Jetstream.

[ianB]

Am i correct in thinking that a strong jetstream will mean bad viewing conditions, even if the transparancy and seeing index looks good?

The jetstream for my area tonight will be around 120 knots.

As the transparancy will be good i was thinking of going out but then i had a look at the jetstream and now think it will be pointless but would like to hear your comments just in case i am wrong. ( you have the experience whereas i dont )

Thanks.

ian

[OzStarGazer]

Unfortunately yes, I think you should choose another day... :(

[astro744]

I suggest you have a look just to see what a jet stream looks like. On the seeing scale it is out of the ball park at the bad end!

Have a look slightly out of focus and you'll get a feel for the speed of the wind. It will show many parallel lines along the direction of the jet stream. Play with the focus and you'll see it quite well.

Jupiter is a good target in a jet stream as it looks horrible and you can barely make out two bands! Try the brighter stars too de-focused inside and outside of focus.

[ianB]

Thank you both for your comments.

[Astro_Bot]

I've just been looking at the sky, and the stars are indeed twinkling rapidly, even bright ones.

It was the same last night: excellent transparency, crap seeing.

The jetstream charts say it all. However, there is allegedly a "lull" in the jetstream, due over SEQ somewhere between 12 midnight and 6am, where 200-300mb airspeed should drop to 40 knots or so. Given the otherwise crisp, clean and cloudless sky, it might be worth a session in the wee hours ... as long as you rug up!

[ianB]

Thanks Astro, i will see how i feel later.
I have just returned from a bbq and the stars look very crisp and the moon beautiful.
I really dont know how low the jetstream ever gets but obviously the lower the better.
At the moment i have a red wine in one hand my pet bird on my shoulder and about to watch Flash Gorden.

[OzStarGazer]

I really wanted to view something yesterday, so I tried. It was fine with a low-power eyepiece, but anything more than that was terrible...

[Wavytone]

You can find out what the jetstream is doing:

Go to http://www.bom.gov.au/aviation/?ref=ftr

Press "Accept"

On the left hand side, select 'Aviation Observations', this expands to a submenu;

Select 'Aerological Diagrams', and choose a city near or west of your location. West, because at high altitude the prevailing windstream is westerly and ideally you should choose a site upwind of your location.

These are produced by the release of a meteorological balloon carrying a telemetry package and a radar reflector allowing its height and location to be tracked as it rises; from this the BOM calculates the wind speed and direction at altitudes up to the upper atmosphere.

The BOM provides a more detailed explanation of how to read the tick marks (wind speed) and direction.

When the jetstream dies down below 40 km/h the seeing is usually very good, however such nights are rare.

A good clue is a large high pressure system with the centre over your location (learn to read the synoptic maps).

[ianB]

Thanks Wavytone, i will take a look now.

[ianB]

If i am reading that chart correctly its around 65 knots at 15 km for Brisbane.

[Pinwheel]

I love the first time you see Wang's daughter walk by, I'm 100% sure she's not wearing knickers.:eyepop:

[Astro_Bot]

You mean Ming's daughter? Anyway, in this day and age, I'm sure there's an app for that. :)

[Pinwheel]

Your right "Ming" not "Wang" :thanx: