That's not what the Batsignal is supposed to look like!

By Phil Plait | September 23, 2012 7:00 am

The dark night rises?

[Click to stimulatedemissionate.]

Nope. This way cool picture is actually the Very Large Telescope observatory in Chile, though that really is a laser being shot into the sky. Our atmosphere boils and writhes, distorting the view of the stars. There’s a layer of sodium atoms in the atmosphere far above the ground, and the laser is designed to make them glow. This creates a very bright point-like source of light that the telescope can view, and measure in real time how the atmosphere is messing up the observation. This can then be compensated using very fast computers and adjustable mirrors, and the result is a far sharper image than could be obtained otherwise.

During this 30 minute exposure, the Earth rotated enough to trail the stars, and the laser was moved to stay on target. That’s why the stars are curves, and the normally pencil-thin laser looks like it does. It makes for a pretty slick effect! Shorter exposures are pretty amazing, too, and I have several linked in the Related Posts section below for your amusement.

Image credit: ESO/J. Girard


Related Posts:

Beam me up!
INSANELY cool picture of Comet Lovejoy
Very Large Telescope, Very Stunning Time Lapse Video
Oh great. Now we have lightning equipped with lasers.

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (22)

  1. Messier Tidy Upper

    Great image, cheers. :-)

    The dark night rises?

    No, its just an artefact of our frame of reference and being planet bound on a world with non-tidally locked rotation! ;-)

    (Sun “rises” and Sun “sets” [why not ‘sun falls?’] are an illusion too – it is the horizon that is shifting as our Earth spins – although our Sun is orbiting our Galaxy too.)

    Oh & btw.

    Our atmosphere boils ..

    Can an admixture of gases technically “boil” or is that process not restricted to liquids?

    Overly pedantic? Moi? ;-)

    PS. Checks patent closely, grants poetic license.

  2. Wzrd1

    @MTU, gotta give you that one. More like convection cells than boiling liquids, huh? :)

    What is the power output of the artificial star lasers?

  3. Chris

    @2 Wxrd1

    At least according to the Keck site, it is a 10-14 W pulsed laser tuned to the sodium D line making a guide star between magnitude 9.5 and 11. I’m guessing theirs is pretty similar.

    http://www2.keck.hawaii.edu/optics/lgsao/lgsbasics.html

  4. DLC

    Estoy señor murciélago !

  5. Wzrd1

    @Chris, thanks. Somehow, I missed that info on the Keck site. I saw others using 4 watt pulsed units.
    I’d love to see their circuitry on that system! :D

  6. Little question about the colour of the laserbeam.
    We all use green lasers to point out things to people. So why do they use an orange/yellow one?
    Are they easier to pump out more Wattage? Or is it more focused? Or because it throws a better “star”?
    So many questions and I´m sure only one right answer.

  7. Toiski

    SkyGazer:It’s because of its connection with the sodium atoms, which occur at a relatively high altitude. The reflection comes back through a large portion of the atmosphere, whereas a laser that matched the absorption wavelenghths of, say, nitrogen, would produce a signal heavily weighted towards the lower reaches of the atmosphere. Also, tuning to a particular wavelength that matches an atom’s absorption wavelength maximises the light that is emitted in return. Chris’ link gives some technical details, but the gist is that this particular wavelength gives a strong signal from high up in the atmosphere.

  8. Chris

    @6 Skygazer
    It’s orange/yellow because it is tuned to the Sodium D line. It is a doublet of lines around 589 nm which is in the yellow part of the spectrum. Think of the sodium vapor street lights which cast a yellowish hue. The reason they use the sodium line is because of the sodium in the upper atmosphere which comes from micrometeorites burning up in the atmosphere. Which is fortunate because the star is formed at the top of the atmosphere so when we see it we can remove the atmospheric turbulence through adaptive optics.

