Starship Asterisk*

Alnitak, Alnilam, Mintaka

Explanation: Alnitak, Alnilam, and Mintaka, are the bright bluish stars from east to west (lower right to upper left) along the diagonal in this gorgeous cosmic vista. Otherwise known as the Belt of Orion, these three blue supergiant stars are hotter and much more massive than the Sun. They lie about 1,500 light-years away, born of Orion's well-studied interstellar clouds. In fact, clouds of gas and dust adrift in this region have intriguing and some surprisingly familiar shapes, including the dark Horsehead Nebula and Flame Nebula near Alnitak at the lower right. The famous Orion Nebula itself is off the right edge of this colorful star field. The well-framed, wide-field telescopic image spans about 4 degrees on the sky.

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Oh so lovely!!!

Note, among other things, that Alnilam - the middle star in Orion's Belt - has cleared away the gas and dust around itself with its powerful stellar wind. According to Hipparcos measurements, Alnilam may be considerably farther away from us than Alnitak and Mintaka, the other two Belt stars. Alnilam is certainly more massive than Mintaka - the upper right star in the Belt for us northerners - and therefore it blows a stronger wind. Alnitak may be younger than Alnilam and not as evolved. Alnitak is the Belt star that seems to be swathed in red and yellow nebulosity.

Ann

I was only admiring these three stars in the sky last evening - the other way up from here!
But how I wish I could resolve all those beautiful colours with my own eyes as well.

Beautiful image! Great to see them in context with the Horsehead and Flame nebulas.

Fantastic image. Great to see the tear drop nebula amongst the Alnilam and Mintaka. One of my favourites nebs.

jase wrote:Fantastic image. Great to see the tear drop nebula amongst the Alnilam and Mintaka. One of my favourites nebs.

There is a nice image of the Teardrop nebula here, which I had not heard of before:

http://cosmicphotos.com/gallery/image.p ... lbum_id=11


I think that the image is too large to link.
M

PS. Info from the photographer here: http://www.lightbuckets.com/forums/showthread.php?t=138
Interestingly, the name is... "Jase"...

In the Hipparcos catalogue

http://www.atlasoftheuniverse.com/stars.html

the distances to Alnitak and Mintaka are given as 820 and 920ly respectively, way closer than Alnilam (1300ly). But in this APOD they are all given as the same distance in the Orion Neb (1500ly). Don't know which is correct.

Always a pleasure to see one of my favorite areas....really nice.

:---[===] *

It looks like someone tried to sign his NAME in the dust in the lower right corner.

:---[===] *

MysticLipstick wrote:In the Hipparcos catalogue

http://www.atlasoftheuniverse.com/stars.html

the distances to Alnitak and Mintaka are given as 820 and 920ly respectively, way closer than Alnilam (1300ly).
But in this APOD they are all given as the same distance in the Orion Neb (1500ly). Don't know which is correct.

Indeed.

The APOD needs a rewrite that clearly places the Belt stars in the foreground of the well studied clouds.

jase wrote:Fantastic image. Great to see the tear drop nebula amongst the Alnilam and Mintaka. One of my favourites nebs.

It would have been a beautiful image had not the creator decided to mar it with his ownership details. True, cutting off a chunk isn't too onerous but that rather spoils the owners original work and I'm not sure that's strictly legal.
Don't people know they can watermark images invisibly?
This one's not a keeper, which is a pity as Mintaka's my very most favourite star.

Actually, people who submit images to APOD are encouraged to leave a small note in the corner like that.

Galaxian wrote:Don't people know they can watermark images invisibly?

I didn't, or at least I don't think I use software which can and I might not know how to find it if it was there. Regardless, owners may do as they please, for whatever reasons. The fact that this APOD was selected might indicate that it is not a big issue to the APOD judges.

Perhaps you would like to propose the details of a standard method for owners to assert their moral rights? Personally, the variation doesn't bother me at all.

You can put copyright information in the EXIF headers but not everyone knows how to look at those. Leaving a name and website URL in one of the corners is the best way to ensure that anyone viewing the image out of its intended context will be able to easily determine the origin as long as it doesn't get cropped off. EXIF headers could serve as a backup in that case but sometimes image editing programs strip them too.

