Skippysky chart question

[ianB]

Hi all,
Recently someone pointed me in the direction of the Skippysky chart ( thank youn) to access what the viewing conditions are like in my area, SE QLD.

One thing confuses me, when for example i check SE QLD for " transparency " it may show all Red, meaning very bad for viewing, but at the same time when i click "Seeing " it comes up as Blue, meaning good.

So how come it says the transparency is very bad but its good seeing?

Maybe you can read and understand the chart better than i, if so maybe you can explain this to me, I read the Help section but i am none the wiser.

Thanks,
Ian

[SkyWatch]

The "seeing" refers to the atmospheric turbulence etc, particularly the upper atmosphere. I think it is mainly influenced by the jet stream, which is above the cloud layers. So if the seeing is "good" and if you could blow away all those pesky clouds, you would be able to get nice sharp star images.
I usually look mainly at the cloud predictions (total cloud). If it is clear then I check "seeing" to see whether it is likely I will get good images.
"Transparency" refers to how much muck is in the air. This is mainly cloud, so "transparency" largely mimics the cloud patterns, but it could be dust in the upper atmosphere- so you can have no cloud, and good seeing, but lousy transparency: that is when you will be OK looking at bright objects, but faint fuzzies will be even fainter.
Conversely, you could have no cloud, good transparency, and lousy seeing: that's when planets look crap, stars scintillate like mad, but faint fuzzies aren't too bad. (And if you check the jet stream then, you will usually find it is very strong.)
There's more to it than that, but hopefully that makes some sense. No doubt Andrew Cool, who developed the site, can explain a lot more if you contact him.
The other thing to note about SkippySky is that I believe it generally uses data that has about a 20km sample size or resolution, so it has its imperfections. It is as good as you can currently get with the data that is in the public domain.
The other site I often turn to is from the Brisbane Storm Chasers website, with real-time satellite images: http://realtime2.bsch.au.com/vis_sat2.html?region=aus&loop=no&images=&allday=&start=&stop=#nav

-it is a great one to cross-check with SkippySky.

All the best,

Dean

PS: I notice that IceinSpace has imperfections too: it is telling me that where you are in the Sunshine Coast is currently 14,544km from me in Adelaide... In which direction I wonder? ;)

[ianB]

Thank you for your help, It has been very helpful to me as I now haveva much better understanding and it will aid me in being able to read the chart with more clarity.

Many thanks

Ian


( Thanks R, I tried to reply but my control panel is playing up, many thanks )

[andrew_d_cool]

Hi Ian and Dean,

Seeing is related to turbulence in the atmosphere, caused by thermal variations at different heights. The best that can be (cheaply) done with the GFS model data is to work with the wind speeds at 10m and at the Tropopause (Jetstream) levels. The lower layers (Boundary and Surface) of the atmosphere have a greater effect on Seeing, and the algorithm in SkippySky reflects this. The effect of the Jetstream has been downgraded quite a bit since SkippySky went live in Dec 2008.

Transparency is a measure of the amount of water vapour in the atmosphere. Water vapour molecules block out starlight, and effectively make things dimmer. So yes, you can have good Seeing in terms of little wind/turbulence, but the air can be chockers with water vapour at the same time.

Regards,

Andrew Cool
www.skippysky.com.au (http://www.skippysky.com.au)

[SkyWatch]

Thanks Andrew, you are a legend.

- Dean

[ianB]

Thanks Andrew,
I appreciate your explanation, i guess we need to wait for those rare times when both seeing and transparency are in the blue.
Tonight it will be good seeing but bad transparency but i will still have a look.
I refer to your site all the time, many thanks.
ian