APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02)

Post a reply


This question is a means of preventing automated form submissions by spambots.
Smilies
:D :) :ssmile: :( :o :shock: :? 8-) :lol2: :x :P :oops: :cry: :evil: :roll: :wink: :!: :?: :idea: :arrow: :| :mrgreen:
View more smilies

BBCode is ON
[img] is ON
[url] is ON
Smilies are ON

Topic review
   

Expand view Topic review: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02)

Oh... Rayleigh?

by neufer » Mon Apr 22, 2013 2:06 pm

James Lesley wrote:
8-) What I see is blue.
http://en.wikipedia.org/wiki/Visible_spectrum wrote:
A typical human eye will respond to wavelengths from about (far violet) 390 to (far red) 700 nm.
  • 1) Rayleigh λ−4 scattering law (violet/red) ratio: (390/700)4 = 10.4

    2) Rayleigh–Jeans λ−4 black body radiation law (violet/red) ratio: (390/700)4 = 10.4

    The Blue–Jeans Horsehead Nebula λ−8 scattered radiation law (violet/red) ratio: (390/700)8 = 108
http://en.wikipedia.org/wiki/Rayleigh_scattering wrote:
<<Rayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. [The λ−4 dependence of Rayleigh scattering is based on classical physical arguments.] Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle therefore becomes a small radiating dipole whose radiation we see as scattered light.

The Rayleigh scattering cross-section is given by: Image

The Rayleigh scattering coefficient for a group of scattering particles is the number of particles per unit volume N times the cross-section. As with all wave effects, for incoherent scattering the scattered powers add arithmetically, while for coherent scattering, such as if the particles are very near each other, the fields add arithmetically and the sum must be squared to obtain the total scattered power.>>
http://en.wikipedia.org/wiki/Rayleigh%E2%80%93Jeans_law wrote:
<<In physics, the Rayleigh–Jeans law attempts to describe the spectral radiance of electromagnetic radiation at all wavelengths from a black body at a given temperature through classical arguments.

For wavelength λ, it is: Image

In 1900, the British physicist Lord Rayleigh derived the λ−4 dependence of the Rayleigh–Jeans law based on classical physical arguments. A more complete derivation, which included the proportionality constant, was presented by Rayleigh and Sir James Jeans in 1905. The Rayleigh–Jeans law revealed an important error in physics theory of the time. The law predicted an energy output that diverges towards infinity as wavelength approaches zero (as frequency tends to infinity) and measurements of energy output at short wavelengths disagreed with this prediction.>>

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Ann » Mon Apr 22, 2013 2:58 am

James Lesley wrote:8-) What I see is blue. Is that a big cloud of oxigen?
I agree with you that blue is cool! :D :D :D

But the blue cloud is a reflection nebula, so the cloud doesn't emit its own light, unlike, say, blueish planetary nebulae whose blue-green light is really due to oxygen. Instead, this is a reflection nebula, similar to the blue "mist" surrounding the Pleiades.

The blue "cloud" we see is starlight scattered by surrounding dust. The starlight is intrinsically blue, too, which makes the reflection nebula so obviously blue.

Ann

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by James Lesley » Mon Apr 22, 2013 2:13 am

8-) What I see is blue. Is that a big cloud of oxigen?

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by MargaritaMc » Wed Apr 03, 2013 10:25 pm

Anthony Barreiro wrote:
neufer wrote:
Anthony Barreiro wrote:
(P.S. -- This discussion reminds me of descriptive vs. prescriptive grammar.)
  • Grammar's seeking bet. Armor ticking arson burden barter an shirker cockles.
"O Grammar, water bag mousy gut!"
Click to play embedded YouTube video.
My Android won't play RealPlayer so I'm in the dark about 'Armor ticking arson' :roll:
Mairzy Doats doesn't come anywhere NEAR that ¿ story? in incomprehensibility!

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Beyond » Wed Apr 03, 2013 12:30 am

HEY!! I have enuff trubell wit inglash :!:

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Anthony Barreiro » Tue Apr 02, 2013 11:22 pm

neufer wrote:
Anthony Barreiro wrote:
(P.S. -- This discussion reminds me of descriptive vs. prescriptive grammar.)
  • Grammar's seeking bet. Armor ticking arson burden barter an shirker cockles.
"O Grammar, water bag mousy gut!"