Also, silly graphics tricks. Not an "invisible" watermark but a very sneaky one just for fun. See if you can find it. Note: It might be completely obvious if you are red-green colorblind but I'm not sure about that.

What a gloriously beautiful image. If I had created something like this, I would certainly sign my name to it. By the way, who does that Van Gogh guy think he is, scrawling his name on an otherwise perfectly beautiful picture of daisies?

On a more serious note, I want to shout out to one of my favorite multiple star systems, Sigma Orionis, the relatively bright star that's directly above the Horse's head in this image, forming a nearly equilateral triangle with the Horsehead and Alnitak. Sigma Ori is actually five incredibly big, hot, bright young stars all gravitationally bound to one another. Rogelio's picture shows the big hot binary AB pair as a single star, the C component of the system to the lower right, and the resolved DE pair to the upper right, and this is how it looks through a small telescope under decent observing conditions. Sigma Ori appears less bright that the three brightest stars of Orion's belt simply because it is further away. In reality it's hella bright and going to give future astronomers a very interesting supernova to observe.

Anthony Barreiro wrote:
Sigma Ori appears less bright that the three brightest stars of Orion's belt simply because it is further away. In reality it's hella bright and going to give future astronomers a very interesting supernova to observe.

I only partly agree. Yes, the brightest components of Sigma Orionis are very bright, and they will almost certianly produce a supernova in the future - or two!! But I don't agree that Sigma Orionis looks fainter than the Belt stars simply because it is farther away than Alnitak, Alnilam and Mintaka. In particular, I am not at all sure that it is necessarily farther away than Alnilam.

Stars grow brighter as they age, and that is true even for hot stars, before they turn into swollen giants or supergiants. Sigma Orionis is - as you pointed out - a young cluster, indeed so young that even its most massive member, Sigma Orionis A, is unevolved. It is still on the main sequence, fusing hydrogen in its core. And while it is an O-type star, it is about as cool as an O-type star can be, with a spectral classification of O9.5.

I have taken an intense interest in the properties of blue stars, and one thing that I think I have learnt is that you just can't guess the brightness of hot star from its spectral classification or B-V index. The best way to find out about its brightness is indeed to measure the exact distance to it. The distance to Sigma Orionis has not been well measured at all, for two reasons: The small cluster is far away, and the two brightest components are sufficiently well separated to be clearly resolved, and sufficiently close to one another to play hell with one another's parallaxes.

So we don't really know how far away Sigma Orionis is, although it is probably farther away than Alnitak and Mintaka. But in my opinion, Sigma Orionis is certainly fainter (and possibly no farther away) than Alnilam, at least. Alnilam appears to be an absolutely hugely bright and massive star. Unlike main sequence stars Sigma Orionis, Alnilam is evolved and classified as a supergiant of spectral class B0Ia. According to its (uncertain) Hipparcos parallax, Alnilam might be as bright as 64,000 times the Sun in visual light. That is an enormous brightness for a star as hot as spectral class B0, since it will radiate most of its energy as ultraviolet light. It must be admitted that Alnilam is not as hot as Sigma Orionis A. Jim Kaler estimates the temperature of Alnilam at 25,000 K, while Sigma Orionis A has a likely temperature of 32,000 K. However, Alnilam is certainly a much bigger star than Sigma Orionis A.

And we may compare Alnilam with Rigel. We are often taught that Rigel is a fantastically bright and massive blue supergiant. Yes, Rigel is impressive, but it pales when compared with Alnilam. The V magnitude of Rigel (11,500 K) may be some 49,000 times that of the Sun, compared with perhaps 64,000 times that of the Sun for Alnilam. But because Alnilam is more than twice as hot as Rigel, it emits many times more ultraviolet light than Rigel.

Alnilam, as far as I can understand, is one of the truly, truly bright hot stars that are moderately close to the Earth. Not many other nearby very hot stars stand out because of their high output of V light on top of their fantastic production of ultraviolet light. As for Sigma Orionis, it may well be quite bright (even in V light) for its spectral class, but I don't think that it will ever turn into an "Alnilam".

