APOD: M27: Not a Comet (2015 Aug 20)

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APOD: M27: Not a Comet (2015 Aug 20)

Post by APOD Robot » Thu Aug 20, 2015 4:11 am

Image M27: Not a Comet

Explanation: While hunting for comets in the skies above 18th century France, astronomer Charles Messier diligently kept a list of the things he encountered that were definitely not comets. This is number 27 on his now famous not-a-comet list. In fact, 21st century astronomers would identify it as a planetary nebula, but it's not a planet either, even though it may appear round and planet-like in a small telescope. Messier 27 (M27) is an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core. The nebula forms as the star's outer layers are expelled into space, with a visible glow generated by atoms excited by the dying star's intense but invisible ultraviolet light. Known by the popular name of the Dumbbell Nebula, the beautifully symmetric interstellar gas cloud is over 2.5 light-years across and about 1,200 light-years away in the constellation Vulpecula. This impressive color composite highlights details within the well-studied central region and fainter, seldom imaged features in the nebula's outer halo. It incorporates broad and narrowband images recorded using filters sensitive to emission from sulfur, hydrogen and oxygen atoms.

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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Boomer12k » Thu Aug 20, 2015 2:00 pm

Just awesome, and one of my personal favorites to view...I LOVE the detail of the outer halo area...Visually not much more than a cloudy patch, with photography the details are quite stunning...with different filters even more layers of detail can be brought out.
Science is SOOOOO amazing....

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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Case » Thu Aug 20, 2015 4:20 pm

APOD Robot wrote:While hunting for comets in the skies above 18th century France, astronomer Charles Messier diligently kept a list of the things he encountered that were definitely not comets. This is number 27 on his now famous not-a-comet list.
Besides objects that were definitely not comets, Messier did discover 13 comets. :clap:

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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Tszabeau » Thu Aug 20, 2015 4:26 pm

If I was dictator of astronomy, it would be called "The Flag Waver". I don't see "The Dumbbell" in this view, at all.

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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Chris Peterson » Thu Aug 20, 2015 5:42 pm

Tszabeau wrote:If I was dictator of astronomy, it would be called "The Flag Waver". I don't see "The Dumbbell" in this view, at all.
Because the name is a reflection of its visual appearance. At an eyepiece, you only see what is red in this image (and you see it as gray). It's those two lobes that give it the dumbbell appearance. It's actually one of the better named visual objects.
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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Ron-Astro Pharmacist » Thu Aug 20, 2015 6:52 pm

The history of mapping the sky has undergone quite dynamic changes since the days of Messier. I would bet there have been more than a few books written its history. If anyone has suggestions I’d love to hear about them. Given today’s title I find it interesting that some of his objects were not. Or at least they were difficult to find after his list was published. Since then the amount of data created could probably fill a “cloud”.

Or cloud a brain. :? I suspect reading a history of the effort to map the sky would help many of us reign supreme :) in understanding astronomy.
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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by hoohaw » Thu Aug 20, 2015 7:10 pm

Case wrote:
APOD Robot wrote:While hunting for comets in the skies above 18th century France, astronomer Charles Messier diligently kept a list of the things he encountered that were definitely not comets. This is number 27 on his now famous not-a-comet list.
Besides objects that were definitely not comets, Messier did discover 13 comets. :clap:
He would, today, be (almost) totally forgotten, were it not for hist list of what he apparently considered annoying celestial objects.

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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by ta152h0 » Thu Aug 20, 2015 7:33 pm

is ultraviolet radiation the same as " black light " tube I have here at home ? Some plastics glow very bright when I turn on the fixture
and so does tide soap when painted on the wall
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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by geckzilla » Thu Aug 20, 2015 7:44 pm

ta152h0 wrote:is ultraviolet radiation the same as " black light " tube I have here at home ? Some plastics glow very bright when I turn on the fixture
and so does tide soap when painted on the wall
Yeah, but you are only seeing violet light coming from the black light. Your clothes detergent has some chemicals called optical brighteners in it that stick to your clothing and when UV light hits them they emit some visible blue light back. It's cheating to make the clothes look whiter. I read about this a while back in an article about scientists using tampons to detect pollution. The brighteners attach to the tampons if they're there and then they glow, indicating the presence of detergents in the water. http://www.wired.com/2015/03/glowing-ta ... age-leaks/
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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Joe Stieber » Thu Aug 20, 2015 7:47 pm

