Starship Asterisk*

by **Ron-Astro Pharmacist** » Fri Feb 14, 2014 9:53 pm

Beyond wrote:Here's one example of a somewhat rigidly defined border.

bth_MilkyWayBar.jpg

I wish I could see a rigidly defined border. It's more like a Milky "Whey" around here, even on the best of nights.

by **Anthony Barreiro** » Fri Feb 14, 2014 8:04 pm

BDanielMayfield wrote:Can anything within 3,000 ly NOT be inside the Milky Way?

No. Everything within 3000 light years of our solar system is within the Milky Way. Let's not make this more complicated than it needs to be.

by **Beyond** » Fri Feb 14, 2014 2:36 pm

Here's one example of a somewhat rigidly defined border.

: bth_MilkyWayBar.jpg (8.1 KiB) Viewed 6821 times

by **rstevenson** » Fri Feb 14, 2014 1:48 pm

BDanielMayfield wrote:Can anything within 3,000 ly NOT be inside the Milky Way?

As so often with these sorts of binary questions, the answer must be "it depends."

The disk of the Milky Way is on average about 1000 ly thick, and we're not too far from the middle of that disk, so if we only count stars within the average thickness of the disk as part of the Milky Way, then something 3000 ly away from us could indeed be well outside of the Milky Way. But there is no official border, of course. The stars just get fewer and farther between. And we musn't forget the huge spheroid of dark matter which must surely be counted as part of the Milky Way, and which extends a good deal further than 3000 ly from us.

Alternatively, it might be fair to regard anything gravitationally bound to the Milky Way to be "in" the Milky Way, which could conceivably include everything out to about the point where something would be gravitationally disrupted by, say, the Magellanic Clouds -- or about 180,000 ly, according to one article I read.

So it depends on your definition of the Milky Way and on how rigidly you define its border.

Rob

by **BDanielMayfield** » Fri Feb 14, 2014 4:14 am

Ann wrote:But even though Simeis 147 is not as nearby as 300 light-years, but is rather at a distance of 3,000 light-years, it is not necessary to be quite as careful and conservative as wikipedia when it comes to pinning down the host galaxy of the supernova that produced this supernova remnant:

Simeis 147, also known as the Spaghetti Nebula, SNR G180.0-01.7 or Sharpless 2-240, is a supernova remnant (SNR) that may have occurred in the Milky Way
Yes, well, I'd say that that is probable!

Ann

That is very funny Ann. And the Wikipedia uncertainty as to Simeis 147’s membership in this galaxy is also highlighted in the tabular description, where right on the third line it lists:

Wikipedia wrote:Host galaxy Unknown

But several lines down the chart it gets the distance right:

Distance 3,000 light-years (0.92 kpc)

Can anything within 3,000 ly NOT be inside the Milky Way? Only if something can be inside the MW while also not being a member of the MW...

Maybe it forgot to pay its membership dues?

Bruce

by **Ann** » Fri Feb 14, 2014 1:41 am

Again, this is a stunning image. I don't think I've ever seen IC 405 and IC 410 in the same image as Simeis 147, and it the effect of seeing them together is fantastic.

Obviously the statement that Simeis 147 is 300 light-years away is wrong. That would make it very close in view of the nature of it, and I don't think there are any known supernova remnants within that distance of the solar system. There are several stars in the picture that are farther away than that, for example AE Aurigae which is lighting up the Flaming Star Nebula (on the right in the picture in the link).

But even though Simeis 147 is not as nearby as 300 light-years, but is rather at a distance of 3,000 light-years, it is not necessary to be quite as careful and conservative as wikipedia when it comes to pinning down the host galaxy of the supernova that produced this supernova remnant:

Simeis 147, also known as the Spaghetti Nebula, SNR G180.0-01.7 or Sharpless 2-240, is a supernova remnant (SNR) that may have occurred in the Milky Way

Yes, well, I'd say that that is probable!

Interestingly enough, the most famous supernova remnant of them all, the Crab Nebula, is located not so far away from Simeis 147 in the sky. According to wikipedia, the Crab Nebula is about twice as far away as Simeis 147, about 6,500 light-years away. The Crab Nebula is only about a thousand years old compared with about 40,000 years for Simeis 147. Simeis 147 is also intrinsically more than ten times larger than the Crab Nebula, about 150 light-years versus 11 light-years for the Crab. So it is no wonder that Simeis 147 looks large in our skies.