  9. #1 MTU:
    Why do we say “sun set”?
    Because in Egyptian mythology, the evil god of the night, who was the deadly enemy of Horus, the Sun God, was called Set. The myth was that the cycle of day and night was an eternal battle between Horus and Set; every night, Set overcame Horus, and banished him to the underworld – then in the morning, Horus overcame Set again, and rose back into the sky. The word “horizon” comes from “Horus is risen”.
    The Egyptians were the first culture to divide the day into hours; the word “hour” also comes from Horus.
    You may also notice the resemblance between the names “Set” and “Satan” – which is not a coincidence!
    The mythical life story of Horus was in fact an astronomical fable to describe the daily and annual motions of the Sun in the sky – but it contains some details which are strangely familiar… Horus supposedly lived on Earth in human form; he was born from a virgin on 25 Dec, performed miracles, and travelled with 12 followers. He died by crucifixion, was dead for three days, then was resurrected and rose to Heaven.
    Yes, the familiar story of You Know Who, which a billion people believe to this day, is nothing more than the umpteenth rehash of the myth of Horus, which predates it by 3000 years!!!!
    If you’re interested, you can read more about the connection between Jesus, Horus and astronomy on my web site, under “Son of God, or Sun of God?”

  10. George Martin

    Chris at #8 said:
    Think of the sodium vapor street lights which cast a yellowish hue.

    That is the low pressure sodium lights; is that correct? I think that the high pressure sodium lights give a white glow. People seem not to like the low pressure sodium lights because of the “yellowish” glow even though they are really as bright as the high pressure sodium lights.

    George

  11. Messier Tidy Upper

    @2. Wzrd1 :

    @MTU, gotta give you that one. More like convection cells than boiling liquids, huh?

    Exactly! :-)

    @9. Neil Haggath : Cheers for that! I’d never thought of that mythological association / connection before, makes sense. :-)

    @4. DLC : “Estoy señor murciélago!”

    I don’t understand that one, sorry. :-(

    Translation anyone por favour? (Spanish / Portugese?)

  12. Søren Furbo Skov

    10. George Martin Said:
    That is the low pressure sodium lights; is that correct?

    Low pressure sodium lights give a pure yellow light. It is monochromatic, so no colors can be perceived under it. High pressure sodium lights give a broader spectrum, but is still focused on the sodium D line, so they are still yellow-orange, just not as pure as the low-pressure variant. It is a spectrum, so colors differences can be perceived. The low pressure variant is more energy efficient, so it is preferred along roads mostly for cars, but not seeing colors is not nice, so in cities, the high-pressure version is preferred.

  13. Don

    @11

    Google translates to “I’m Mr. Bat”, in other words, “I am Batman”.

  14. Thanks for the explanation! Now I get it.

  15. Nigel Depledge

    @ Don (12) –
    Aw, and there was me thinking the comment was about a Lamborghini . . .

  16. Nigel Depledge

    [Devil’s advocate mode]
    @ Neil (9) –

    But, but , but . . .

    That goes no way to explaining the uses “tea set”, “set up”, “set down”, “set out”, “set off”, “set to”, or any of the other 128 uses of the word “set”. It only explains that one use regarding the setting of the sun. (Well, OK, 2 if you count the noun and the verb separately, which the OED does.)

    And it implies but doesn’t explain a link between Satan and tennis! Ha, you can’t explain that, can you??!!111!!!!

    [/Devil’s advocate mode]

  17. Infinite123Lifer

    I should probably apologize for this ahead of time. There apology offered.

    For Neil Haggath @ 9

    Now there is one “Horus-scope” I can handle! Thanks for that.

  18. sean

    Why do they go through all of the added complexity of make the mirrors move, if they have the information to adjust the mirrors why don’t they do it in software and use a regular telescope

  19. You know you’re a real astrophotography nerd when:

    You can look at a “streaked” time-exposure photo of the sky, like the one in this picture, and still be able to make out constellations.

    I’m not that good yet….

  20. Take THAT, stars! Pew pew pew!

    Srsly, I have at least half a dozen desktop wallpapers that are photos of this observatory :)

  21. @13. Don :

    Google translates to “I’m Mr. Bat”, in other words, “I am Batman”.

    Ah, now makes sense. Cheers. :-)

  22. Nigel Depledge

    Sean (18) said:

    Why do they go through all of the added complexity of make the mirrors move, if they have the information to adjust the mirrors why don’t they do it in software and use a regular telescope

    Because the air is doing different things above different parts of the scope.

    Therefore, to compensate, they need to rapidly change the shape of the mirror.

    D’you see?

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