APOD: The Great Carina Nebula (2024 Apr 19)

Comments and questions about the APOD on the main view screen.
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APOD: The Great Carina Nebula (2024 Apr 19)

Post by APOD Robot » Fri Apr 19, 2024 4:05 am

Image The Great Carina Nebula

Explanation: A jewel of the southern sky, the Great Carina Nebula is more modestly known as NGC 3372. One of our Galaxy's largest star forming regions, it spans over 300 light-years. Like the smaller, more northerly Great Orion Nebula, the Carina Nebula is easily visible to the unaided eye. But at a distance of 7,500 light-years it lies some 5 times farther away. This stunning telescopic view reveals remarkable details of the region's glowing filaments of interstellar gas and obscuring cosmic dust clouds. The Carina Nebula is home to young, extremely massive stars, including the still enigmatic variable Eta Carinae, a star with well over 100 times the mass of the Sun. Eta Carinae is the bright star above the central dark notch in this field and left of the dusty Keyhole Nebula (NGC 3324).

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Ann
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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by Ann » Fri Apr 19, 2024 6:58 am

I'm somewhat critical of the colors of this APOD.

APOD 19 April 2024 annotated.png
The Great Carina Nebula. Image Credit & Copyright: Demison Lopes
Carina Nebula Harel Boren annotated.png
The Great Carina Nebula. Credit: Harel Boren

Harel Boren's image is an RGB one, but I don't know what filters were used for today's APOD, although I suspect a red hydrogen alpha filter and a bit of green OIII. The OIII filter (if one has been used) would contribute to the greenish-white tint of the region around Eta Carina and further up along a dark ridge at upper right in the APOD. I can't protest against the greenish tint here, because undoubtedly there is a good amount of green OIII emission here.

What I don't like about the APOD is the fact that the cool red stars are the same shade of red as the hydrogen alpha nebula. That doesn't happen. "Red" stars are some shade of yellow-orange, but hydrogen alpha is red-red. It may be lightened to a pink shade in the presence of hydrogen beta.

Take a look at the star HD 92397 at upper right in both the APOD and in Harel Boren's image. In the APOD it looks like a white star with a brick-red halo. In Harel Boren's image it looks almost all white. Well, the true color of HD 92397 is very similar to the color of Aldebaran. HD 92307 is the same spectral class as Aldebaran, although several times more luminous.

HD 92397 in APOD 19 April 2024.png
HD 92397 is the same color as Aldebaran, but it is the same color
as the red emission nebula in the APOD.

HD 94096, by contrast, is a brilliant red supergiant whose B-V index is even redder than that of mu Cephei (the "Garnet" star).


But HD 94096 is not as luminous as mu Cephei. The Gaia parallax of mu Cep puts it at a distance of more than 27,000 light-years - far beyond the Carina Nebula! - and coupled with its V brightness of 4.08, gives it a V (yellow-green) luminosity of 1.3 million times that of the Sun! In yellow-green light, from a cool red supergiant star! In infrared (I) light, its magnitude of 0.22 gives it a luminosity of 45 million times the Sun!!!! And a even farther infrared wavelengths, (K), its luminosity is 270,000,000 times the Sun!!!! :shock: 😮 😮 😲 Is this even possible, or is the Gaia parallax wrong?

The Gaia parallax of HD 94096 doesn't make this star so humongously bright. Even at K wavelengths, it is "no more than" some 700,000 times that of the Sun. Still, it is even more deeply orange in color as Mu Cephei.

As for HD 93070, it may be a long-period variable similar to Mira. I tried to find a good visible-light picture of Mira on the net, but it was hopeless. Mira is "known" for being very red, and for that reason the internet images of Mira have been reddened to a ludicrous hue. Mira's B-V index is modest, around +1, and even its R magnitude is unremarkable. However, it is extremely infrared-bright. At visible (V) wavelengths, it is only 16 times brighter than the Sun! 16 times, can you believe it? But at K wavelengths, Mira is 50,000 times brighter than the Sun! Can you believe it?

So anyway. All red stars are the same shade of red in today's APOD, but in Harel Boren's RGB image, the red stars come in different shades.

Ann
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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by johnnydeep » Fri Apr 19, 2024 5:02 pm

As usual, I'm failing to place this apparent close-up in the larger image shown here:


I'd guess it's the black V slightly to the left and downward from the center, but the angle of that V doesn't seem to match?
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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by Christian G. » Fri Apr 19, 2024 6:18 pm

The Southerners who can feast their eyes on the Carina Nebula anytime they want are lucky people!

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Ann
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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by Ann » Fri Apr 19, 2024 6:21 pm

johnnydeep wrote: Fri Apr 19, 2024 5:02 pm As usual, I'm failing to place this apparent close-up in the larger image shown here:


I'd guess it's the black V slightly to the left and downward from the center, but the angle of that V doesn't seem to match?
APOD 19 April 2024 detail.png
Carina Nebula HST annotated.png

Ann
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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by johnnydeep » Fri Apr 19, 2024 6:42 pm

Ann wrote: Fri Apr 19, 2024 6:21 pm
johnnydeep wrote: Fri Apr 19, 2024 5:02 pm As usual, I'm failing to place this apparent close-up in the larger image shown here:


I'd guess it's the black V slightly to the left and downward from the center, but the angle of that V doesn't seem to match?
APOD 19 April 2024 detail.png
Carina Nebula HST annotated.png

Ann
Thanks! And boy was I barking up the wrong tree:

carina nebula - two views.jpg
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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by starsurfer » Fri Apr 19, 2024 10:17 pm

I had no idea that NGC 3324 referred to the Keyhole Nebula. Guess I was wrong about it referring to the Gabriela Mistral Nebula.

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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by Ann » Sat Apr 20, 2024 4:15 am

starsurfer wrote: Fri Apr 19, 2024 10:17 pm I had no idea that NGC 3324 referred to the Keyhole Nebula. Guess I was wrong about it referring to the Gabriela Mistral Nebula.

Wikipedia wrote:


:lol2:

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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by johnnydeep » Sat Apr 20, 2024 1:06 pm

starsurfer wrote: Fri Apr 19, 2024 10:17 pm I had no idea that NGC 3324 referred to the Keyhole Nebula. Guess I was wrong about it referring to the Gabriela Mistral Nebula.
You’re correct and the APOD text is wrong.
https://en.wikipedia.org/wiki/NGC_3324 wrote: NGC 3324 is an open cluster in the southern constellation Carina, located northwest of the Carina Nebula (NGC 3372)[3][4] at a distance of 9,100 ly (2,800 pc) from Earth.[2] It is closely associated with the emission nebula IC 2599, also known as Gum 31.[5] The two are often confused as a single object, and together have been nicknamed the "Gabriela Mistral Nebula" due to its resemblance to the Chilean poet.[6][7][8] NGC 3324 was first catalogued by James Dunlop in 1826.[3]
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Re: APOD: The Great Carina Nebula (2024 Apr 19)

Post by VictorBorun » Sun Apr 21, 2024 8:48 pm

Suppose a 100 suns mass in Eta Carinae is where the most of interstellar matter went from a large volume like 30 light years sphere.
Did all that matter form an oblique black globe of 3 light years on its way to collapsing into the star?
That would imply that compressing the volume by 1000 times and compressing the area by 100 times (perpendicularly to our line of sight) would make the interstellar dust go from transparent to oblique.

Is it how much dust there really is in the interstellar space?
Suppose we send a probe to a star 4 ly away. Our probe would have to break through a layer of dust only 100 times less dense than an oblique layer of dust? Really?