Anthony Barreiro asked if there is a reflection nebula around Beta Tauri. No, there isn't, but to the right of the star there is a brownish patch of mostly unlit nebulosity. I have to wonder of this patch is part of the integrated flux nebula, the high galactic nebula clouds of our galaxy.

Again, what a stunning image this is!

Ann

by **Anthony Barreiro** » Thu Feb 13, 2014 10:07 pm

Chris Peterson wrote:
Anthony Barreiro wrote:One question: is there a reflection nebula around Beta Tauri?
No. It's just that to bring up the intensity of dimmer parts of the field resulted in the massively overexposed star showing its wings- some from diffraction, but most probably from scatter and internal reflections. In a way that's good, since with bright stars in deep images you can usually only get a reasonable indication of their color from their halo artifacts, as the cores are saturated on all channels, meaning they look white.

Thanks, I thought it would be something like that. I've never noticed any hint of nebulosity around El Nath visually through a telescope (except when my sky is hazy!), nor read about a reflection nebula there.

by **Chris Peterson** » Thu Feb 13, 2014 10:00 pm

Anthony Barreiro wrote:One question: is there a reflection nebula around Beta Tauri?

No. It's just that to bring up the intensity of dimmer parts of the field resulted in the massively overexposed star showing its wings- some from diffraction, but most probably from scatter and internal reflections. In a way that's good, since with bright stars in deep images you can usually only get a reasonable indication of their color from their halo artifacts, as the cores are saturated on all channels, meaning they look white.

by **Anthony Barreiro** » Thu Feb 13, 2014 9:46 pm

This is an amazingly beautiful image. I also appreciate the mouse-over labels for the different objects. Before I stumbled over the rollover feature, I was twisting my head around trying to remember where M36 and M38 were in relation to Beta Tauri. Then, voila, everything fell in place. Now I wish the field had been a little wider to include M37! Regarding the depth of field, it seems pretty deep to me. I think I can even make out a young Charles Foster Kane playing in the stardust of Simeis 147.

One question: is there a reflection nebula around Beta Tauri?

by **rgendler** » Thu Feb 13, 2014 9:23 pm

Chris Peterson wrote:
Ron-Astro Pharmacist wrote:Speaking of depth of field - have attempts been made to create a view that appears with depth? It would be fascinating to view this photo with depth as with 3D graphics. I would think that with know distances to these objects one might be artificially created. Don’t they create 3D views using two different camera angles which may be simulated by some very creative computer genius? (Not me)
Yes, people have created 3D simulations from astronomical images. Personally, I don't care for them, because while they are really little more than artistic interpretations, they look so real that people may take them as accurate representations of physical reality.

Agree completely. Many of the 3-D astronomical presentations I've seen are done by software arbitrarily placing objects in the foreground and background without any consideration as to their real position in the sky. They look cool but they aren't representations of reality.

by **Chris Peterson** » Thu Feb 13, 2014 4:57 pm

Ron-Astro Pharmacist wrote:Speaking of depth of field - have attempts been made to create a view that appears with depth? It would be fascinating to view this photo with depth as with 3D graphics. I would think that with know distances to these objects one might be artificially created. Don’t they create 3D views using two different camera angles which may be simulated by some very creative computer genius? (Not me)

Yes, people have created 3D simulations from astronomical images. Personally, I don't care for them, because while they are really little more than artistic interpretations, they look so real that people may take them as accurate representations of physical reality.

by **Ron-Astro Pharmacist** » Thu Feb 13, 2014 4:47 pm

Chris Peterson wrote:
geckzilla wrote:Yeah, I get it. You're just...so..funny...
I don't. The links are just confusing. All deep sky astronomical objects are at the same distance optically, infinity, so any discussion of depth of field, depth of focus, etc is meaningless.

