Starship Asterisk*

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.

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!

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

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!

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

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!

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?

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.

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.

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.)

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.

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.

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.

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