APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Comments and questions about the APOD on the main view screen.
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APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by APOD Robot » Tue Sep 06, 2016 4:05 am

Image The Whirlpool Galaxy and Beyond

Explanation: Follow the handle of the Big Dipper away from the dipper's bowl, until you get to the handle's last bright star. Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messier's famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (left), NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici. Though M51 looks faint and fuzzy to the human eye, the above long-exposure, deep-field image taken earlier this year shows much of the faint complexity that actually surrounds the smaller galaxy. Thousands of the faint dots in background of the featured image are actually galaxies far across the universe.

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Ann
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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Ann » Tue Sep 06, 2016 4:32 am

I'm always glad to see a fine galaxy picture as an APOD!
APOD Robot wrote:
Follow the handle of the Big Dipper away from the dipper's bowl, until you get to the handle's last bright star.
That star is blue Alkaid, the only B-type star in the Big Dipper. Though I must say that some of the five (or six, with Mizar) A-type stars in the Big Dipper are bright and blue for A-type stars (though not Mizar).

Nice image! It's fun to see the yellow tidal tails of NGC 5195. This yellow galaxy has no gas available with which to form new stars, but it can still send long streamers of yellow stars out along paths decided by the motions and the gravitational forces of the interaction of these galaxies.

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Tucker512 » Tue Sep 06, 2016 7:42 am

The "above long-exposure" link in the description is to a different picture with a different scope by a different person.

heehaw

Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by heehaw » Tue Sep 06, 2016 9:25 am

Great image! I've seen so many photos of M51over the years that I think I know it well. Of course I don't, and this photo nicely jolts me. And of course we are still not seeing, at all, MOST of what is actually there, which is the dark matter!

NCTom

Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by NCTom » Tue Sep 06, 2016 10:45 am

There is an awesome mass of stars below 5194 in this photo. Would they be stolen from 5195 as it passed in some former encounter? Did 5195 destroy the end of an arm of 5194 and left the remnants scattered across space? A combination of both?

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Fred the Cat » Tue Sep 06, 2016 3:35 pm

Our fascination with "The Whirlpool" begins at an early age. Especially the spin cycle. Though the second video may not be totally correct it does put a different spin on the motion of our solar system and captures your imagination about our whirlpool and shapes in nature. 8-)
Last edited by Fred the Cat on Tue Sep 06, 2016 4:03 pm, edited 1 time in total.
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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by eric12 » Tue Sep 06, 2016 3:40 pm

The APOD articles are often confusingly written. I cannot tell if the fuzzy blob is part of the whirpool.

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Ann » Tue Sep 06, 2016 4:00 pm

NCTom wrote:There is an awesome mass of stars below 5194 in this photo. Would they be stolen from 5195 as it passed in some former encounter?
The tidal forces of the interaction between M51 and NGC 5195 have certainly "torn loose" many stars from both galaxies and dumped them in space. There are, indeed, quite large numbers of "homeless" ejected stars "between galaxies", in intergalactic space, especially in dense galaxy clusters.
Did 5195 destroy the end of an arm of 5194 and left the remnants scattered across space?


If you ask me, the main effect of the interaction between M51 (NGC 5194) and NGC 5195 has been a strengthening of the spiral arms of M51. In my opinion, the arms of M51 have almost certainly grown longer and brighter because of the galaxy's interaction with NGC 5195.
Spiral galaxy M100. Probable photographer:
David Malin.
M51. NASA and The Hubble Heritage Team (STScI/AURA).
Consider spiral galaxy M100 at left. It is quite obvious that the "bright", starforming arms of M100 extend only about half a turn around the galaxy's center. But where the bright star formation ends, faint intermediate-aged stellar populations take over and keep on winding around the galaxy's core, extending the arms to at least double the length.

Now consider M51 at right. M51 and M100 are both grand design galaxies, with two major arms elegantly winding around the galaxy's core and bulge. But a very important difference between M51 and M100 is that the arms of M51 remain bright and starforming as they wind a full turn around the galaxy's core.










Take a look at the picture of M51 at left. It is obvious that there is a "kink" in each arm of M51. One kink is at about 2 o'clock and the other at 10 o'clock. I believe that these kinks mark where the arms were tidally pulled and star formation was stimulated because of M51's interaction with NGC 5195. In other words: the main effect on M51 of the interaction with NGC 5195 has been to stimulate star formation and enhance the bright spiral structure.
NGC 6240. Photo: Adam Block.
Interactions between galaxies don't always lead to an enhanced spiral structure. Consider NGC 6240. This distorted galaxy is a merger product, and it sure doesn't look so "spirally". But the two galaxies that have created the present mess may once have looked much like M51 and NGC 5195.

And, who knows, sometime in the future M51 and NGC 5195 may look much like NGC 6240.