Speaking of depth of field - have attempts been made to create a view that appears with depth? It would be fascinating to view this photo with depth as with 3D graphics. I would think that with know distances to these objects one might be artificially created. Don’t they create 3D views using two different camera angles which may be simulated by some very creative computer genius? (Not me)

by **rstevenson** » Thu Feb 13, 2014 3:13 pm

Chris Peterson wrote:
rstevenson wrote:Thanks geckzilla. I had a hunch they meant something like that, but was surprised when I couldn't find a rigorous definition for either since they're used so widely.
Just to expand on Geck's comments, think of the range of exposures for extended astronomical objects as a distribution. In fact, if it's a widely imaged object, the distribution will probably be somewhat Gaussian. Anyway, the "deep" versions will be those with exposure times on the upper wing of the distribution. Thus, no absolute definition, just a relative one.

I'm guessing the upper wing of the Gaussian distribution of the feed consumed by your horses would indicate which horse ate the most? So by deduction, I can now conclude that the upper wing of the Gaussian distribution of astronomical exposures would indicate the longer exposures? Thanks ... I think.

Rob

by **Chris Peterson** » Thu Feb 13, 2014 3:07 pm

geckzilla wrote:Yeah, I get it. You're just...so..funny...

I don't. The links are just confusing. All deep sky astronomical objects are at the same distance optically, infinity, so any discussion of depth of field, depth of focus, etc is meaningless.

by **Chris Peterson** » Thu Feb 13, 2014 3:04 pm

rstevenson wrote:Thanks geckzilla. I had a hunch they meant something like that, but was surprised when I couldn't find a rigorous definition for either since they're used so widely.

Just to expand on Geck's comments, think of the range of exposures for extended astronomical objects as a distribution. In fact, if it's a widely imaged object, the distribution will probably be somewhat Gaussian. Anyway, the "deep" versions will be those with exposure times on the upper wing of the distribution. Thus, no absolute definition, just a relative one.

by **rstevenson** » Thu Feb 13, 2014 2:47 pm

Thanks geckzilla. I had a hunch they meant something like that, but was surprised when I couldn't find a rigorous definition for either since they're used so widely.

Rob

by **geckzilla** » Thu Feb 13, 2014 2:27 pm

Yeah, I get it. You're just...so..funny...

by **neufer** » Thu Feb 13, 2014 2:23 pm

geckzilla wrote:
Neither of those articles have anything to do with astronomical imagery, Art.

It's essentially a photograph which is
taking in "the crowded field" of "Downtown Auriga"
containing all sort of objects at many different distances.

by **geckzilla** » Thu Feb 13, 2014 1:58 pm

Neither of those articles have anything to do with astronomical imagery, Art.

by **neufer** » Thu Feb 13, 2014 1:50 pm

rstevenson wrote:
Once again we have an image which is described as "deep". I often see the terms "deep field" and "wide field" applied to astronomical images. (Searching for "deep field" on the APOD site brings up 90 references.) But even after years of looking at such images, I'm not sure I understand what those terms really mean. I checked three on-line dictionaries of astronomy, including the Oxford one, and none of them defined either term, which seems more than a little odd. Could some helpful astronomer enlighten me?

http://en.wikipedia.org/wiki/Depth_of_field wrote:
<<In optics, particularly as it relates to film and photography, depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions. In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, a small DOF may be more effective, emphasizing the subject while de-emphasizing the foreground and background. In cinematography, a large DOF is often called deep focus, and a small DOF is often called shallow focus.

Many lenses for small- and medium-format cameras include scales that indicate the DOF for a given focus distance and f-number; the 35 mm lens in the image above is typical. That lens includes distance scales in feet and meters; when a marked distance is set opposite the large white index mark, the focus is set to that distance. The DOF scale below the distance scales includes markings on either side of the index that correspond to f-numbers. When the lens is set to a given f-number, the DOF extends between the distances that align with the f-number markings.

