APOD: Perseids and MAGIC (2022 Aug 11)

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APOD: Perseids and MAGIC (2022 Aug 11)

Post by APOD Robot » Thu Aug 11, 2022 4:05 am

Image Perseids and MAGIC

Explanation: On August 11, 2021 a multi-mirror, 17 meter-diameter MAGIC telescope reflected this starry night sky from the Roque de los Muchachos European Northern Observatory on the Canary Island of La Palma. MAGIC stands for Major Atmospheric Gamma Imaging Cherenkov. The telescopes can see the brief flashes of optical light produced in particle air showers as high-energy gamma rays impact the Earth's upper atmosphere. To the dark-adapted eye the mirror segments offer a tantalizing reflection of stars and nebulae along the plane of our Milky Way galaxy. But directly behind the segmented mirror telescope, low on the horizon, lies the constellation Perseus. And on that date the dramatic composite nightscape also captured meteors streaming from the radiant of the annual Perseid meteor shower. This year the Perseid shower activity will again peak around August 13 but perseid meteors will have to compete with the bright light of a Full Moon.

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by Ann » Thu Aug 11, 2022 5:10 am

MagicPerseid001_1024[1].jpg
Perseids and MAGIC. Photo: Urs Leutenegger.
APOD 11 August 2022 annotated.png

To see the annotations in the picture at right, click to see full size.

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by MarkBour » Thu Aug 11, 2022 5:46 am

Ah, thanks for the labelling.
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by De58te » Thu Aug 11, 2022 10:33 am

Oh yeah, it's Perseid shower time this weekend! Thanks for reminding me. As I grow older the calendar dates seem to swarm together in a meaningless mob. Another day just like thousands of others come before. By the way, I presume the meteors are the long streaks and the gamma rays are the sparkling dots?

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by Chris Peterson » Thu Aug 11, 2022 1:21 pm

De58te wrote: Thu Aug 11, 2022 10:33 am Oh yeah, it's Perseid shower time this weekend! Thanks for reminding me. As I grow older the calendar dates seem to swarm together in a meaningless mob. Another day just like thousands of others come before. By the way, I presume the meteors are the long streaks and the gamma rays are the sparkling dots?
There are no gamma rays visible in this image! Did you forget to include some kind of ha-ha emoji with your comment?
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by orin stepanek » Thu Aug 11, 2022 1:38 pm

MagicPerseid001_1024.jpg
Ah! 8-) Nice telescope!
perseid11aug18-p.gif
Click on to see perseid! :wink:
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by DL MARTIN » Thu Aug 11, 2022 3:51 pm

What accounts for the break in the streak of some meteorites?

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by Fred the Cat » Thu Aug 11, 2022 4:02 pm

Chris Peterson wrote: Thu Aug 11, 2022 1:21 pm
De58te wrote: Thu Aug 11, 2022 10:33 am Oh yeah, it's Perseid shower time this weekend! Thanks for reminding me. As I grow older the calendar dates seem to swarm together in a meaningless mob. Another day just like thousands of others come before. By the way, I presume the meteors are the long streaks and the gamma rays are the sparkling dots?
There are no gamma rays visible in this image! Did you forget to include some kind of ha-ha emoji with your comment?
You may not be able to see them but they're sparkling there. :wink:
Sparkly Dots.jpg
:thumb_up:
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by VictorBorun » Thu Aug 11, 2022 5:36 pm

orin stepanek wrote: Thu Aug 11, 2022 1:38 pm MagicPerseid001_1024.jpg
Ah! 8-) Nice telescope!
perseid11aug18-p.gif
Click on to see perseid! :wink:
Funny way to snapshot it: the tricky reflection of the secondary mirror's upper leg makes it look like stretching all the way down to the bottom edge of the primary mirror.
As if we can support the secondary mirror from one side of the dish

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by VictorBorun » Thu Aug 11, 2022 5:38 pm

I wonder why a Cherenkov telescope would be so strange.
Why so many so small parts?
Why no dome to protect from the bad weather?

