APOD: Island Universe, Cosmic Sand (2021 Aug 14)

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APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by APOD Robot » Sat Aug 14, 2021 4:06 am

Image Island Universe, Cosmic Sand

Explanation: Stars in our own Milky Way Galaxy are scattered through this eye-catching field of view. From the early hours after midnight on August 13, the 30 second exposure of the night sky over Busko-Zdroj, Poland records the colorful and bright trail of a Perseid meteor. Seen near the peak of the annual Perseid meteor shower it flashes from lower left to upper right. The hurtling grain of cosmic sand, a piece of dust from periodic comet Swift-Tuttle, vaporized as it passed through planet Earth's atmosphere at almost 60 kilometers per second. Just above and right of center, well beyond the stars of the Milky Way, lies the island universe known as M31 or the Andromeda Galaxy. The Andromeda Galaxy is the most distant object easily visible to the naked-eye, about 2.5 million light-years away. The visible meteor trail begins only about 100 kilometers above Earth's surface, though. It points back to the meteor shower radiant in the constellation Perseus off the lower left edge of the frame. Follow this bright perseid meteor trail below and left to the stars of NGC 869and NGC 884, the double star cluster in Perseus.

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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Astronymus » Sat Aug 14, 2021 6:04 am

Saw one lousy grain. Weather was bad and I will not mention the light pollution.
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by De58te » Sat Aug 14, 2021 11:41 am

I just saw 3 in a row in about 3 minute time some 2 hours ago. From my bathroom window. I thought "Oh cool, the skies have cleared and the meteor shower is occurring." Then I thought "Holy (you know what) it is 5 AM and I am too tired for this. Going back to bed."

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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by orin stepanek » Sat Aug 14, 2021 12:03 pm

IMG_20210813_143919.jpg
Nice: meteor and a good view of Andromeda!
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by johnnydeep » Sat Aug 14, 2021 8:07 pm

Ok, so I haven't thought much about meteor showers before, but now have two questions:

1. The text mentions that this meteor was caused by a piece of dust travelling at 60 km/s through the rarefied upper atmosphere. A mere spec of dust - perhaps sand grain sized as suggested by the title - can really appear this spectacular? Also, how do we really know how big these particles are? I assume they range in size.

2. Here comes my lack of 3D visualization skill again: Why do these always appear to radiate from a point in Perseus? Is it always the exact same point on the celestial sphere or is it moving over time? I would think that since the cause of these meteors is the Earth passing through the Sun-orbiting debris left behind after the passage of comet Swift-Tuttle, that the point where Earth crossed its path wouldn't remain fixed. Hmm, thinking some more, I guess orbits are pretty fixed in space after all (except for slow precession over time - https://en.wikipedia.org/wiki/Apsidal_precession) so that if two orbits cross once, they will continue to cross periodically for quite a while.
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Eclectic Man » Sat Aug 14, 2021 8:58 pm

What is happening at the end of the meteor trail? It looks as if the meteor has split in two and the parts flown apart and at least one bit seems to be following a curved path.

Any explanations?

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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Chris Peterson » Sat Aug 14, 2021 9:36 pm

johnnydeep wrote:
Sat Aug 14, 2021 8:07 pm
Ok, so I haven't thought much about meteor showers before, but now have two questions:

1. The text mentions that this meteor was caused by a piece of dust travelling at 60 km/s through the rarefied upper atmosphere. A mere spec of dust - perhaps sand grain sized as suggested by the title - can really appear this spectacular? Also, how do we really know how big these particles are? I assume they range in size.
There is a reasonably reliable relationship between luminous flux and mass. So as a rule, if we have a photometric measurement we can estimate mass. And if we know what it is made of, we can go from mass to size. In fact, this meteor produced a persistent train, so it was almost certainly larger than a grain of sand. Probably more like the size of a marble.
2. Here comes my lack of 3D visualization skill again: Why do these always appear to radiate from a point in Perseus? Is it always the exact same point on the celestial sphere or is it moving over time? I would think that since the cause of these meteors is the Earth passing through the Sun-orbiting debris left behind after the passage of comet Swift-Tuttle, that the point where Earth crossed its path wouldn't remain fixed. Hmm, thinking some more, I guess orbits are pretty fixed in space after all (except for slow precession over time - https://en.wikipedia.org/wiki/Apsidal_precession) so that if two orbits cross once, they will continue to cross periodically for quite a while.
Indeed, the orbit of the particles for any given shower is quite stable. The particles are cleared from the orbit, either towards or away from the Sun, by various forces over a period of a few thousand years. If there is still an active comet in the orbit, the particles are replenished near each perihelion. But comets aren't active forever, either. So showers are short lived in astronomical terms- typically no more than a few thousand years.

