APOD: Dust of the Orion Nebula (2012 Feb 06)

[Chris Peterson]

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

Yes.

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.

Yes, it does seem remarkable. But despite the low concentrations, there is lots of time for things to bump together. Also, at the time of formation, many molecules are created in environments much denser than the nebula they eventually end up in... like in stellar cores, and in stellar atmospheres. The nature of elements defines what forms: silicates are common because silicon and oxygen are common, and like to combine in certain well defined ways. The environment means that the dust is mineralogically distinct from what you typically find on Earth. But looking at the bigger picture, not radically different at all.

[BMAONE23]

Did anyone noticed the several lines of different angles through the image?

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

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

[Chris Peterson]

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

Maybe, but it's very odd so many would be parallel. I think we're seeing geosynchronous and geostationary satellites, which lie in a band above the equator, placing their path right through the Orion Nebula area for the temperate northern latitudes (including Spain, where this image was made). The color is then determined by the filter in place when that satellite passed over. With a field size of about 3°, the trail lengths make sense for the subexposure times.

[Flase]

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.

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?

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.

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

It's amazing how much skin a human being sheds. Maybe we should eat it to replenish our bodies.

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]

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?

Yes. But our eyes base color on both wavelength and intensity. When you change the intensity, you change the color. Pure H-alpha, from a reference tube, looks like anything from pinkish-white to saturated red, depending on how bright the source is.

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.

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.

I'm often blunt as well. I wasn't challenging your aesthetic opinion, which is, of course, quite validly your own. I was only pointing out that this image isn't "false color" in the sense that term is applied to astronomical images.

[Flase]

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]

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.

Sorry. You are not wrong in your thinking.

[GWARmachine]

I notice multiple horizontal lines in this image. I am new to astrophotography and every time I photograph the Great Nebula I end up with horizontal lines that I can't explain. Is this the busiest part of the sky for us? Can anyone help explain? Thank you.

[Joe Stieber]

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

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.

[Chris Peterson]

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.

Not just geostationary satellites, but also geosynchronous satellites- many of which are close to the geostationary band. That's why we see multiple objects.

[tytower1]

Whats going down here?
This is M45 Pleiades !!

What are you doing with the images to produce this rubbish
Who chooses what colours are used ?
On what basis are these images colours altered ? What data sources are aberated?

[geckzilla]

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.

[Chris Peterson]

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.

And the colors aren't even totally arbitrary. This would reasonably be described as "true color", since a set of RGB data is mapped to an RGB display. Certain aspects of the color, such as saturation, are defined by the imager. But on the whole, the hues are accurate.

[geckzilla]

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

[Chris Peterson]

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

Never fails <g>.

(Are you some kind of pessimist, to see your statement as "semi-false" rather than "semi-true"?)

[geckzilla]

Yes. Actually, I love working with negative space.

[Psnarf]

--
Obquote:

"Good friend, for Jesus' sake, forbeare
To dig the dust enclosed heare!
Blest be ye man that spares thes stones
And curst be he that moves my bones."
-William Shakespeare, Holy Trinity Church, Stratford-upon-Avon, England.

http://www.gutenberg.org/files/14662/14 ... 4662-h.htm
http://www.presscom.co.uk/halliwell/newboke.html pg. 65.
http://www.project-hamlet.info/playwright.html
http://lightnincharlie.com/Page4.html
http://oreald.com/b4/ch148.html

[DavidLeodis]

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]

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.

Unless I misinterpreted several images, it's pretty much dead center. The individual stars are obscured by their own brightness.

[Chris Peterson]

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.

It's blown out in this image, so only a hint of it is seen (I needed to adjust the contrast to pick out any structure). But it's right here:

trap.jpg (22.88 KiB) Viewed 2056 times

[DavidLeodis]

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.

[Chris Peterson]

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.

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.

(Of course, many stars are saturated in nebula images. That does two things- destroys their color information, and makes them appear larger. For most stars, this doesn't really affect how we see the image much. But the Trapezium cluster stars are so close together that the increase in image diameter caused by saturation causes them to overlap. So we end up seeing them as a sort of blob, rather than individually resolved stars.)

[neufer]

[b]Jules Léotard (1842 – 1870)[/b]

---

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.

<<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.">

Click to play embedded YouTube video.

Click to play embedded YouTube video.

[khris210]

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]

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.

It would not matter how close you were to the Orion Nebula, you would never see it as anything more than gray- perhaps just a bit of green if your eyes are particularly sensitive.

Images described as "true color" were made in such a way that they appear similar to how they would appear to our eyes assuming that those eyes were more sensitive, but otherwise had the same response. Images described as "false color" fall into three categories: those that have had their actual colors shifted to others in order to make some sort of detail more apparent, those that map specific narrow emission bands to broad color ranges, and those that had no "color" to begin with (such as radio or ultraviolet), and had those bands mapped into colors so we can see them at all.