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Re: Science and Astronomy Questions

04 Feb 2023 06:28

Is it really spherical though or more like a torus?  I always envisioned it like a torus because there is the "hole" in the middle (where the planets are.)
At closer distances it is more like a disk extending out from the Kuiper belt, but at larger distances it transitions to a gigantic and diffuse spherical shell, like this:

Image

Note that the above graphic shows distances on a logarithmic scale -- otherwise you wouldn't be able to see everything at once. The spherical shell part is much bigger and holds far more volume than the disk-like part. The majority of objects in the Oort Cloud are in that spherical region. We know that it must be shaped like that because incoming long period comets have very little preference for inclination. They can come from any direction with nearly equal probability.

Image
 
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Re: Science and Astronomy Questions

04 Feb 2023 16:28

Is it really spherical though or more like a torus?  I always envisioned it like a torus because there is the "hole" in the middle (where the planets are.)
At closer distances it is more like a disk extending out from the Kuiper belt, but at larger distances it transitions to a gigantic and diffuse spherical shell, like this:

Image

Note that the above graphic shows distances on a logarithmic scale -- otherwise you wouldn't be able to see everything at once. The spherical shell part is much bigger and holds far more volume than the disk-like part. The majority of objects in the Oort Cloud are in that spherical region. We know that it must be shaped like that because incoming long period comets have very little preference for inclination. They can come from any direction with nearly equal probability.

Image
Wow Wat, I can't thank you enough for showing this distribution map/graph.  My mind thinks geometrically, so now I can picture what they look like.  That very rare green comet I've been trying to see this week-- do we have any idea which part of the cloud it comes from and how long its period might be?  Two colors that are very rare in in astronomy (especially with stars) are green and purple, so I've been wanting to see this green comet.  I think I need to be far away from light pollution, since it's magnitude 5 and for an extended object, that wouldn't be visible in the suburbs?  Would an optical aid help (either 10x50 or 12x60 binoculars)?
 
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Re: Science and Astronomy Questions

04 Feb 2023 18:03

Green comets are not rare. The vast majority of them are green (the color comes from C2 molecules which are common component of a comet's coma), and ones bright enough to see with the naked eye show up every few years on average. Sometimes there are several in the same year. I've even photographed them by accident before just because they happened to be in the field of view while I was doing Milky Way photography. But this one is diffuse and faint, and hard to see from any urban setting. It's way over-hyped. There will be better ones. :) 

Honestly, the only particularly interesting thing about this comet (C/2022 E3 ZTF) is that it passed fairly close to Earth, so it had a fairly fast apparent motion on the sky. And it briefly gave a good showing of an anti-tail as it crossed the ecliptic -- a trick of the viewing angle. Now, though, it's getting farther away and fainter, and the approaching full Moon is drowning it out.
 
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Re: Science and Astronomy Questions

05 Feb 2023 07:25

Personally, I think cloud is the right descriptor — after all is it not spherical in shape? Whereas a belt is more or less a ring. And where in the definition of "cloud" is there mention of a specific density? :)
Exactly. :)  We use belts to describe diffuse but disk-like distribution of objects, and clouds for diffuse but more spherical distribution of objects.
Is it really spherical though or more like a torus?  I always envisioned it like a torus because there is the "hole" in the middle (where the planets are.)
So... a sphere of varying density is a torus in your world?

Moderator edit: this post didn't answer anything nor add to the discussion. The topic was already explained in detail anyway, so please cut it out with the pointless passive aggression.
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Re: Science and Astronomy Questions

06 Feb 2023 07:12

Green comets are not rare. The vast majority of them are green (the color comes from C2 molecules which are common component of a comet's coma), and ones bright enough to see with the naked eye show up every few years on average. Sometimes there are several in the same year. I've even photographed them by accident before just because they happened to be in the field of view while I was doing Milky Way photography. But this one is diffuse and faint, and hard to see from any urban setting. It's way over-hyped. There will be better ones. :) 

Honestly, the only particularly interesting thing about this comet (C/2022 E3 ZTF) is that it passed fairly close to Earth, so it had a fairly fast apparent motion on the sky. And it briefly gave a good showing of an anti-tail as it crossed the ecliptic -- a trick of the viewing angle. Now, though, it's getting farther away and fainter, and the approaching full Moon is drowning it out.
I know, but in my light polluted part of the country, the only thing that I can really see from here are stars (and only the really bright ones) so it would be interesting to see a green object in the sky.  The only other comet I've ever seen was Hale Bopp.  Now that you mention it, I do remember that a high percentage of the shooting stars in the Perseids are green.  It's hard to tell the color of them from near NYC but when I saw them from the Poconos that one summer, their color stood out much more.  I've been trying to compile a list of what the different colors of shooting stars mean-- thanks for explaining what green is for-- I wonder if the same is true for green shooting stars? In my list I had green shooting stars listed under nitrogen (burning N2 in the atmosphere), but maybe it's CO2 instead?  I had yellow listed as CO2, blue listed as O2, purple listed as O3, red listed as Argon and orange listed as H2O.  Those were the different shooting star colors I saw that one year I watched the Perseids in the Poconos.