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by ta152h0 » Tue Sep 06, 2016 4:46 pm

is it possible to determine if the stars shown in this image are on this side of the galaxy by manipulating the f stop and the focus ?
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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by BMAONE23 » Tue Sep 06, 2016 4:57 pm

In this DEEP exposure, it is abundantly clear that NGC 5195 is obviously the M51s Good Right Hand. But who is the accusatory finger pointing at??

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Chris Peterson » Tue Sep 06, 2016 5:00 pm

ta152h0 wrote:is it possible to determine if the stars shown in this image are on this side of the galaxy by manipulating the f stop and the focus ?
No. Optically, everything in the field is at infinite distance.
Chris

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Zuben L. Genubi

Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Zuben L. Genubi » Tue Sep 06, 2016 5:15 pm

The brilliant color comes from the "long exposure"? This is a true-color photo? WOW! Beautiful!

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Chris Peterson » Tue Sep 06, 2016 5:24 pm

Zuben L. Genubi wrote:The brilliant color comes from the "long exposure"? This is a true-color photo? WOW! Beautiful!
No, the color has almost nothing to do with the exposure time. It is "true-color" only in the sense that the data planes were acquired using RGB filters. The saturation of the colors has been greatly increased by post-processing to emphasize certain features of the objects. This could also be processed to yield a more natural color appearance, just as much shorter exposures could be given this vibrancy by processing choices.

What the long exposure time (necessitated in part by the very small 115mm telescope aperture) offers is improved signal-to-noise, allowing faint detail to be separated from the background.
Chris

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tao

Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by tao » Tue Sep 06, 2016 6:42 pm

Hi everyone,

What are those 3 little white dots up and right of the Whirlpool Galaxy? :?:
They are also visible (as a trio of yellow-ish, blue an red-ish dots) on the other "long-exposure" link image.

Is their position apparent or are they really in a neat little arc?
Just curious... :ssmile:

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Chris Peterson » Tue Sep 06, 2016 6:50 pm

tao wrote:Hi everyone,

What are those 3 little white dots up and right of the Whirlpool Galaxy? :?:
They are also visible (as a trio of yellow-ish, blue an red-ish dots) on the other "long-exposure" link image.
Stars.
Is their position apparent or are they really in a neat little arc?
Three points minimally define an arc, so that's not surprising. Their apparent even spacing is almost certainly a function of our viewing position. It is unlikely that the three stars are the same distance from us, so the plane they define is probably not perpendicular to our line of sight.
Chris

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Astro Joe » Tue Sep 06, 2016 10:21 pm

The narrative says "Thousands of the faint dots in background of the featured image are actually galaxies far across the universe." I'm curious if any of these have been named, numbered, or otherwise noted. Are they too distant for Hubble to see?

Visual_Astronomer

Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Visual_Astronomer » Tue Sep 06, 2016 10:23 pm

I'll chime in once again and point out that even through a large telescope, this object is far too faint to excite the cones of the eye, so it is "really" colorless.

Nevertheless, M51 is one of my favorite galaxies visually. Even a casual observer can see the spiral structure through a small scope at a dark site.

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Colors

Post by geoffrey.landis » Tue Sep 06, 2016 11:05 pm

It would be nice if APOD images had at least a little discussion of what the colors mean.

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Re: Colors

Post by geckzilla » Tue Sep 06, 2016 11:20 pm

geoffrey.landis wrote:It would be nice if APOD images had at least a little discussion of what the colors mean.
Stick around... that's one of the most common discussions had here. So much so that your comment almost comes off as satire.
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NCTom

Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by NCTom » Wed Sep 07, 2016 1:47 am

Thanks, Ann. I appreciate the time you put into your response and all the info.

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by DavidLeodis » Wed Sep 07, 2016 8:46 am

The explanation states the image was "taken earlier this year" (thus 2016) but in the information with the image brought up through the "the above long-exposure, deep-field image" it states "April, 2009". I'm :?.

Edit. I've now found that the link is to an image in a Jon Christensen astrophotography website and thus nothing to do with Álvaro Ibáñez Pérez. It therefore seems to be an unnecessarily confusing link to have used.
Last edited by DavidLeodis on Wed Sep 07, 2016 7:23 pm, edited 2 times in total.

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Re: Colors

Post by Ann » Wed Sep 07, 2016 2:44 pm

geoffrey.landis wrote:It would be nice if APOD images had at least a little discussion of what the colors mean.
In RGB images (taken through red, green and blue filters), cool stars look yellow. Hot stars look blue.

To human eyes, most stars are very faintly colored. The yellow-colored stars are easiest to spot. You should easily be able to pick out Betelgeuse in Orion, Aldebaran in the Hydades, Arcturus in Bootes, Dubhe in the Big Dipper and Antares in Scorpius in the night sky because of their color.

One reason why the yellow stars stand out is because the bright yellow ones, which belong to spectral classes K or M, are relatively rare. Most bright stars in the sky are hotter than the Sun and belong to spectral classes A or B. They typically look very white in the sky. Some stars, like Vega, often look quite blue when observed through a telescope.
The stars whose colors are easiest to spot are the strongly colored binaries. The most famous such binary is probably Albireo in Cygnus. The primary star is a K-type giant star, cooler than the Sun, and the secondary is a B-type star, hotter than the Sun.

