APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

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APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by APOD Robot » Mon Jul 25, 2016 4:08 am

Image Deep Magellanic Clouds Image Indicates Collisions

Explanation: Did the two most famous satellite galaxies of our Milky Way Galaxy once collide? No one knows for sure, but a detailed inspection of deep images like that featured here give an indication that they have. Pictured, the Large Magellanic Cloud (LMC) is on the top left and the Small Magellanic Cloud (SMC) is on the bottom right. The surrounding field is monochrome color-inverted to highlight faint filaments, shown in gray. Perhaps surprisingly, the featured research-grade image was compiled with small telescopes to cover the large angular field -- nearly 40 degrees across. Much of the faint nebulosity is Galactic Cirrus clouds of thin dust in our own Galaxy, but a faint stream of stars does appear to be extending from the SMC toward the LMC. Also, stars surrounding the LMC appear asymmetrically distributed, indicating in simulations that they could well have been pulled off gravitationally in one or more collisions. Both the LMC and the SMC are visible to the unaided eye in southern skies. Future telescopic observations and computer simulations are sure to continue in a continuing effort to better understand the history of our Milky Way and its surroundings.

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by rj rl » Mon Jul 25, 2016 5:36 am

A little unrelated, but does the inversion itself highlight some features somehow? Are we better at seeing black against white than white against black?

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Ann » Mon Jul 25, 2016 6:01 am

Very interesting.

According to Sidney van den Bergh's The Galaxies of the Local Group (2000), the LMC was a a quiescent galaxy with little star formation for billions of years. Then three billion years ago it started forming stars at an elevated rate, and about one billion years ago or less it was practically starbursting. It is still forming stars at a high rate.

There has been speculation that the Large and the Small Magellanic Clouds began interacting at some time in the past, and that this may have triggered increased star formation. My gut feeling, for what it is worth, suggests to me that the LMC and the SMC may have passed quite close to one another one billion years ago (or less), and that this may have coincided with and perhaps caused the most intense star formation in the LMC.

Even if we bear in mind that the Large and the Small Magellanic Clouds differ considerably not only in size but in mass, it is clear that the LMC is both yellower and more ultraviolet than the SMC. That is to say that the LMC has a well-defined yellow population (in its bar), wheras the SMC lacks an obvious and concentrated old population. But the LMC also has many more and larger emission nebulas and clusters of hot stars than the SMC.

This suggests to me that the LMC has more of a history as a galaxy than the SMC, but it also has larger reservoirs of gas. It could well be that it has stolen some of its present starforming material from the SMC. In fact, it seems to have stolen some of its stars from the SMC:
http://www.space.com/18277-milky-way-la ... stars.html wrote:

New simulations suggest that the Large Magellanic Cloud (LMC) snatched a stream of stars from its neighbor, the Small Magellanic Cloud (SMC), when the two galaxies collided 300 million years ago.
So they collided 300 million years ago? That is quite recently. And "collided" is a strong word. It seems to me that a true head-on collision with the SMC should have distorted the LMC so much that its bar should look less straight than it does today. Of course, we don't know what sort of collision it really was (assuming it happened at all), and I guess it is possible that the bar of the LMC could have survived unscathed, while its spiral arms (assuming it had any) could have been messed up. And the SMC in its present form could be a large, well-mixed and somewhat gas-deficient assembly of debris from from that collision.

But all things considered, I think that a real head-on collision as recently as 300 million years ago should have produced more present-day chaos and galactic upheaval than we see today.

In any case, there is definitely evidence of past interactions between the LMC and the SMC, however you look at it. In Sidney van den Bergh's book there is an illustration showing star clusters located between the LMC and the SMC, forming a sort of bridge between the two galaxies.

I have to wonder what will happen when (or if) our own Milky Way starts snaring the LMC in the same way that the LMC snared the SMC. Will the LMC sparkle even more with star formation when (or if) it is plunging helplessly toward the Milky Way, or will it turn on the lights in our own galaxy?

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Ann » Mon Jul 25, 2016 6:04 am

rj rl wrote:A little unrelated, but does the inversion itself highlight some features somehow? Are we better at seeing black against white than white against black?
I think we are better at seeing black against white. After all, humanity have eyes that work best in daylight conditions, when the background is "white".

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Chris Peterson » Mon Jul 25, 2016 6:14 am

rj rl wrote:A little unrelated, but does the inversion itself highlight some features somehow? Are we better at seeing black against white than white against black?
Not black versus white, but grays. We're better at seeing a feature just slightly darker than a light background than we are something just slightly lighter than a dark background. Our eyes work best with lots of signal. So looking at negatives of astronomical imagery is a common trick to enhance subtle structure.
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Knight of Clear Skies » Mon Jul 25, 2016 9:19 am

Great image and an interesting bit of astro-archaeology. One minor error I noticed in the description is that it was taken with a camera lens, not small telescopes. The diffraction spikes on the bright stars caught my eye, a clear indication that a lens with an internal iris has been used. Checking the linked paper they used a 50mm f1.4 lens on a CCD camera for the background widefield, but it doesn't say what they stopped it down to. I'm not sure what they used for the coloured galaxy inserts, does anyone know please?

