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Reasonable wind speed for viewing?

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#1 yemtig

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Posted 22 October 2017 - 06:07 PM

What would be a reasonable max wind speed for viewing in a 10" dobsonian?  And since I'm in a high desert area, would a "dew shield" be beneficial for a "dust shield" since this is an open tube design.  Any experience would be helpful, I am just trying to figure most things out from the get go..

 

Mike



#2 csrlice12

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Posted 22 October 2017 - 06:38 PM

I usually go out at 10mph and below.  Above 15, forget it.  No dew/dust shield needed.  You'll want to get away from the ABQ and Santa Fe light domes.  The Chaco Canyon area is great.  Also the area between San Antonio (stop at the Owl Cafe for a green chili burger) and Ruiodoso is as dark as you can find anywheres.  There's also some ghost towns in that area for exploring.  The Jamez pueblo area isn't too far from you and is fairly dark.  If its a truss dob, you will want a shroud.


Edited by csrlice12, 22 October 2017 - 06:41 PM.

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#3 kfiscus

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Posted 22 October 2017 - 06:49 PM

Shrouds are usually great but they can act as sails when the wind picks up. I'll stargaze if it's below 20 mph. I can park my van near enough to my scope to block the wind if necessary. There is one good thing about wind- it can help keep the mosquitoes away...
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#4 Mike W.

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Posted 22 October 2017 - 06:55 PM

I see a problem with the game plan here, the green chili burger may before ,,,,,,,,,,,

 

and this being a thread about winds,,,,,,,,,,


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#5 Achernar

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Posted 22 October 2017 - 07:07 PM

If it's above 15 or 20mph, forget it. Your telescope could weathervane in the wind, and the turbulence generated will ensure poor seeing. I can't use my 15-inch in such conditions, and my 10-inch certainly won't be useable if the wind is above 20mph. It will also make it a lot colder for you. Also, you need a shroud for a truss tube to keep out stray light, wind currents and dust out of the light path. Your body heat can create currents of warm air in the light path too. A fabric shroud keeps all of that out of the light path. An additional baffle on the opposite side from the focuser will keep stray light from getting directly into the eyepiece.

 

Taras


Edited by Achernar, 22 October 2017 - 07:09 PM.


#6 Jon Isaacs

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Posted 22 October 2017 - 07:10 PM

Mike:

 

We all have our crosses to bear.  In some places , it's dew and pollen, gallons of insect repellent, short nights in the summer, cold nights in the winter.  For many,  clear nights are few and far between. 

 

For me and many others in the southwest, it's the wind and dust.  We have an anemometer and I will observe when the winds are between 20 mph and 30 mph but I will try to hide behind the garage or even move a car to try to block the wind.  I do choose the scope I'll use based on wind.  Under 15 mph, I'll use the 22 inch, over 20 mph, it'll be the 12.5 inch which is short and squat. 

 

Not everyone is as enthusiastic about observing in the wind and when it's cold,  it cuts the night short.  One night last year it was about 33° F and the wind was blowing between 25 mph-30 mph , I packed it in after 2 hours..  I think back..  I'm wonder,  what was I thinking? 

 

Your 10 inch Dob should quite good in the winds.  As far as protection,  I'd be more concerned about dust and sand finding it's way its way into the azimuth bearings,  it's only a few inches off the ground. 

 

When it's windy,  lower magnifications are in order.. 

 

Edit: my two larger Scopes do not have shrouds,  as Ken says,  they act as sails. When it's windy,  body heat is the least of ones problems. 

 

Jon



#7 yemtig

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Posted 22 October 2017 - 08:12 PM

Windy and cold describes my winter conditions quite well..  I really just wanted a general guideline..  So maybe stay out until 15mph winds hit and get a shield that can protect my bearings on my dob base as I'm using it?  Any advice on possible ways to clean out your tube after a windy night (10-15mph)? 


