splitting zeta orionis

[stevoggo (Stephen)]

Hi All,
I have been observing for about a year...i never realised how few nights this means I can get out...bad weather...moon too bright...i am too tired ...etc.
Anyway i have been out to the Pony Club onetime...and it was great...i have an 8"dob correctly collimated. On the night I was using a friends eyepiece...not sure what type ....but it was not super high magnification and I split Zeta Orionis, and viewed it no problem...i have since read that it is a three star system and thought I would revisit it and try to see the third star.
Except now...in my back garden...which is quite rural....except for the street light....I can't even see two stars!
On the astronomy now podcast it says Zeta orionis is easy to split...but I couldn't....
Was it just a bad night for viewing? are my plossels not good enough to split it? or was it light pollution?
I guess i am asking...how easy or hard is it to split Zeta Orion with an 8" dob...and If it is easy...why couldn't I last week?
Many thanks to all the great people who help the newbies in here
Steve
PS yes my scope was adjusted to the temperature...

[barx1963 (Malcolm)]

According to Haas's book the seperation of A and B Zeta Oionis is only 2.6", so you could need a fairly high power to split. Her observation aws at 200x, so what Ep and power were you using?
The C star is only 8.5 mag but is nearly a full minute away.

While you are in that part of the sky, try out Iota Orionis, sep on that one is 11.3", so will give you a clearer idea of resolving power of your scope and EPs.

Malcolm

[stevoggo (Stephen)]

Hi,
sorry I haven't got my eyepieces right here but I think my highest was a 9mm plossel...thanks for the advice I will try Ionis
Many thanks again...I'll reply once I have checked out the eyepieces..
Cheers
Steve

[stevoggo (Stephen)]

oops Iota

[barx1963 (Malcolm)]

I assume the Focal length of your scope is 1200mm which will give you 133x with a 9mm. To get 200x you would need a 6mm EP. I would think that 133 probably isn't enough to split. If you have a 5 or 6mm EP, it may be hard to use as eyerelief and and exit pupil are tight, so a barlow can help, a 2x barlow will give you 266x in the 9mm.

[Robh (Rob)]

According to the WDS catalog, zeta Orionis has components Aa,Ab, B and C.
Aa and Ab (mags 2 and 4) are spectroscopic, too close for visual observation.
B is mag 3.7, separation only 2.4". As Malcolm stated, you will need at least 200x and good seeing to split it from the primary.
Component C is given as mag 9.55 almost 60" away and is not particularly bright.

If you are after a really nice multiple star in Orion check out sigma (σ) Orionis. It is just off Alnitak (ζ) in the belt of Orion. It actually consists of five stars of magnitudes 6.3, 6.6, AB, 8.8 with separations of 41”, 13” and 11” from the primary AB. They should be easily separated at a magnification of 100x or more. The primary AB of magnitudes 4 and 5.3 is too close to split, components only 0.3” apart.

Regards, Rob.

[Coen]

Orion has no shortage of nice double stars, some personal favourites (subject to change):

• Trapezium (who does not mention this one?), challenge seeing the 5th & 6th stars depending on aperture and seeing, probably no issue with 8"
• Sigma (on the "sword" side of the belt), challenge seeing the red star with smaller aperture and has fainter nice almost mirrored triple nearby
• Eta (on the opposite to the sword side of the belt), nice close double test for seeing and aperture (3.6 & 4.9 at 1.7")
• Lambda (one of the triangle in the head/neck or Orion), lovely colours (3.5 & 5.5 at 4.3")
• Rigel has a nice companion close in with high magnitude difference (0.3 & 6.8 at 9.4")

Zeta is quoted as 1.9 & 3.7 at 2.4".

Have a look at: http://www.iceinspace.com.au/forum/s...ad.php?t=56206 for a member's pictures of a few of them, especially eta and sigma.