APOD: Vega and Comet 12P/Pons-Brooks (2023 Dec 08)

APOD Robot · Post by **APOD Robot** » Fri Dec 08, 2023 5:08 am

Vega and Comet 12P/Pons-Brooks

Explanation: On December 4, periodic Comet 12P/Pons-Brooks shared this telescopic field of view with Vega, alpha star of the northern constellation Lyra. Fifth brightest star in planet Earth's night, Vega is some 25 light-years distant while the much fainter comet was about 21 light-minutes away. In recent months, outbursts have caused dramatic increases in brightness for Pons-Brooks though. Nicknamed the Devil Comet for its hornlike appearance, fans of interstellar spaceflight have also suggested the distorted shape of this comet's large coma looks like the Millenium Falcon. A Halley-type comet, 12P/Pons-Brooks last visited the inner Solar System in 1954. Its next perihelion passage or closest approach to the Sun will be April 21, 2024. That's just two weeks after the April 8 total solar eclipse path crosses North America. But, highly inclined to the Solar System's ecliptic plane, the orbit of periodic Comet 12P/Pons-Brooks will never cross the orbit of planet Earth.

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Ann · Post by **Ann** » Fri Dec 08, 2023 6:53 am

Yes, that's an APOD that I like!

: Vega and Comet 12P/Pons-Brooks. Image Credit & Copyright: Dan Bartlett

That's a lovely color contrast between blue Vega and the greenish comet! But wait. Vega is white, didn't you know that?

Today's caption links to this description of Vega:

Jim Kaler wrote:

Vega is a classic class A (A0) white main sequence dwarf star, like the Sun quietly running off the nuclear fusion of hydrogen deep in its core, with a sort of average effective surface temperature of about 9500 degrees Kelvin. Its white color and apparent brightness made it a basic standard against which the apparent magnitudes of other stars are compared.

Okay, see if you can find Vega in the picture below - it must be an intensely white star, right?

The Summer Triangle and the northern Milky Way. Credit: Alan Dyer.

Well, actually - Vega is the one blue star in Alan Dyer's picture, at top center right. The blue color must be a mistake, of course, because Vega is the very definition of whiteness! Isn't it?

Anyway, enough ranting! The comet looks nice in the APOD, too.

APOD Robot wrote:
Nicknamed the Devil Comet for its hornlike appearance

Yes, you can actually see the horns in today's APOD!

So, to summarize, nice horn-adorned pale green Comet 12/Pons-Brooks and nice blue Vega!!!

Ann

johnnydeep · Post by **johnnydeep** » Fri Dec 08, 2023 4:03 pm

APOD wrote:But, highly inclined to the Solar System's ecliptic plane, the orbit of periodic Comet 12P/Pons-Brooks will never cross the orbit of planet Earth.

I don't see how being highly inclined to the ecliptic (and hence also Earth's orbit) implies it will never cross Earth's orbit. The comet's perihelion is 0.78 AU, so inclined or not, I don't see why it couldn't cross Earth's orbit at some point. But maybe my 3D sense is failing me again.

Chris Peterson · Post by **Chris Peterson** » Fri Dec 08, 2023 4:11 pm

johnnydeep wrote: ↑Fri Dec 08, 2023 4:03 pm
APOD wrote:But, highly inclined to the Solar System's ecliptic plane, the orbit of periodic Comet 12P/Pons-Brooks will never cross the orbit of planet Earth.
I don't see how being highly inclined to the ecliptic (and hence also Earth's orbit) implies it will never cross Earth's orbit. The comet's perihelion is 0.78 AU, so inclined or not, I don't see why it couldn't cross Earth's orbit at some point. But maybe my 3D sense is failing me again.

Simply being highly inclined to the ecliptic tells us nothing about the possibility of crossing Earth's orbit. This body doesn't cross our orbit because... it doesn't cross our orbit! Something we can conclude from ALL of its orbital elements, of which inclination is just one.

(Consider, as just one example, Comet Swift-Tuttle, responsible for the Perseids. It is hugely inclined at 113°. Almost at right angles to the ecliptic. It doesn't currently cross the Earth's orbit, but it's very close and has probably crossed in the past, and could again in the future.)

johnnydeep · Post by **johnnydeep** » Fri Dec 08, 2023 4:15 pm

Chris Peterson wrote: ↑Fri Dec 08, 2023 4:11 pm
johnnydeep wrote: ↑Fri Dec 08, 2023 4:03 pm
APOD wrote:But, highly inclined to the Solar System's ecliptic plane, the orbit of periodic Comet 12P/Pons-Brooks will never cross the orbit of planet Earth.
I don't see how being highly inclined to the ecliptic (and hence also Earth's orbit) implies it will never cross Earth's orbit. The comet's perihelion is 0.78 AU, so inclined or not, I don't see why it couldn't cross Earth's orbit at some point. But maybe my 3D sense is failing me again.
Simply being highly inclined to the ecliptic tells us nothing about the possibility of crossing Earth's orbit. This body doesn't cross our orbit because... it doesn't cross our orbit! Something we can conclude from ALL of its orbital elements, of which inclination is just one.