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by neufer » Tue Apr 02, 2013 10:26 pm

Anthony Barreiro wrote:
(P.S. -- This discussion reminds me of descriptive vs. prescriptive grammar.)
  • Grammar's seeking bet. Armor ticking arson burden barter an shirker cockles.

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Anthony Barreiro » Tue Apr 02, 2013 10:19 pm

Chris Peterson wrote:
500pesos wrote:Why oh why do astronomers insist on mispronouncing the Greek alphabet? It is not letter Nu, nor Mu. It's Ni and Mi (pronounced 'nee' and 'mee' as in the English words see, fee or bee).
And by the way, Pi is also pronounced 'pee', as in... pee, not 'paï' as in pie - but fine I guess it's too late to do anything about that, sigh.
You are making the mistake of assuming your pronunciations are correct. In English, they are not. Nu and Mu are the correct spellings of those Greek letters, and nyu and myu are the correct pronunciations. Just because they are pronounced one way in modern Greek doesn't mean that the pronunciations used by other languages are incorrect.

If you made a reference to Ni Scorpii, it is you who would be incorrect and likely misunderstood.
Gentlepersons, there are many words and letters that are pronounced differently in different languages, idioms, and dialects. Context is everything. It's true that if somebody giving an astronomy lecture in the US referred to "Nee Scorpii" they would probably be met with blank stares. At the least they would need to clarify that in modern Greek that's how "Nu" is pronounced, and they would probably resign themselves to using the English (mis)pronunciations of Greek letters. It's equally true that a foreign astronomer living in Athens would need to learn to pronounce letters correctly in modern Greek in order to be able to communicate and get around.

Now that I've learned the Greek alphabet well enough to find my way through the Bayer star catalogue, I find it fascinating to learn that modern Greeks pronounce everything differently than I've learned. The world is infinitely more diverse than I will ever comprehend, and that gives me joy and hope.

(P.S. -- This discussion reminds me of descriptive vs. prescriptive grammar.)

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Boomer12k » Tue Apr 02, 2013 9:40 pm

It would be sooooo much nicer, if it weren't sooooo dusty!!! LOL!!! :lol2:

:---[===] *

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Boomer12k » Tue Apr 02, 2013 9:39 pm

That is a "horse of a different color"....

:---[===] *

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Chris Peterson » Tue Apr 02, 2013 4:59 pm

Psnarf wrote:Today's APOD image might have been taken through a ground 1981 Celestron C-8 8" Schmidt Cassegrain telescope. Perhaps that might explain the 8 radial artifacts emanating from each bright star and the faint blue globe at the end of the radial arms? There are probably 2-5 stars in that cluster generating the reflection nebula.
SCTs don't show linear diffraction artifacts. That is one reason they are popular for imaging. (Refractors don't show them, either, but it is impractical to produce refractors with large apertures, whereas it is common with SCTs.)

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by stephen63 » Tue Apr 02, 2013 4:03 pm

Psnarf wrote:How soon we forget...http://apod.nasa.gov/apod/ap060808.html That image could have been taken through one of the Star Shadows Remote Observatory telescopes operated remotely. http://www.starshadows.com

Today's APOD image might have been taken through a ground 1981 Celestron C-8 8" Schmidt Cassegrain telescope. Perhaps that might explain the 8 radial artifacts emanating from each bright star and the faint blue globe at the end of the radial arms? There are probably 2-5 stars in that cluster generating the reflection nebula.
It might have been, but it wasn't. It was taken through a Canon EF 200mm f/2.8L II USM lens stopped down to f/3.5. The radial artifacts come from the 8 blades used for the lens diaphragm. :)

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Psnarf » Tue Apr 02, 2013 3:44 pm

How soon we forget...http://apod.nasa.gov/apod/ap060808.html That image could have been taken through one of the Star Shadows Remote Observatory telescopes operated remotely. http://www.starshadows.com

Today's APOD image might have been taken through a ground 1981 Celestron C-8 8" Schmidt Cassegrain telescope. Perhaps that might explain the 8 radial artifacts emanating from each bright star and the faint blue globe at the end of the radial arms? There are probably 2-5 stars in that cluster generating the reflection nebula.