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by starsurfer » Mon Jul 25, 2016 11:16 am

David Martinez-Delgado is a legend, what a great guy! Love the work he's doing and his idea for an amateur network for a galaxy survey is very inspired. You can check out more tidal stream related stuff here.

I'm deeply fond of the LMC and its many multitudinous nebulae, this image by Johannes Schedler shows them nicely.

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by starsurfer » Mon Jul 25, 2016 11:19 am

Also forgot to mention that this image was taken with a wide angle lens and not a small telescope. If it was a small telescope, it would have been a mosaic of many frames. I think the description should mention the field of view in degrees.

To me, the faint features are more apparent in a positive image? Maybe my brain is just weird? :cry: :lol2:

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ESO: Deep View of the Large and Small Magellanic Clouds

Post by bystander » Mon Jul 25, 2016 2:00 pm

Deep View of the Large and Small Magellanic Clouds
ESO Picture of the Week | 2016 July 25

Each of the thousands of spots in this new image represents a distant star, and the glittering blue holes reveal glimpses of our neighbouring galaxies, the Large and Small Magellanic Clouds. Although this image looks as if it was made on a large scale telescope it was in fact captured from ESO’s La Silla Observatory using a portable setup consisting of a SBIG STL-11000M CCD camera and a Canon prime lens. It was presented in a scientific paper alongside state-of-the art simulations, in an exciting example of how a small camera, a fast lens, a long exposure time and one of the world’s best astronomical sites can reveal huge faint features better than even a big telescope.

This deep image was captured using the LRGB method, and provides an insight into the actual process of creating spectacular astrophotography. Many challenges face those attempting to photograph the night sky, including interference from light sources other than the object being photographed, and capturing objects in sufficient depth.

Trying to maximise the signal received from the target, whilst minimising input from other sources — known as noise — is a crucial aspect of astrophotography. The optimisation of the signal to noise ratio is far more easily achieved in black-and-white than in colour. Therefore a clever trick often employed to capture a high-quality image is the use of a luminance exposure, which produces richly detailed monochrome images like the one seen here. Colour details from images taken through colour filters can then be overlaid or inset, as the Magellanic Clouds have been here. ...

A History of Collisions Between the Magellanic Clouds
Nova | American Astronomical Society | 2016 July 11

Recent deep observations of the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way, have revealed a faint arc of stars extending from its northern outskirts. Was this stream created by the gravitational pull of the Milky Way? Or could it have a more violent source? ...

Low Surface Brightness Imaging of the Magellanic System: Imprints of
Tidal Interactions between the Clouds in the Stellar Periphery
- Gurtina Besla et al
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Chris Peterson » Mon Jul 25, 2016 2:10 pm

Knight of Clear Skies wrote:One minor error I noticed in the description is that it was taken with a camera lens, not small telescopes.
A camera lens is a small telescope.
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Fred the Cat » Mon Jul 25, 2016 2:12 pm

rj rl wrote:A little unrelated, but does the inversion itself highlight some features somehow? Are we better at seeing black against white than white against black?
No but it helps us see the six-legged spiders more easily! :wink:
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Knight of Clear Skies » Mon Jul 25, 2016 3:49 pm

Chris Peterson wrote:
Knight of Clear Skies wrote:One minor error I noticed in the description is that it was taken with a camera lens, not small telescopes.
A camera lens is a small telescope.
Not really, no, the 50mm lens in question doesn't provide much in the way of magnification. ;)

(Optically speaking, the design of a camera lens is very different from a refractor, which are simple designs optimised to produce a flat field at infinity. Lenses need to produce a colour corrected image at a range of focal distances, here's a diagram of the lens in question:

Image

Lenses do a good job for astrophotography but typically need to be stopped down a little to produce a flat field, as this often isn't a major design consideration. I find myself wondering if a specialist design would do a better job for widefield imaging, but given the economies of scale involved in current camera lens production it's probably a moot point for astrophotographers.)

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Knight of Clear Skies » Mon Jul 25, 2016 3:51 pm

Sorry, looks like I wasn't logged in when posting the above. ^

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by MarkBour » Mon Jul 25, 2016 4:16 pm

Fred the Cat wrote:
rj rl wrote:A little unrelated, but does the inversion itself highlight some features somehow? Are we better at seeing black against white than white against black?
No but it helps us see the six-legged spiders more easily! :wink:
All of the "spiders" I see in this image appear to have the proper number of 8 legs ...

Why didn't they just leave the whole image in the gray-scale? Why did they insert distinct "pretty" images of the two galaxies?
The main image would have been nearly black there, I assume, but I'd like to see it. Do we have a version?