It's disappointing how difficult it is to see the color in celestial objects from near or within a large city. 
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Re: Science and Astronomy Questions

06 Feb 2023 07:15

Exactly. :)  We use belts to describe diffuse but disk-like distribution of objects, and clouds for diffuse but more spherical distribution of objects.
Is it really spherical though or more like a torus?  I always envisioned it like a torus because there is the "hole" in the middle (where the planets are.)
So... a sphere of varying density is a torus in your world?

Moderator edit: this post didn't answer anything nor add to the discussion. The topic was already explained in detail anyway, so please cut it out with the pointless passive aggression.
Huh, how did you get sphere of varying density = torus from my post?  I never said such a thing.  I asked if it was spherical or more like a torus....never equating the two to mean the same thing.  This sure is a reach by you to try and start an argument for no reason.

The mod is right so this discussion should end.
 
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Re: Science and Astronomy Questions

06 Feb 2023 08:21

I know, but in my light polluted part of the country, the only thing that I can really see from here are stars (and only the really bright ones) so it would be interesting to see a green object in the sky.  The only other comet I've ever seen was Hale Bopp. 
Even with binocs and from a dark sky, the green color of the comet was not easily discernible to me by eye. It's just too dim, only becoming spectacular through long exposure astrophotography. Green color in aurora are much more obvious by eye, or in some meteors like you mentioned.

I remember Hale-Bopp vividly. That was indeed a spectacular comet by naked eye, even from within a city. :)
 
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Re: Science and Astronomy Questions

06 Feb 2023 08:34

It's a faint comet (I don't really understand the hype, which seems to be centered around that it has an orbit of 50,000 years (quite roughly?), but I digress).  But I was able to find it in video from a meteor camera, despite exposure times of 1/25 second.  It was supposed to be magnitude 4.5, but appeared fainter, which is likely due to it's fuzziness whereas stars are point sources.
komet2.jpg
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Re: Science and Astronomy Questions

06 Feb 2023 08:49

I know, but in my light polluted part of the country, the only thing that I can really see from here are stars (and only the really bright ones) so it would be interesting to see a green object in the sky.  The only other comet I've ever seen was Hale Bopp. 
Even with binocs and from a dark sky, the green color of the comet was not easily discernible to me by eye. It's just too dim, only becoming spectacular through long exposure astrophotography. Green color in aurora are much more obvious by eye, or in some meteors like you mentioned.

I remember Hale-Bopp vividly. That was indeed a spectacular comet by naked eye, even from within a city. :)
One of my special memories with my dad :-)  The other celestial one was the spectacular Leonid Meteor Storm of 2001.  To have those separated only by a few years was amazing.  Even from Nassau County we could see up to 100 of them every minute, and not just small streaks, but big bright fireballs.  You didn't even have to be looking straight up at the sky to see them-- it was like a silent fireworks display!

https://www.cometwatch.co.uk/brightest- ... h-history/

I was going through this list (brightest comets since the 1930s)..... and Hale Bopp is up in 8th place at -0.8.  I'm trying to remember why I didn't see Comet McNaught, was it mostly only visible from the Southern Hemisphere?  At Mag -5.5 and in 4th place on this list it would have been spectacular even from here.  I didn't see Comet NEAT or Hyakutake from here either (though I remember their names.)  I'm also surprised that PAN-STARRS isn't on this list (though I didn't see that one either.)
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Re: Science and Astronomy Questions

06 Feb 2023 08:53

It's a faint comet (I don't really understand the hype, which seems to be centered around that it has an orbit of 50,000 years (quite roughly?), but I digress).  But I was able to find it in video from a meteor camera, despite exposure times of 1/25 second.  It was supposed to be magnitude 4.5, but appeared fainter, which is likely due to it's fuzziness whereas stars are point sources.

komet2.jpg
Mid, are they even sure about that period?  I read that they aren't even sure if it will ever return.  Maybe it has a parabolic path or even hyperbolic?

Yes, I was worried about not being able to see it at Mag 5, because the light is spread out-- turns out I see I'm not missing much lol.