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Chris Peterson » Tue Apr 02, 2013 2:24 pm

500pesos wrote:Why oh why do astronomers insist on mispronouncing the Greek alphabet? It is not letter Nu, nor Mu. It's Ni and Mi (pronounced 'nee' and 'mee' as in the English words see, fee or bee).
And by the way, Pi is also pronounced 'pee', as in... pee, not 'paï' as in pie - but fine I guess it's too late to do anything about that, sigh.
You are making the mistake of assuming your pronunciations are correct. In English, they are not. Nu and Mu are the correct spellings of those Greek letters, and nyu and myu are the correct pronunciations. Just because they are pronounced one way in modern Greek doesn't mean that the pronunciations used by other languages are incorrect.

If you made a reference to Ni Scorpii, it is you who would be incorrect and likely misunderstood.

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by stephen63 » Tue Apr 02, 2013 1:46 pm

Fantastic image!

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by 500pesos » Tue Apr 02, 2013 1:39 pm

Why oh why do astronomers insist on mispronouncing the Greek alphabet? It is not letter Nu, nor Mu. It's Ni and Mi (pronounced 'nee' and 'mee' as in the English words see, fee or bee).
And by the way, Pi is also pronounced 'pee', as in... pee, not 'paï' as in pie - but fine I guess it's too late to do anything about that, sigh.

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by emc » Tue Apr 02, 2013 1:22 pm

Neufer's post is an apropos reflection. Speaking of reflections... A horse is a horse unless it's something else. In eighth grade art class, I started a plaster sculpture modeling the Blue Horse logo. I had to change it to a ram head when I carved the ears too short.
Attachments
LooseLeafBlueHorse.JPG
LooseLeafBlueHorse.JPG (25.67 KiB) Viewed 3608 times

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Astronymus » Tue Apr 02, 2013 10:57 am

More kind of Ghost Horse Nebula.


Let's find its headless rider. :wink:

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by neufer » Tue Apr 02, 2013 10:37 am

Click to play embedded YouTube video.

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Ann » Tue Apr 02, 2013 8:55 am

Image
Source: bluerosevideos.com
So maybe there are blue roses, too? :ssmile:

Even though http://en.wikipedia.org/wiki/Blue_rose wrote:
Blue roses, often portrayed in literature and art as a symbol of love and prosperity to those who seek it, do not exist in nature as a result of genetic limitations being imposed upon natural variance.
Although in this legend of the blue rose, white roses look blue by the light of the full moon! How appropriate for Starship Asterisk*!

(Or maybe not... it could be that I just made us drift too far off topic now. Sorry.)

Ann

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by MargaritaMc » Tue Apr 02, 2013 8:27 am

Ann wrote:Why thanks, Margarita, it looks lovely!

So there are blue horses of the Earth after all! :D

Ann
There is a legend in the Blue Grass country of Kentucky as well.
http://www.visitlex.com/blue-horse.php
Image
Although no one has real evidence that blue horses exist, there are many tales of sightings across the region from legions of true believers. Legend has it that a horse called "Big Lex" turned blue from grazing in nourishing bluegrass pastures his entire life. Perhaps he found the very source of these limestone rich waters. Be on the lookout for a big blue horse as you drive around the backroads that are home to hundreds of horse farms in the area -- you might just see the legendary blue horse yourself.
Margarita

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Ann » Tue Apr 02, 2013 8:18 am

Why thanks, Margarita, it looks lovely!

So there are blue horses of the Earth after all! :D

Ann

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by MargaritaMc » Tue Apr 02, 2013 8:14 am

Image

A present for Ann!

Margarita

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Ann » Tue Apr 02, 2013 5:53 am

Boomer12k wrote:Uuuuuuuuuu, Ann must be in 7th Heaven!

Very nice shot.

:---[===] *
Yes, why do our Earthly members of the Equus family not come in this cerulean color here, too? :mrgreen:

Ann

Re: APOD: IC 4592: The Blue Horsehead Nebula... (2013 Apr 02

by Boomer12k » Tue Apr 02, 2013 5:35 am

Uuuuuuuuuu, Ann must be in 7th Heaven!

Very nice shot.

:---[===] *

Top