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Sirius-ly freaking out

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#1 Colinstar

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Posted 06 December 2019 - 11:57 PM

So, I just went outside and my eyes were arrested as I looked up at the sky over Sioux Falls...what is THAT in the southwestern sky?

 

Oh...it must be a helicopter.

 

Well, that's what I thought at first, because the flashes appeared to extend the width of a full Moon.

 

It's Sirius, and tonight it is Sirius-ly freaking out.

 

It's flashing red and it's flashing blue.   

 

Does anyone else on this forum ever get mesmerized by the flashing of Sirius?

 

Okay, full disclosure:  I am mostly in to the aesthetics of the hobby and don't remember why these phenomena appear to happen.

 

I guess we can chalk it up to the area's below average transparency and poor seeing tonight; also maybe bad light pollution in this part of town?

 

Atmospheric disturbances?

 

Can any of those be the reasons?

 

What other factors are in play?


Edited by Colinstar, 06 December 2019 - 11:58 PM.

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#2 Napp

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Posted 07 December 2019 - 12:00 AM

Bad seeing caused by Sirius being low near the horizon so you are looking through much more of the earth's atmosphere.  Common with brighter stars near the horizon.  Can also produce an illusion of movement.


Edited by Napp, 07 December 2019 - 12:03 AM.

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#3 RyanSem  Happy Birthday!

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Posted 07 December 2019 - 12:06 AM

Love that, happens to me with Capella all the time too. 


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#4 Redbetter

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Posted 07 December 2019 - 02:19 AM

Southeastern sky perhaps?  Sirius is not in the southwest in the early evening this time of year.


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#5 MEE

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Posted 07 December 2019 - 03:30 AM

Venus is in the SW in the evening
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#6 JOEinCO

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Posted 07 December 2019 - 03:43 AM

Venus is in the SW in the evening

My thought, exactly....

 

Sirius hasn't risen yet in the early evening, and doesn't even break the horizon until about 9pm these days.


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#7 sg6

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Posted 07 December 2019 - 10:54 AM

Atmosphere acting a bit prism like.

Splits the light into colors - Sirius being White will have most of the sprectrum and a fair bit of blue. So colors are split and the light is also moved by the variable refraction so it comes into and out of view.

 

Capella is said to be better as it is a close double of about 500K difference in temperature so you have 2 different spectra being split and bounced around.



#8 JoeInMN

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Posted 07 December 2019 - 11:18 AM

Here is the Stellarium view from Minneapolis yesterday... A bright evening object in the southwest these days is most likely Venus. Being such a bright object, wobbling and flashing different colors through an unsteady atmosphere when low in the sky, makes it one of the traditional go-to explanations for UFO sightings.

 

stellarium_191206_sw.png



#9 Keith Rivich

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Posted 07 December 2019 - 03:54 PM

So, I just went outside and my eyes were arrested as I looked up at the sky over Sioux Falls...what is THAT in the southwestern sky?

 

Oh...it must be a helicopter.

 

Well, that's what I thought at first, because the flashes appeared to extend the width of a full Moon.

 

It's Sirius, and tonight it is Sirius-ly freaking out.

 

It's flashing red and it's flashing blue.   

 

Does anyone else on this forum ever get mesmerized by the flashing of Sirius?

 

Okay, full disclosure:  I am mostly in to the aesthetics of the hobby and don't remember why these phenomena appear to happen.

 

I guess we can chalk it up to the area's below average transparency and poor seeing tonight; also maybe bad light pollution in this part of town?

 

Atmospheric disturbances?

 

Can any of those be the reasons?

 

What other factors are in play?

Low altitude and turbulence...Sirius is a favorite to show kids when low in the sky. I'll take the scope slightly out of focus and let them take in all the colors.


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#10 clearwaterdave

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Posted 08 December 2019 - 04:02 PM

When Sirius is rising I have a good view of it from my recliner.,Some nights I liken it a disco ball.,Sometimes a little ca can be nice.,



#11 Rocklobster

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Posted 08 December 2019 - 10:23 PM

I find it very odd just how much more it scintillates than any other star. Even Venus doesn't and it's far brighter.

And yes, to reply to your original post, sometimes it goes totally crazy where I live as well.


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Edited by Rocklobster, 08 December 2019 - 10:24 PM.


#12 Colinstar

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Posted 09 December 2019 - 12:30 PM

Redbetter...correct...southeastern sky.   I was extremely tired when I wrote that.  I was in Sirius need of sleep!


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#13 Redbetter

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Posted 09 December 2019 - 04:07 PM

Redbetter...correct...southeastern sky.   I was extremely tired when I wrote that.  I was in Sirius need of sleep!

That is what I guessed, southeast.  While it could have been Venus if in the southwest, it is far less likely to shimmer and change color so much because Venus has considerable angular size, while Sirius is a point source.

 

FWIW I get east and west backward out here frequently, because the mountains are on the "wrong side" relative to the places where I grew up.  Nevermind that the big mountains were hundreds of miles away at the closest to me back then, and now they start only 20 minutes away. 



#14 Achernar

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Posted 09 December 2019 - 05:52 PM

When I see Sirius flashing blue, red, and every other color of the rainbow, I know the seeing is very poor or downright bad. That means either just using low-power eyepieces or simply trying again on another night.

 

Taras



#15 Frisky

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Posted 15 December 2019 - 03:17 AM

If you look below Sirius (south) you can find M41 A.K.A. the Little Beehive. It's a nice cluster, even in light-polluted skies.

 

Joe



#16 Dave Mitsky

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Posted 15 December 2019 - 03:31 AM

The colors are likely the result of atmospheric prismatic dispersion and the rapid scintillation caused by bad seeing.

http://www.astropix....l_story/vd.html

 

https://cseligman.co...cdispersion.htm

 

https://britastro.org/node/9058

https://scienceproje...winkling-stars/



#17 B l a k S t a r

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Posted 15 December 2019 - 01:33 PM

I've seen this effect vividly a number of times but the most outstanding was Alpha Centauri and Beta Centauri looking like a cop car chase from 13°N. Just couldn't hear the sirens. 




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