Atmospheric scintillation - A few shots I took of Sirius to demonstrate this phenomena

I've seen a few posts recently (and in the past) about "objects in the night sky that flash different colours". One of the more recent posts had a link to a long exposure photograph someone took of this phenomena which was talked about on C2C.

Having seen this phenomena before, and photographed the occasional star, I thought I'd try to recreate the effect seen in photographs like the one linked to above with a star that is well known to "flash various colours" or scintillate AKA "twinkle" - Sirius.

It was clear last night, and Sirius was twinkling fairly nicely, so I decided to set up a camera and have a go at photographing it. Visually, it seemed to mostly be twinkling blues and greens. I didn't notice any strong red or orange.

I didn't have much time (dinner was smouldering) but I managed to take 16 shots with a long lens and a DSLR on a fixed tripod. I also only managed to take exposures of 6.5 second length, even though I tried to change the exposure, but I was fumbling in the dark somewhat. I tried moving the camera around a little differently each time to get a variety of results. The best shots are posted below.

First is a shot of Sirius where I did not attempt to move the camera. Exposure details: 6.5 seconds @ F4 (ISO 800).


I found Sirius in my planetarium software. It's the star that is at the top right hand corner of the "About Sirius" window in this screenshot.


I've identified and labeled the 4 brightest stars in the following crop of the first photograph I posted accordingly, so there can be no doubt the bright object in the frame was Sirius :

A = Sirius
B = TYC 5954-737-1
C = TYC 5954-251-1
D = TYC 5953-3315-1


I zoomed in on my planetarium software a bit, and took this screenshot. As you can see, the four brightest stars in the previous image match up perfectly.


Now that the identity of the object is confirmed, here are a few shots where I moved the camera around a bit during the exposure, to simulate the camera shake that would be expected during a long exposure where the camera was hand held.

In this shot the colours came out quite nicely. Exposure details: 6.5 seconds @ F4 (ISO 800).


In this crop of the above image the colours can be seen a bit better.


In this shot I slightly defocused the lens, which resulted in this interesting effect. Exposure details: 6.5 seconds @ F4 (ISO 800).


Here's a crop of the above shot.



I think the effect matches very closely that seen in the C2C UFO photograph, keeping in mind that that photograph is probably at least 100% crop (perhaps even enlarged beyond the original size).

Try it for yourself. You don't need an expensive camera or lens. Any camera will do pretty much. Some quite interesting effects can be achieved with a little ingenuity, like this beautiful image which made NASA's APOD last year.


Related links:
Astro Bob
Sirius scintillation

Nice effect and interesting.

As to cause...

Do you suppose that the effect is the result of atmospheric instability resulting in the spectrum being diffused?

If multiple stars were given the same long exposure with shaken camera effect, would they all manifest similar color variations?

Hi thanks for your post.
What a good idea to move the camera etc and so bring out Sirius's spectrum.
I have a notion but only a notion as follows.
Sirius is the brightest star in our night sky - it appears to be brightest because it is so very near in relation to other stars - We view all stars through our atmosphere and so are viewing through our atmosphere which acts as a lens. What we are seeing is the light from Sirius inter acting with our atmosphere.
However the lens affect which is also like a magnifier fails when out of Earths atmosphere.
When asked about this - The Appolo 11 astronaughts said they had navigated by the stars with use of their instruments. Yet the navigator stated that he had not seen any stars by naked eye observation.
How strange that must have been - To be in complete black space with only Venus the Moon and the the Sun rising and setting.
Sirius is also known to be a double star (at least) Sirius A being the big blue star we see but also its invisible companion Sirius B an ancient White Dwarf Star. The cycle of Sirius B around A takes 50 years and is eleptical and it is said when it comes to its closest point to Sirius A it "excites" Sirius A drawing off matter from it's surface -Then when Sirius B reaches its futhest point it sheds this matter or material causing a shimmering affect.
Could it be that if we measured the shimmering it would increase more or decrease more over the said 50 year cycle?

reply to post by Frira


Yes if they were all bright enough for it. That's the thing why this works great with sirius.

Thanks OP. I've been tripping out on this all summer.. but does that explain why so many other stars do it or why ive watched and seen them move up,down and all over the place? I know next to nothing of astronomy ..
Also, why does it seems that there are an odd number of red/orange stars/planets out there? Any clarification would be very helpful.

reply to post by PhantomPlague


Red Orange stars are just that Red Orange stars. They are stars like Alderbaran and Betelguese that are generally older stars. They are in the process of shedding or expanding their outer layers - Some will eventually super nova. Our Sun will eventually turn into a giant red star but not for millions of years yet - so no worries.
Young stars are generally blue in colour - Our sun is said to be a yellow star - sorts middle aged.
Hope this helps

reply to post by C.H.U.D.


