, but I wouldn't say it's completely useless to mention here.
    • The article that line is a link to (and that the line was extracted from) states (in the first paragraph no less): "as bright as the planet Venus".

      Which considering the time frame of the original observation is as precise as you are going to get.

      I'm going to take a punt that 99.9% of people get a more accurate idea from "as bright as the planet Venus" (provided they know which dot in the night sky you are referring to by that name) than "an apparent magnitude of -4.5".

  • Couldn't hold his pee pee!

    • Tycho's elk and dwarf
      Tycho was said to own one percent of the entire wealth of Denmark at one point in the 1580s and he often held large social gatherings in his castle. He kept a dwarf named Jepp (whom Tycho believed to be clairvoyant) as a court jester who sat under the table during dinner. Pierre Gassendi wrote[6] that Tycho also had a tame elk, and that his mentor the Landgrave Wilhelm of Hesse-Kassel (Hesse-Cassel) asked whether there was an animal faster than a deer. Tycho replied, writing that there

  • Here is a link to an article by one of the researchers involved in this work []

    As the article suggests, the biggest benefit of using light echoes is that the SPECTRUM of the original supernova can be obtained. In other words, while today we mostly see the direct-path light emitted by the supernova's gas remnant, light echoes let us see all the wavelengths of the light emitted at the time of the explosion.


    • wow... that brings up a whole mess of possibilities! For instance, we can tell from the amount of light reflected and the intensity of reflection, what a local mass is made of (by the absorption spectrum) and extrapolate how dense it is. In the same manner, we can tell what a star is made of (hydrogen and helium, usually, with a mess of other elements up to iron - after which nuclear reactions are endothermic) by its emission spectrum, and if we can be sure that these light echoes are of the same wavelength

      • That's an interesting idea. You could hypothetically look at the light emitted by the pre-supernova star, as it was reflected off a nebula. The trouble is that, before the explosion, the star isn't especially bright (well, a heck of a lot dimmer than a supernova). Hence the reflected light wouldn't stand out very much, and I doubt you could subtract out the light on the nebula due to other sources. But you might catch the rising part of the supernova's light curve.


  • Was he playing D&D 436 years ago? There was no XBox back then o_O
  • By Neruos (Score:1, Insightful)

    by Anonymous Coward

    all these high powered telescopes that can 'supposely' see 10000000000x millions of light years away and yet there are no close up's of the moon, the flag on the moon, the machines left on the moon or any other human impact images of the moon from multiple sources across the world. No images exist except those from the 1969.

    why? Think about it.

    • you look at the moon through a small telescope (don't do this on a full moon, you'll burn your retinas!). Oh wait, that prenthesis is the whole point of the exercise. Deep space telescopes such as Hubble are insanely photosensitive. They can't even use HST to look at Earth's surface, it'll overload the CCD sensors. Light reflected by the lunar surface is unfiltered raw sunlight. You'd be better off using interferometry to look for your landing sites... it's better for your eyes and better for your cameras..

Where it is a duty to worship the sun it is pretty sure to be a crime to examine the laws of heat. -- Christopher Morley