APOD: Finding NEOWISE (2020 Jul 18)

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APOD: Finding NEOWISE (2020 Jul 18)

Post by APOD Robot » Sat Jul 18, 2020 4:08 am

Image Finding NEOWISE

Explanation: If you can see the stars of the Big Dipper, you can find comet NEOWISE in your evening sky tonight. After sunset look for the naked-eye comet below the bowl of the famous celestial kitchen utensil of the north and above your northwestern horizon. You're looking for a fuzzy 'star' with a tail, though probably not so long a tail as in this clear sky snapshot taken from Los Padres National Forest in California on the evening of July 16. Recent photographs of C/2020 F3 (NEOWISE) often show this comet's broad dust tail and fainter but separate ion tail extending farther than the eye can follow. Skygazers around the world have been delighted to find NEOWISE, surprise visitor from the outer Solar System.

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Avent » Sat Jul 18, 2020 5:40 am

Rage. Rage against the dying of the light. As this comet fades from my sight. As a stem fights every day against that loss of the light. If only to make a seed to continue the fight.

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by XgeoX » Sat Jul 18, 2020 12:41 pm

Very nice photo. I like how natural it looks, no garish tacked on out of scale foreground. The grain is nice too, reminds me of the shots in “Astronomy” and “Sky and Telescope” in the 70’s and 80’s.

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by orin stepanek » Sat Jul 18, 2020 12:53 pm

NEOWISEBelowBigDipper-7-16-2020-TomMasterson1081.jpg

Oh So that's where Neowise came from? It spilled
out of the Big Dipper! :mrgreen:
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Robot » Sat Jul 18, 2020 1:50 pm

What causes the apparent curvature of the dust trail?

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Chris Peterson » Sat Jul 18, 2020 2:04 pm

Robot wrote:
Sat Jul 18, 2020 1:50 pm
What causes the apparent curvature of the dust trail?
The dust trail is curved. As particles move outward from the comet's orbit, they orbit slower (basic orbital mechanics). So the tail curves.
Chris

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by neufer » Sat Jul 18, 2020 2:39 pm

Chris Peterson wrote:
Sat Jul 18, 2020 2:04 pm
Robot wrote:
Sat Jul 18, 2020 1:50 pm

What causes the apparent curvature of the dust trail?
The dust trail is curved. As particles move outward from the comet's orbit, they orbit slower (basic orbital mechanics). So the tail curves.
Art Neuendorffer

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Sa Ji Tario » Sat Jul 18, 2020 2:58 pm

Each particle that belongs to the body of the comet retains the movement, if it divides, all the pieces would go the same way if there were no other force to modify it. In the case of comet dust, this is the arrangement of the nucleus by solar heat and UV radiation, once outside the body, the solar wind slows it down and is slightly in orbit, but it follows the same path as the nucleus. As it rotates, the front jets are faster than the side jets and the rear jets are the slowest, so extensive flow forms and all of the lost material remains in the same orbit through which the core passed , if the orbit is curved the flow also. -
When the Earth crosses it, it generates the "star showers"

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Chris Peterson » Sat Jul 18, 2020 3:03 pm

Sa Ji Tario wrote:
Sat Jul 18, 2020 2:58 pm
Each particle that belongs to the body of the comet retains the movement, if it divides, all the pieces would go the same way if there were no other force to modify it. In the case of comet dust, this is the arrangement of the nucleus by solar heat and UV radiation, once outside the body, the solar wind slows it down and is slightly in orbit, but it follows the same path as the nucleus. As it rotates, the front jets are faster than the side jets and the rear jets are the slowest, so extensive flow forms and all of the lost material remains in the same orbit through which the core passed , if the orbit is curved the flow also. -
When the Earth crosses it, it generates the "star showers"
The material ejected from a comet does not follow the same orbit as the nucleus. It follows a similar orbit, which becomes less similar over time.
Chris

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by johnnydeep » Sat Jul 18, 2020 3:04 pm

APOD Robot wrote:
Sat Jul 18, 2020 4:08 am
Image Finding NEOWISE

Explanation: If you can see the stars of the Big Dipper, you can find comet NEOWISE in your evening sky tonight. After sunset look for the naked-eye comet below the bowl of the famous celestial kitchen utensil of the north and above your northwestern horizon. You're looking for a fuzzy 'star' with a tail, though probably not so long a tail as in this clear sky snapshot taken from Los Padres National Forest in California on the evening of July 16. Recent photographs of C/2020 F3 (NEOWISE) often show this comet's broad dust tail and fainter but separate ion tail extending farther than the eye can follow. Skygazers around the world have been delighted to find NEOWISE, surprise visitor from the outer Solar System.
Two questions:

1. Is the statement in blue necessarily true? I would think it would depend on how high the big dipper is in the sky. If it's not high enough, the comet will still be below the horizon, right? That is, whether you can see the comet or not still depends on your latitude.

2. The stars of the big dipper look enhanced to me. Are they? The image details didn't say. They are never that glaring to the eye that I've ever seen.
"To Boldly Go......Beyond The Fields We Know."

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Chris Peterson » Sat Jul 18, 2020 3:21 pm

johnnydeep wrote:
Sat Jul 18, 2020 3:04 pm
APOD Robot wrote:
Sat Jul 18, 2020 4:08 am
Image Finding NEOWISE

Explanation: If you can see the stars of the Big Dipper, you can find comet NEOWISE in your evening sky tonight. After sunset look for the naked-eye comet below the bowl of the famous celestial kitchen utensil of the north and above your northwestern horizon. You're looking for a fuzzy 'star' with a tail, though probably not so long a tail as in this clear sky snapshot taken from Los Padres National Forest in California on the evening of July 16. Recent photographs of C/2020 F3 (NEOWISE) often show this comet's broad dust tail and fainter but separate ion tail extending farther than the eye can follow. Skygazers around the world have been delighted to find NEOWISE, surprise visitor from the outer Solar System.
Two questions:

1. Is the statement in blue necessarily true? I would think it would depend on how high the big dipper is in the sky. If it's not high enough, the comet will still be below the horizon, right? That is, whether you can see the comet or not still depends on your latitude.

2. The stars of the big dipper look enhanced to me. Are they? The image details didn't say. They are never that glaring to the eye that I've ever seen.
Statement 1 is broadly accurate. The comet is currently at a declination of +48°, which is less than that of the Big Dipper. As you travel south, the Dipper will disappear over the horizon before the comet. But certainly, the fact that they have different right ascensions also means they have different rising and setting times, so depending on the time the Dipper may be visible and the comet not. What the statement really means is that if you can see the Dipper in your sky, you can also see the comet... but not necessarily at the same time.

And yes, the stars of the Dipper have clearly been enhanced.
Chris

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by johnnydeep » Sat Jul 18, 2020 4:10 pm

Chris Peterson wrote:
Sat Jul 18, 2020 3:21 pm
johnnydeep wrote:
Sat Jul 18, 2020 3:04 pm
APOD Robot wrote:
Sat Jul 18, 2020 4:08 am
Image Finding NEOWISE

Explanation: If you can see the stars of the Big Dipper, you can find comet NEOWISE in your evening sky tonight. After sunset look for the naked-eye comet below the bowl of the famous celestial kitchen utensil of the north and above your northwestern horizon. You're looking for a fuzzy 'star' with a tail, though probably not so long a tail as in this clear sky snapshot taken from Los Padres National Forest in California on the evening of July 16. Recent photographs of C/2020 F3 (NEOWISE) often show this comet's broad dust tail and fainter but separate ion tail extending farther than the eye can follow. Skygazers around the world have been delighted to find NEOWISE, surprise visitor from the outer Solar System.
Two questions:

1. Is the statement in blue necessarily true? I would think it would depend on how high the big dipper is in the sky. If it's not high enough, the comet will still be below the horizon, right? That is, whether you can see the comet or not still depends on your latitude.

2. The stars of the big dipper look enhanced to me. Are they? The image details didn't say. They are never that glaring to the eye that I've ever seen.
Statement 1 is broadly accurate. The comet is currently at a declination of +48°, which is less than that of the Big Dipper. As you travel south, the Dipper will disappear over the horizon before the comet. But certainly, the fact that they have different right ascensions also means they have different rising and setting times, so depending on the time the Dipper may be visible and the comet not. What the statement really means is that if you can see the Dipper in your sky, you can also see the comet... but not necessarily at the same time.

And yes, the stars of the Dipper have clearly been enhanced.
Thanks!
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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Boomer12k » Sat Jul 18, 2020 9:07 pm

I have a good view of the Big Dipper, but haven't been able to find the comet... too many trees in the way, even from my deck... I can see parts of the horizon, but just can't seem to get the comet... but a great picture like this is... um... GREAT...

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by neufer » Sat Jul 18, 2020 9:17 pm

Chris Peterson wrote:
Sat Jul 18, 2020 3:03 pm
Sa Ji Tario wrote:
Sat Jul 18, 2020 2:58 pm

Each particle that belongs to the body of the comet retains the movement, if it divides, all the pieces would go the same way if there were no other force to modify it. In the case of comet dust, this is the arrangement of the nucleus by solar heat and UV radiation, once outside the body, the solar wind slows it down and is slightly in orbit, but it follows the same path as the nucleus. As it rotates, the front jets are faster than the side jets and the rear jets are the slowest, so extensive flow forms and all of the lost material remains in the same orbit through which the core passed , if the orbit is curved the flow also. -
When the Earth crosses it, it generates the "star showers"
The material ejected from a comet does not follow the same orbit as the nucleus. It follows a similar orbit, which becomes less similar over time.
Gravity drops off inversely with solar radial distance squared.

Radiation pressure also drops off inversely with solar radial distance squared.

Ergo:
similar particles will travel on elliptical orbits that (roughly) match up with the initial nucleus velocity at their time of ejection.
(Solar wind is negligible for the dust tail.)
Art Neuendorffer

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Chris Peterson » Sat Jul 18, 2020 9:21 pm

neufer wrote:
Sat Jul 18, 2020 9:17 pm
Chris Peterson wrote:
Sat Jul 18, 2020 3:03 pm
Sa Ji Tario wrote:
Sat Jul 18, 2020 2:58 pm

Each particle that belongs to the body of the comet retains the movement, if it divides, all the pieces would go the same way if there were no other force to modify it. In the case of comet dust, this is the arrangement of the nucleus by solar heat and UV radiation, once outside the body, the solar wind slows it down and is slightly in orbit, but it follows the same path as the nucleus. As it rotates, the front jets are faster than the side jets and the rear jets are the slowest, so extensive flow forms and all of the lost material remains in the same orbit through which the core passed , if the orbit is curved the flow also. -
When the Earth crosses it, it generates the "star showers"
The material ejected from a comet does not follow the same orbit as the nucleus. It follows a similar orbit, which becomes less similar over time.
Gravity drops off inversely with solar radial distance squared.

Radiation pressure also drops off inversely with solar radial distance squared.

Ergo:
similar particles will travel on elliptical orbits that (roughly) match up with the initial nucleus velocity at their time of ejection.
(Solar wind is negligible for the dust tail.)
Oh no, they don't. They move outward and they slow down. I've run enough million particle models of comet ejecta to have a very good idea of how those particles behave. Nor is solar wind neglible- it certainly can't be ignored in models if you want to know where material ends up- especially after a few orbits of short period comets, the ones that are responsible for meteor showers.
Chris

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by De58te » Sat Jul 18, 2020 11:27 pm

I can never be a real astronomer since I can't get my head around some concepts. Many sites have said that Neowise has passed the sun and is now heading out of the solar System. They also say Neowise is approaching Earth and will be the closest on July 23. Then it will pass Earth by. Now I was taught in school that the comet tail always points away from the Sun regardless of its true direction. So if it is approaching Earth, shouldn't the tail actually be pointing more or less towards Earth until July 24? Why is the tail in the photo at 90 degrees to Earth?

