APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

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APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by APOD Robot » Mon Mar 02, 2020 5:05 am

Image Sharpless-308: The Dolphin Nebula

Explanation: Blown by fast winds from a hot, massive star, this cosmic bubble is much larger than the dolphin it appears to be. Cataloged as Sharpless 2-308 it lies some 5,200 light-years away toward the constellation of the Big Dog (Canis Major) and covers slightly more of the sky than a Full Moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the featured expansive image is dominated by the glow of ionized oxygen atoms mapped to a blue hue.

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Ann » Mon Mar 02, 2020 6:52 am

Color shmolor, who cares?

When discussing a Wolf-Rayet nebula, we may say that the nebula itself is all that interests us, and then we don't care about the ionizing central star. Or else we may say that the central star is indeed interesting, and it is interesting for two reasons: 1, it has indeed created the nebula, and 2, it is not done with its shenanigans, since it is going to go supernova in the moderately near future. 💥

So let's say that we acknowledge that the Wolf-Rayet star itself, called EZ CMa, is of some interest. We may decide that the only thing that interests us about it is its stellar wind 🌟, whose strength and duration we may try to roughly judge by looking at the shape and size of the nebula.

Or else, we may say that we might just possibly gain a little bit of knowledge about the properties of EZ CMa by looking at its color. In doing so, it is very helpful to look at stars in the same field. The brightest star in today's APOD is orange, and indeed, this star is a cool K-type supergiant star, Omicron-1 CMa, with a B-V index of +1.74. That color index is suitable for a somewhat red or reddened orange K-type star. Its orange color reflects the star's cool temperature, which is probably around 4,000 K.

As we can see if we look at the APOD, the EZ CMa is just as orange as its bright neighbor. Does that mean that the temperature of EZ CMA is similar to that of Omicron-1 CMa?
Jim Kaler wrote about EZ CMa:

EZ CMa is classed as a mid-temperature (relative to the set) WN4 star of 89,000 Kelvin with a radius of just 2.65 times that of the Sun, a luminosity of 400,000 Suns, and a current mass of 19 Suns.
89,000 Kelvin is about 20 times as hot as a typical K-type star like Omicron-1 CMa. So why do the hues of Omicron-1 CMa and EZ CMa look much the same? Is it because all the stars in today's APOD look orange? No, they don't, as a quick check will reveal. Many stars in the field look blue.

Wolf-Rayet stars are typically dusty and reddened by the dust of their own making. Could EZ CMa be sufficiently dust-reddened to actually look like an orange K-type star, even though it is 20 times hotter?

Answer: No. The B-V index of EZ CMa is -0.05, which is bluer than Vega.




















I'd say that the reason why blisteringly hot and even-to-the-eye blue-white star EZ CMa is the same color as cool orange supergiant Omicron-1 CMa in the APOD is because those who produced the APOD didn't care about the color of the ionizing central star of the nebula. But it is certainly possible to bring out the color difference between a hot and a cool star even in narrowband photography, as the picture at right demonstrates.

A little more than a year ago, another picture of the Dolphin Nebula was the APOD. But in that case, the photographer did a good job at bringing out a color difference between the hot central star and its cool supergiant neighbor.

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Boomer12k » Mon Mar 02, 2020 7:47 am

I did not know it was a bubble nebula... great image.

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by starsurfer » Mon Mar 02, 2020 1:52 pm

A challenge for everyone, can anyone find the secret hidden planetary nebula? :D

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by TheZuke! » Mon Mar 02, 2020 2:39 pm

starsurfer wrote:
Mon Mar 02, 2020 1:52 pm
A challenge for everyone, can anyone find the secret hidden planetary nebula? :D
The little bubble at the "bottom" of the dolphin?

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by orin stepanek » Mon Mar 02, 2020 2:41 pm

Dolphin_Pleiades_960.jpg
I see a picture within a picture! :wink:
Dolphin_Pleiades_960.jpg
Also! :mrgreen:
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Orin

Smile today; tomorrow's another day!

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by TheZuke! » Mon Mar 02, 2020 2:48 pm

TheZuke! wrote:
Mon Mar 02, 2020 2:39 pm
starsurfer wrote:
Mon Mar 02, 2020 1:52 pm
A challenge for everyone, can anyone find the secret hidden planetary nebula? :D
The little bubble at the "bottom" of the dolphin?
Or...
it is a smaller nebula inside the dolphin, and it resulted in shaping the dolphin's "snout".

