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Max Wind speed for observing
Posted: Sat Feb 18, 2012 1:53 am
Has anyone got an opinion on what would be the maximum wind speeds for observing. I'm looking to go out with a friend tomorrow night but we have quite gusty wind here right now and according to the weather forecast the speed is 25mph just now. Looking forward to tomorrow night it should drop to about 11-13mph.
I've never been out with the scope in any kind of wind other than a small breeze and I'm worried about vibration caused by the wind ruining any steady views. As we know, at high magnifications, the least vibration can make viewing near impossible.
Has anyone been out in these conditions and did it ruin you're observing?
Posted: Sat Feb 18, 2012 9:04 am
The best view I ever had from a light polluted town was in a near gale, probably 50mph wind.
I was using a 123mm f/5 refractor on a mahogany garden tripod with simple brass altaz. pillar head.
The view was so good because very clean North Sea air had almost nil pollutants for the light to reflect off.
I clearly saw the two eyes in the Owl nebula and both parts of the Veil Nebula.
However, I protected myself by having the coal shed keep off direct wind.
No filters were used.
I suppose where you are there may be very dark skies.
And modern scopes may not be up to it. I don't think a lightweight modern set up is so good.
The mahogany tripod I used had little side area for the wind to blow on.
And no moving or lightweight flimsy parts.
You also have to realise that in the wrong location a 50mph wind can become 75mph by channeling of buildings or structures.
Many strong trees here were blown down by this effect.
The resultant wind speed was perhaps 90mph.
A very large tree missed my car by a foot.
Several enormous Cooling towers perhaps in Yorkshire, were demolished because the wind speed was drastically increased by the bad placement of several cooling towers and some city locations are notorious for this effect.
In Helsinki when it was minus 34C on certain city corners the slight wind was increased to give a wind chill of minus 50C.
So you need to seek shelter from the wind and reduce the wind speed acting on the scope.
I don't think a driven scope on a lightweight mount will be very good.
But I think with a wind speed of 25 mph reducing it to 15mph by shielding will work, but maybe not with the drive on.
Certainly 15x70 binoculars can be used in 25mph plus winds, but don't drop or knock the cheap versions with poorly secured prisms.
Hope this helps.
Posted: Sat Feb 18, 2012 9:07 am
I used a magnification of 75x in the above conditions with no problem.
When I say no moving parts the two axes were very firmly located so even a 50mph wind would not move them, although they were easily moved by hand.
The tension or friction was adjusted just by tightening the large brass bolts.
The three rigid mahogany legs would also not move as long as I held onto the tripod.
The coal shed probably reduced the 50mph wind to 30mph or 35 mph.
Posted: Sat Feb 18, 2012 10:35 am
In addition to the above I had a 150mm f/10 Maksutov Cassegrain mounted on an extremely sturdy Ex WD aluminium tripod. This had square channel legs in two sections and an extremely sturdy top.
I had a sturdy altaz head made for this.
The tripod would easily support a 150lb. person sitting on the top.
The tripod was not heavy nor was the scope.
It too could be used in very windy conditions.
So I would say that in such conditions a sturdy altaz is best.
I think there is an AZ4 Skywatcher mount ? that might be suitable.
The other way to go would be with a skeleton Newtonian where there is almost no side resistance.
Posted: Sun Feb 19, 2012 5:23 pm
Thanks for your replies.
I went out last night. A few miles down the coast and found a place which is quite open but was able to set up next to a bush which was about 5-6 ft tall to get a but of shelter. The wind speed was about 14 or 15 mph. We had beautiful clear skies.
I was able to observe Jupiter and its moons which were all in a straight line. Interestingly the wind didn't seem to cause too much vibration but the view of Jupiter wasn't great. I got good focus but it just didn't seem very sharp and therefore was difficult to see any real detail. I had a much better view from my garden 2 weeks ago which has street lights all around. I could see the bands no problem but not last night.
Last night I also observed Mars (for the first time) but the wind seemed to have other ideas. The vibration was just too much. I couldn't get a good look for long enough to try and pick out any detail. Still great to look at though. Also looked at the pliedes and M42 which I had no problems with at all. Spectacular as always. I then turned my attention to the andromeda galaxy which I have only observed once from my garden. That time, all I got was a faint fuzzy and had high hopes that I would see more detail last night in pretty dark skies. I was disappointed only to get a faint fuzzy again last night although it was still a beautiful site all the same.
We were planning to view Saturn once it came up high enough over the horizon at about midnight but a combination of the poor seeing, annoying winds and the cold overcame us and we headed home at about 10:30.
We still really enjoyed the night and look forward to the next one.
I have been tempted to upgrade my tripod and mount but in normal conditions the standard one does a good job so I think I'll put it down on the priority list a bit before renewing my broken motors and getting a webcam.
Posted: Sun Feb 19, 2012 6:12 pm
We went out with our local AS to one of our observing spots last night.
My view of Andromeda was as you described it too. A faint blur. Nothing like some of the views I have had in the past. I was unimpressed, but we did get to see a glimpse of M33 and in the same field of view... Which was nice
I was blooming cold last night. The wind made it unbearable at times.
It felt a lot colder than it did on the last outing where it went down to -4, even though it stayed above freezing. The wind was the killer!
I might stick to ham radio, at least I can do this in my warm radio shack
The view of the Double cluster in Perseus was quite nice. I could se it unaided. It looked nice through the scope. Pliedes, as always was a joy as was M42.
So general opinion was that viewing last night was far from ideal, but there were still a few jewels to see. We returned home about 22:00.
I might wait for Saturn to to appear early before venturing out again
Posted: Sun Feb 19, 2012 6:38 pm
Perhaps M32 not M33, which is a large low surface brightness galaxy not very near M31.
Best regards, David
Posted: Sun Feb 19, 2012 6:39 pm
Yes, the temp according to my car was 3 degrees but it felt much lower. I am also thinking of waiting until Saturn is up earlier before my next outing but you never know.
Posted: Sun Feb 19, 2012 8:28 pm
Perhaps it was 32, but this seems very close. They were on opposite edges of the view at X50. It was a tiny smudge, barely visible. Only noticeable using averted vision. Nice to see them both in the same view whatever they were.
Just been out in the garden and found M31 through the bins. The first time I've seen it from home