The radiant is a vanishing point illusion. The meteors are all moving parallel to each other, coming from the direction of their radiant (actually, from an apparent direction that depends both on their actual vector and the vector of the Earth's motion). Think of the appearance of snow in the headlights as you drive down the road. Each snowflake is traveling in the same direction as all the other snowflakes, but you see them radiating outward from a point ahead of the car.
Chris

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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Chris Peterson » Sat Aug 14, 2021 9:42 pm

Eclectic Man wrote:
Sat Aug 14, 2021 8:58 pm
What is happening at the end of the meteor trail? It looks as if the meteor has split in two and the parts flown apart and at least one bit seems to be following a curved path.

Any explanations?
That's not the trail, it's the train. Dust and ionized gas that persists for seconds or minutes after the meteor has burned up, and which is blowing in high altitude winds. It shows up because this is a long exposure, even though the meteor itself only lasted a second or two.
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Chris Peterson » Sat Aug 14, 2021 9:54 pm

De58te wrote:
Sat Aug 14, 2021 11:41 am
I just saw 3 in a row in about 3 minute time some 2 hours ago. From my bathroom window. I thought "Oh cool, the skies have cleared and the meteor shower is occurring." Then I thought "Holy (you know what) it is 5 AM and I am too tired for this. Going back to bed."
I stayed in bed. But my camera never sleeps. 297 Perseids over the last 7 nights, most the last three nights. (Another 106 meteors that are associated with other active showers are not in this composite.)
_
2021-Perseids-(per-spo)-2.jpg
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by johnnydeep » Sun Aug 15, 2021 6:45 pm

Chris Peterson wrote:
Sat Aug 14, 2021 9:36 pm
johnnydeep wrote:
Sat Aug 14, 2021 8:07 pm
Ok, so I haven't thought much about meteor showers before, but now have two questions:

1. The text mentions that this meteor was caused by a piece of dust travelling at 60 km/s through the rarefied upper atmosphere. A mere spec of dust - perhaps sand grain sized as suggested by the title - can really appear this spectacular? Also, how do we really know how big these particles are? I assume they range in size.
There is a reasonably reliable relationship between luminous flux and mass. So as a rule, if we have a photometric measurement we can estimate mass. And if we know what it is made of, we can go from mass to size. In fact, this meteor produced a persistent train, so it was almost certainly larger than a grain of sand. Probably more like the size of a marble.
2. Here comes my lack of 3D visualization skill again: Why do these always appear to radiate from a point in Perseus? Is it always the exact same point on the celestial sphere or is it moving over time? I would think that since the cause of these meteors is the Earth passing through the Sun-orbiting debris left behind after the passage of comet Swift-Tuttle, that the point where Earth crossed its path wouldn't remain fixed. Hmm, thinking some more, I guess orbits are pretty fixed in space after all (except for slow precession over time - https://en.wikipedia.org/wiki/Apsidal_precession) so that if two orbits cross once, they will continue to cross periodically for quite a while.
Indeed, the orbit of the particles for any given shower is quite stable. The particles are cleared from the orbit, either towards or away from the Sun, by various forces over a period of a few thousand years. If there is still an active comet in the orbit, the particles are replenished near each perihelion. But comets aren't active forever, either. So showers are short lived in astronomical terms- typically no more than a few thousand years.

The radiant is a vanishing point illusion. The meteors are all moving parallel to each other, coming from the direction of their radiant (actually, from an apparent direction that depends both on their actual vector and the vector of the Earth's motion). Think of the appearance of snow in the headlights as you drive down the road. Each snowflake is traveling in the same direction as all the other snowflakes, but you see them radiating outward from a point ahead of the car.
Thanks, Chris!
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by johnnydeep » Sun Aug 15, 2021 6:47 pm

