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Mysterious spikes on Sirius: Cause?

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21 replies to this topic

#1 Starman1

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Posted 05 December 2021 - 02:01 PM

On Friday night, I observed Sirius--the sky around it was quite dark right up to the star, and there were 4 strong spikes, of course, from the spider vanes on the scope.

 

But I noticed that, right at the star, there were numerous, too numerous to count, very small spikes coming out from the star about the same length as the diameter of the spurious disc.

 

I'm not sure I've ever noticed that before.  No dark lines in the very tiny spikes, and they were all uniform in brightness.

 

Does anyone think the cause is diffraction caused by a rough edge to the field stop in the eyepiece?

Or the lens in the eye?  Or the rough edge to the wooden baffles in my scope (2 above the mirror and the two UTA rings farther up)?

 

If it were simply a rough mirror surface, it would cause a uniform glow, but this was a smooth, perfectly round, spurious disc with maybe 300 distinct spikes about spurious disc diameter in length, coming

out from the star at every angle of the compass.  They didn't move, and didn't oscillate (seeing was superb).

 

Like this, only the number of spikes was much much larger, and they were very very short--the length of the width of the spurious disc:

https://www.istockph...16258-324855709

 

There is nothing that protrudes into my scope, so the mini-spikes had to be a diffraction caused by something else.

Can the atmosphere itself be a cause? 

 

A mystery, since no one else has ever commented about it in any posts I've read.


Edited by Starman1, 05 December 2021 - 02:04 PM.

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#2 The60mmKid

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Posted 05 December 2021 - 02:06 PM

Whatever the explanation, I move to henceforth refer to this phenomenon as "the hair of the dog."


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#3 Starman1

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Posted 05 December 2021 - 04:30 PM

A few further details:

No mirror clips in use.  I rotate them out of the way when using the scope.  My scope has a stop at +10°, so it can't go below that altitude.

 

The bevel on the edge of the mirror is at a sharp angle and throws all reflected light to the side.

 

This isn't a fuzziness, like that caused by rough optics, poor seeing, etc.

When that happens, the spurious disc is not distinct and smooth and round, as it was Friday night.

Usually, the Spurious disc is then a blob with spikes and focus is somewhat indeterminate.

 

It was distinctly a series of spikes, like diffraction spikes, but a LOT thinner and a LOT shorter.

And with darkness in between each of them.

All uniform in brightness and length.

 

But, oddly, no diffraction rings around Sirius at all--not one.  Just the spurious disc and these artifacts.

Lots of other stars had diffraction rings around them--usually just one.

I would have expected several rings, with each ring much fainter than the next inner.

But, no rings, just the super-short spikes.  Or maybe I should call them spikelets.

I've never seen that before, but it is a rare night when 500x yields a single diffraction ring around medium brightness stars, as on Friday night.

I could have gone much higher without image breakdown.



#4 EJN

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Posted 05 December 2021 - 05:15 PM

Did you try rotating you head to see if they rotated with it? I see spikes on bright stars from my eyes, but they are not uniform like what you describe.



#5 Starman1

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Posted 05 December 2021 - 05:40 PM

Did you try rotating you head to see if they rotated with it? I see spikes on bright stars from my eyes, but they are not uniform like what you describe.

I did not.  But I am totally familiar with astigmatism, and this wasn't it.

I was wearing glasses, but I did not see any such effects on dimmer stars or any stars that night.

Transparency was excellent, seeing was superb, and the relative humidity under 10%.

 

I am very familiar with spikes on stars when I don't wear my glasses.  But I was wearing glasses--a new prescription that corrects naked eye stars to tiny points.

Had there been just a few spikes or had spikes gone only in one direction, I would have blamed something else.

Contrast in the field was really great, with a black background in the field and tiny little pinpoint stars at 200x.

I also saw over a dozen stars in NGC206, so the scope was going very deep since seeing and transparency were excellent.

At higher power (~400x), 9 stars in the Trapezium were visible.

