Seeing and Transparency. What is the diference?

[Swoop1]

I have seen many mentions of seeing and transparency. 

What is the difference between the two and how are they measured?

Thanks.

[Woolnut]

20 minutes ago, Swoop1 said:

I have seen many mentions of seeing and transparency. 

What is the difference between the two and how are they measured?

Thanks.

This should be of use  

 

[jetstream]

1 hour ago, Swoop1 said:

I have seen many mentions of seeing and transparency. 

What is the difference between the two and how are they measured?

Thanks.

This is a great question and well worth discussion. Understanding this is one of the keys to great views and what object to pick and when.

I hope some others chime in...

[Swoop1]

I think I am getting a handle on this now. 

Poor seeing is the result of things like thermals off warm roofs/ dark fields etc.

My personal bugbear at my home is viewing something when the boiler kicks in and the gasses from the flue make my view like looking throught he surface of a choppy swimming pool......

[Swoop1]

1 hour ago, Woolnut said:

This should be of use  

Thanks Woolnut

 

[laudropb]

Seeing refers to how steady an object appears in the eyepiece. It is usually measured on a scale of 1 to 4, where 1 is very steady with no shimmering or appearing to go out of focus. 2 is steady but short periods of shimmering. 3 is mainly shimmering but periods of a stable image and 4 is unsteady all the time and not possible to make meaningful observations. Experience at the eyepiece makes this simple measurement fairly accurate.

Transparency refers to how clear your sky is. High clouds, dust or water vapour in the atmosphere will obscure your image as will light pollution, man made or Lunar. I just record whether it is good, average or bad. Again experience at the eyepiece will help to decide. Often I record it as good/ average.

[Woolnut]

7 minutes ago, Swoop1 said:

Thanks Woolnut

No worries, i know i didn't answer your question exactly however some of the responses in that other thread explain the difference! (At the time i had about 5 minutes... Not long enough for a proper response )

[Swoop1]

laudropb, thanks for that- it is starting to make sense now.

[Charic]

Several of my work colleagues know of my interest in astronomy, and there have been several questions in the past,  some difficult, possibly just testing/trialing  my knowledge?  as they could quite easily find out themselves, having the www at their fingertips!  but I have most often used the analogy of a the coin in a  swimming pool when it comes to describing  conditions above.

An example is given here............http://www.skyatnightmagazine.com/feature/general-guide/guide-seeing-and-atmospheric-transparency

[Stu]

There is some interesting stuff about seeing on Damien Peach's website.

The Pickering scale is one measure of seeing which is described here:

http://www.damianpeach.com/pickering.htm

Impact of seeing on planetary view is shown here:

http://www.damianpeach.com/seeingscale.htm

I think of the difference between seeing and transparency in terms of the benefits they have for different types of observing.

Good seeing conditions are mainly relevant for higher power views of the planets, the moon and sun, plus double stars. You need the atmosphere to be stable in order for the fine detail to be resolved properly.

Good transparency is often more important for low to mid power observing of nebulae and galaxies. These objects are often much larger than planets, but much, much fainter (with low surface brightness) so are easily washed out if the sky has any haze or is full of dust and pollutants. I have had consecutive nights with very similar darkness levels when I could see the North America Nebula on one night and not the other; purely down to differences in sky transparency.

I must say I find the scales for transparency to be less satisfactory than those for seeing because other variables can influence the number of stars you can see i.e. Light pollution. I think transparency has to be measured on the basis of understanding what an excellent night looks like at a certain site. E.g. If you can see all seven stars in Ursa Minor on a clear and transparent night, but only 5 on another clear night with poor transparency then it indicates a certain point on the scale.

The other problem with a scale for transparency is that it is quite common to have a fair amount of cloud around but for the clear gaps to be showing lovely transparency (as happened the other night after Doris). How does this fit on any scale??

This document has some useful information in it too regarding all the various scales.

http://www.astronomylogs.com/pages/resource/pdf/14 Seeing and Transparency.pdf

Stu