APOD: Fleming's Triangular Wisp (2023 Nov 21)

[APOD Robot]

Fleming's Triangular Wisp

Explanation: These chaotic and tangled filaments of shocked, glowing gas are spread across planet Earth's sky toward the constellation of Cygnus as part of the Veil Nebula. The Veil Nebula itself is a large supernova remnant, an expanding cloud born of the death explosion of a massive star. Light from the original supernova explosion likely reached Earth over 5,000 years ago. The glowing filaments are really more like long ripples in a sheet seen almost edge on, remarkably well separated into the glow of ionized hydrogen atoms shown in red and oxygen in blue hues. Also known as the Cygnus Loop and cataloged as NGC 6979, the Veil Nebula now spans about 6 times the diameter of the full Moon. The length of the wisp corresponds to about 30 light years, given its estimated distance of 2,400 light years. Often identified as Pickering's Triangle for a director of Harvard College Observatory, it is perhaps better named for its discoverer, astronomer Williamina Fleming, as Fleming's Triangular Wisp.

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[JohnD]

Nice pic!
It raises for me the question, how/why are the 'veils' of nitrogen and oxygen so separated? This applies to aurorae too, when in Earth's atmosphere the gases are so intimately mixed, yet are seen as separate features.
All are due to high energy radiation/particles striking the gas atoms. They arrive at a wide range of frequencies that should set all of them aglow at once, so why only certain atoms in certain places?
John

[smitty]

Looks more rectangular to me, with the longer axis vertical in the image. But then what do I know?

[Chris Peterson]

Nice pic!
It raises for me the question, how/why are the 'veils' of nitrogen and oxygen so separated? This applies to aurorae too, when in Earth's atmosphere the gases are so intimately mixed, yet are seen as separate features.
All are due to high energy radiation/particles striking the gas atoms. They arrive at a wide range of frequencies that should set all of them aglow at once, so why only certain atoms in certain places?
John

With auroras, the gases are well mixed, but they only produce emission lines when they exist as specific low densities, which is why different colors occur at different heights.

In the case of planetary nebulas and supernova remnants, at least part of the issue is that the gases aren't even uniformly mixed.

[JohnD]

Thank you, Chris!

[GoatGuy]

It was … for a minute … a head-scratcher: how exactly does 6 times visual 'size' of Luna (0.5°) correspond to 30 light years, given 2400 LY distance.

Upon closer reading, it became more apparent.

The Veil Nebula is (((6 × 0.5°) ÷ 360) × (2π)) × 2400 LY = 125 LY in total span. The Wisp is only a fraction of that, and not given in angular extent. So 30 LY is certainly believable. 25% of the whole Veil Nebula.

Gotcha.
Thanks again.
GoatGuy

[orin stepanek]

Great Nebula By Fleming!

[johnnydeep]

Nice pic!
It raises for me the question, how/why are the 'veils' of nitrogen and oxygen so separated? This applies to aurorae too, when in Earth's atmosphere the gases are so intimately mixed, yet are seen as separate features.
All are due to high energy radiation/particles striking the gas atoms. They arrive at a wide range of frequencies that should set all of them aglow at once, so why only certain atoms in certain places?
John

With auroras, the gases are well mixed, but they only produce emission lines when they exist as specific low densities, which is why different colors occur at different heights.

In the case of planetary nebulas and supernova remnants, at least part of the issue is that the gases aren't even uniformly mixed.

And why wouldn't the gases in the nebula be uniformly mixed?

[Chris Peterson]

Nice pic!
It raises for me the question, how/why are the 'veils' of nitrogen and oxygen so separated? This applies to aurorae too, when in Earth's atmosphere the gases are so intimately mixed, yet are seen as separate features.
All are due to high energy radiation/particles striking the gas atoms. They arrive at a wide range of frequencies that should set all of them aglow at once, so why only certain atoms in certain places?
John

With auroras, the gases are well mixed, but they only produce emission lines when they exist as specific low densities, which is why different colors occur at different heights.

In the case of planetary nebulas and supernova remnants, at least part of the issue is that the gases aren't even uniformly mixed.

And why wouldn't the gases in the nebula be uniformly mixed?

Mainly, I think, because the star is layered by element when it explodes, so the concentration of elements in the expanding shell or shells isn't uniform.

[Randall_Rathbun]

I tried to get the Chandra people to look for the pulsar from the Cygnus Loop but they begged off. Next I contacted the James Webb people and they said sorry submission time has passed. Is anyone doing science?

[johnnydeep]

With auroras, the gases are well mixed, but they only produce emission lines when they exist as specific low densities, which is why different colors occur at different heights.

In the case of planetary nebulas and supernova remnants, at least part of the issue is that the gases aren't even uniformly mixed.

And why wouldn't the gases in the nebula be uniformly mixed?

Mainly, I think, because the star is layered by element when it explodes, so the concentration of elements in the expanding shell or shells isn't uniform.

Ok, but in that case I would expect to see mostly onion-like shells of different colors (or elements) with different layers not repeating the same color. But here we see the same colors alternating many times.

[starsurfer]

I think the name of Pickering's Triangle was given by Williamina Fleming? I love all the various planetary nebulae she discovered.

[johnnydeep]

I think the name of Pickering's Triangle was given by Williamina Fleming? I love all the various planetary nebulae she discovered.

Well, the Fleming's Triangular Wisp link in the text had this to say:

In 1904, Fleming noticed the tangle of filaments in the center of the Veil Nebula in Cygnus. The director's name was attached to the discovery, perhaps by custom, probably with Fleming's approval (she'd named her son after the director after all). Hence the common name for this nebula: "Pickering's Triangle.

So, she probably approved of the name even if she didn't outright pick the name!