Chris Peterson wrote:
Tszabeau wrote:If I was dictator of astronomy, it would be called "The Flag Waver". I don't see "The Dumbbell" in this view, at all.
Because the name is a reflection of its visual appearance. At an eyepiece, you only see what is red in this image (and you see it as gray). It's those two lobes that give it the dumbbell appearance. It's actually one of the better named visual objects.
Indeed, "Dumbbell" is a good visual description. An "apple core" would also a good visual description. M27 is a pretty bright as far as deep-sky objects go, and with my 12.5-inch scope visually, I see it as a pale blue-green color. The blue-green color also accounts for the visual contrast enhancement provided by an O-III filter passing wavelengths near 500 nm.

Because of the dumbbell or apple core shape, and that it really looks nebulous, M27 doesn't fit the "planetary" moniker so well from the appearance standpoint. Same thing for the Ring Nebula (M57) which looks like a little donut. In contrast, many of the small planetary nebulae, e.g., the Blue Snowball (NGC 7662), do look like small bluish discs visually in a scope -- superficially like Uranus or Neptune -- so it's understandable that when first seen in an earlier times, they were suspected of being new planets, at least until they didn't show motion with respect to the background stars.

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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Chris Peterson » Thu Aug 20, 2015 7:50 pm

ta152h0 wrote:is ultraviolet radiation the same as " black light " tube I have here at home ? Some plastics glow very bright when I turn on the fixture
and so does tide soap when painted on the wall
Yes, although the part of the spectrum designated UV covers a wide range of energies (wavelengths). A black light is just barely out of the visible (indeed, it overlaps the visible, which is why you see violet glow). The radiation at this long wavelength is non-ionizing, and the intensity is too low to have much physiological impact (although much brighter lights in this wavelength range are used for tanning).
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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by Ron-Astro Pharmacist » Fri Aug 21, 2015 3:59 pm

Ron-Astro Pharmacist wrote:The history of mapping the sky has undergone quite dynamic changes since the days of Messier. I would bet there have been more than a few books written its history. If anyone has suggestions I’d love to hear about them.
Online blurbs that I ran across include:

http://sci.esa.int/gaia/53196-the-oldest-sky-maps/
http://www.smithsonianmag.com/history/t ... 44/?no-ist
http://skyserver.sdss.org/dr1/en/astro/ ... he_sky.asp

Author Nick Kanas has written a few books too:

http://starizona.com/acb/Star-Maps-Hist ... 60C71.aspx
https://www.britastro.org/journal_item/5869
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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by starsurfer » Fri Aug 21, 2015 4:21 pm

Joe Stieber wrote:when first seen in an earlier times, they were suspected of being new planets, at least until they didn't show motion with respect to the background stars.
When they were first observed in the 18th century, planetary nebulae were not thought of as new planets by the observers of the time. This name was given to this category of nebula by William Herschel as to him, the ones he observed resembled the telescopic views of planets. I know a lot of people complain about this name but I think its perfect!

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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by ta152h0 » Fri Aug 21, 2015 8:10 pm

this obje ct looks like Eta Carinae if you could see it from the long end
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Re: APOD: M27: Not a Comet (2015 Aug 20)

Post by geckzilla » Fri Aug 21, 2015 8:16 pm

starsurfer wrote:
Joe Stieber wrote:when first seen in an earlier times, they were suspected of being new planets, at least until they didn't show motion with respect to the background stars.
When they were first observed in the 18th century, planetary nebulae were not thought of as new planets by the observers of the time. This name was given to this category of nebula by William Herschel as to him, the ones he observed resembled the telescopic views of planets. I know a lot of people complain about this name but I think its perfect!
It would be fine if it were not so easily confused for having an actual relationship to planets. Take, for example, the early name protoplanetary nebula which has fallen out of use in favor of preplanetary nebula because protoplanetary was too easily confused with protoplanetary disc. It's really no good at all, if you ask me.
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