Testing limits of CPC 1100 at 2800 meters altitude location

[beka]

Hi everyone, I am located at an altitude of 2800 meters and I wish to check how much of an advantage this is for visual astronomy. So far I have not tried to push the limits of the CPC 1100. Recenty I have viewed Saturn with a 9mm eyepiece (311X) and it looked sharp enough to take even more magnification. What would be a challenging test for this telescope, like maybe a close double star?

[baggywrinkle]

I would have thought that with 2800 meters of less dense air to see through even naked eye seeing should be streets ahead of sea level.

What sort of ground is around your observing area? How quickly can it lose heat or heat up?

Why not just try more magnification?

[ronin]

It is never really possible to say, simply what you might say is OK I might say is poor.

Used to read a lot of posts where when just about everyone was having trouble getting 120x-150x one person was "always" getting 300x and higher. They seemed to be heavily of the opinion that a big image was always better, almost to the exclusion of all else, and that is fine if it is what you want.

Splitting a double is when you can just tell there are 2 stars there from the sort of figure of 8 that the 2 airy discs make, which is a big difference to looking at Albireo, Almaak and others and getting two distinct stars. However both are defined as having split a double star.

So the capabilities of the scope will depend on what it is that you consider the important factors and to what extent.

[beka]

My observing area is residential with some lawns. I have tried higher magnification than 311x on Saturn and Jupiter but I do not think I saw any further detail. Short of serious scientific stufff with cameras and so on I was thinking that double stars would be a good test. The best observatory sites are said to have a seeing of 0.4 arcseconds. The CPC manual  gives resolutions 0.50 and 0.42 arcseconds( for Rayeigh Criterion and Dawes Limit which I do not understand). I do not expect to get near this but shouldn't it be possible to check if double stars with separations of say 1 to 2 arcseconds are split visually?

[beka]

I found a list of double stars at the Sky and Telescope site and on that list is b398 with a separation of 1.8 arcseconds. Members are Mag 8.7 and 8.8 so I think this would be a good test. Problem is I don't know how to find this star. Which catalog follows this designation. I searched on Stellarium but it does not know this star.

[John]

Sub-arc second pair would be a harder test I'd have though. My little 4" refractor can split an equal brightness double with 1.6 arc seconds separation without too much difficulty and I'm only 300 ft above sea level !

[ollypenrice]

You won't find many (or any?) members with experience of tropical observing sites at nearly 3000 metres elevation. In principle altitude is good and in practice it usually is as well. Almost invariably? Well, wind can be a devil.

You're in an unusual position and should experiment. This should be fun!

Olly

[Merlin66]

If you try Cartes du Ciel software, you can download the Washington Double star catalogue and use that to identify suitable targets....

The difference between the Rayliegh and Dawes limit is the amount of overlap of the Airy disks of the two stars.

If you apply a high magnification to a third mag star, what do you see?? If you have good collimation you should see a small tight circle (Airy disk) surrounded by faint rings.....

[beka]

If the 4' can do 1.6 arcsecs then I should try for tighter doubles I guess. I will download the WDS catalog for Cartes Du Ceil and try to test over this weekend. Merlin66 - thanks for the explanation on the Rayliegh verses Dawes measurements. I had collimated the scope some time back but I will check if it is needed. Will let you all know how things turn out.

[beka]

I did not manage to download Cartes du Ceil on the family computer running Windows 8 (could not tether to my phone).I checked castor (2 arcsecond separation) and with a 9mm eyepeice the space between the stars looked large enough that 1 arcsecond seems possible. I also spent some time on the trapezium in Orion. The 5th and 6th stars were easy but I could see the seeing conditions changing every few minites so that at times they would almost blur out of view. I checked Jupiter at around 45 degree altitude and could managed to see the equatorial plus north and south temperate belts but little detail. On Jupiter I have seen much better other times. I will continue to try to push the limits but I think this last wasn't the best day.

[John]

If Orion is well placed for you, the star Alnitak (zeta Orionis), the lowest (from the UK) of the 3 "belt" stars, is a nice challenge. I think the separation of the close pair is around 3 arc seconds but there is quite a brightness difference which adds to the challenge. Another good close double in Orion is the nearby Eta Orionis where the A & B componants are separated by 1.8 arc seconds. 

Have fun !

[alan potts]

I guess that at 2,800m the one thing you will not have near by is a City, so straight away your going to be at a dark site. The only thing that I would have thought would spoil things is water vapour in the air and heat. though of course you will be cooler higher up. I am at 650 meters and I fully believe that helps and for you at the very least you have 2800m less air to loo through.

Alan

[beka]

Hi Alan, I wish that I was not near a city but actually I am in the outskirts of Addis Ababa our capital :-) The sky is not very dark, about Magnitude 4.5 to 5 my estimate would be. Orion is well placed so I will check out the stars you mentioned.

[beka]

Thanks for your suggestions John, last statement above was for your post. Will check out the stars you mentioned. I am kind of new to this forum so could I just ask, how do you enter the list of equipment you have at the end of each post?

[Merlin66]

You can add a signature panel, this will appear on every message you post.

Click the small arrow next to your name ( In the header bar, right hand side) and select "my profile"

Hope this helps.

[beka]

So I finally managed to check out Eta Orionis. I could see that it was split with a 15mm eyepiece (~187X) with a clear space between the stars. It was closer than Castor though. Searching on the Internet the current separation seems to be 1.5 arcsecs. Most people interested in double stars seem to use refractors. I don't think I have seen a comparison on "double star performance" between refractors and SCTs.

[John]

You can "up the bar" now then with 32 Orionis and 52 Orionis

They are a bit tougher ....

[beka]

Hi John,

I finally managed to view 52 Orionis (I tried 32 Orionis first but realized there was a branch in the line of sight). I could not see that it was double when doing a quick check with a 15mm eyepiece at 187x. I wasn't sure I had the right star at first so I did not look for very long. It was clearly split with a black gap between the stars with a 9mm eyepiece at 311x. Separation was even more clear at 400x with a 7mm Celestron Axiom eyepiece. Other people seem to be able to spit this star at magnifications lower than 200x so I do not know if the problem is with my eyesight or the quality of the eyepieces (apart from the axiom the other eyepieces are from the Celestron 1.25" eyepiece and filter kit).

All the best