Seeing v's Transparency

[Dave47tuc (David)]

Originally Posted by janoskiss

In a nutshell:-
transparency: how much light the atmosphere transmits.
seeing: how turbulent the atmosphere is.

I'm a bit late on this but I liked this comment. Very well said.

[ballaratdragons (Ken)]

Originally Posted by ving

actually i think theres been another thread named the same thing.
actually at the bottom of this page theres links to 3 threads covering seeing vs trans.

Oops! I should've done a site search first.

Originally Posted by janoskiss

In a nutshell:-
transparency: how much light the atmosphere transmits.
seeing: how turbulent the atmosphere is.

Now, that makes sense! Thanks Steve.

BUT! if it is overcast, is it 0/10 seeing or 0/10 transparency? and don't say both coz that doesn't clear up the question.

[janoskiss (Steve H)]

You're talking about a singularity, Ken. You're asking something like: "What is the latitude coordinate of the south pole" or "What is the right ascension of one of the celestial poles?"

[ballaratdragons (Ken)]

Huh!

Steve, If seeing is measured by how 'turbulent the atmosphere is' then on a dead calm overcast night the seeing is 10/10 but transparency is 0/10.
That's using your answer as a measurement.

If I am still wrong then I just don't get your answer at all because on a dead calm night there are no turbulents.

[janoskiss (Steve H)]

I think transparency of 0/10 means you can't see anything. No starlight gets through the atmosphere. Then seeing is undefined because there is nothing to see.

[asimov (John)]

That would be correct, as far as I can see ken....If you have 50% cloud cover, then you would have 5/10 tranparency. If it were 50% fogged out (in your opinion) then you would have 5/10 transparency there as well....I'm just theorising here of course! I ASSUME this is how it works..

[ballaratdragons (Ken)]

So, the 'seeing' scale is useless in that sense coz everything would come down to transparency.

[asimov (John)]

I would assume, yes. I KNOW for a fact I'm going to have ZERO trans. the next 3 days cos' it's going to P down for 3 days!! (Grrrr!)

[janoskiss (Steve H)]

seeing = quantity
transparency = quality
(of light)



quantity = 0 implies quality is irrelevant.
But with quantity > 0, quality becomes important.

[ballaratdragons (Ken)]

Sorry but I still don't get it.

Take tonight for a good example. The sky is absolutely crystal clear (strange but true) so give it 10/10 transparency. It is beautiful up there tonight.

But it is not worth setting up as there is a strong wind howling through. So the seeing is about 1/10.

Is that correct.

If that is right then that goes against everything I have ever read in books and on the net.

I have only ever been taught (and read) about 1 method, and that method was called 'seeing' and it covered both scales. Tonight, on the scale I was taught, would be called approx 5/10 seeing.

[janoskiss (Steve H)]

Donno. I just make it up as I go along. (Seriously.)
It works for me...

[ballaratdragons (Ken)]

LOL!

At the Camp we will have to design a simple method for evaluating the sky and set it as an international standard.

Something like a scale from 'Mud' to 'Crystal'

[janoskiss (Steve H)]

I don't know where light pollution enters the equation either Ken. I'm sure that at Star Camp, anything without clouds in the way will be a 10/10 for me.

[ballaratdragons (Ken)]

If it is going to be anything like a few months ago when I checked the Camp out in the dark we are in for spectacularly unbelievable skies. About 30 days to go!!!!!!!!!!!!

[Dave47tuc (David)]

In a bigger nut shell

You look up and see a few Stars say. Not the Milky Way but no obvious cloud.
Transparency poor. Say 2-5. Most probably high cloud or pollution.

You look up and see the Milky Way easy black sky Stars every where
Transparency 5-5.

Next you see Transparency at 5-5 as above but the Stars twinkle. You look into the scope say at Jupiter very Jumpy every image washed out say. Seeing poor say 1-5.
But Transparency is good. Happens a lot.

Next you get Transparency at 2-5 can’t really see the Milky Way but Stars seem Steady. Look at Jupiter for example. Very steady image lots of detail.
Seeing great ( I wish) 4 or 5-5.
Transparency poor say 2-5.

Does that help?

[janoskiss (Steve H)]

Dave, it sounds like a quantity-quality set of measures you be describing you mighty knight of the skies. (i like your new avatar)

So you'd put the effects of light pollution in the seeing (quantity) category. Makes sense, because one would measure starlight intensity relative to the background sky.

[Stu]

If there is a lot of light pollution then you can't pick out faint objects so the transparency is not good.
Seeing is excellent when the light that gets through is not diffacted at all.

or, a more practical way..

The transparency is crap when you neighbour turns the outside light on.
The seeing is bad when you look across the top of a hot barbeque and your neighbours light appears to be moving.

[Dave47tuc (David)]

Originally Posted by janoskiss

So you'd put the effects of light pollution in the seeing (quantity) category. Makes sense, because one would measure starlight intensity relative to the background sky.

No light pollution affects Transparency, it blocks out the Star light.

You can still get good seeing in the middle of Melbourne.

[ballaratdragons (Ken)]

It's starting to make sense! Funny though, I would've named them the other way around. Swap transparency and seeing and it seems to make more sense!!

[janoskiss (Steve H)]

Sorry I was getting confused with the terminology there. I did mean transparency, which is the quantity measure.