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Ann » Mon Mar 02, 2020 5:42 pm

TheZuke! wrote:
Mon Mar 02, 2020 2:39 pm
starsurfer wrote:
Mon Mar 02, 2020 1:52 pm
A challenge for everyone, can anyone find the secret hidden planetary nebula? :D
The little bubble at the "bottom" of the dolphin?
Hidden planetary.png


You're right! You found it. :D

Ann
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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by starsurfer » Mon Mar 02, 2020 7:15 pm

TheZuke! wrote:
Mon Mar 02, 2020 2:39 pm
starsurfer wrote:
Mon Mar 02, 2020 1:52 pm
A challenge for everyone, can anyone find the secret hidden planetary nebula? :D
The little bubble at the "bottom" of the dolphin?
Well done! Your prize is finding out its name, which is PN G234.9-09.7 and was discovered less than 20 years ago.

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Ann » Mon Mar 02, 2020 8:58 pm

I note that Chris Peterson has had no objections so far to my criticism of the star colors in the Dolphin Nebula in today's APOD.

The fact that Chris has not found fault with my reasoning brings me pleasure. :ssmile:

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Psnarf » Mon Mar 02, 2020 9:15 pm

I still believe it is a space phage in the process of engulfing and consuming its prey. PN G234.9-09.7 is it's youngling.

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Chris Peterson » Mon Mar 02, 2020 10:36 pm

Ann wrote:
Mon Mar 02, 2020 8:58 pm
I note that Chris Peterson has had no objections so far to my criticism of the star colors in the Dolphin Nebula in today's APOD.

The fact that Chris has not found fault with my reasoning brings me pleasure. :ssmile:

Ann
Mainly, I just don't care much about color in images.
Chris

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by neufer » Tue Mar 03, 2020 12:04 am

Chris Peterson wrote:
Mon Mar 02, 2020 10:36 pm
Ann wrote:
Mon Mar 02, 2020 8:58 pm

I note that Chris Peterson has had no objections so far to my criticism of the star colors in the Dolphin Nebula in today's APOD.

The fact that Chris has not found fault with my reasoning brings me pleasure. :ssmile:
Mainly, I just don't care much about color in images.
Art Neuendorffer

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Ann » Tue Mar 03, 2020 6:13 am

Chris Peterson wrote:
Mon Mar 02, 2020 10:36 pm
Ann wrote:
Mon Mar 02, 2020 8:58 pm
I note that Chris Peterson has had no objections so far to my criticism of the star colors in the Dolphin Nebula in today's APOD.

The fact that Chris has not found fault with my reasoning brings me pleasure. :ssmile:

Ann
Mainly, I just don't care much about color in images.
Okay, Chris, but do you agree that it is a good thing if two stars of wildly different temperatures and very different color indexes are shown to be different colors in a narrowband image? Particularly if other stars in the same image are displaying different colors?

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by ta152h0 » Fri Mar 06, 2020 3:56 am

There is a Wolf-Rayet 104 that's scheduled to be a problem for life on Earth. Pass the ice cold one.
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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by Chris Peterson » Fri Mar 06, 2020 5:08 am

Ann wrote:
Tue Mar 03, 2020 6:13 am
Chris Peterson wrote:
Mon Mar 02, 2020 10:36 pm
Ann wrote:
Mon Mar 02, 2020 8:58 pm
I note that Chris Peterson has had no objections so far to my criticism of the star colors in the Dolphin Nebula in today's APOD.

The fact that Chris has not found fault with my reasoning brings me pleasure. :ssmile:

Ann
Mainly, I just don't care much about color in images.
Okay, Chris, but do you agree that it is a good thing if two stars of wildly different temperatures and very different color indexes are shown to be different colors in a narrowband image? Particularly if other stars in the same image are displaying different colors?
That depends upon what the intent of the data presentation is. Some images are best in B&W.
Chris

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Re: APOD: Sharpless-308: The Dolphin Nebula (2020 Mar 02)

Post by neufer » Fri Mar 06, 2020 2:29 pm


Chris Peterson wrote:
Fri Mar 06, 2020 5:08 am

Some images are best in B&W.
https://en.wikipedia.org/wiki/Black_and_white wrote:
<<Some modern film directors will occasionally shoot movies in black-and-white as an artistic choice. The use of black-and-white in the mass media often connotes something "nostalgic" or historic. The film director Woody Allen has used black-and-white a number of times since Manhattan (1979), which also had a George Gershwin derived score. The makers of The Good German (2006) used camera lenses from the 1940s, and other equipment from that era, so that their black-and-white film imitated the look of early noir. Monochrome film stock is now rarely used at the time of shooting, even if the films are intended to be presented theatrically in black-and-white. Movies such as John Boorman's The General (1998) and Joel Coen's The Man Who Wasn't There (2001) were filmed in color despite being presented in black-and-white for artistic reasons. Raging Bull (1980) and Clerks (1994) are two of the few well-known modern films deliberately shot in black-and-white. In black-and-white still photography, many photographers choose to shoot in solely black-and-white since the stark contrasts enhance the subject matter. Some formal photo portraits still use black-and-white. Many visual-art photographers use black-and-white in their work.>>
Art Neuendorffer