Slashdot Mirror

← Back to Stories (view on slashdot.org)

Volunteers Use Annular Eclipse To Measure Sun More Accurately

Posted by timothy on from the maybe-it's-just-been-eating-differently dept.

Anonymous Squonk writes "The measurement of the sun currently in use was actually calculated over 120 years ago, and is off by hundreds of kilometers. Thousands of ordinary Japanese citizens worked together to improve this estimate. By measuring the borders of the 'ring of fire' effect of the recent eclipse, and using the known size and distance from the Earth of the sun, the radius of the Sun was measured as 696,010 kilometers, with a margin of error of only 20 kilometers."

26 of 75 comments (clear)

  1. Incidentally... by fuzzyfuzzyfungus · · Score: 4, Interesting

    I very strongly doubt that this is relevant on the scale of recorded human history and naked-eye observation; but doing all that mass-energy conversion and indiscriminate radiating must be slowly changing the sun's size, with some sort of balance between loss of mass and thermal expansion or contraction.

    I'm told that the 'expands and engulfs the inner planets' stage will be dramatic; but is the expectation before that event a very, very gradual shrinking or something more complex?

    1. Re:Incidentally... by Anonymous Coward · · Score: 2

      Well, I would assume a gradual expansion.

      Since the more reactions happen, the more mass it loses, thus the attraction on the nearby atoms/molecules lessen, thus allowing them to go a bit further away.

    2. Re:Incidentally... by SuricouRaven · · Score: 4, Interesting

      Don't forget the cycle too. Sunspots go up, sunspots go down.. that means a change in temperature, and as basically a ball of gas a change in temperature means a change in volume. I don't know how significent this pulsing effect would be, but if you can do measurements to 20km it might be measurable.

    3. Re:Incidentally... by Anonymous Coward · · Score: 5, Informative

      The Sun is growing right now and it is getting brighter by the day. This is not occurring at a rapid rate at the present time. It is due to the slow accumulation of helium in the core of the Sun. Helium doesn't undergo fusion at this time (not hot enough). The increase in helium would imply a decrease in the fusion rate, but due to maintaining a hydrostatic equilibrium, the temperature of the core increases and the fusion rate actually increases. This causes the radius to increase.

    4. Re:Incidentally... by Grayhand · · Score: 2

      Answer: Yes. The sun will continue to gradually shrink until it runs out of H to burn.

      Actually the opposite is true. Our sun is doomed to end up a red giant and eventually the Earth will be eaten by the sun. It's a middle aged star so there are billions of years to go.

    5. Re:Incidentally... by thoughtsatthemoment · · Score: 5, Informative

      To be more precise, the sun will become a red giant in about 5 billions, engulf the earth, and eventually fade as a white dwarf, whose volume is about the same as the earth.

    6. Re:Incidentally... by Hognoxious · · Score: 5, Funny

      You had me in a panic there - I thought you said millions.

      --
      Confucius say, "Find worm in apple - bad. Find half a worm - worse."
    7. Re:Incidentally... by dwye · · Score: 2

      but doing all that mass-energy conversion and indiscriminate radiating must be slowly changing the sun's size

      This assumes that the Sun actually *has* a size, in a real, rather than purely mathematical sense. The outer layers of the Sun are a translucent vacuum. A harder vacuum than we were able to achieve for most of the 20th C, glowing like a neon light so that the visibility through those outer layers is about what the old London Pea Soup fogs were like. If we could view it in infrared, the Sun would have a larger "diameter" than this measurement, and of course smaller if measured from its ultraviolet image, or its X-ray image for that matter.

      They have managed to get the exact size of a balloon in the process of being blown up and released. Not its maximum size or its minimum, but merely that of one random moment in the cycle.

    8. Re:Incidentally... by schroedingers_hat · · Score: 2

      UUID goes up, intelligence goes down.
      You can't explain that.

  2. Manned Mission Needed by Scarletdown · · Score: 5, Funny

    I think to get the most accurate measurement, we need to send a manned mission to the sun and do it the old fashioned way, with a tape measure.

    Of course, to keep from burning up, they will have to go at night.

    --
    This space unintentionally left blank.
    1. Re:Manned Mission Needed by Black+Parrot · · Score: 3, Funny

      Or during an eclipse.

      --
      Sheesh, evil *and* a jerk. -- Jade
    2. Re:Manned Mission Needed by Grayhand · · Score: 4, Funny

      I think to get the most accurate measurement, we need to send a manned mission to the sun and do it the old fashioned way, with a tape measure.

      Of course, to keep from burning up, they will have to go at night.

