Starship Asterisk*

khris210 wrote:I have been visiting APOD for some years now and in the true spirit of dilettantism have often wondered about the colours of the objects shown, but never bothered to dig deeper. Sometimes the colours are described as false but sometimes not, but I have always assumed that if one was in a spaceship and seeing the object with the naked eye it would be in black and white. I was therefore delighted to know that I would see at least the Orion Nebula in the actual colours (more or less). Perhaps future images could indicate more clearly the accuracy of the colours shown.

Chris Peterson wrote:

DavidLeodis wrote:
I would not have thought that the Trapezium was so indistinct in the picture, as being mentioned in the explanation that would seem to me to imply it would be fairly obvious to see in the picture.

The Trapezium stars are so much brighter than the surrounding nebula that they are almost always blown out in images like this. It is possible, by making exposures with very different lengths and combining them with careful processing to capture both nebulosity and the individual stars. But this sort of high dynamic range processing is tricky.

http://en.wikipedia.org/wiki/Flying_Trapeze wrote:
<<The flying trapeze is a specific form of the trapeze in which a performer jumps from a platform with the trapeze so that gravity makes the trapeze swing. The performance was invented in 1859, by a Frenchman named Jules Léotard who connected a bar to some ventilator cords above the swimming pool in his father's gymnasium in Toulouse, France. After practicing tricks above the pool, Leotard performed his act in the Cirque Napoleon. The traditional flier's costume, the leotard, is named after him. In the early years of young Mr. Leotard's performances, the flying trapeze did not have the safety net as is typically seen today. He would perform over a series of mattresses on a raised runway to give the audience a better view of his tricks or "passes.">

DavidLeodis wrote:Thanks geckzilla and Chris. Your help is appreciated. :)

I would not have thought that the Trapezium was so indistinct in the picture, as being mentioned in the explanation that would seem to me to imply it would be fairly obvious to see in the picture.

DavidLeodis wrote:The explanation seems to imply that the Trapezium is visible in the picture. If it is I would be grateful if someone could please tell me where it is.

DavidLeodis wrote:The explanation seems to imply that the Trapezium is visible in the picture. If it is I would be grateful if someone could please tell me where it is.

geckzilla wrote:See, I totally tricked Chris into replying by making a semi-false statement.

geckzilla wrote:Don't be rude, ty. First, it's not the Pleiades. Second, the colors are arbitrary. You're entitled to your opinion but don't be nasty about it.

Joe Stieber wrote:There are several nearly-horizontal lines running across the picture. They are evidently trails from geostationary satellites, or the remnants of such trails that were largely erased by the photographer. These satellites are parked over the earth's equator and parallax from photographer's location in Spain would make them appear south of the celestial equator, sometimes in the the neighorhood of M42, which has a declination of about 5 degrees south (we get a similar effect here in New Jersey which is nominally at the same latitude as Spain). Since these satellites are stationary and the background sky is moving westward at 15 degrees/hour, a scope tracking on the background sky causes the trailing.

Délicate Frénésie wrote:Did anyone noticed the several lines of different angles through the image?
Are they artifacts of the computation used to produce the image?

Flase wrote:

Chris Peterson wrote:

Am I wrong in thinking that elemental hydrogen is still the most common constituent of nebulae?

Absolutely. The total mass of even the dustiest nebula is overwhelmingly from atomic and molecular hydrogen, followed by helium. The mass of all that dust doesn't amount to more than one or two percent of the total.

This is ambiguous. I think you mean to say that I am right in thinking that.

Chris Peterson wrote:

Am I wrong in thinking that elemental hydrogen is still the most common constituent of nebulae?

Absolutely. The total mass of even the dustiest nebula is overwhelmingly from atomic and molecular hydrogen, followed by helium. The mass of all that dust doesn't amount to more than one or two percent of the total.

Flase wrote:Aren't the colours of glowing nebulae defined by emission lines at specific frequencies? If you don't do anything but turn the brightness up and down, doesn't that keep these frequencies the same?

Am I wrong in thinking that elemental hydrogen is still the most common constituent of nebulae?

Sorry I don't want to be rude about this picture. I'm just blunt and when I do say something's wonderful, it really means something. You know where you are with me.

Chris Peterson wrote:This isn't a false-color image. It's straight LRGB, meaning the hues approximately match human vision. As always with objects too dim to stimulate color vision, the choice of how saturated to show the colors is entirely arbitrary. No RGB image, from nearly B&W to gaudy color, is more or less "accurate" than any other. All are inaccurate in terms of what the eye can see, so how to present the data is a matter of aesthetics, not science.

Chris Peterson wrote:

jerhoad wrote:What is the chemical composition of this 'dust'? I'm pretty sure it is not what I find on my baseboards around the house. If it is merely hydrogen, why not just say 'hydrogen'?

Most of the dust you find around your house is made up of dead skin and other organics. But the dust that blows in from the outside isn't all that different from what you find in a dusty nebula- basically consisting of silicates (although in the details, there are many differences). Also, the dust in a nebula is typically smaller than the dust in your house, and much more tenuous- I'd guess the amount of dust in your house (no reflection on your housekeeping!) would be enough to fill thousands of cubic kilometers in a dusty nebula.

BMAONE23 wrote:Looking closely at the enlarged image, the lines appear to have parallel Green and Red tinges to them. They are most likely artifact from passing aircraft during the 15 minute exposures

Délicate Frénésie wrote:Did anyone noticed the several lines of different angles through the image?

Are they artifacts of the computation used to produce the image?

jerhoad wrote:Thanks Chris - and the obvious followup is: the silcates are the end products of prior star generations?

Elements are produced in those explosions; it seems molecules would need a somewhat different environment in which to form. Given the very low concentrations of matter in the interstellar medium, it is quite amazing that these elements find each other and form more complex molecules.