A final note on Sigma Orionis. David Malin claimed that it is Sigma Orionis that ionizes the red "curtain" of luminosity that provides a backdrop to the Horsehead Nebula. That's as good a claim to fame as anything - for Sigma Orionis, that is - if you ask me!

Ann

geckzilla wrote:Also, silly graphics tricks. Not an "invisible" watermark but a very sneaky one just for fun. See if you can find it. Note: It might be completely obvious if you are red-green colorblind but I'm not sure about that.

I had to do a little image manipulation, but I think I got it.
Rob

rstevenson wrote: I had to do a little image manipulation, but I think I got it.
Rob

Yup! I also studied red-green color blindness a little and came to the realization it works fine if you have that too. Now I think I can simulate what any red-green color blind person sees with the Photoshop channel mixer.

Ha-ha, wadda watermark.

Galaxian wrote:It would have been a beautiful image had not the creator decided to mar it with his ownership details. True, cutting off a chunk isn't too onerous but that rather spoils the owners original work and I'm not sure that's strictly legal. Don't people know they can watermark images invisibly?

Watermarks are used to avoid copyright infringements. In this case, the author simply wants to "sign" the image - which is what you don't like - and he chose one of the areas where it could less interfere with the view of the photograph as a whole (usually that's one of the lower corners). I know because I'm the author No need to start a debate, we all have our preferences.

geckzilla wrote:Also, silly graphics tricks. Not an "invisible" watermark but a very sneaky one just for fun. See if you can find it. Note: It might be completely obvious if you are red-green colorblind but I'm not sure about that.

straya.jpg

I'm not colourblind at all AFAIK, but my mind doesn't respond strongly to colour, either. I can make out a yellowish "Nitpicker!" in your original straya image. In my line of work, that would be called a hack and would be frowned upon.

Nitpicker wrote:I'm not colourblind at all AFAIK, but my mind doesn't respond strongly to colour, either. I can make out a yellowish "Nitpicker!" in your original straya image. In my line of work, that would be called a hack and would be frowned upon.

Well, it's impossible for me to say without going to your house and looking at your screen to see if it's your monitor displaying it better for you or if you are more sensitive to blue than I am. I can see some slight yellowing but only because I put it there. I can't read it unless I look at the blue channel.

RBAndreo wrote:Watermarks are used to avoid copyright infringements. In this case, the author simply wants to "sign" the image - which is what you don't like - and he chose one of the areas where it could less interfere with the view of the photograph as a whole (usually that's one of the lower corners). I know because I'm the author No need to start a debate, we all have our preferences.

Hello, Mr. Andreo.

Ann, thank you for the lesson about stellar evolution. I really appreciate it. My initial love for Sigma Orionis grows from how interesting it looks through a little telescope, so it's great to learn more about it. I knew that A and B are young main sequence O stars, but I didn't know that they're less bright than they will be after they evolve off the main sequence. Of course it makes sense as you explain it. The fact that Sigma Ori might backlight the Horsehead nebula would be more personally exciting to somebody with a bigger telescope and a camera.

geckzilla wrote:

Nitpicker wrote:I'm not colourblind at all AFAIK, but my mind doesn't respond strongly to colour, either. I can make out a yellowish "Nitpicker!" in your original straya image. In my line of work, that would be called a hack and would be frowned upon.

Well, it's impossible for me to say without going to your house and looking at your screen to see if it's your monitor displaying it better for you or if you are more sensitive to blue than I am. I can see some slight yellowing but only because I put it there. I can't read it unless I look at the blue channel.]

I wouldn't say it jumped out at me. I had to zoom in before I could see it well enough, and it was still very low contrast. Interesting nonetheless, thanks geckzilla.

And thanks for the lovely picture, too, Mr Andreo.

geckzilla wrote:Actually, people who submit images to APOD are encouraged to leave a small note in the corner like that.

Oh. Didn't know that. Sorry.
Why?