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#1 Steve Moon

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Posted 17 January 2013 - 02:40 AM

OK. So I brought my 8" dob outside last night and tonight. After spent an hour last night and only 30 minutes tonight I had to come back in cause the viewing was HORRIBLE!

I'm living in California near L.A. area and the weather suddenly got cold for last few days (45-55 when I was out).

I cooled down my scope for at least an hour and a half. I was looking at Moon and Jupiter and guess what. They were 'boiling'. Or shaking.

First I was thinking it was the heat that obstruct the viewing because the temperature difference from high to low was about 30*.

But it was around 10pm and I was looking at Jupiter high in the sky. Should it not be affected by heat then?

The next thing came to my mind was the optics. I looked into the primary mirror and no dews were visible. BUT when I closely looked into the primary, I could see rainbow color sprinkles (I can't explain any better) were visible on the reflection of the inside of OTA through the primary. By directly looking at the inside of OTA, no 'rainbow color' was visible so I don't know if the reflection in the primary was just because of the mirror or was actually 'invisible' light dews. (by the way, the dew point was nearly 20* according to weather.com and it was around 45* when I was out.)

I was fine with views until the last week when the weather was not cold as it is now. I'm thinking it is related to the cold weather.

Anyone can explain what it is?

The problem is not really noticeable on these pics but I'm attaching two pics of Moon. One was taken last night and the other one a month ago. Both were taken with same device (iPhone 5) and focused to its best under the given condition. If you see the edge and details of craters, you will notice how bad the condition was on last night's pic.

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#2 Steve Moon

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Posted 17 January 2013 - 02:41 AM

And this is the one from a month ago.

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#3 MessiToM

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Posted 17 January 2013 - 03:04 AM

Looks like turbulent air. Bad "seeing" you stated a big temp drop rite?

#4 GlennLeDrew

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Posted 17 January 2013 - 03:07 AM

Indeed, it appears to be quite bad atmospheric 'seeing', or turbulence. While watching, it will look rather like gazing through slightly disturbed water. An apt comparison, as the atmosphere is a fluid.

#5 Steve Moon

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Posted 17 January 2013 - 03:13 AM

Looks like turbulent air. Bad "seeing" you stated a big temp drop rite?


I wrote everything that might be related to the condition.
Yes, I am complaining about bad seeing and big temp drop was one of my guess.

So the turbulent air was the term I was looking for!

#6 Steve Moon

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Posted 17 January 2013 - 03:16 AM

While watching, it will look rather like gazing through slightly disturbed water. An apt comparison, as the atmosphere is a fluid.


That just sounds like what I experienced. I described it as 'boiling' and I can substitue what you wrote with the word 'boiling'. :grin:

#7 Jon Isaacs

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Posted 17 January 2013 - 04:49 AM

While watching, it will look rather like gazing through slightly disturbed water. An apt comparison, as the atmosphere is a fluid.


That just sounds like what I experienced. I described it as 'boiling' and I can substitue what you wrote with the word 'boiling'. :grin:


When you are looking through a telescope at the moon, you are looking through a column of air that is the diameter of the scope and a minimum of about 60 miles thick and can be many hundreds depending on the angle/elevation. That column has to be very steady, free of turbulence, to get a steady view. Poor seeing is like looking through a mirage but magnified.

"Seeing" is generally pretty good in coastal southern California, better than most places, so it is easy to be spoiled. But like anywhere, it can be bad and even down right horrible. The worst seeing in southern California is generally when the Santa Ana winds blow over the mountains from the deserts to the east.

ClearDarkSky is what many use to get an estimate of their seeing, it doesn't always work but it's pretty decent.

Good seeing is the key to good high magnification views, if the seeing isn't solid, you are pretty much stuck. The reason the Hubble Telescope is so effective is that there are no issues with atmospheric stability. By research standards, it's a pretty small scope but it can operate at it's theoretical resolution because it is operating in space, free of atmospheric turbulence.

There are things one can do to minimize the effect of the seeing. Viewing an object at culmination, that is as close to the zenith as it gets, means you are looking through the minimum of air. Even if the seeing is reasonably good, it's best to avoid looking near the horizon for planetary and double star observation. Looking over buildings, trees, parking lots, these are all heat sources that cause local disturbances. Looking through the heat rising from a neighbors dryer vent or chimney is always instructive.

One can get some idea of the seeing by looking for twinkling stars. If they are twinkling, you are magnifying that twinkle.

Bottom line: Seeing is important. One of my favorite quotes on the subject is by Cloudy Nights member and author, "Uncle" Rod Mollise (paraphrased):

"When it comes to planetary viewing, the seeing is not the most important thing, it's pretty much the only thing."

Jon

#8 MikeBOKC

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Posted 17 January 2013 - 08:42 AM

Imagine lying on the bottom of a swimming pool and looking up and trying to read something written on the bottom of the diving board. If the water is relatively still you probably can read it; if the kids are doing cannonballs probably not. Same with the atmosphere.

#9 sslcm56

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Posted 21 January 2013 - 12:33 PM

Collimation!






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