 

No such artifacts on any other star.  Even Rigel was a small spurious disc with a diffraction ring and its companion was very bright.

Only Sirius had the spikiness and it did not scintillate whatsoever.  Steady and sharp.

I'll post an illustration (I'd guess 1-2" in length):

Attached Thumbnails

  • Sirius.jpg

Edited by Starman1, 05 December 2021 - 05:41 PM.


#6 Keith Rivich

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Posted 05 December 2021 - 06:48 PM

On Friday night, I observed Sirius--the sky around it was quite dark right up to the star, and there were 4 strong spikes, of course, from the spider vanes on the scope.

 

But I noticed that, right at the star, there were numerous, too numerous to count, very small spikes coming out from the star about the same length as the diameter of the spurious disc.

 

I'm not sure I've ever noticed that before.  No dark lines in the very tiny spikes, and they were all uniform in brightness.

 

Does anyone think the cause is diffraction caused by a rough edge to the field stop in the eyepiece?

Or the lens in the eye?  Or the rough edge to the wooden baffles in my scope (2 above the mirror and the two UTA rings farther up)?

 

If it were simply a rough mirror surface, it would cause a uniform glow, but this was a smooth, perfectly round, spurious disc with maybe 300 distinct spikes about spurious disc diameter in length, coming

out from the star at every angle of the compass.  They didn't move, and didn't oscillate (seeing was superb).

 

Like this, only the number of spikes was much much larger, and they were very very short--the length of the width of the spurious disc:

https://www.istockph...16258-324855709

 

There is nothing that protrudes into my scope, so the mini-spikes had to be a diffraction caused by something else.

Can the atmosphere itself be a cause? 

 

A mystery, since no one else has ever commented about it in any posts I've read.

I see these little spikes all the time in my 25". Not sure the optical cause either, I'm curious.



#7 Tony Flanders

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Posted 06 December 2021 - 06:05 AM

Myopia is a first-order aberration; astigmatism is a second-order aberration; both are readily correctable with eyeglasses. Optical systems, most definitely including the human eye, also usually have strong third- and fourth-order aberrations, which are not readily correctable. I'm guessing that this "hair" is caused by your own eye, and is due to one of those higher-order aberrations. It's totally unsurprising that you would see it on Sirius and not any fainter star, just as you see diffraction spikes caused by your telescope's spider on bright stars but not on faint stars. Obviously the faint stars have spikes too, but on faint stars the spikes are too faint to see.


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#8 Starman1

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Posted 06 December 2021 - 10:23 AM

Tony,

 

You might be right.  It's also possible the higher order aberrations are in the eyepiece.

However, I have never read about this particular aberration or diffraction before--ever.

And I don't remember seeing it before--ever.  Apparently Keith has, though.

 

One possibility in the back of my mind was that telescope mirrors made on a machine will have radial swirls or lines

in the surfaces and even though a mirror maker like Carl Zambuto (the maker of the mirror in my scope) minimizes these with very fine polishing,

it is possible that in superb seeing this could cause a radial diffraction in the star image.  In normal seeing, what I saw would be masked by energy being

dumped into the diffraction rings and creating a bloated star image.

 

I often have excellent seeing at my home.  I should look for this with my 102mm Apo to see if it shows up in the refractor.

I usually don't spend much time looking at Sirius, but perhaps I should.



#9 Migwan

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Posted 10 December 2021 - 08:21 AM

Does it look the same with the other eye or are there differences?   


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#10 Starman1

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Posted 10 December 2021 - 12:01 PM

Yes, the same in both eyes and at all magnifications, though high power revealed it more.



#11 Migwan

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Posted 10 December 2021 - 04:30 PM

Good deal.  Not the eye.   



#12 Procyon

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Posted 19 December 2021 - 10:44 PM

Nice 4-5 page write up on Sirius in Burnham's Celestial Handbook volume 1. It's also called the sparkling star. Says it may have been a red star 2000 years ago. Who knows what's going on there now. Someone take some pics of it smile.gif.

