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Thread: 2017 - Eclipse

  1. #1
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    2017 - Eclipse

    Here I'm not questioning the light bending, I just wanted to know if there was an attempt to measure the light bending of the 2017 solar eclipse?

    If so is the measured light bending in agreement with the prediction of GR (within error range)?


    Many thanks,
    philippeb8

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    Quote Originally Posted by philippeb8 View Post
    Here I'm not questioning the light bending, I just wanted to know if there was an attempt to measure the light bending of the 2017 solar eclipse?

    If so is the measured light bending in agreement with the prediction of GR (within error range)?
    I guess I just want to know the most precise deflection angle ever measured.

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    I see that this guy was planning on testing it out using off the shelf tools, but I can't find his results anywhere; he may not have posted them yet (although I see that he has included a graph showing the deviation plotted from someone else observing the 1973 eclipse).

    Interestingly, Hipparcos measured star positions with sufficient precision that it was necessary to include corrections from general relativity (after all, the gravity from the Sun will affect the light from all the stars we see, not just the ones closest to it). In this case, the difference was on the order of a few milliarcseconds, and the data was analyzed to see if there were any deviations from the expected apparent changes in position due to general relativity; none were found.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by Grey View Post
    I see that this guy was planning on testing it out using off the shelf tools, but I can't find his results anywhere; he may not have posted them yet (although I see that he has included a graph showing the deviation plotted from someone else observing the 1973 eclipse).

    Interestingly, Hipparcos measured star positions with sufficient precision that it was necessary to include corrections from general relativity (after all, the gravity from the Sun will affect the light from all the stars we see, not just the ones closest to it). In this case, the difference was on the order of a few milliarcseconds, and the data was analyzed to see if there were any deviations from the expected apparent changes in position due to general relativity; none were found.
    I'd be surprised NASA didn't repeat this experiment with light grazing the Sun. Alas I can't find anything on this either.

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    Quote Originally Posted by philippeb8 View Post
    I'd be surprised NASA didn't repeat this experiment with light grazing the Sun. Alas I can't find anything on this either.
    I would be surprised if NASA did go to the expense of repeating it, when other proposed missions are already hurting for funding. That would be like driving a carpet tack into a coffin which is already secured with numerous railroad spikes.

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    Quote Originally Posted by Hornblower View Post
    I would be surprised if NASA did go to the expense of repeating it, when other proposed missions are already hurting for funding. That would be like driving a carpet tack into a coffin which is already secured with numerous railroad spikes.
    I don't see how pointing the Hubble telescope in the right direction is expensive.

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    Quote Originally Posted by philippeb8 View Post
    I'd be surprised NASA didn't repeat this experiment with light
    grazing the Sun. Alas I can't find anything on this either.
    Do you mean using the Hubble Space Telescope to observe stars
    very close to the Sun during the total eclipse? That wouldn't be
    possible. HST can't be pointed close to the Sun because it is so
    bright that it would damage the optics. I don't remember exactly
    how close it can get, but the Sun has to be given fairly wide berth.
    If HST happened to pass through the Moon's shadow at all, it
    would only be for a few seconds.

    -- Jeff, in Minneapolis
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    Quote Originally Posted by Jeff Root View Post
    Do you mean using the Hubble Space Telescope to observe stars
    very close to the Sun during the total eclipse? That wouldn't be
    possible. HST can't be pointed close to the Sun because it is so
    bright that it would damage the optics. I don't remember exactly
    how close it can get, but the Sun has to be given fairly wide berth.
    If HST happened to pass through the Moon's shadow at all, it
    would only be for a few seconds.

    -- Jeff, in Minneapolis
    That's right, they would not be able to slew it fast enough to get out of harm's way.

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    Quote Originally Posted by Jeff Root View Post
    Do you mean using the Hubble Space Telescope to observe stars
    very close to the Sun during the total eclipse? That wouldn't be
    possible. HST can't be pointed close to the Sun because it is so
    bright that it would damage the optics. I don't remember exactly
    how close it can get, but the Sun has to be given fairly wide berth.
    If HST happened to pass through the Moon's shadow at all, it
    would only be for a few seconds.

    -- Jeff, in Minneapolis
    You get the idea...

    NASA got other telescopes that observes the Sun already such as the IRIS telescope. In fact we don't even need to wait for an eclipse anymore.

