APOD: Perseids Around the Milky Way (2020 Aug 17)

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APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by APOD Robot » Mon Aug 17, 2020 4:05 am

Image Perseids Around the Milky Way

Explanation: Why would meteor trails appear curved? The arcing effect arises only because the image artificially compresses (nearly) the whole sky into a rectangle. The meteors are from the Perseid Meteor Shower that peaked last week. The featured multi-frame image combines not only different directions from the 360 projection, but different times when bright Perseid meteors momentarily streaked across the sky. All Perseid meteors can be traced back to the constellation Perseus toward the lower left, even the seemingly curved (but really straight) meteor trails. Although Perseids always point back to their Perseus radiant, they can appear almost anywhere on the sky. The image was taken from Inner Mongolia, China, where grasslands meet sand dunes. Many treasures also visible in the busy night sky including the central arch of our Milky Way Galaxy, the planets Saturn and Jupiter toward the right, colorful airglow on the central left, and some relatively nearby Earthly clouds. The Perseid Meteor Shower peaks every August.

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by Chris Peterson » Mon Aug 17, 2020 4:17 am

APOD Robot wrote:
Mon Aug 17, 2020 4:05 am
All Perseid meteors can be traced back to the constellation Perseus toward the lower left, even the seemingly curved (but really straight) meteor trails.
Well... almost straight. In actuality, the meteor paths really are curved, as gravity pulls the hypersonic meteoroids towards the center of the Earth. That deviation from a straight path is not visible to the eye, but is readily measured by well calibrated cameras.
Chris

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A vent

Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by A vent » Mon Aug 17, 2020 6:08 am

Tails curling. The sky is falling. And Betelgeuse is belching. Then the sun falls to the night. Tommorow will be bright. So, long as we have sight? If only to see those tails curling.

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by orin stepanek » Mon Aug 17, 2020 10:28 am

PerseidBridge_Zhang_1080_annotated.jpg
A busy photo; but still nice! :D
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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by neufer » Mon Aug 17, 2020 1:48 pm

Chris Peterson wrote:
Mon Aug 17, 2020 4:17 am
APOD Robot wrote:
Mon Aug 17, 2020 4:05 am

All Perseid meteors can be traced back to the constellation Perseus toward the lower left, even the seemingly curved (but really straight) meteor trails.
Well... almost straight. In actuality, the meteor paths really are curved, as gravity pulls the hypersonic meteoroids towards the center of the Earth. That deviation from a straight path is not visible to the eye, but is readily measured by well calibrated cameras.
  • Spacetime is curved; meteor paths are straight.
Art Neuendorffer

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by Chris Peterson » Mon Aug 17, 2020 2:05 pm

neufer wrote:
Mon Aug 17, 2020 1:48 pm
Chris Peterson wrote:
Mon Aug 17, 2020 4:17 am
APOD Robot wrote:
Mon Aug 17, 2020 4:05 am

All Perseid meteors can be traced back to the constellation Perseus toward the lower left, even the seemingly curved (but really straight) meteor trails.
Well... almost straight. In actuality, the meteor paths really are curved, as gravity pulls the hypersonic meteoroids towards the center of the Earth. That deviation from a straight path is not visible to the eye, but is readily measured by well calibrated cameras.
  • Spacetime is curved; meteor paths are straight.
Well, that would be true in a vacuum. The situation is somewhat complicated by aerodynamic effects, however.
Chris

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by Sa Ji Tario » Mon Aug 17, 2020 2:23 pm

Chris wrote
RJN wrote

In a vacuum some laws will be fulfilled, but when a meteor does not point exactly to the center of the Earth, the dynamic effects of the atmosphere and gravity modify the straightness of the trajectory (to the best of my knowledge and understanding)

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by Chris Peterson » Mon Aug 17, 2020 2:33 pm

Sa Ji Tario wrote:
Mon Aug 17, 2020 2:23 pm
Chris wrote

In a vacuum some laws will be fulfilled, but when a meteor does not point exactly to the center of the Earth, the dynamic effects of the atmosphere and gravity modify the straightness of the trajectory (to the best of my knowledge and understanding)
Art's point (a fine one, in both senses of the word) was that paths apparently curved by gravity alone are, in the mathematics of general relativity, actually straight lines (geodesics) through curved spacetime. The ballistic path we observe for a meteor can be thought of as straight, even though it is curved in the 3D manifold we directly observe. My response to that was that when we consider the effects of the gas the meteoroid is moving through, the actual shape of the path is no longer dictated by gravity alone.
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Sa Ji Tario

Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by Sa Ji Tario » Mon Aug 17, 2020 3:07 pm

Correct and thanks

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by johnnydeep » Mon Aug 17, 2020 3:36 pm