It had more spikes than in this picture right? (From Burnham's book).

20211219_223729.jpg

Edited by Procyon, 19 December 2021 - 10:47 PM.


#13 Starman1

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Posted 20 December 2021 - 12:37 AM

Nice 4-5 page write up on Sirius in Burnham's Celestial Handbook volume 1. It's also called the sparkling star. Says it may have been a red star 2000 years ago. Who knows what's going on there now. Someone take some pics of it smile.gif.

It had more spikes than in this picture right? (From Burnham's book).

20211219_223729.jpg

The star had a spurious disc and at least a hundred small spikes sticking out maybe 1 to 1.5 arc seconds.

#14 Mr.Furley

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Posted 20 December 2021 - 07:30 PM

This obscured photo appears to show something like what you are describing?

https://3c1703fe8d.s...mageobscure.jpg
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#15 Starman1

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Posted 20 December 2021 - 07:58 PM

This obscured photo appears to show something like what you are describing?

https://3c1703fe8d.s...mageobscure.jpg

Yes, exactly. If the black in the center were the spurious disc.

I just can't figure where the diffraction comes from--perhaps just the way the atmosphere scatters light in exceptionally good seeing?



#16 Fiske

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Posted 20 December 2021 - 08:31 PM

I have seen small hair-like projections (filia) on bright stars in various binoculars, including an APM16x70 ED MS. A  beautiful and pleasing effect. No idea what causes it. wink.gif It would be interesting to know more about the phenomena.

 

 



#17 Astro_3lnr

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Posted 24 December 2021 - 04:53 PM

I did not.  But I am totally familiar with astigmatism, and this wasn't it.

I was wearing glasses, but I did not see any such effects on dimmer stars or any stars that night.

Transparency was excellent, seeing was superb, and the relative humidity under 10%.

 

I am very familiar with spikes on stars when I don't wear my glasses.  But I was wearing glasses--a new prescription that corrects naked eye stars to tiny points.

Had there been just a few spikes or had spikes gone only in one direction, I would have blamed something else.

Contrast in the field was really great, with a black background in the field and tiny little pinpoint stars at 200x.

I also saw over a dozen stars in NGC206, so the scope was going very deep since seeing and transparency were excellent.

At higher power (~400x), 9 stars in the Trapezium were visible.

 

No such artifacts on any other star.  Even Rigel was a small spurious disc with a diffraction ring and its companion was very bright.

Only Sirius had the spikiness and it did not scintillate whatsoever.  Steady and sharp.

I'll post an illustration (I'd guess 1-2" in length):

Was it Sirius A or B?



#18 Starman1

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Posted 24 December 2021 - 05:29 PM

Was it Sirius A or B?

Sirius A only.

And looked similar to the image linked in post 13.



#19 Astro_3lnr

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Posted 24 December 2021 - 05:57 PM

Sirius A only.

And looked similar to the image linked in post 13.

According to esahubble.org. The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system.

 

Hope this helps



#20 Starman1

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Posted 24 December 2021 - 06:56 PM

According to esahubble.org. The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system.

 

Hope this helps

Those are not the things being looked at in the image, nor are they the things being discussed.

If you look at the image in post 13, you'll see, in the blue glow surrounding the occulted image of Sirius, hundred of small faint radial spikes within the blue.

It is those small, faint radial spikes that are the topic of discussion.



#21 Astro_3lnr

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Posted 25 December 2021 - 06:40 PM

Those are not the things being looked at in the image, nor are they the things being discussed.

If you look at the image in post 13, you'll see, in the blue glow surrounding the occulted image of Sirius, hundred of small faint radial spikes within the blue.

It is those small, faint radial spikes that are the topic of discussion.

Do you have a real picture of it?



#22 Procyon

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Posted 25 December 2021 - 10:06 PM

Do you have a real picture of it?

lol.gif
 




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