Chris Peterson wrote:
Sat Aug 14, 2021 9:54 pm
De58te wrote:
Sat Aug 14, 2021 11:41 am
I just saw 3 in a row in about 3 minute time some 2 hours ago. From my bathroom window. I thought "Oh cool, the skies have cleared and the meteor shower is occurring." Then I thought "Holy (you know what) it is 5 AM and I am too tired for this. Going back to bed."
I stayed in bed. But my camera never sleeps. 297 Perseids over the last 7 nights, most the last three nights. (Another 106 meteors that are associated with other active showers are not in this composite.)
_
2021-Perseids-(per-spo)-2.jpg
So are the 4 (at least) that appear to be following quite different paths from the Perseids that are shown in your pic also from other active showers?
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Chris Peterson » Sun Aug 15, 2021 10:47 pm

johnnydeep wrote:
Sun Aug 15, 2021 6:47 pm
Chris Peterson wrote:
Sat Aug 14, 2021 9:54 pm
De58te wrote:
Sat Aug 14, 2021 11:41 am
I just saw 3 in a row in about 3 minute time some 2 hours ago. From my bathroom window. I thought "Oh cool, the skies have cleared and the meteor shower is occurring." Then I thought "Holy (you know what) it is 5 AM and I am too tired for this. Going back to bed."
I stayed in bed. But my camera never sleeps. 297 Perseids over the last 7 nights, most the last three nights. (Another 106 meteors that are associated with other active showers are not in this composite.)
_
2021-Perseids-(per-spo)-2.jpg
So are the 4 (at least) that appear to be following quite different paths from the Perseids that are shown in your pic also from other active showers?
They might be sporadics (which I lump in with the Perseids, because my system includes in sporadics anything it can't tie to a radiant, because the trail is too short or there's distortion near the horizon, or there's noise). But a few of them really will be sporadics. That said, the position of the radiant changes over the night (although the Perseid radiant is always above the horizon from my location), so you do end up with shower members that don't look like it.
Chris

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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by johnnydeep » Sun Aug 15, 2021 10:55 pm

Chris Peterson wrote:
Sun Aug 15, 2021 10:47 pm
johnnydeep wrote:
Sun Aug 15, 2021 6:47 pm
Chris Peterson wrote:
Sat Aug 14, 2021 9:54 pm


I stayed in bed. But my camera never sleeps. 297 Perseids over the last 7 nights, most the last three nights. (Another 106 meteors that are associated with other active showers are not in this composite.)
_
2021-Perseids-(per-spo)-2.jpg
So are the 4 (at least) that appear to be following quite different paths from the Perseids that are shown in your pic also from other active showers?
They might be sporadics (which I lump in with the Perseids, because my system includes in sporadics anything it can't tie to a radiant, because the trail is too short or there's distortion near the horizon, or there's noise). But a few of them really will be sporadics. That said, the position of the radiant changes over the night (although the Perseid radiant is always above the horizon from my location), so you do end up with shower members that don't look like it.
Ok. And what’s the cause of the dashed or dotted appearance of most of the streaks in your pic? I thought it might be related to length, but there are short ones that are dashed and some that aren’t.
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Chris Peterson » Sun Aug 15, 2021 11:28 pm

johnnydeep wrote:
Sun Aug 15, 2021 10:55 pm
Chris Peterson wrote:
Sun Aug 15, 2021 10:47 pm
johnnydeep wrote:
Sun Aug 15, 2021 6:47 pm


So are the 4 (at least) that appear to be following quite different paths from the Perseids that are shown in your pic also from other active showers?
They might be sporadics (which I lump in with the Perseids, because my system includes in sporadics anything it can't tie to a radiant, because the trail is too short or there's distortion near the horizon, or there's noise). But a few of them really will be sporadics. That said, the position of the radiant changes over the night (although the Perseid radiant is always above the horizon from my location), so you do end up with shower members that don't look like it.
Ok. And what’s the cause of the dashed or dotted appearance of most of the streaks in your pic? I thought it might be related to length, but there are short ones that are dashed and some that aren’t.
The dashed looking meteors are a consequence of their speed and the interlacing of the camera. Also dotted, if you look closely, are at least four star trails and Jupiter's trail.
Chris

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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by johnnydeep » Mon Aug 16, 2021 12:58 pm

Chris Peterson wrote:
Sun Aug 15, 2021 11:28 pm
johnnydeep wrote:
Sun Aug 15, 2021 10:55 pm
Chris Peterson wrote:
Sun Aug 15, 2021 10:47 pm