    This information is more important than you think. But I can't say why here.

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    Quote Originally Posted by philippeb8 View Post
    I don't see how pointing the Hubble telescope in the right direction is expensive.
    In addition to what others have said, the HST is booked solid doing various research projects. Why would they take the time to do measurements that no one is interested in and have been made numerous times?

    And NASA doesn't operate it, the Space Telescope Science Institute does (which is a collaboration of various universities).
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    Quote Originally Posted by Swift
    In addition to what others have said, the HST is booked solid doing various research projects. Why would they take the time to do measurements that no one is interested in and have been made numerous times?
    Mainly to see if it's consistent with kappa and another reason I PMed you.

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    Quote Originally Posted by philippeb8 View Post
    Mainly to see if it's consistent with kappa and another reason I PMed you.
    What is kappa?

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    Quote Originally Posted by Hornblower View Post
    What is kappa?
    https://en.wikipedia.org/wiki/Einstein%27s_constant

  14. #14
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    NASA had/has a DYI page for it

    SAS has a paper on the 2017 attempt done by Sky and Telescope. According to the paper, that he expected to have a 0.01 arcsec error using high end, but amateur equipment. However, it seems this number was based on raytracing and not what he expected to see in the field with that equipment.

    New link.
    Last edited by Solfe; 2018-Jan-13 at 04:55 AM.
    Solfe

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    Quote Originally Posted by Solfe View Post
    (The link points to a Chrome extension)

  16. #16
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    Quote Originally Posted by philippeb8 View Post
    (The link points to a Chrome extension)
    Oops. In my head, the link points back to cold medicine. I edited it, so it should work right.
    Solfe

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    It's true that Hubble can't take images close to the Sun for physical reasons (risk of damaging the telescope). But note that, as I pointed out above, the ESA used Hipparcos to do exactly what you're suggesting: verify that the Sun's gravity changes the apparent positions of the stars that we observe by the amount predicted by general relativity. It's just that Hipparcos measures star positions so precisely that it's not necessary to wait for a solar eclipse and observe the stars closest to the Sun at the time. Instead, you can see the effect in all the stars that Hipparcos observes, with the size of the effect depending on how close to the Sun the line of sight to the star is when observed (in fact, Hipparcos measures positions so precisely that we must take the general relativistic effect into account when using it's measurements, in the same way that we essentially verify predictions from general relativity every time we use GPS).
    Conserve energy. Commute with the Hamiltonian.

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    The state of the art in measuring the Sun's gravitational deflection uses very-long-baseline radio interferometry, where interference from sunlight is not such a big problem and sub-milliarcsecond accuracy is possible. Already in 1991, this paper (behind paywall) stated in the abstract,

    Radio observations using very-long-baseline interferometry (VLBI) can measure the deflection of electromagnetic radiation by the Sun's gravitational field with an accuracy of better than 1 milliarcsecond, and can thus be used to test General Relativity. For an object at an angle a from the centre of the Sun, the expected deflection is (1 + γ) (Ms/re)((l + cos α)/(l-cos α))1/2, where Ms is the mass of the Sun in geometrized units (1.477 105 cm), re is the distance from the Earth to the Sun in cm, and y is a parameter whose value is 1 if General Relativity is correct but which takes on different values in other theories of gravity. For γ = 1, the deflection is 1,750 mas at the Sun's limb, 4 mas at α =90 and 0 at α = 180. Our analysis of ten years of VLBI data, including observations of objects in the range 2.5 < a< 178, yields an estimate γ = 1.0002 with a formal standard error of 0.00096 and an estimated standard error of 0.002.
    Their large-angle data parallel what was already mentioned for HIPPARCOS. This analysis suggests that a similar global analysis of the full-mission GAIA data will give an error on γ almost as low as 10-8.

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    Quote Originally Posted by ngc3314 View Post
    The state of the art in measuring the Sun's gravitational deflection uses very-long-baseline radio interferometry, where interference from sunlight is not such a big problem and sub-milliarcsecond accuracy is possible. Already in 1991, this paper (behind paywall) stated in the abstract,



    Their large-angle data parallel what was already mentioned for HIPPARCOS. This analysis suggests that a similar global analysis of the full-mission GAIA data will give an error on γ almost as low as 10-8.
    It is indeed precise:
    http://www.nrao.edu/pr/2009/gravity/

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