APOD: In the Center of the Trifid Nebula (2015 Oct 11)

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APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by APOD Robot » Sun Oct 11, 2015 4:09 am

Image In the Center of the Trifid Nebula

Explanation: Clouds of glowing gas mingle with dust lanes in the Trifid Nebula, a star forming region toward the constellation of the Archer (Sagittarius). In the center, the three prominent dust lanes that give the Trifid its name all come together. Mountains of opaque dust appear on the right, while other dark filaments of dust are visible threaded throughout the nebula. A single massive star visible near the center causes much of the Trifid's glow. The Trifid, also known as M20, is only about 300,000 years old, making it among the youngest emission nebulae known. The nebula lies about 9,000 light years away and the part pictured here spans about 10 light years. The above image is a composite with luminance taken from an image by the 8.2-m ground-based Subaru Telescope, detail provided by the 2.4-m orbiting Hubble Space Telescope, color data provided by Martin Pugh and image assembly and processing provided by Robert Gendler.

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by Boomer12k » Sun Oct 11, 2015 9:17 pm

Since this is Sunday this is a repeat?

Well, it is a spectacular repeat!!!

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Isaiah 40:26

Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by Isaiah 40:26 » Mon Oct 12, 2015 3:49 am

The Flux Capacitor Nebula
Image
:D

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by neufer » Mon Oct 12, 2015 4:15 am

http://messier.seds.org/m/m020.html wrote:
<<The Trifid Nebula's distance is rather uncertain, with values between 2,200 light years (Mallas/Kreimer; Glyn Jones has 2,300) and about 7,600 light years (C.R. O'Dell 1963). The Sky Catalog 2000 gives 5,200 light years, a value which is also used by Archinal and Hynes (2003), and which we adopt here. The WEBDA database has 3140, the Hubble Press Release of Jeff Hester (STScI-PRC99-42) gives "about 9000" light years.>>
http://asterisk.apod.com/viewtopic.php?f=9&t=34995&p=246251 wrote:
As seen here, the Trifid lies only 5,500 light-years away [in the Carina–Sagittarius Arm] and is about 30 light-years across.
APOD Robot wrote:
The nebula lies about 9,000 light years away [in the Crux-Scutum–Centaurus Arm] and the part pictured here spans about 10 light years.
Art Neuendorffer

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by tomatoherd » Mon Oct 12, 2015 12:39 pm

Art: I'm sure computers worked hard to compile these hypothetical Milky Way arms out of stellar positions/concentrations, but why, if they are true, does the MW have so many arms? I don't recall seeing any spiral galaxy on APOD with that many....

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by DavidLeodis » Mon Oct 12, 2015 12:47 pm

The "luminance" in the explanation is a link to the definition of luminance. I've long assumed that luminance simply meant light that was not a specific colour (such as red, green and blue filters are specific). The definition of luminance does not seem to mean what I thought it meant (not that I really understand the definition :? and a bit :oops: ). I would be grateful if someone could please give an easier to understand definition of what luminance means in astrophotography.

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by neufer » Mon Oct 12, 2015 1:55 pm

tomatoherd wrote:
Art: I'm sure computers worked hard to compile these hypothetical Milky Way arms out of stellar positions/concentrations, but why, if they are true, does the MW have so many arms? I don't recall seeing any spiral galaxy on APOD with that many....
  • Perhaps you've never looked that hard.
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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by starsurfer » Mon Oct 12, 2015 1:59 pm

DavidLeodis wrote:The "luminance" in the explanation is a link to the definition of luminance. I've long assumed that luminance simply meant light that was not a specific colour (such as red, green and blue filters are specific). The definition of luminance does not seem to mean what I thought it meant (not that I really understand the definition :? and a bit :oops: ). I would be grateful if someone could please give an easier to understand definition of what luminance means in astrophotography.
The luminance filter used for astrophotography (usually marked as L) is a clear filter that is used for the definition of detail and brightness and contrast information for a particular imaging target. Most images have the luminance exposure longer than the RGB data for the sake of improved detail.

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by Chris Peterson » Mon Oct 12, 2015 2:02 pm

DavidLeodis wrote:The "luminance" in the explanation is a link to the definition of luminance. I've long assumed that luminance simply meant light that was not a specific colour (such as red, green and blue filters are specific). The definition of luminance does not seem to mean what I thought it meant (not that I really understand the definition :? and a bit :oops: ). I would be grateful if someone could please give an easier to understand definition of what luminance means in astrophotography.
In astrophotography (and imaging in general) "luminance" usually refers to the intensity channel of the data ("intensity" being another word with a technical meaning different from how it is used by imagers). So it is, as you suggest, just the image without color information attached- essentially, what you get if you convert a color image to B&W.

More technically, however, photometricists- people interested in extracting useful information from light, and those concerned with the energy of light, use a somewhat bewildering collection of rigorously defined concepts, including intensity, luminance, luminous intensity, flux, irradiance, and many more. These consider things like the angle of emission, area of collection, variation in energy with wavelength, and other factors that are usually not of concern to imagers.
Chris

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by tomatoherd » Mon Oct 12, 2015 2:29 pm

So, does it seem the MW structurally more resembles the Pinwheel than Andromeda? And within the Pinwheel, it looks like the arms fork or branch a lot, with prob. only two close in to the galactic center.

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by Chris Peterson » Mon Oct 12, 2015 2:41 pm

tomatoherd wrote:So, does it seem the MW structurally more resembles the Pinwheel than Andromeda? And within the Pinwheel, it looks like the arms fork or branch a lot, with prob. only two close in to the galactic center.
The Milky Way is quite different from Andromeda. It is a barred spiral, with a pair of arms coming off the bar (as is usual). Within this broad structure lie two or more additional minor arms, which may be independent of the two major arms, or may be related forks. It's very difficult to tell from our inside view.
Chris

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Re: APOD: In the Center of the Trifid Nebula (2015 Oct 11)

Post by DavidLeodis » Mon Oct 12, 2015 7:55 pm

Thank you starsurfer and Chris for your help with my query. :)