They might be sporadics (which I lump in with the Perseids, because my system includes in sporadics anything it can't tie to a radiant, because the trail is too short or there's distortion near the horizon, or there's noise). But a few of them really will be sporadics. That said, the position of the radiant changes over the night (although the Perseid radiant is always above the horizon from my location), so you do end up with shower members that don't look like it.
Ok. And what’s the cause of the dashed or dotted appearance of most of the streaks in your pic? I thought it might be related to length, but there are short ones that are dashed and some that aren’t.
The dashed looking meteors are a consequence of their speed and the interlacing of the camera. Also dotted, if you look closely, are at least four star trails and Jupiter's trail.
So are the dashed ones are the faster ones or the slower ones? And wouldn't all the Perseids be moving at about the same speed? Now, if I only knew which one was Jupiter and which ones were star trails. I've numbered a few here with #4 pointing to a very faint thin one. And did I even catch Jupiter? And what span of time does your image represent?

Perseid Trails Et Al.JPG
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by Chris Peterson » Mon Aug 16, 2021 11:58 pm

johnnydeep wrote:
Mon Aug 16, 2021 12:58 pm
Chris Peterson wrote:
Sun Aug 15, 2021 11:28 pm
johnnydeep wrote:
Sun Aug 15, 2021 10:55 pm


Ok. And what’s the cause of the dashed or dotted appearance of most of the streaks in your pic? I thought it might be related to length, but there are short ones that are dashed and some that aren’t.
The dashed looking meteors are a consequence of their speed and the interlacing of the camera. Also dotted, if you look closely, are at least four star trails and Jupiter's trail.
So are the dashed ones are the faster ones or the slower ones? And wouldn't all the Perseids be moving at about the same speed? Now, if I only knew which one was Jupiter and which ones were star trails. I've numbered a few here with #4 pointing to a very faint thin one. And did I even catch Jupiter? And what span of time does your image represent?
Perseids all move at the same speed through space and the atmosphere. They do not have the same angular speed across the sky. Consider one that is coming directly from the radiant. It is moving straight towards you and doesn't appear to move at all. The farther the meteor is in the sky from the radiant, the greater its apparent speed.

The really bright fireball near "270" occurred at 2021-08-10 04:47:36 MDT. So it definitely isn't pointing back at the Perseid radiant. Almost certainly this is a true sporadic. You can see information about this event, including a video, here.

Here's an annotated image with my best estimate for the stars causing the trails. You can hover over it to hide the annotation.
_
Click to view full size image 1 or image 2
Chris

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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by johnnydeep » Tue Aug 17, 2021 1:11 pm

Chris Peterson wrote:
Mon Aug 16, 2021 11:58 pm
johnnydeep wrote:
Mon Aug 16, 2021 12:58 pm
Chris Peterson wrote:
Sun Aug 15, 2021 11:28 pm


The dashed looking meteors are a consequence of their speed and the interlacing of the camera. Also dotted, if you look closely, are at least four star trails and Jupiter's trail.
So are the dashed ones are the faster ones or the slower ones? And wouldn't all the Perseids be moving at about the same speed? Now, if I only knew which one was Jupiter and which ones were star trails. I've numbered a few here with #4 pointing to a very faint thin one. And did I even catch Jupiter? And what span of time does your image represent?
Perseids all move at the same speed through space and the atmosphere. They do not have the same angular speed across the sky. Consider one that is coming directly from the radiant. It is moving straight towards you and doesn't appear to move at all. The farther the meteor is in the sky from the radiant, the greater its apparent speed.

The really bright fireball near "270" occurred at 2021-08-10 04:47:36 MDT. So it definitely isn't pointing back at the Perseid radiant. Almost certainly this is a true sporadic. You can see information about this event, including a video, here.

Here's an annotated image with my best estimate for the stars causing the trails. You can hover over it to hide the annotation.
_
Click to view full size image 1 or image 2
Perfect, thanks for taking the time! [ I'll have to use that hover image feature sometime, though I don't think it will work with uploaded images, just urls. ]
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Re: APOD: Island Universe, Cosmic Sand (2021 Aug 14)

Post by neufer » Tue Aug 17, 2021 3:10 pm

Of the Perseids that pass within 2 earth radii of the center of the Earth 3 out of 4 miss the Earth.

Those that just miss the Earth are deflected by about 2º ~ [(11 km/s)/(60 km/s)]2 radians.

The rest are deflected by 1º to 2º.
Art Neuendorffer