Scintillation of Sirius

[alan potts]

We all know that Sirius is famous for this scintillation effect. What I would like to know is, is scintillation a direct effect of seeing, as tonight I have never seen Sirius with so little as it is outside at the moment. The only problem is it is so windy I could not get a scope out on it, I am sure seeing the Pup will be easier.

I have seen this (the Pup) a good number of times but the star gets up to about 32 degrees above the horizon from here.

Alan

[acey]

Yes, the twinkling of stars is entirely due to turbulence in the atmosphere. The brighter the star, and the closer to the horizon, the more it will be seen to twinkle - which is why Sirius is so much noted for the effect. But even in high winds it's possible to have steady seeing, because the turbulence that disrupts seeing is an effect of heat differences in the air (like the shimmering effect seen on a very hot day). Air parcels at different temperature have different refractive indices, and this is what causes the shimmering or twinkling. But a mass of moving air at the same temperature will transmit light equally at all parts. Hence you could have a big air mass rushing past at gale force, and the seeing could be very steady.

[alan potts]

Acey,

It is not the wind that I am worried about for the seeing it is the fact that the scope will almost spin, it is really bad tonight even by UK standards. It is normally still as a mill pond, and I mean no wind at all, my Bresser W/station is telling me it's 40-45 K/h, no good for seeing anything.

Alan.

[alan potts]

Well the wind has dropped to a reasonable 15k/h and dropping off all the time. The sky out there to-night is just like you never see. I have a 70mm ED scope out and it is on Sirius, I have never seen this star so steady. It is clear white and forming a point of light for 10-15 seconds at a time with minimal scintillation in between. I am going to let it cool down better and see if I can see the pup star.

70mm scope, I don't even know if it is possible in so small but even at Mag 60 I really believe I can see it.

The problem I always have is I know where it is and have seen it a good few times in my mid-range scopes but never in my 12 inch. I do know one thing I have never seen a sky like this in the UK, not even when out night walking, as I have done many times. Believe it or not M41 is easily visible with the naked eye and I can see stars on the horizon without a scope. In binos they are steady and observable, it really is a sky you could sell in a shop.

I will let you know how I got on.

Alan.

[PeterW]

Few months ago. Came downstairs one night to find Sirius rock steady and even the stars at the bottom of canis major not twinkling.... Betthe imagers got some good Jupiter shots. Too cold and too late for me to go out. Always worth checking how much twinkling there is, especially lower down, give you a good indication ofnthe best things to go and try observing.

Peterw

[Robstargazer15]

Stars tend to twinkle while low in the sky. I have even seen stars twinkling near the zenith, rarely though.

[alan potts]

Well what a night. We talked earlier about scintillation, I could not see any on a star except Sirius and that was only every now and then. Even brighish stars way below Canis Major which you cannot see from England were still and without scitt' through a scope, albeit a small one.

Did I see the double star of Sirius: I looked for 2 hours in prestine conditions and I am going to say no! However I think I did, this could just be that I know exactly where it is. I always find that the many tiny aberations and scintillations that this star is famous for can so easily be mistaken for the Pup.

Jupiter was incredible through the 70mm at X120 and the Orion Nebula, well if I could not see the scope I would have thought I was using a much larger one. Even at a somewhat small X12 with a 35mm Panoptic the nebulosity was massive, so clear and clean was the sky. I was able to see all the trapezium stars at X30, well four of them.

Where I am I always get fabulous skies after rain and with wind, as last night the wind dies away and leaves a sky to die for or sell (I must work on that one, how to get it in a box). We had rain all day which cleared the 10 inches of snow, an extra 15 degrees of temperature as well as 40 K/H winds. Then by 10PM it was clear and still, wish you all could have a sky the same, if you got something like this once every 2 weeks, I bet I wouldn't read so many complaints about weather ( all justified ).

This morning at 5 oclock there was some scintillation back again, ( I did get 5 hrs sleep BTW) so over night it changed a little, Antares was the star with the problem this time, this is my next target for double splitting. From my balcony though I could see right down to the lower stars of the sting, so it was still clear. I have tried and tried with Antares but so far cannot see this one, I believe I am seeing it elongated and some greeny colour in there but this of course could just be down to conditions. I will be setting my alarm soon and having a go because I believe the secret to this one is early morning skies. There is of course always a down side, at 5 in the morning here in February it can be minus 25-30, that's cold! It is so cold that the scopes goto will only work on a mains supply and the handsets will not function properly.

Hope some of you enjoyed the report but I would sooner you all to have been here.

Alan.

[chiltonstar]

Sounds like you've got a nice location Alan! Even here, once or twice recently I've noticed that the seeing has been excellent, even with strong winds - as you say, sometimes Sirius barely twinkles and stars near the zenith are rock steady.

Roll on better weather so we can all go back to chasing some more challenging doubles!

Chris

[alan potts]

Chris,

I live in the middle of Bulgaria that is why I have such clear sky, no towns nearby.

Alan.

[alan potts]

What a difference a day makes, now it's twinkle twinkle little star but it is still low.

Alan.