Hi,
>Skippysky's seeing predictions seem to be tied to the jetstream and >ignore all other factors. Almost always it displays Pickering 8 or more
I don't know where you've picked up the idea that SkippySky's Seeing uses the Pickering Scale.
I suggest that you read the online Help file, for which a link is provided on every SkippySky page.
>be tied to the jetstream and >ignore all other factors.
Seeing as calculated by professional astronomers involves a temperature function derived from temperatures taken at many levels through the atmosphere. Basically, changes in temperature between adjacent air layers cause turbulence, which in turn causes poor Seeing. The temperature profile can be matched to a vertical profile of Seeing.
Now given that you don't pay for SkippySky, I can only afford the bandwidth to download wind vector data at ground level and at the Tropopause, which if you had to pick two levels of atmospheric winds that
strongly influence Seeing, those two would be very high on your list.
SkippySky uses a weighted algorithm to assign the relative contribution of wind at those two levels to poor Seeing, and scales the result from 0..10,
a scale that simply suggests bad Seeing to better Seeing.
That algorithm has been adjusted "down" twice to make it harder to achieve higher Seeing indicies.
It is NOT in any way linked to arcsec resolution, or the Pickering Scale, or any other *******'s Scale.
Remember too that the GFS model operates at 0.25 degrees resolution. You cannot and must not expect it to predict the precise conditions over the clothesline in your backyard. (how many times have I typed that...?)
Think of trends in the data, and not absolutes.
Kind Regards,
Andrew
www.skippysky.com.au
Quote:
Originally Posted by pgc hunter
I would ignore both Skippysky and 7timer's seeing predictions.
Skippysky's seeing predictions seem to be tied to the jetstream and ignore all other factors. Almost always it displays Pickering 8 or more for Melbourne (with 1 being terrible and 10 being perfect on this scale).... which is obviously bulldust. I've gone out on many a night when skippysky predicted excellent seeing, only to be met with mush and mud.
However, I will say Skippysky is very useful for predicting cloud 24-48 hours out.
7timer on the other hand always tends to predict the worst possible seeing at the same times during every 24 hour cycle and always throws up a pattern of the worst seeing on the scale during the night, and better during the day regardless of time of year or jetstream conditions... atleast for Melbourne anyway. Again, this is far from accurate.
Gauging the severity of star twinkling by the naked eye is one age old method, and while twinkling stars suggest poor seeing, it is not fail-safe. One evening I saw some of the worst twinkling and baulked at the idea of getting the scope out, but a few hours later I was enjoying one of the top 5 sessions of my life.
The only sure-fire way of figuring out the seeing is getting out there with the scope...
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