Very nice!

What camera and what focal length of lens did you use

The effect is caused by thermal instabilities in the atmosphere causing it to act as a weak lens. Since a star is basically a near point source of light the chromatic aberration is greatly exaggerated causing it to flicker between red and blue.

This is really cool, I love the effect, and how a "shaky hand camera" can actually bring it out for us to visualize! I had always thought the "twinkling" was supposed to have something to do with Sirius (and others) being a binary (or ternary) system, but I never really looked into the physics of why it causes the twinkle and the coloring.

I use to wonder why certain stars changed colour at night... Thank you for the pictures...

reply to post by C.H.U.D.


I did the same thing some months ago, with this result.



I don't remember what star I used as the target of my photo.

reply to post by ArMaP


Very nice shot - Must try this out myself
Thanks

Facinating results,whenever I see pictures of anything to do with the galaxy/planets I get this weird sinking,droping feeling in my stomach.

Thanks to everyone for the replies and comments.

I'll try and reply to a few of the posts now, but it's getting late and I'm going away for a few days.

Originally posted by Frira
As to cause...

Do you suppose that the effect is the result of atmospheric instability resulting in the spectrum being diffused?

Basically, yes.

If our atmosphere had a completely even temperature through out, we would not see the phenomena, but because of effects like "rising thermals", and sharp temperature differences between pockets of air that are next to each other, light is refracted/bent and split into it's constituent colours. Each pocket of air acts like a prism, when light from the star passes through it on it's way to your eye.

This is possible since how much the air bends light depends on it's temperature, which alters what is known as the "refractive index" of the medium (in this case air) that the light is passing through.

I think the best example most people will be familiar with is, on a very hot day, if you look across a long flat expanse of road/runway/concrete, you can "see" the heat rising and the air shimmering. That is what the air is doing when you are seeing a star twinkle.

Astro Bob does a good job of explaining how the phenomenon works.

Originally posted by Frira
If multiple stars were given the same long exposure with shaken camera effect, would they all manifest similar color variations?

It would depend on a number of factors. The main ones being:

Altitude above the horizon, which influences how much atmosphere you/the camera is having to see through. The thickest part of our atmosphere huggs the surface of earth, so if you are looking at a star that's on or close to the horizon, you will be seeing through much more atmosphere than if you look at a star that is directly above your head. The more atmosphere you are looking through, the more chance there is of seeing scintillation.

and

The brightness of the star.

Sirius is the brightest star visible from the Northern hemisphere, and because it never rises high above the horizon, it scintillates more than most.

The reason the planets don't scintillate as much as stars (although they still can scintillate) is because they are not as close to perfect point sources as stars are, due to them being relatively closer to us. There is a more detailed explanation of this here, at the bottom of the page.


reply to post by artistpoet


Interesting idea, but I think the ever changing nature of our atmosphere would overwhelm and mask any. subtle effects due to the binary nature of Sirius. It would certainly be a very challenging aspect to investigate.

Sorry for the delay, but I had to spend longer away than I was expecting. Anyway, back to the topic at hand...

Firstly, before I forget, there is one thing I would like to point out about the photographs I took,which is that where I did not move the camera much (or at all), the colors in the trails produced averaged out to white, which of course we all know is all of the colours of the visible spectrum combined. Where I moved the camera a bit more quickly, the colors came out much better in the trails.

In most of my shots, I either moved too fast or too slow to get very colourful trails, so do experiment a bit if you try this.

Originally posted by PhantomPlague
but does that explain why so many other stars do it or why ive watched and seen them move up,down and all over the place?

It's because whenever we look at a star, we are looking at it through our atmosphere, and our atmosphere is distorting what we are seeing.

As for the second part of your question, the autokinetic effect can make stars (and other things) appear to move about. Have a read of what I wrote about it recently here.

Originally posted by PhantomPlague
Also, why does it seems that there are an odd number of red/orange stars/planets out there? Any clarification would be very helpful.

artistpoet IMO did a good job of answering this question.

Originally posted by wmd_2008
reply to post by C.H.U.D.

 

What camera and what focal length of lens did you use

I used a Canon !Ds MkII and 600 mm lens. The camera is not "that" important though. Similar results as I got could be achieved with any camera capable of long exposure, and a reasonably long lens. The sensor on the camera I used is actually a bit of a disadvantage in this situation, although a long lens helps offset the disadvantage.

Originally posted by ArMaP
reply to post by C.H.U.D.

 

I did the same thing some months ago, with this result.

Nice shot, and thanks for re-posting it ArMaP

Now that I've seen it, I remember seeing it when you posted it before. I thought someone had tried it before but I couldn't remember who or when.