The funny/ironic thing about comets.....the ones that get all the media attention in advance aren't the great ones, the ones that sneak up on us turn out to be better than expected.
 
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Re: Science and Astronomy Questions

07 Feb 2023 00:52

Mid, are they even sure about that period?  I read that they aren't even sure if it will ever return.  Maybe it has a parabolic path or even hyperbolic?
Its orbit is changing during its plunge through the solar system. Inbound its eccentricity was slightly less than 1 with an orbital period of about 50,000 years, but outgassing and/or gravitational tugs from the planets are giving it a slight boost, and on the way out its eccentricity is now extremely close to or even slightly greater than 1, so it might never return. 

This is actually a pretty common thing. Most long-period comets have eccentricities very close to 1, so it doesn't take much to put them onto a hyperbolic orbit. This is how interstellar comets are born. (They can also be ripped directly away from Oort Clouds by nearby passing stars.) We expect there are huge numbers of them out there and we have already seen a few from other stars. The most famous of course being ʻOumuamua, which was probably not an alien construction but just an interstellar comet being a little surprising, which for a class of object so newly discovered... is not at all surprising.
 
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Re: Science and Astronomy Questions

07 Feb 2023 03:22

Mid, are they even sure about that period?  I read that they aren't even sure if it will ever return.  Maybe it has a parabolic path or even hyperbolic?
Its orbit is changing during its plunge through the solar system. Inbound its eccentricity was slightly less than 1 with an orbital period of about 50,000 years, but outgassing and/or gravitational tugs from the planets are giving it a slight boost, and on the way out its eccentricity is now extremely close to or even slightly greater than 1, so it might never return. 

This is actually a pretty common thing. Most long-period comets have eccentricities very close to 1, so it doesn't take much to put them onto a hyperbolic orbit. This is how interstellar comets are born. (They can also be ripped directly away from Oort Clouds by nearby passing stars.) We expect there are huge numbers of them out there and we have already seen a few from other stars. The most famous of course being ʻOumuamua, which was probably not an alien construction but just an interstellar comet being a little surprising, which for a class of object so newly discovered... is not at all surprising.
Still fascinating though, interstellar comets!  Maybe we'll live to see a rogue planet passing through our solar system one day!  I bet that would generate some excitement.  One of the first sci fi books I read was "When Worlds Collide" and its sequel "After Worlds Collide."

Something I found amazing about comets, especially the solar grazers and the really bright "Great Comets" was that they're thought to all have been part of the same giant primordial object?  Going back through the records all the way back to the Great Comet of 1106 and earlier reports through antiquity, it seems like they were part of a giant object that broke up into smaller comets with each return?  I find that absolutely fascinating-- the complete object was nearly as bright as the sun according to these reports and had a tail that stretched from horizon to horizon!  It broke up into smaller objects while people were viewing it!

https://en.wikipedia.org/wiki/Kreutz_su ... et_of_1882

https://en.wikipedia.org/wiki/X/1106_C1
 
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Re: Science and Astronomy Questions

07 Feb 2023 13:46

Mid, are they even sure about that period?  I read that they aren't even sure if it will ever return.  Maybe it has a parabolic path or even hyperbolic?
Exactly.  That figure must be taken with a grain of salt.  And the main reason why this comet became such a celebrity seems to be that somewhat random guess, because with such a long return period the comet is "rare".  Well, yes, it's surely a long time since it last visited the inner solar system (if it ever did), but it's not uncommon for comets to have such orbits.  There probably are a dozen other comets currently in our neightbourhood, just even fainter ones, and chances are good that a few of them have somewhat similar return periods.
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Re: Science and Astronomy Questions

11 Feb 2023 13:38

Is it really spherical though or more like a torus?  I always envisioned it like a torus because there is the "hole" in the middle (where the planets are.)
So... a sphere of varying density is a torus in your world?
Moderator edit: this post didn't answer anything nor add to the discussion. The topic was already explained in detail anyway, so please cut it out with the pointless passive aggression.
Huh, how did you get sphere of varying density = torus from my post?  I never said such a thing.  I asked if it was spherical or more like a torus....never equating the two to mean the same thing.  This sure is a reach by you to try and start an argument for no reason.

The mod is right so this discussion should end.
Just for the record, the "I always envisioned it like a torus" part.
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Re: Science and Astronomy Questions

11 Feb 2023 13:53

But that doesn't equate a torus with a sphere, they are topologically distinct....but this has already been discussed.  The random inclination variation (which I didn't know about before) is why it's a sphere and not a torus.

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