APOD: NGC 5195: The Dot under the Question... (2013 Aug 31)

APOD Robot · Post by **APOD Robot** » Sat Aug 31, 2013 4:07 am

NGC 5195: The Dot under the Question Mark

Explanation: Dwarf galaxy NGC 5195 is best known as the smaller companion of spiral M51, the Whirlpool galaxy. Seen together they seem to trace the curve and dot of a cosmic question mark, recorded in Lord Rosse's 19th century drawings as one of the original spiral nebulae. Dwarfed by enormous M51 (aka NGC 5194), NGC 5195 spans about 20,000 light-years. A close encounter with M51 has likely triggered star formation and enhanced that galaxy's prominent spiral arms. Processed from image data available in the Hubble Legacy Archive, this majestic close-up of NGC 5195 makes it clear that the dwarf galaxy now lies behind M51. A tidal bridge of dark dust clouds and young blue star clusters stretches from the outskirts of M51 on the right, appearing in silhouette against the dwarf galaxy's yellowish glow. The famous pair of interacting galaxies lie some 30 million light-years away, toward the handle of the Big Dipper, and the constellation of the Hunting Dogs.

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Beyond · Post by **Beyond** » Sat Aug 31, 2013 4:26 am

I didn't realize that today's APOD title was so accurate. I couldn't find a question mark anywhere... till i hit the links. F-O-R-E!! A hole er, question mark in one.
Datsa very Big dot

Ann · Post by **Ann** » Sat Aug 31, 2013 5:49 am

Beyond wrote: Datsa very Big dot

It is very big for a dot indeed. What I wonder is exactly how small it is for a galaxy.

Back when I first read about M51 and NGC 5195, in Burnham's Celestial Handbook, I was told - or so I seem to remember! - that NGC 5195 was about as massive as M51. Obviously Burnham is no longer an authority on such things.

Take a look at this picture, however. Clearly NGC 5195 is much smaller than M51, but its yellow bulge is bigger than the yellow bulge of M51. Most of the mass of a galaxy is usually found in its bulge. Has there been any estimates at how much mass these two galaxies contain?

Ann

Boomer12k · Post by **Boomer12k** » Sat Aug 31, 2013 6:17 am

More like a "9".....

I always seem to get a more sideways shot....

Took that from the driveway. I live in a city neighborhood. A street light is less than 100 feet away....who needs to go to the country...plus my telescope weighs 100 lbs, and I don't have a truck...

:---[===] *

Ann · Post by **Ann** » Sat Aug 31, 2013 6:33 am

Interesting picture, Boomer. Judging from your picture, it could be that the really bright part of the bulge of M51 is actually larger than the really bright part of the bulge of NGC 5195.

Ann

orin stepanek · Post by **orin stepanek** » Sat Aug 31, 2013 11:47 am

I think together they look like someone's ear!

Psnarf · Post by **Psnarf** » Sat Aug 31, 2013 1:54 pm

http://messier.seds.org/more/m051_rosse.html

I assume the glow is not reflection or emission from dust and gasses interacting with a central star, but is actually made of unresolved individual stars? There appears to be a similar galaxy to the bottom left of NGC5195. (In the enlarged version, that small galaxy looks like the dot under a question mark made up of the curving dust cloud over the center of NGC5195.) If the glow is composed of unresolved individual stars, there are a few stars that seem to be dimmed from being behind the glow. If the glow is individual stars, would not the background stars be occulted by the foreground stars?

robolt · Post by **robolt** » Sat Aug 31, 2013 3:08 pm

APOD often refers to dust clouds as in this narrative. What comprises the clouds and how dense are they?

Gustave · Post by **Gustave** » Sat Aug 31, 2013 3:55 pm

Can you advise which stars are associated with M51 as opposed to foreground stars?

ta152h0 · Post by **ta152h0** » Sat Aug 31, 2013 4:19 pm

we should pool our resources . I have a truck but no telescope. On how powerful are two little words " lies behind " and all of a sudden the image becomes clear as a bell.

Ann · Post by **Ann** » Sat Aug 31, 2013 6:52 pm

Gustave wrote:Can you advise which stars are associated with M51 as opposed to foreground stars?

I can find only two stars that are definite foreground stars. One is a white star located near twelve o'clock. This star has obvious diffraction spikes. A very orange point of light near 6 o'clock also appears to have diffraction spikes and is likely also a foreground star.

The only individual light in M51 or NGC 5195 that could show diffraction spikes when photographed by the Hubble Telescope is a supernova. But while M51 has had several recorded supernovae, none appear to have been located where we can see the white and the orange points of light. They are therefore modest MIkly Way foreground stars, not M51 objects.

We can see a lot of stars that clearly belong to M51. We can see many young star clusters in M51, and we can see many of their individual blue stars. Interestingly, we can see a number of orange stars of about the same brightness scattered over the face of M51. These stars are almost certainly individual red giants or supergiants.