(Consider, as just one example, Comet Swift-Tuttle, responsible for the Perseids. It is hugely inclined at 113°. Almost at right angles to the ecliptic. It doesn't currently cross the Earth's orbit, but it's very close and has probably crossed in the past, and could again in the future.)

Ok, so the implication in the text is wrong. But now, what does "crossing Earth's orbit" really mean? It can't just mean crossing Earth's orbital plane.

Chris Peterson · Post by **Chris Peterson** » Fri Dec 08, 2023 4:17 pm

johnnydeep wrote: ↑Fri Dec 08, 2023 4:15 pm
Chris Peterson wrote: ↑Fri Dec 08, 2023 4:11 pm
johnnydeep wrote: ↑Fri Dec 08, 2023 4:03 pm

I don't see how being highly inclined to the ecliptic (and hence also Earth's orbit) implies it will never cross Earth's orbit. The comet's perihelion is 0.78 AU, so inclined or not, I don't see why it couldn't cross Earth's orbit at some point. But maybe my 3D sense is failing me again.
Simply being highly inclined to the ecliptic tells us nothing about the possibility of crossing Earth's orbit. This body doesn't cross our orbit because... it doesn't cross our orbit! Something we can conclude from ALL of its orbital elements, of which inclination is just one.

(Consider, as just one example, Comet Swift-Tuttle, responsible for the Perseids. It is hugely inclined at 113°. Almost at right angles to the ecliptic. It doesn't currently cross the Earth's orbit, but it's very close and has probably crossed in the past, and could again in the future.)
Ok, so the implication in the text is wrong. But now, what does "crossing Earth's orbit" really mean? It can't just mean crossing Earth's orbital plane.

It means that the two orbits intersect.

johnnydeep · Post by **johnnydeep** » Fri Dec 08, 2023 4:30 pm

Chris Peterson wrote: ↑Fri Dec 08, 2023 4:17 pm
johnnydeep wrote: ↑Fri Dec 08, 2023 4:15 pm
Chris Peterson wrote: ↑Fri Dec 08, 2023 4:11 pm

Simply being highly inclined to the ecliptic tells us nothing about the possibility of crossing Earth's orbit. This body doesn't cross our orbit because... it doesn't cross our orbit! Something we can conclude from ALL of its orbital elements, of which inclination is just one.

(Consider, as just one example, Comet Swift-Tuttle, responsible for the Perseids. It is hugely inclined at 113°. Almost at right angles to the ecliptic. It doesn't currently cross the Earth's orbit, but it's very close and has probably crossed in the past, and could again in the future.)
Ok, so the implication in the text is wrong. But now, what does "crossing Earth's orbit" really mean? It can't just mean crossing Earth's orbital plane.
It means that the two orbits intersect.

But how close is considered intersecting? Earth passing through a comet's debris donut, I suppose?

Chris Peterson · Post by **Chris Peterson** » Fri Dec 08, 2023 4:41 pm

johnnydeep wrote: ↑Fri Dec 08, 2023 4:30 pm
Chris Peterson wrote: ↑Fri Dec 08, 2023 4:17 pm
johnnydeep wrote: ↑Fri Dec 08, 2023 4:15 pm

Ok, so the implication in the text is wrong. But now, what does "crossing Earth's orbit" really mean? It can't just mean crossing Earth's orbital plane.
It means that the two orbits intersect.
But how close is considered intersecting? Earth passing through a comet's debris donut, I suppose?

The orbits are defined by mathematical ellipses. Those are what intersect. So in reality they never do. But the distance between the two orbits at their minimum that you want to consider intersecting depends on what you're doing. It could be quite large when considering potentially dangerous asteroids, since none of these orbits are perfectly stable, and we can't perfectly propagate their positions all that far into the future. Once an object is close enough in time, you would start worrying about the distance in terms of the radius of the Earth!

johnnydeep · Post by **johnnydeep** » Fri Dec 08, 2023 6:57 pm

Chris Peterson wrote: ↑Fri Dec 08, 2023 4:41 pm
johnnydeep wrote: ↑Fri Dec 08, 2023 4:30 pm
Chris Peterson wrote: ↑Fri Dec 08, 2023 4:17 pm
It means that the two orbits intersect.
But how close is considered intersecting? Earth passing through a comet's debris donut, I suppose?
The orbits are defined by mathematical ellipses. Those are what intersect. So in reality they never do. But the distance between the two orbits at their minimum that you want to consider intersecting depends on what you're doing. It could be quite large when considering potentially dangerous asteroids, since none of these orbits are perfectly stable, and we can't perfectly propagate their positions all that far into the future. Once an object is close enough in time, you would start worrying about the distance in terms of the radius of the Earth!