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by Ann » Thu Aug 11, 2022 6:31 pm

Sorry! My annotation was wrong! What I called the Lion Nebula is indeed just IC 1396, the Elephant Trunk Nebula! :oops:

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by johnnydeep » Thu Aug 11, 2022 7:45 pm

DL MARTIN wrote: Thu Aug 11, 2022 3:51 pm What accounts for the break in the streak of some meteorites?
I don't see any breaks in the streaks. But if I did, they would simply be caused by the non homogenous content of the meteor as it burned away.
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by johnnydeep » Thu Aug 11, 2022 7:46 pm

Alright, what's the cause of the blurriness in the reflection we see in top half of the mirror?
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by VictorBorun » Thu Aug 11, 2022 7:51 pm

johnnydeep wrote: Thu Aug 11, 2022 7:46 pm Alright, what's the cause of the blurriness in the reflection we see in top half of the mirror?
all streaks are parallel and close ones are of the same length.
They must be long-exposure stars' tracks.
Why some part of the sky in the mirror show longer star tracks, I don't understand

DL MARTIN

Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by DL MARTIN » Thu Aug 11, 2022 9:17 pm

In Orin Stepanek's lower entry, the meteorite had a break in its streak. I've seen it, myself in Canada. I thought it might be the meteorite bouncing off the atmosphere since the one I saw seemed parallel to the Earth.

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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by johnnydeep » Thu Aug 11, 2022 9:27 pm

DL MARTIN wrote: Thu Aug 11, 2022 9:17 pm In Orin Stepanek's lower entry, the meteorite had a break in its streak. I've seen it, myself in Canada. I thought it might be the meteorite bouncing off the atmosphere since the one I saw seemed parallel to the Earth.
Ah, THAT meteor streak and break! The same explanation applies. BTW, you can click the quote button to reply to a specific post to make it clear what you are referring to.
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by MarkBour » Thu Aug 11, 2022 11:33 pm

VictorBorun wrote: Thu Aug 11, 2022 7:51 pm
johnnydeep wrote: Thu Aug 11, 2022 7:46 pm Alright, what's the cause of the blurriness in the reflection we see in top half of the mirror?
all streaks are parallel and close ones are of the same length.
They must be long-exposure stars' tracks.
Why some part of the sky in the mirror show longer star tracks, I don't understand
Capture.JPG

This is just the way a parabolic reflector acts if you are off to the side of (an incomplete) paraboloid.
  • Recall that the great feature of a parabolic reflector is that it will gather light to a point.
  • What that would mean, if you're at the exact focus, is that someone far away could see your image reflected all over the surface -- stretched across it all.
  • We're off to the side of the dish. So only part of the dish is in the right orientation to be doing much gathering for us. That band from about 60% of the way up the dish to about 80% of the way to the top is in a position to somewhat spread imagery for you, so the star tracks there appear as stretched out line segments, more pronounced than the rest of the dish.
  • We're sort of just looking at a "funhouse mirror".
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by johnnydeep » Fri Aug 12, 2022 2:02 pm

MarkBour wrote: Thu Aug 11, 2022 11:33 pm
VictorBorun wrote: Thu Aug 11, 2022 7:51 pm
johnnydeep wrote: Thu Aug 11, 2022 7:46 pm Alright, what's the cause of the blurriness in the reflection we see in top half of the mirror?
all streaks are parallel and close ones are of the same length.
They must be long-exposure stars' tracks.
Why some part of the sky in the mirror show longer star tracks, I don't understand
Capture.JPG

This is just the way a parabolic reflector acts if you are off to the side of (an incomplete) paraboloid.
  • Recall that the great feature of a parabolic reflector is that it will gather light to a point.
  • What that would mean, if you're at the exact focus, is that someone far away could see your image reflected all over the surface -- stretched across it all.
  • We're off to the side of the dish. So only part of the dish is in the right orientation to be doing much gathering for us. That band from about 60% of the way up the dish to about 80% of the way to the top is in a position to somewhat spread imagery for you, so the star tracks there appear as stretched out line segments, more pronounced than the rest of the dish.
  • We're sort of just looking at a "funhouse mirror".
Thanks! That almost makes sense to me but I can't quite convince myself how far away things would look to an off axis observer looking at the mirror from a short distance as in this APOD. I'd think that you would see a more continuously varying stretching of images across the surface than what we see here, which seems to be a band of extreme stretching surrounded by almost no stretching across most of the rest of the mirror. I wish I had a small parabolic mirror to experiment with.
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by MarkBour » Fri Aug 12, 2022 4:39 pm

