James Webb Space Telescope

Discussion in 'Environmental Discussion' started by bwilson4web, Mar 19, 2022.

  1. tochatihu

    tochatihu Senior Member

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    Planetary (ring) nebulas are suitable infrared targets because of all that dust. They have nothing to do with planets and I don't know how they got stuck with that name. Earth's sun (and possession there may be hard to justify) will probably end up as a ring nebula, 9 billion or so years in future, after having cooked off Earth along with other milestones.

    This one is 2000 light years away and popped ~8000 years ago. I guess that refers to the first pop as there have been at least 8. It would probably have been an interesting sight to southern hemispherians 8000 years ago. Outermost ring diameter is a light year which seems to imply that dust is expanding at 1/16 the speed of light. So it is not just a lot of dust, it's in a big hurry.

    Edit: strikethrough. Wrong.
     
    #21 tochatihu, Jul 12, 2022
    Last edited: Jul 12, 2022
  2. fuzzy1

    fuzzy1 Senior Member

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    Centuries ago, astronomers with early telescopes could see their round shape, similar to planets, quite distinct from twinkling point-source stars. The description stuck. https://en.wikipedia.org/wiki/Planetary_nebula

    Wouldn't that be a more leisurely 1/16,000 the speed of light? Slower now than Earth's orbit around the Sun, though it took huge amounts of energy to eject it from that central star.

    Back when Hubble took its photos of this nebula, the gas expansion speed was listed as 9 miles/second:
    A Glowing Pool of Light: Planetary Nebula NGC 3132

    Ancient Chinese astronomers have given us quite precise pop dates for other objects like this. While this one should have been within viewing range for those in the south part of that region, I haven't heard of any surviving records going anywhere near that far back.
     
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  3. tochatihu

    tochatihu Senior Member

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    1/16000 it is. Off by 3 orders of magnitude is pretty much off. Mi scusi.

    ==
    Now there's a thought: How are mass and energy apportioned when a star novas? Photons fly away, mass of shell gets energy from the shock wave (and flies away slower), remains of star sit there is some form. This may be unknowable with current data. Surely if could only be considered by someone careful with all those zeroes.
     
    #23 tochatihu, Jul 12, 2022
    Last edited: Jul 12, 2022
  4. tochatihu

    tochatihu Senior Member

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    Also thanks for planetary... Still does not 'work' for me because planet means wanderer. Planets wander in our sky view because their solar orbits differ and we see them from a peculiar (in the midst) vantage point. Nebulas don't wander. Hrumph.

    Twinkle pertains to light source subtended angle vs. scale of atmospheric turbulence (a few km up). Perhaps we have already doodled with that here.
     
  5. fuzzy1

    fuzzy1 Senior Member

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    Yes, planetary nebula don't wander. That is probably why 'nebula' was tacked on.

    But these weren't regular stars either. Stars lack visible discs, and twinkle. These things have visible discs (which the early telescopers had already found to be characteristic of the wanders), and don't twinkle.
     
  6. ammdb

    ammdb Member

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    The larger the primary mirror, the better the angular resolution.
     
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  7. tochatihu

    tochatihu Senior Member

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    I understand JWST' angular resolution exceeds Hubble where their frequency (spectra, wavelength, 'colors') overlap. JWST looks at much longer infrared wavengths and there it's angular resolution decreases linearly.

    Previous IR space telescope Spitzer primary mirror was <1 m diameter. It will be much exceeded by JWST.
     
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  8. ammdb

    ammdb Member

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  9. fuzzy1

    fuzzy1 Senior Member

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    ... when observing at the same wavelength.

    The Rayleigh criterion for angular resolution is:

    upload_2022-7-12_20-50-8.png

    Yes, Webb has a larger D than Hubble, but its gamma (a range, not a single number) increased even more.
     
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  10. fuzzy1

    fuzzy1 Senior Member

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  11. tochatihu

    tochatihu Senior Member

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  12. ke4ahr

    ke4ahr New Member

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    It will be sad to bid adieu to Hubble, but the JWST is the telescope we wish we had, but it's got a lot of great tech on-board, and we've learned from our past very well. Hopefully in ten to twenty years, we will have the first resupply mission out there to it, using a space-borne unmanned vehicle to autonomously service and refill the satellite.
     
  13. fuzzy1

    fuzzy1 Senior Member

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    I hope Hubble gets replaced with another visible light telescope. It sees a whole lot of things that JWST cannot see.

    JWST observes primarily in the infrared bands, with little overlap of Hubble. While picking up additional valuable information from nearby objects, this IR vision absolutely essential for looking back at the early Universe, where all signals are very severely red-shifted. But this also means it can't pick up plenty of valuable Hubble-level information from objects that are closer and not nearly so red-shifted.

    The two machines are complimentary.
     
  14. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Maybe we can re-purpose a(nother) reccie bird?

    I'm wondering where the boundaries would be for a visible light gatherer in LEO?
    How big can you make one?

    Hubble is 30-year-old tech 'speculatively' based on older tech, but if you don't have to buy a cloak of invisibility for it, I'm wondering if you could get a larger unit in not-so-LEO, or maybe even get a BOGO on two KH-x birds and physically or electronically gang them together?
    "MAYBE" NASA could work a deal with the USSP on a joint venture...
    I know that one of the...ah...."benefits" of Hubble is that it's orbit makes it non-useful for reading the local news, and so we'd have to work some things out with the kids wearing the eyeshades, but we have a LOT of hardware........

    If we ever beat our swords into plowshares, without having to plow for those that do not(!) perhaps we can look to the heavens a bit.....'more.'
     
  15. fuzzy1

    fuzzy1 Senior Member

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    There are plenty of new sensor technologies in Webb, of sorts vastly more useful to astronomers than the remote newspaper readers, and with greatly boosted pixel counts, which the newspaper readers are very likely already using too. A new Hubble upgraded with Webb-like sensors in visible and UV light and built to last an additional two or three decades, would be worthwhile even without a larger mirror or higher orbit.
     
  16. tochatihu

    tochatihu Senior Member

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    Agree with both above. Launch ready Hubble sized primary mirrors can do a lot with current tech in the optical path.

    I am more pessimistic than some about clutter in LEO. Would want to see long-term valuable things like this in 1000 km orbits or higher.
     
  17. fuzzy1

    fuzzy1 Senior Member

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    A bit more comment ...
    It seems very unlikely that the existing KH-x birds would be useful for astronomy. The downward-looking birds would use sensors for very bright light, not the very dim light that most astronomers commonly use. And I strongly suspect that the down-looking birds have mirrors configured to be very near-sighted, built to focus at distance ranges not overlapping the infinity that all astronomical telescopes need. Do note that when using diffraction-limited optics of this size, LEO to ground isn't anywhere close to 'infinity'.

    As for ganging two instruments, it can't yet be done electronically for optical instruments, only radio telescopes. While the technology keeps moving in that direction, it just isn't there today. So for now, and probably for my lifetime, the instruments must be physically tied together.
     
  18. tochatihu

    tochatihu Senior Member

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  19. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Oh BOY, pizza night.

    Bob Wilson
     
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