To us humans, the Sun is "white". A better way of putting it is to say that daylight is "white", or neutral. To our eyes, therefore, stars cooler than the Sun look yellowish, whereas stars hotter than the Sun look blue-white. But when the night sky is full of blue-white stars, we typically think they all look white.

Although blue-white stars dominate the night sky, such stars are really quite rare. The huge majority of stars in the Milky Way are small cool stars, much smaller and cooler than the Sun and yellow in color. But they are so faint that we simply don't see them, certainly not with the naked eye.

Small cool stars are yellow and faint because their "fusion engines" run so slowly and produce so relatively little energy. Large cool stars are yellow and bright because their "fusion engines" run furiously, but since they have used up most of their prime fuel they now run on reserve fuel, farther and farther from their own centers. In the process, they puff up and become simply enormous in size. Their "surfaces" or photospheres are yellow and cool because they are so far from where the energy that lights them up is produced.

Hot young stars are bright because they are very massive, and they are still running on "prime fuel", and they are large but not stupendously huge in size. Their "surfaces" or photospheres are so hot that they are blue-white.
Image
NGC 7129. Photo: Adam Block.
NGC 604 in galaxy M33. Photo: ESA/Hubble.
















When several stars are born from the same molecular cloud, the most massive and brightest ones are the bluest. That can be seen even in NGC 7129 at left, which is a site of low-mass star formation. Smaller yellow stars are also born here, but the blue stars will dominate.

In a region of high-mass star formation, such as NGC 604 in galaxy M33, the small cool yellow stars are too faint to be seen. The near invisibility of the small stars is because the bright massive young stars are so bright - it's like putting a candle in front of the mid-day Sun and trying to spot the flame. (Well, Hubble can spot the small yellow stars.) And you can indeed see a few bright orange stars among the blue ones in NGC 604. They are red giants or supergiants, which have run out of their "prime fuel" and swollen to gigantic sizes. These stars will die soon, which in astronomical terms means that they have only, at best, a few million more years to live.

So the massive stars die young, but the small cool yellow stars remain. In a galaxy where no more bright young stars remain, only the small cool stars (and a few moderate yellow giants) will persist. That means that if you see an all-yellow galaxy, like NGC 5195, then basically all the stars in it are old. (Note that when you see a bright yellow galaxy, or a bright yellow part of a galaxy, then that galaxy or that part of a galaxy must contain huge numbers of old stars. That's because old stars are mostly faint, and it takes huge numbers of them to produce a bright galaxy or a bright central part of a galaxy.)
M51. Photo: Bill Snyder.
But when you see a multi-colored galaxy whose photo has been taken through RGB filters, then yellow means (huge numbers of) old stars, blue means (fewer but brighter) young stars, pink means gas clouds which have been ionized (usually by hot bright stars) and made to emit a lot of red and some blue-green light, dark brown means dust and light brown might mean a faint population of (not so many) old stars, perhaps mixed with dust.

Hope that helped!

Ann
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pgp

Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by pgp » Sun Sep 11, 2016 11:40 pm

Ridiculous image. Hugely over-saturated bauble. It's disappointing to see APOD posting images that have nothing to do with reality.

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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by Ann » Mon Sep 12, 2016 5:37 am

pgp wrote:Ridiculous image. Hugely over-saturated bauble. It's disappointing to see APOD posting images that have nothing to do with reality.
M51 and NGC 5195. Photo: Chase Preuninger - Own work from
http://www.rawastrodata.com/dso.php?typ ... ies&id=m51
I'm going to stick my neck out and post a picture that is slightly too big, just because it is informative.

The picture at left gives a pretty good idea of what M51 and NGC 5195 look like "for real". It could be argued that all galaxy images should look like this one.

You could also say that it is all right to post galaxy pictures that are highly resolved, as long as the color is "realistic" and therefore muted. That is certainly a reasonable position.

The APOD of September 6, 2016, is brightly colored. The color itself carries information. The purpose of saturating the color of this APOD is probably twofold: it does make it easier to extract "color information" from the picture, and the photographer probably wants to appeal to people who love bright colors.

For those who know what RGB color means in astrophotography, the APOD is arguably more informative that the picture I have posted here. On the other hand: it is not bad to be reminded of the "true color saturation" of galaxies.

Ann
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Re: APOD: The Whirlpool Galaxy and Beyond (2016 Sep 06)

Post by geckzilla » Mon Sep 12, 2016 5:43 am

The only argument aside from personal aesthetic preference I have regarding saturation is that when the saturation of an image is increased too far, the dynamic range of the color itself is lost. Thus, places which were faintly red, say, become strongly red along with all other red areas, including the already strongly red. In the end, it really doesn't matter that much for APOD. Brightly colored images probably reach a wider audience, though.
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