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#8 yemtig

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Posted 22 October 2017 - 08:15 PM

If it's above 15 or 20mph, forget it. Your telescope could weathervane in the wind, and the turbulence generated will ensure poor seeing. I can't use my 15-inch in such conditions, and my 10-inch certainly won't be useable if the wind is above 20mph. It will also make it a lot colder for you. Also, you need a shroud for a truss tube to keep out stray light, wind currents and dust out of the light path. Your body heat can create currents of warm air in the light path too. A fabric shroud keeps all of that out of the light path. An additional baffle on the opposite side from the focuser will keep stray light from getting directly into the eyepiece.

 

Taras

Are you talking about flocking the tube opposite the focuser?  Planning on doing that, wish the guy at protostar would get his act together...  Really want his stuff, but can settle for others after hearing the horror stories....

 

Mike


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#9 yemtig

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Posted 22 October 2017 - 08:24 PM

I usually go out at 10mph and below.  Above 15, forget it.  No dew/dust shield needed.  You'll want to get away from the ABQ and Santa Fe light domes.  The Chaco Canyon area is great.  Also the area between San Antonio (stop at the Owl Cafe for a green chili burger) and Ruiodoso is as dark as you can find anywheres.  There's also some ghost towns in that area for exploring.  The Jamez pueblo area isn't too far from you and is fairly dark.  If its a truss dob, you will want a shroud.

I love the Jemez and am on the west mesa anyways...  The local astronomy club looks like they view every month or two at a nice darksky area where I mountainbike..  Plan on meeting up with those peeps this next friday for a meeting/stargazing event.. Most of my viewing will be from my backyard, but I will adjust as needed.

 

mike


Edited by yemtig, 22 October 2017 - 08:25 PM.

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#10 SonnyE

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Posted 23 October 2017 - 01:36 AM

I do almost all of my imaging from a pet spot in my back yard.

I gravitated to it as I tried different places. But this is best for me because I have a sheltered area where our typically bad winds come from. (And the obnoxious bright lighting from a condo complex across a ditch behind us.)

Is there any way for you to find a sheltered area on the leeward side from the wind?

Like downwind from your house, so it breaks the gusts?



#11 csrlice12

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Posted 23 October 2017 - 11:02 AM

So yourviewing spot is a pet toilet?



#12 PNW

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Posted 23 October 2017 - 12:58 PM

I once set up my Nextsar 8 on the back deck on a clear night in 20-30mph winds with higher gusts. The house provided a lee shore to protect from all but the higher gusts. The view of the Orion Nebula was 3 dimentional and picture perfect. Occasionally a gust would wiggle the image, but it was a wow moment. I don't know what the exact physics of that night was, but it taught me to not limit myself to predictions. Sometimes you win, and sometimes you lose. 



#13 GeneT

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Posted 23 October 2017 - 05:36 PM

I have viewed with a Dob with wind gusts of 35-40 mph. However, I had to hold onto the telescope the entire time because they would would kick up without notice. I agree that steady wind of 10 mph or more would cancel my evening.


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#14 SeaBee1

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Posted 24 October 2017 - 07:16 AM

I have viewed in 10+mph winds with both my scopes, both vibrated enough that the eyepiece view gave me a headache, though the 10 inch was a bit more stable. I have viewed with both at less than 10 mph with no problem. I don't think 10 mph is the cutoff for every scope/user combo, which leads me to believe it is perhaps a combo of user tolerance and scope mechanics concerning what the cutoff might be. Jon Isaacs can view satisfactorily in nearly gale force winds, and as he stated, he will choose his instrument based on the wind speed, if wind is a factor. For me, it is ~10 mph, discovered, of course, by trial and error.

 

YMMV really comes into play here...

 

Keep looking up!

 

CB


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#15 Ulmer Spatz

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Posted 24 October 2017 - 07:57 AM

I am just trying to figure most things out from the get go..

 

 

If you are looking at wind speeds predicted by a weather service, keep in mind that most weather services define 'surface' in the context of wind variables as 10 meter (33 feet) above ground. Just a few feet above ground, wind speeds generally will be much less than the ones predicted.


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#16 Feidb

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Posted 24 October 2017 - 08:22 AM

I have a 16-inch Dob with a cloth light shield over truss tubes and it's pretty rock steady. When the winds are annoying enough to knock the cloth into the light path, well...