APOD Robot wrote:
Mon Aug 17, 2020 4:05 am
Image Perseids Around the Milky Way

Explanation: Why would meteor trails appear curved? The arcing effect arises only because the image artificially compresses (nearly) the whole sky into a rectangle. The meteors are from the Perseid Meteor Shower that peaked last week. The featured multi-frame image combines not only different directions from the 360 projection, but different times when bright Perseid meteors momentarily streaked across the sky. All Perseid meteors can be traced back to the constellation Perseus toward the lower left, even the seemingly curved (but really straight) meteor trails. Although Perseids always point back to their Perseus radiant, they can appear almost anywhere on the sky. The image was taken from Inner Mongolia, China, where grasslands meet sand dunes. Many treasures also visible in the busy night sky including the central arch of our Milky Way Galaxy, the planets Saturn and Jupiter toward the right, colorful airglow on the central left, and some relatively nearby Earthly clouds. The Perseid Meteor Shower peaks every August.
I see two apparent trails that don't point like the others: in fact, they are almost perpendicular to the other trails. Are they also Perseids, or perhaps something else, like satellites?
Perseid Trails or Something Else.JPG
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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by neufer » Mon Aug 17, 2020 4:24 pm

Chris Peterson wrote:
Mon Aug 17, 2020 2:33 pm

Art's point (a fine one, in both senses of the word) was that paths apparently curved by gravity alone are, in the mathematics of general relativity, actually straight lines (geodesics) through curved spacetime. The ballistic path we observe for a meteor can be thought of as straight, even though it is curved in the 3D manifold we directly observe. My response to that was that when we consider the effects of the gas the meteoroid is moving through, the actual shape of the path is no longer dictated by gravity alone.
Assuming most of the aerodynamic forces are due to pure drag; meteors maintain straight (geodesic) lines through curved spacetime.

Once hit (indoor) badminton shuttlecocks travel in straight (geodesic) lines (at light velocities) through barely curved spacetime.
Art Neuendorffer

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by Chris Peterson » Mon Aug 17, 2020 4:28 pm

neufer wrote:
Mon Aug 17, 2020 4:24 pm
Chris Peterson wrote:
Mon Aug 17, 2020 2:33 pm

Art's point (a fine one, in both senses of the word) was that paths apparently curved by gravity alone are, in the mathematics of general relativity, actually straight lines (geodesics) through curved spacetime. The ballistic path we observe for a meteor can be thought of as straight, even though it is curved in the 3D manifold we directly observe. My response to that was that when we consider the effects of the gas the meteoroid is moving through, the actual shape of the path is no longer dictated by gravity alone.
Assuming most of the aerodynamic forces are due to pure drag; meteors maintain straight (geodesic) lines through curved spacetime.

Once hit (indoor) badminton shuttlecocks travel in straight (geodesic) lines (at light velocities) through barely curved spacetime.
Indeed. But meteoroids are not spherical, and high resolution imagery of them in flight demonstrates that their path is remarkably erratic (all the more since all but the smallest also fragment as they travel).
Chris

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by Chris Peterson » Mon Aug 17, 2020 7:34 pm

johnnydeep wrote:
Mon Aug 17, 2020 3:36 pm
I see two apparent trails that don't point like the others: in fact, they are almost perpendicular to the other trails. Are they also Perseids, or perhaps something else, like satellites?

Perseid Trails or Something Else.
On my peak night, the camera caught 150 meteors total.

116 Perseids
21 Alpha Capricornids
7 Kappa Cygnids
6 Southern Delta Aquarids

So about one quarter of all the meteors were something other than Perseids.
Chris

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by neufer » Mon Aug 17, 2020 7:45 pm

neufer wrote:
Mon Aug 17, 2020 4:24 pm

Assuming most of the aerodynamic forces are due to pure drag; meteors maintain straight (geodesic) lines through curved spacetime.

Once hit (indoor) badminton shuttlecocks travel in straight (geodesic) lines (at light velocities) through barely curved spacetime.
My bad(minton?) :!: :oops:

All "true" forces result in curved motion in spacetime.
Art Neuendorffer

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Re: APOD: Perseids Around the Milky Way (2020 Aug 17)

Post by johnnydeep » Mon Aug 17, 2020 8:24 pm

Chris Peterson wrote:
Mon Aug 17, 2020 7:34 pm
johnnydeep wrote:
Mon Aug 17, 2020 3:36 pm
I see two apparent trails that don't point like the others: in fact, they are almost perpendicular to the other trails. Are they also Perseids, or perhaps something else, like satellites?

Perseid Trails or Something Else.
On my peak night, the camera caught 150 meteors total.

116 Perseids
21 Alpha Capricornids
7 Kappa Cygnids
6 Southern Delta Aquarids

So about one quarter of all the meteors were something other than Perseids.
Thanks - good to know!
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