Ann

neufer · Post by **neufer** » Sat Aug 31, 2013 10:20 pm

http://messier.seds.org/more/m097_rosse.html wrote:
Lord Rosse's drawings of M97, the Owl Nebula

Drawing of the Owl Nebula by William Parsons, the Third Earl of Rosse. He comments his observations of March 11, 1848:

"Two stars considerably apart in the central region: dark penumbra around each spiral arrangements." (On many occasions only one star seen and spiral form doubtful.)

Looking through Lord Rosse's 6-foot telescope, Thomas Romney Robinson, a priest and friend of the Earl, remarked in 1848: "A most intricate group of spiral arcs disposed around two starry centers, looking like the visage of a monkey."

The second star was not seen in the location marked in this drawing by later observers.

just carl · Post by **just carl** » Sat Aug 31, 2013 10:24 pm

Why can't someone point to what is being mentioned. I have no idea where anything discussed is.

geckzilla · Post by **geckzilla** » Sun Sep 01, 2013 12:39 am

just carl wrote:Why can't someone point to what is being mentioned. I have no idea where anything discussed is.

Right away, Your Highness.

(click to enlarge!)

stephen63 · Post by **stephen63** » Sun Sep 01, 2013 5:07 am

neufer wrote:
http://messier.seds.org/more/m097_rosse.html wrote:
Lord Rosse's drawings of M97, the Owl Nebula

Drawing of the Owl Nebula by William Parsons, the Third Earl of Rosse. He comments his observations of March 11, 1848:

"Two stars considerably apart in the central region: dark penumbra around each spiral arrangements." (On many occasions only one star seen and spiral form doubtful.)

Looking through Lord Rosse's 6-foot telescope, Thomas Romney Robinson, a priest and friend of the Earl, remarked in 1848: "A most intricate group of spiral arcs disposed around two starry centers, looking like the visage of a monkey."

The second star was not seen in the location marked in this drawing by later observers.

Ann · Post by **Ann** » Sun Sep 01, 2013 6:16 am

Psnarf wrote:http://messier.seds.org/more/m051_rosse.html

I assume the glow is not reflection or emission from dust and gasses interacting with a central star, but is actually made of unresolved individual stars? There appears to be a similar galaxy to the bottom left of NGC5195. (In the enlarged version, that small galaxy looks like the dot under a question mark made up of the curving dust cloud over the center of NGC5195.) If the glow is composed of unresolved individual stars, there are a few stars that seem to be dimmed from being behind the glow. If the glow is individual stars, would not the background stars be occulted by the foreground stars?

Foreground stars can indeed occult background stars. Take a look at this picture of M51 (the large galaxy which is only partly seen in today's APOD). There is a foreground star with diffraction spikes at about 1 o'clock, and there is another one at about 3 o'clock. These two foreground stars could well be occulting a star in M51.

However, stars are (comparatively) tiny in size and very widely separated. For a foreground star to actually occult a background star, both stars have to be perfectly aligned along our line of sight. That probably doesn't happen very often.

Ann

Ann · Post by **Ann** » Sun Sep 01, 2013 6:22 am

neufer wrote:
http://messier.seds.org/more/m097_rosse.html wrote:
Lord Rosse's drawings of M97, the Owl Nebula

Drawing of the Owl Nebula by William Parsons, the Third Earl of Rosse. He comments his observations of March 11, 1848:

"Two stars considerably apart in the central region: dark penumbra around each spiral arrangements." (On many occasions only one star seen and spiral form doubtful.)

Looking through Lord Rosse's 6-foot telescope, Thomas Romney Robinson, a priest and friend of the Earl, remarked in 1848: "A most intricate group of spiral arcs disposed around two starry centers, looking like the visage of a monkey."

The second star was not seen in the location marked in this drawing by later observers.

Ummm... Art, if you don't mind - aren't you discussing the wrong Messier object?

The Owl Nebula is located not all that far from M51 and NGC 5195 in our skies. But the Owl Nebula and M51 are not all that close together, either.

Give us a hint as to why you wrote about the Owl Nebula. Maybe something like this: Gee, that NGC 5195 actually looks quite a bit like the Owl Nebula?

Ann

neufer · Post by **neufer** » Sun Sep 01, 2013 11:33 am

Ann wrote:
Ummm... Art, if you don't mind - aren't you discussing the wrong Messier object?

The Owl Nebula is located not all that far from M51 and NGC 5195 in our skies. But the Owl Nebula and M51 are not all that close together, either.

Give us a hint as to why you wrote about the Owl Nebula. Maybe something like this: Gee, that NGC 5195 actually looks quite a bit like the Owl Nebula?

A Rosse is a Rosse is a Rosse.

Beyond · Post by **Beyond** » Sun Sep 01, 2013 12:38 pm

Rosse... an ARTistic Impression in the ground.

: l.jpg (18.49 KiB) Viewed 4163 times

He does it again

Ann · Post by **Ann** » Sun Sep 01, 2013 3:41 pm

neufer wrote: A Rosse is a Rosse is a Rosse.

