Newly upgraded solar telescope sees first light


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Early image from upgraded solar telescope.

Astronomers have finished a major instrument upgrade of the GREGOR solar telescope in the Canary Islands, making it possible for them to observe features on the Sun’s surface as small as thirty miles in diameter.

The image to the right is an example of the telescope’s new capability, showing the Sun’s granular surface features. From the introduction of the paper describing the upgrade:

GREGOR is Europe’s largest solar telescope. … Its 1.5 m diameter with an optical footprint of 1.44 m allows us to resolve structures on the Sun as small as 50 km at 400 nm.

…A past drawback of GREGOR was that its image quality did not reach the theoretical limit, partly because a risk was taken with untested technologies, such as silicon carbide mirrors, which could not be polished well enough, and partly because of design problems. These difficulties have recently been solved by replacing all silicon carbide mirrors with mirrors made of Zerodur, which can be polished to the required quality, and by redesigning the AO relay optics. GREGOR now operates at its diffraction limit. [emphasis mine]

In other words, the initial mirrors did not work as promised, requiring them to replace them to get the telescope to function as initially designed. By the image above, it looks like their upgrade has worked admirably.

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8 comments

  • Steve Richter

    does the radiation which is emitted by the Sun leave the surface in a perpendicular path? I read once that radiation has been bouncing around for some time when it finally reaches the surface and travels into space. Which would imply that radiation leaves the Sun at all sorts of angles to the surface.

    But radiation that is leaving the surface of the Sun at an angle will not reach the Earth, correct? I am thinking of a distant star. Light emitted from a star would have to leave the star perpendicular to its surface in order to arrive years later on Earth.

    Thinking about this I can see it does not make much sense. But would still like to ask the question.

    My actual question is, has the majority of the radiation from the Sun that hits the Earth come from one location on the Sun’s surface? Or has it just angled off from all locations of the Sun’s surface? If there is a sunspot that erupts on the Sun which is located where the majority of radiation from the sun is emitted that travels to the Earth, would that dramatically impact the amount of radiation hitting the Earth?

  • Alex Andrite

    Mystery is a good word.
    For now.

  • Edward

    Steve Richter asked: “But radiation that is leaving the surface of the Sun at an angle will not reach the Earth, correct?

    We can see the entire disk of the sun, because the radiation (light) comes off at all angles.

  • LocalFluff

    @Steve Richter
    Limb darkening might interest you:
    http://spiff.rit.edu/classes/phys440/lectures/limb/limb.html

  • Max

    Steve;
    There’s an old popular fable that says; “light emits from the center of the sun and works its way up & out, over millions of years until it’s emitted from the surface”. Not true.
    Place a flashlight upside down onto a surface and see how long it takes to come out the other side.
    Or go into a cave to see sunlight from millions of years ago work its way through the soil to light up the cave. Then remember that the sun is far more dense than any materials on earth.

    Light/heat/solar wind is emitted by the Corona sphere (above the chromosphere) which is about 2000 km above the photosphere.
    The light from the corona sphere literally shines down on the black body surface of the sun making it glow and light up bright at the same time that it shines outward to the galaxy.

    The only exception to this is the sun spots. Dark areas that are so magnetic that they shine at a higher wavelength that our eyes can’t see. With the UV camera, the spots appear to be the brightest part of the entire sun.

    Local fluffs chart in the link above is correct. So is the reason for the limb to be darker than the center. Light traveling through the dense atmosphere of the sun at an angle has a higher chance to be blocked than the light coming from the center of the disk. But some of the words describing it are not correct.

    It describes that “it gets hotter” at the photosphere when the opposite is true. The coldest part of the sun is just above the surface of the photosphere which is 9,500°F.
    Then the chart correctly shows that as you rise into the coronasphere, that the temperature sores to over 2 million°F.

    The temperature at the center of the Sun is estimated, because we have no way of actually measuring it, to be over 50 million°F.

    This discrepancy is a source of much controversy. It’s like putting a block of ice on a cookie sheet and put it in the oven on maximum temperature then coming back in million years and the ice block is still there.

    Same with the controversy of the sun being fueled by hot fusion. All nuclear reactions have a byproduct of alpha beta and gamma rays. Gamma rays have a wavelength so short that 1/2 of all gamma that hit the earth pass right through it. That’s why gamma detectors are put in salt mines deep in the earth.
    For the sun to be nuclear, there should be a “factor of three” more gamma at a minimum. Enough to sterilize this planet.

    Unless there’s a process that has not been discovered yet… our hopes are the solar probe will find some evidence of it.

  • @LocalFluff:

    Thanks for the link. That was fun! And learned a new definition for ‘caustic’.

  • MadRocketSci

    @Max:
    I’m pretty sure gammas don’t penetrate more than meters into anything. I think you’re thinking of neutrinos, very light neutral leptons (sort of like a chargeless electron) that are emitted as a byproduct of fusion reactions in the sun. These the Earth is pretty transparent to, and we can actually image the sun looking down through the earth using these.

    The neutrino detectors are buried in old mines in order to block out everything else but the neutrinos.

  • Max

    Thank you Mad Man, you are correct. (how embarrassing, my high school science class was only 40 years ago)
    I was thinking “Alpha, Beta, Gamma” with gamma having a shortest wave, when it should’ve been “electrons, protons, neutrons” with the neutron having virtually no wavelength allowing it to pass right through entire earth.
    You are right about the neutron detectors, deep in the earth to be shielded from cosmic rays, preferably in salt mines to be away from Granite and other sources of radioactive decay. These detectors can pick up nuclear activity, atomic bomb testing, supernovas in other galaxies … which would not be possible if our sun was a huge nuclear furnace. It would be like mounting a telescope in the center of a very bright city. Virtually useless.

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