johnnydeep wrote: Fri Aug 12, 2022 2:02 pm Thanks! That almost makes sense to me but I can't quite convince myself how far away things would look to an off axis observer looking at the mirror from a short distance as in this APOD. I'd think that you would see a more continuously varying stretching of images across the surface than what we see here, which seems to be a band of extreme stretching surrounded by almost no stretching across most of the rest of the mirror. I wish I had a small parabolic mirror to experiment with.
By the way, I should apologize for sounding so sure of myself in my explanation. I think it's right, but as you think about it, it's good to be skeptical of it. In particular, I don't know how much, or in what ways this depends on our position relative to the mirror. Also, I am thinking that a fast exposure would not have shown so obvious of an effect, but once you get a long exposure with star tracks, even if they were only short tracks, then the mirror effect can exaggerate them. I don't think it can exaggerate perfect points of light, though it would still spread the distances between them (?)
Capture.JPG

Want a parabolic mirror to experiment with? I thought you'd never ask! The one in my previous image was stolen from an advertisement, and the owner was selling that mirror for $399. Or, a smaller one is quite economical. Here's one that's about 12" in diameter and going for about $35 on Amazon. I'm wondering if it is true, high-quality, parabolic, though.
:-)

Of course, any amateur's reflecting telescope will have such a mirror, but I don't want to rip apart mine to get a look at it off-center. I'd never get it back together just right, I think. And the only way to look at it in the scope is straight on.

I'd love to take a trip to La Palma to see these MAGIC scopes.
capture2.jpg
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by johnnydeep » Fri Aug 12, 2022 7:49 pm

MarkBour wrote: Fri Aug 12, 2022 4:39 pm
johnnydeep wrote: Fri Aug 12, 2022 2:02 pm Thanks! That almost makes sense to me but I can't quite convince myself how far away things would look to an off axis observer looking at the mirror from a short distance as in this APOD. I'd think that you would see a more continuously varying stretching of images across the surface than what we see here, which seems to be a band of extreme stretching surrounded by almost no stretching across most of the rest of the mirror. I wish I had a small parabolic mirror to experiment with.
By the way, I should apologize for sounding so sure of myself in my explanation. I think it's right, but as you think about it, it's good to be skeptical of it. In particular, I don't know how much, or in what ways this depends on our position relative to the mirror. Also, I am thinking that a fast exposure would not have shown so obvious of an effect, but once you get a long exposure with star tracks, even if they were only short tracks, then the mirror effect can exaggerate them. I don't think it can exaggerate perfect points of light, though it would still spread the distances between them (?)
Capture.JPG

Want a parabolic mirror to experiment with? I thought you'd never ask! The one in my previous image was stolen from an advertisement, and the owner was selling that mirror for $399. Or, a smaller one is quite economical. Here's one that's about 12" in diameter and going for about $35 on Amazon. I'm wondering if it is true, high-quality, parabolic, though.
:-)
That one looks like it shows continuously variable stretching (plus other distortions) across the whole of the mirror, not just in a band. Of course, the sky is a uniform blue, so it's impossible to tell what's happening there.
Of course, any amateur's reflecting telescope will have such a mirror, but I don't want to rip apart mine to get a look at it off-center. I'd never get it back together just right, I think. And the only way to look at it in the scope is straight on.

I'd love to take a trip to La Palma to see these MAGIC scopes.
...
There are those big "skeletal" DOBs that could be played with without disassembling them:
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by MarkBour » Fri Aug 12, 2022 10:20 pm

johnnydeep wrote: Fri Aug 12, 2022 7:49 pm There are those big "skeletal" DOBs that could be played with without disassembling them:
https://www.cloudynights.com/uploads/mo ... _thumb.jpg
Yes, if you could play with one of those, that ought to do it!
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Re: APOD: Perseids and MAGIC (2022 Aug 11)

Post by johnnydeep » Sat Aug 13, 2022 12:02 pm

MarkBour wrote: Fri Aug 12, 2022 10:20 pm
johnnydeep wrote: Fri Aug 12, 2022 7:49 pm There are those big "skeletal" DOBs that could be played with without disassembling them:
https://www.cloudynights.com/uploads/mo ... _thumb.jpg
Yes, if you could play with one of those, that ought to do it!
Yup, but sadly, I don't have one :(
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