Tips for spliting Sirius...

[Craig.a.c (Craig)]

I was wondering if anyone could give me some tips on how to slpit sirius.
I have been using an ND filter at 100x and higher magnifications but just can't seem to split it. I have even tried viewing in and out of focus.

Cheers - Craig.

[PhilW]

Here's a few random ideas:
1) Use a cooling fan on your mirror to get it down to ambient temperature
2) Make sure your collimation is spot on
3) Try when it's high in the sky & you're viewing through less atmosphere
4) Keep trying. Close doubles can be very sensitive to seeing conditions. A case in point is Antares: some nights I can split it with ridiculous ease, & other nights not at all.

[Craig.a.c (Craig)]

Thanks PhilW.
I always have the cooling fan running for atleast an hour before I start to observe. As for the collimation, its not spot on but is pretty good at the moment (as far as I can tell).

[astro_south (Andrew)]

I found earlier this year that chasing it in the twighlight made it easier to see. I think this has to do with less contrast between Sirius and the background. It was still within the flare of Sirius, but it was a persistent dot within the flare. Perhaps the early morning is the way to go after leaving your scope out all night. Sirius will be high in the sky and the seeing is likely to have settled. It is also handy to know where to look, and from memory the Pup was following Sirius across the sky - that narrows it down for you

[leon]

Errr. maybe an axe, sorry couldn't help myself, just stuffing around, other than that I don't have the slighest idea.

Leon

[Starkler (Geoff)]

Excellent seeing is whats required. The type you only see a handful of times each year ( in Melbourne anyway) .

That, and some patience at the eyepiece waiting for those moments of great seeing.

[ausastronomer (John Bambury)]

Hi Craig,

As Geoff indicated the critical thing is good seeing. Other factors mentioned by other posters are also important.

1) A well cooled scope. Depending on temperature variance from day to night and the rate of temperature drop during the night, you might need maybe 3 to 4 hours at least, not 1 hour. I have had nights where my 10" newt has taken well over 3 hours to properly equilibrate, and the images settle properly. I have had nights where my 18" Obsession has not equilibrated all night; and images were still dancing at dawn, with the rising sun coming over the horizon. IISAC 2007 at Lostock where temperatures ranged from >40° C by day to <10° C at night was clear evidence of this. From sun down to sun up the scope never caught up to the rapidly falling air temperature on each of the 3 nights, with high power images turning to complete mush.

2) A well collimated scope. Close enough isn't good enough IMO for high power work.

3) Sirius needs good elevation so you are looking through less atmosphere.

The goal is to try the split at higher magnifications which increases the "apparent" distance between the primary and secondary. All of the above factors contribute to your ability to "crank the power up" and keep the airy disk of Sirius as small in size as possible so that the diffracted light does not interfere with the dim view of Sirius B.

The larger the telescope the better because as aperture increases the size of the airy disk of any star decreases, in this case the primary, increasing the apparent gap between primary and secondary.

I have split it in my 10" scope at 300X and you should be able to split it in your 12" scope at that power, or near it. You are going to struggle at 100X because it is rare you would get seeing and other influencing factors good enough to give you adequate separation at that power. However, there may be the odd very rare night you could do it. When seeing and conditions permit, it is an easy split in my 18" at 300X.

Cheers,
John B