 

As for bobbing the scope around, the majority of my viewing is done at 102X with an 82 degree EP, so it can take a bit of bobbing. However, the real factor is the temperature, for one, and how much it blows my charts around on the table. Also, if I'm looking very high up and the wind moves the scope when I let go of it...

 

As for wind speed, I'm not really sure.

 

There are occasional gusts = no big deal.

 

Steady breeze = borderline annoying.

 

Steady wind = annoying verging on quitting.

 

Strong gusts settling to a stiff breeze = pack it up.

 

Miles per hour? Hard to say. I've never measured it. The Clear Sky Clock may say one thing but the actual site where I usually observe is eight miles away in an open area, whereas I'm a bit sheltered. That might or might not make a difference with dampening or venturi effect. Therefore, exact MPH which is always a range, say 11-16 MPH or something, is vague as it is.

 

I'll go with my assessment above and avoid the numbers.

 

Besides, I'm allergic to math.



#17 wrvond

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Posted 01 November 2017 - 02:04 PM

Hot, cold, wind, rain, humid, or dry. If I'm not comfortable I'm staying indoors and so is my scope.  ;)


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#18 Redbetter

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Posted 01 November 2017 - 03:44 PM

As has been stated, typical wind speeds reported are for heights considerably above the ground.  Typically the speed is lower at ground level and I can often tell a difference a few feet up on the ladder.  When the wind starts to pick up there is more vibration/movement in the eyepiece at high power--not just movement of the image caused by poor seeing.    Using a vehicle, fence, or structure to block the wind usually helps. 

 

As for shrouds, the only time I recall using my 20" without a shroud was recently when the evening began quite windy.  That proved to be a mistake.  Every time someone had lights nearby at ground level or a car drove by, etc. the field was lit up and the scope was unusable for faint fuzzies.  I lost a lot of time that session waiting for people to leave.  



#19 havasman

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Posted 01 November 2017 - 04:52 PM

Your 10 inch Dob should quite good in the winds.  As far as protection,  I'd be more concerned about dust and sand finding it's way its way into the azimuth bearings,  it's only a few inches off the ground. 

 

When it's windy,  lower magnifications are in order.

That.

And...

Like most things relative to observing, the answer varies and you'll work out your preferences over time. But if it's been a while since a clear night the wind may be deemed insignificant and you may be satisfied with lower magnifications that are less diminished by the shaking. 

Generally >15-18 mph can present limitations and you just have to decide whether and how to deal with them. Whether it's steady or gusty has a big influence too. 



#20 Starman1

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Posted 02 November 2017 - 02:00 PM

What would be a reasonable max wind speed for viewing in a 10" dobsonian?  And since I'm in a high desert area, would a "dew shield" be beneficial for a "dust shield" since this is an open tube design.  Any experience would be helpful, I am just trying to figure most things out from the get go..

 

Mike

Probably <10mph if sustained, and gusts to ~15mph.

Less than 5mph you can ignore.

More than 15mph, and you'll have to hold onto the scope all the time.  That's really annoying.

I've done it, but didn't enjoy it.



#21 Jon Isaacs

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Posted 03 November 2017 - 05:24 AM

 

What would be a reasonable max wind speed for viewing in a 10" dobsonian?  And since I'm in a high desert area, would a "dew shield" be beneficial for a "dust shield" since this is an open tube design.  Any experience would be helpful, I am just trying to figure most things out from the get go..

 

Mike

Probably <10mph if sustained, and gusts to ~15mph.

Less than 5mph you can ignore.

More than 15mph, and you'll have to hold onto the scope all the time.  That's really annoying.

I've done it, but didn't enjoy it.

 

 

That probably depends on the scope.. With my 25 inch F/5, it was quite stable in a wind, I'd quit because I was blowing around, not the scope.  If I avoided observing when the wind exceeded 15 mph, I'd miss out on a lot of nights.  In a worst case scenario, a short focal 4 inch refractor on a sturdy  alt-az mount is a viable alternative. My equipment is chosen and configured with the wind in mind.

 

Regarding lights and shrouds, that can be a problem. My dark sky location is private so cars and such are not a problem and when traveling, the locations are isolated with essentially zero traffic.

 

Joshua Tree March 2017 1.jpg
 
Jon



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