Deep focus is a photographic and cinematographic technique using a large depth of field. Depth of field is the front-to-back range of focus in an image — that is, how much of it appears sharp and clear. Consequently, in deep focus the foreground, middle-ground and background are all in focus. This can be achieved through use of the hyperfocal distance of the camera lens.>>

http://en.wikipedia.org/wiki/Deep_focus wrote:
[b][color=#0000FF][size=125]A deep focus shot: everything, including the hat in the foreground and the boy (young Kane) in the distance, is in sharp focus.[/size][/color][/b]
<<Deep focus is achieved with large amounts of light and small aperture. It is also possible to achieve the illusion of deep focus with optical tricks (split focus diopter) or composite two pictures together. It is the aperture of a camera lens that determines the depth of field. Wide angle lenses also make a larger portion of the image appear sharp. The aperture of a camera determines how much light enters through the lens, so achieving deep focus requires a bright mise en scène. Aperture is measured in f-stops (T-stops on lenses for motion picture cameras are f-stops adjusted for the lenses' light transmission, and cannot be used directly for depth of focus determination) with a higher value indicating a smaller aperture.

Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light gathering area of the previous one. The actual size of the aperture will depend on the focal length of the lens.

The opposite of deep focus is shallow focus, in which only one plane of the image is in focus.

In the cinema Orson Welles and his cinematographer Gregg Toland were most responsible for popularizing deep focus.

When deep focus is used, filmmakers often combine it with deep space (also called deep staging). Deep space is a part of mise-en-scene, placing significant actors and props in different planes of the picture. Directors and cinematographers often use deep space without using deep focus, being either an artistic choice or because they don't have resources to create a deep focus look, or both.

Directors may use deep focus in only some scenes or even just some shots. Other auteurs choose to use it consistently throughout the movie, either as a stylistic choice or because they believe it represents reality better. Directors like Kenji Mizoguchi, Orson Welles, Jean Renoir and Stanley Kubrick all used deep focus as part of their signature style.>>

by **geckzilla** » Thu Feb 13, 2014 1:41 pm

rstevenson wrote:Once again we have an image which is described as "deep". I often see the terms "deep field" and "wide field" applied to astronomical images. (Searching for "deep field" on the APOD site brings up 90 references.) But even after years of looking at such images, I'm not sure I understand what those terms really mean. I checked three on-line dictionaries of astronomy, including the Oxford one, and none of them defined either term, which seems more than a little odd. Could some helpful astronomer enlighten me?

Rob

Just "deep" - how long the exposure is. The more photons are collected, the deeper the data. I imagine it like snow piling up.
"Deep Field" - Looking deep into the Universe; probably is used interchangeably with just "deep" by some people but when I read this I think Hubble's deep fields which are the farthest galaxies. Deep fields do also need to be deep exposures due to the nature of trying to capture those precious few ancient photons.
"Wide Field" - Is there any rigorous definition of what is "wide" and what is "narrow" ? I don't know, but wide field could be measured in degrees while narrow fields could be measured in a few arcminutes or arcseconds. "Ultra Wide Field" could be tens of degrees or more.

by **Ironwood** » Thu Feb 13, 2014 12:23 pm

If the image spans about 12 degrees then I estimate that Simeis 147 has a diameter of about four degrees. I don't understand how it can be 300 LY away and 150 LY in diameter and yet only cover four degrees of sky. A six inch object twelve inches from my eye covers far more than four degrees. Something is a bit off somewhere. Oh, I see. I clicked the link and saw that a previous APOD lists Simeis 147's distance at 3000 light years, not 300.

by **rstevenson** » Thu Feb 13, 2014 12:14 pm

Once again we have an image which is described as "deep". I often see the terms "deep field" and "wide field" applied to astronomical images. (Searching for "deep field" on the APOD site brings up 90 references.) But even after years of looking at such images, I'm not sure I understand what those terms really mean. I checked three on-line dictionaries of astronomy, including the Oxford one, and none of them defined either term, which seems more than a little odd. Could some helpful astronomer enlighten me?

Rob

by **starsurfer** » Thu Feb 13, 2014 8:51 am

This is yet another stunning mosaic by Rogelio!! Regarding the title of this APOD, it amuses me that half the image actually represents Taurus. There are also some large and very faint supernova remnants in Auriga itself, a few of them discovered slightly recently. The Messier clusters in Auriga represent some of the best in that catalogue!!

by **Ann** » Thu Feb 13, 2014 6:09 am

Wow, this is a simply fantastic image!!!!

I may comment more later, when I can use my software, but for now... wow.

Ann

Starship Asterisk*

APOD: Downtown Auriga (2014 Feb 13)

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