Just looking at this image, really, I don't get the point of its evidence for a collision or strong interaction. I see a few shape features that could be evidence of their gravitational interaction ... or not.
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Chris Peterson » Mon Jul 25, 2016 4:21 pm

Guest wrote:
Chris Peterson wrote:
Knight of Clear Skies wrote:One minor error I noticed in the description is that it was taken with a camera lens, not small telescopes.
A camera lens is a small telescope.
Not really, no, the 50mm lens in question doesn't provide much in the way of magnification. ;)
Yes, really. A telescope objective doesn't provide any magnification, either.
(Optically speaking, the design of a camera lens is very different from a refractor, which are simple designs optimised to produce a flat field at infinity.
Optically, neither a camera lens or a "telescope" used for imaging is a telescope. But both are optically equivalent- objectives. It is only in terms of engineering that a typical camera lens and a typical astronomical refractor differ- not surprising given different design goals.

Nevertheless, there is no real distinction that needs to be drawn in an astronomical image made with an objective designed to attach to a camera and an objective designed to have an eyepiece. All that is really relevant is the aperture and the focal length- the key parameters for any imaging optical system. The rest is details. Nice to know, but not essential.
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Fred the Cat » Mon Jul 25, 2016 5:26 pm

MarkBour wrote: All of the "spiders" I see in this image appear to have the proper number of 8 legs ...
I'd say that two of them are fangs but it's really that I didn't count. :oops:

Ps – And thanks for pointing it out. I might have woken up tonight in a cold sweat thinking, "Did those diffraction spikes have six or eight points?" and had a hard time getting back to sleep. :ssmile:
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by RJN » Mon Jul 25, 2016 6:10 pm

In the interest of clarity and correctness, I have now changed the words "star streams" to "filaments" in the APOD text. Initially, in my first writing, I had thought that all of the faint filaments were star streams. The lead author of the paper that contains this image corrected me -- many of the filaments are actually Galactic Cirrus dust clouds. I thanked her, made a change in one place of the APOD text, but did not realize that another part of the text then became lacking. My hope is that this is now corrected. I apologize for the oversight. - RJN

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by geckzilla » Mon Jul 25, 2016 8:56 pm

I think Chris once called Hubble Space Telescope a camera. I can see his point, but I'm not sure a lot of people agree with his use of language. ;)
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Chris Peterson » Mon Jul 25, 2016 9:02 pm

geckzilla wrote:I think Chris once called Hubble Space Telescope a camera. I can see his point, but I'm not sure a lot of people agree with his use of language. ;)
Depending on how technical or precise you want to be, the HST can be either a telescope or a camera. What would be incorrect would be to say it isn't a camera. Likewise for today's APOD. It's reasonable to call the optics either a telescope or a camera lens, but it's simply wrong to say it isn't a telescope because it's also a camera lens.
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Tszabeau » Mon Jul 25, 2016 9:42 pm

Where is the center of the Milky Way in relation to the point-of-view in this image?

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Chris Peterson » Mon Jul 25, 2016 10:00 pm

Tszabeau wrote:Where is the center of the Milky Way in relation to the point-of-view in this image?
A long way away. The image is oriented approximately north up, east left. The galactic center is about 75° away to the southwest (far, far out of the frame), which actually means you cross near the south celestial pole and head back north again.
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Tszabeau » Mon Jul 25, 2016 10:19 pm

Chris Peterson wrote:
Tszabeau wrote:Where is the center of the Milky Way in relation to the point-of-view in this image?
A long way away. The image is oriented approximately north up, east left. The galactic center is about 75° away to the southwest (far, far out of the frame), which actually means you cross near the south celestial pole and head back north again.
So... if I was looking up at the SMC and LMC, from the same vantage-point, would the center of the Milky Way be behind me and to my left "under" the horizon?

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Chris Peterson » Mon Jul 25, 2016 10:49 pm

Tszabeau wrote:
Chris Peterson wrote:
Tszabeau wrote:Where is the center of the Milky Way in relation to the point-of-view in this image?
A long way away. The image is oriented approximately north up, east left. The galactic center is about 75° away to the southwest (far, far out of the frame), which actually means you cross near the south celestial pole and head back north again.
So... if I was looking up at the SMC and LMC, from the same vantage-point, would the center of the Milky Way be behind me and to my left "under" the horizon?
It need not be below the horizon. It depends on the location of the pole with respect to your location, too. And your own orientation. At the right place and time you could easily see them both in the same view, 75° apart (even parallel to the horizon).
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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by BMAONE23 » Tue Jul 26, 2016 3:22 am

I would say the Hubble is a fantastic camera with the world's best telescopic lens

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Re: APOD: Deep Magellanic Clouds Image... (2016 Jul 25)

Post by Boomer12k » Tue Jul 26, 2016 4:12 am

Show me the path of the LMC, SMC.....

Also... distortion from other satellites, as well as the Milky Way itself, I should think... was there not an APOD like last year or so, that showed star streams from other satellites and the MW???

I am sure they are all playing off of each other... also, the Andromeda Galaxy at only 2.2 mly.... and closing...

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