: Click to view full size image

Drawing of M51 and NGC 5195 by Lord Rosse

Really? A galaxy is a planetary nebula is a dwarf galaxy?

What is a spiral galaxy?

http://wiki.answers.com/Q/What_is_a_spiral_galaxy wrote:
Answer:
A galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center

What is an elliptical galaxy?

http://answers.ask.com/science/astronom ... cal_galaxy wrote:
Answer:
An elliptical galaxy looks featureless and is bright in appearance. They are varied in shape and sizes. It is made from low-mass stars, but is not the most dominant galaxy in our universe.

What is a planetary nebula?

http://wiki.answers.com/Q/What_is_a_planetary_nebula wrote:
Answer:
A planetary nebula is created when a star blows off its outer layers after it has run out of fuel to burn. These outer layers of gas expand into space, forming a nebula, which is often the shape of a ring or bubble. About 200 years ago, William Herschel called these spherical clouds planetary nebulae because they were round like the planets. At the center of a planetary nebula, the glowing, leftover central part of the star from which it came, can usually still be seen.

What is a Rosse?

http://wiki.answers.com/Q/ wrote:
Excuse me?

Ann

owlice · Post by **owlice** » Sun Sep 01, 2013 3:44 pm

recorded in Lord Rosse's 19th century drawings

BDanielMayfield · Post by **BDanielMayfield** » Sun Sep 01, 2013 4:21 pm

This comment is about 24 hrs late, but Ann, your mention of Burnham’s Celestial Handbook (1966) back in the first comment in this thread prompted me to retrieve my set which I haven’t taken off the shelf in years. I couldn’t confirm your recollection as to it saying what you thought you remembered about the two galaxies having similar masses, but I found this paragraph (beginning on page 371) about NGC 5195 to be of interest:

“Conspicuous in the small telescope, this satellite system gives the appearance of being attached to the north end of the spiral arm of M51. Evidently it does not lie exactly in the plane of the big spiral, since dust lanes of the M51 arm may be seen crossing in front of it. There are also some dust patches on the opposite side, believed to be directly associated with the smaller galaxy itself. The classification of this peculiar system is uncertain. In the Hubble Atlas of Galaxies, A.Sandage (1961) refers to it as an irregular galaxy of the M82 type. Some long-exposure photographs show faint outer filaments which seem to suggest the structure of an incipient barred spiral. On the other hand E.M. and G.R.Burbidge (1964) have classed it as an S0 system. If the superimposed dust clouds and the obscuring matter connected with the arm of M51 were removed, the system would probably resemble an elliptical galaxy. Its light is much redder than that of M51, and true resolution does not appear to have been achieved with any present telescope. The corrected radial velocities of the two objects are fairly comparable; 340 and 390 miles per second in recession.”

With today’s (now yesterday’s) improved image of NGC 5195 a few stars can be resolved, but not near as many as in big bubba, M51. It’s redder color and its faster recessional motion made me wonder if perhaps this galaxy wasn’t in fact connected to M51 at all. It does have a slightly distorted, sort of tri-oval shape, and Wikipedia mentioned the presence of a tidal bridge between the pair, so they must if fact be connected. The color difference is striking however.

geckzilla · Post by **geckzilla** » Sun Sep 01, 2013 4:41 pm

BDanielMayfield wrote:With today’s (now yesterday’s) improved image of NGC 5195 a few stars can be resolved, but not near as many as in big bubba, M51. It’s redder color and its faster recessional motion made me wonder if perhaps this galaxy wasn’t in fact connected to M51 at all. It does have a slightly distorted, sort of tri-oval shape, and Wikipedia mentioned the presence of a tidal bridge between the pair, so they must if fact be connected. The color difference is striking however.

Funny, I was just wondering the same thing about another pair of galaxies I dug out of the HLA the other day. The difference in this case is that the foreground galaxy I think is smaller than the background one, though I couldn't find any specifics on mass for them. The tidal bridge is clearly visible, though. It's rare to find some objects in space that you can nearly perceive the depth of. Certain galaxies like the Sombrero which are nearly edge on give a good impression of it.

Beyond · Post by **Beyond** » Sun Sep 01, 2013 6:30 pm

ha-ha, somehow i missed the "Lord" connection to Rosse, so when i Goggled Rosse, all i got was a Lunar crater named Rosse. Craters, are of course, meteoric artistic impressions in the ground.

stephen63 · Post by **stephen63** » Sun Sep 01, 2013 10:25 pm

Ann wrote: Really? A galaxy is a planetary nebula is a dwarf galaxy?
Ann

How about when it's Bode's nebula

Starship Asterisk*

APOD: NGC 5195: The Dot under the Question... (2013 Aug 31)

APOD: NGC 5195: The Dot under the Question... (2013 Aug 31)

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An excellent likeness!

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Re: An excellent likeness!