Rauf · Post by **Rauf** » Sat Dec 09, 2023 4:50 am

johnnydeep wrote: ↑Fri Dec 08, 2023 6:57 pm
Chris Peterson wrote: ↑Fri Dec 08, 2023 4:41 pm
johnnydeep wrote: ↑Fri Dec 08, 2023 4:30 pm

But how close is considered intersecting? Earth passing through a comet's debris donut, I suppose?
The orbits are defined by mathematical ellipses. Those are what intersect. So in reality they never do. But the distance between the two orbits at their minimum that you want to consider intersecting depends on what you're doing. It could be quite large when considering potentially dangerous asteroids, since none of these orbits are perfectly stable, and we can't perfectly propagate their positions all that far into the future. Once an object is close enough in time, you would start worrying about the distance in terms of the radius of the Earth!

A little late but, this helped me, so it might help you visualize it too:

https://www.astronomy.com/science/the-devil-comet-is-headed-our-way-and-thats-ok/ wrote:Pons-Brooks is on a highly inclined orbit that will bring it down from above the plane of the planets. It will pass through the inner solar system between the orbits of Earth and Venus, never crossing our own planet’s orbit. Credit: TheSkyLive.com 3D Solar System Viewer, Background Image: ESO/S. Brunier

johnnydeep · Post by **johnnydeep** » Sat Dec 09, 2023 2:56 pm

Rauf wrote: ↑Sat Dec 09, 2023 4:50 am
johnnydeep wrote: ↑Fri Dec 08, 2023 6:57 pm
Chris Peterson wrote: ↑Fri Dec 08, 2023 4:41 pm
The orbits are defined by mathematical ellipses. Those are what intersect. So in reality they never do. But the distance between the two orbits at their minimum that you want to consider intersecting depends on what you're doing. It could be quite large when considering potentially dangerous asteroids, since none of these orbits are perfectly stable, and we can't perfectly propagate their positions all that far into the future. Once an object is close enough in time, you would start worrying about the distance in terms of the radius of the Earth!

A little late but, this helped me, so it might help you visualize it too:

PBOrbit.png

https://www.astronomy.com/science/the-devil-comet-is-headed-our-way-and-thats-ok/ wrote:Pons-Brooks is on a highly inclined orbit that will bring it down from above the plane of the planets. It will pass through the inner solar system between the orbits of Earth and Venus, never crossing our own planet’s orbit. Credit: TheSkyLive.com 3D Solar System Viewer, Background Image: ESO/S. Brunier

I don't know - that looks pretty darn close to crossing Earth's orbit to me!

Chris Peterson · Post by **Chris Peterson** » Sat Dec 09, 2023 3:02 pm

johnnydeep wrote: ↑Sat Dec 09, 2023 2:56 pm
Rauf wrote: ↑Sat Dec 09, 2023 4:50 am
johnnydeep wrote: ↑Fri Dec 08, 2023 6:57 pm

A little late but, this helped me, so it might help you visualize it too:

PBOrbit.png

https://www.astronomy.com/science/the-devil-comet-is-headed-our-way-and-thats-ok/ wrote:Pons-Brooks is on a highly inclined orbit that will bring it down from above the plane of the planets. It will pass through the inner solar system between the orbits of Earth and Venus, never crossing our own planet’s orbit. Credit: TheSkyLive.com 3D Solar System Viewer, Background Image: ESO/S. Brunier

I don't know - that looks pretty darn close to crossing Earth's orbit to me!

Not close enough to be considered potentially dangerous... particularly because its highly inclined orbit means it is generally very far from the ecliptic, which means it's not a comet subject to major perturbations from the gas giants. In other words, its orbit is quite stable.

johnnydeep · Post by **johnnydeep** » Sat Dec 09, 2023 8:56 pm

Chris Peterson wrote: ↑Sat Dec 09, 2023 3:02 pm
johnnydeep wrote: ↑Sat Dec 09, 2023 2:56 pm
Rauf wrote: ↑Sat Dec 09, 2023 4:50 am

A little late but, this helped me, so it might help you visualize it too:

PBOrbit.png

I don't know - that looks pretty darn close to crossing Earth's orbit to me!
Not close enough to be considered potentially dangerous... particularly because its highly inclined orbit means it is generally very far from the ecliptic, which means it's not a comet subject to major perturbations from the gas giants. In other words, its orbit is quite stable.

I didn't mean to imply that it was a threat, just that the notion of "close" is subjective and influenced by the particular depiction used.

Starship Asterisk*

APOD: Vega and Comet 12P/Pons-Brooks (2023 Dec 08)

APOD: Vega and Comet 12P/Pons-Brooks (2023 Dec 08)

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Re: APOD: Vega and Comet 12P/Pons-Brooks (2023 Dec 08)

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