Tuesday, February 20th, 2018

Crescent Nebula revisited


Gaze at the dark sky and what do you see? Mostly white stars against a black background. A few of the brighter ones show some color, but the human eye is pretty picky when it comes to transmitting color information to our brain. Really dim stuff always comes out bland and gray. The eye needs a lot of help to see distant Nebulae like the Crescent Nebula. A whole lot of photons have to be collected before color starts to appear. Unfortunately, telescopes don’t come equipped with human eyeball retinas, so the telescope must track a deep sky object with very long exposures. Then it has to be tricked into seeing the colors using color filters that approximate how the eye registers colors for our brains. Complicated, eh?

Crescent Nebula LRGB

But what if it is being viewed by an alien whose single eye is sensitive only to one wavelength, say the Hydrogen-alpha spectrum line, and whose advanced brain doesn’t need color information? He (aliens are always male, aren’t they?) may see something like this,

Crescent Nebula Ha

Larger views of these images with some technical details can be found under Glorious skies.

Another alien just knocked on my door asking for some images using other parts of the color spectrum as registered by mere earthlings. I told him Real Soon Now.

Dave, wondering if these things are really out there.


3 Responses to “Crescent Nebula revisited”
  1. Kyle says:

    There’s this really beautiful song called “life on other planets” I would like to show you by a guy named Bill Mallonee. It was a hit more than a few years ago. I thought this post was really fun to read and look at. Thanks Grandpa!

  2. Dave says:

    So why don’t you send me the song so I can hear it? I looked Mallonee up in Wikipedia, and his band sounds interesting. Or a YouTube of his group.

    Hope you and Angela are doing well and staying warm.

  3. Kyle says:


    sadly this is without his awesome backing band, but you can get a feel for the lyrics. I was gonna just show you it on CD if you’d rather. I forget about the full reaches of the internet sometimes.

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