      A waste of time and money. The eclipse proved that the sun is only slightly larger than the moon. Now you just have to use a tape measure to get an accurate size for the moon. Too bad the astronauts didn't think to take one.

    3. Re:Manned Mission Needed by qu33ksilver · · Score: 4, Funny

      Or during Winter.. You know this was a yahoo question. http://answers.yahoo.com/question/index?qid=20120430182228AAIk7uw

    4. Re:Manned Mission Needed by __aaltlg1547 · · Score: 4, Funny

      Everybody knows a Corona is 12 ounces.

  3. Sorry, can't resist. by jtownatpunk.net · · Score: 3, Funny

    That's a relatively open weave and I can still see your... annular area.

  4. Re:Wouldn't it be great... by Black+Parrot · · Score: 4, Funny

    Wouldn't it be great if people learned foreign languages ? If people would allow foreigners to puplish in their on language ?...
    Yeah too much to ask, I guess.

    IMO everyone should be allowed to puplish in the language of their choice, so long as they do it in the privacy of their own home.

    --
    Sheesh, evil *and* a jerk. -- Jade
  5. Currently in use by zmooc · · Score: 3, Funny

    Good to see they focused their research on the sun that's currently in use and not on one of those old disposed ones!

    --
    0x or or snor perron?!
  6. Wasn't this already known? by Anonymous Coward · · Score: 3, Informative

    NASA seemed to know it's 696,000km long before this experiment.

  7. I missed it by The+Evil+Atheist · · Score: 4, Funny

    Oh well, look on the bright side...

    --
    Those who do not learn from commit history are doomed to regress it.
  8. Re:Wouldn't it be great... by Baron+Eekman · · Score: 3, Informative

    English language version:
    http://ajw.asahi.com/article/behind_news/social_affairs/AJ201205250024

  9. Oh my god by Anonymous Coward · · Score: 5, Funny

    The measurement of the sun currently in use was actually calculated over 120 years ago, and is off by hundreds of kilometers.

    By the best available measurements the sun has shrunk by hundreds of kilometers in a space of 120 years... and in that time is when we've started using solar power. We should stop now while there's still some Sun left.

  10. Define 'Sun' by EasyTarget · · Score: 3, Interesting

    Seriously; it has a atmosphere thousands of miles thick, with a fuzzy, boiling edge..

    The margin of error on this is ludicrous.

    Plus.. of course, it is continually boiling itself off onto space, so even if you could define a 'hard edge' to it, your measurements would become worthless in, say, a few million years ;-)

    --
    "Oops, I always forget the purpose of competition is to divide people into winners and losers." - Hobbes
    1. Re:Define 'Sun' by mister_playboy · · Score: 3, Informative

      Not to mention that it's probably not a perfect sphere, so a single radius doesn't capture its size.

      Wikipedia sayth:

      It is a near-perfect sphere, with an oblateness estimated at about 9 millionths, which means that its polar diameter differs from its equatorial diameter by only 10 km. As the Sun consists of a plasma and is not solid, it rotates faster at its equator than at its poles. This behavior is known as differential rotation, and is caused by convection in the Sun and the movement of mass, due to steep temperature gradients from the core outwards. This mass carries a portion of the Sun’s counter-clockwise angular momentum, as viewed from the ecliptic north pole, thus redistributing the angular velocity. The period of this actual rotation is approximately 25.6 days at the equator and 33.5 days at the poles. However, due to our constantly changing vantage point from the Earth as it orbits the Sun, the apparent rotation of the star at its equator is about 28 days. The centrifugal effect of this slow rotation is 18 million times weaker than the surface gravity at the Sun's equator. The tidal effect of the planets is even weaker, and does not significantly affect the shape of the Sun.

      So more round than you might think. :)

      --
      Do what thou wilt shall be the whole of the Law ::: Love is the law, love under will
  11. How accurate can it be ? by Alain+Williams · · Score: 4, Insightful

    Is this not somewhat akin to trying to measure the depth of a saucepan of boiling water ?

    1. Re:How accurate can it be ? by MalachiK · · Score: 2

      Yeah, but I'd guess it's pretty smooth when you consider the radius of the sun is of the order 10^9 m.

  12. Measured using known dimensions? by n7ytd · · Score: 2

    Japanese citizens worked together to improve this estimate. By measuring the borders of the 'ring of fire' effect of the recent eclipse, and using the known size and distance from the Earth of the sun, the radius of the Sun was measured as 696,010 kilometers, with a margin of error of only 20 kilometers."

    Wow! That's some breakthrough science!