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by Chris Peterson » Sat Jul 18, 2020 11:38 pm

De58te wrote:
Sat Jul 18, 2020 11:27 pm
I can never be a real astronomer since I can't get my head around some concepts. Many sites have said that Neowise has passed the sun and is now heading out of the solar System. They also say Neowise is approaching Earth and will be the closest on July 23. Then it will pass Earth by. Now I was taught in school that the comet tail always points away from the Sun regardless of its true direction. So if it is approaching Earth, shouldn't the tail actually be pointing more or less towards Earth until July 24? Why is the tail in the photo at 90 degrees to Earth?
The comet is not heading towards Earth, except in the sense that it's getting somewhat closer. Its orbit is highly inclined. At the end of June it crossed the ecliptic from south to north. How can you tell from the images whether the tail in inclined towards the Earth or away from it? (And the dust tail seldom points directly away from the Sun. It is subject to other forces. The ion tail is a better indicator of the anti-solar direction.)
Chris

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by neufer » Sun Jul 19, 2020 3:15 am

Chris Peterson wrote:
Sat Jul 18, 2020 9:21 pm
neufer wrote:
Sat Jul 18, 2020 9:17 pm
Chris Peterson wrote:
Sat Jul 18, 2020 3:03 pm

The material ejected from a comet does not follow the same orbit as the nucleus. It follows a similar orbit, which becomes less similar over time.
Gravity drops off inversely with solar radial distance squared.

Radiation pressure also drops off inversely with solar radial distance squared.

Ergo:
similar particles will travel on elliptical orbits that (roughly) match up with the initial nucleus velocity at their time of ejection. (Solar wind is negligible for the dust tail.)
Oh no, they don't. They move outward and they slow down.

I've run enough million particle models of comet ejecta to have a very good idea of how those particles behave.
Particles traveling on elliptical orbits "all move outward and slow down."

However, if the nucleus is on a near parabolic orbit (as in this case) the cometary particles
will travel on hyperbolic orbits that "move outward and slow down" but never return.
Chris Peterson wrote:
Sat Jul 18, 2020 9:21 pm
neufer wrote:
Sat Jul 18, 2020 9:17 pm

(Solar wind is negligible for the dust tail.)
Nor is solar wind neglible- it certainly can't be ignored in models if you want to know where material ends up- especially after a few orbits of short period comets, the ones that are responsible for meteor showers.
https://en.wikipedia.org/wiki/Electric_sail wrote:
<<The electric solar wind sail gets its momentum from the solar wind ions,
whilst a photonic sail is propelled by photons.

Thus, the available pressure is only about 1% of photon pressure.>>
Art Neuendorffer

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Re: APOD: Finding NEOWISE (2020 Jul 18)

Post by SpookyAstro » Sun Jul 19, 2020 5:12 am

Chris Peterson wrote:
Sat Jul 18, 2020 3:21 pm
johnnydeep wrote:
Sat Jul 18, 2020 3:04 pm
APOD Robot wrote:
Sat Jul 18, 2020 4:08 am
Image Finding NEOWISE

Explanation: If you can see the stars of the Big Dipper, you can find comet NEOWISE in your evening sky tonight. After sunset look for the naked-eye comet below the bowl of the famous celestial kitchen utensil of the north and above your northwestern horizon. You're looking for a fuzzy 'star' with a tail, though probably not so long a tail as in this clear sky snapshot taken from Los Padres National Forest in California on the evening of July 16. Recent photographs of C/2020 F3 (NEOWISE) often show this comet's broad dust tail and fainter but separate ion tail extending farther than the eye can follow. Skygazers around the world have been delighted to find NEOWISE, surprise visitor from the outer Solar System.
Two questions:

1. Is the statement in blue necessarily true? I would think it would depend on how high the big dipper is in the sky. If it's not high enough, the comet will still be below the horizon, right? That is, whether you can see the comet or not still depends on your latitude.

2. The stars of the big dipper look enhanced to me. Are they? The image details didn't say. They are never that glaring to the eye that I've ever seen.
Statement 1 is broadly accurate. The comet is currently at a declination of +48°, which is less than that of the Big Dipper. As you travel south, the Dipper will disappear over the horizon before the comet. But certainly, the fact that they have different right ascensions also means they have different rising and setting times, so depending on the time the Dipper may be visible and the comet not. What the statement really means is that if you can see the Dipper in your sky, you can also see the comet... but not necessarily at the same time.

And yes, the stars of the Dipper have clearly been enhanced.
Yes they are burned into the image I wanted to make it clear where the Big Dipper is in the photo, sometimes with wide field panoramas the stars can get 'lost' and don't really appear as how you see them in the night sky, at least that's how I feel about it :-)