Seeing v's Transparency

[ballaratdragons]

OK, you have my curiosity aroused. Many of you keep referring to Seeing 7/10 and Transparency 8/10.

I get the 'score out of ten' bit, but what's the difference between 'Seeing' and 'Transparency'?

I would've thought them to be the same thing. To have good seeing you must have good Transparency! :confused:

See, 20 years at this and I still don't have a clue. By the way Houghy, I gotta ask, are you writing a book in your signature? It takes about 20 minutes to read it. I hope the sequel is better! :rofl:

[h0ughy]

Thanks for asking the Question Ken, I'd like to know too about transparency. Who is awake to teach us!

BTW what wrong with the signature. OK I will modify it Just for you Ken

[asimov]

http://www.astromax.com/aaaa/faq/aa01faq14.htm

[ballaratdragons]

Thanks John. Sounds too confusing for me though. I think I will stick to saying things like "everything was 7/10".

[RapidEye]

Here are a couple more links:

http://www.weatheroffice.ec.gc.ca/astro/transparence_e.html

http://www.weatheroffice.ec.gc.ca/astro/seeing_e.html

They use a 1-5 scale, but same theory applies.

Think about it this way guys:
Transperancy is a measure of how much crud is in the air. More crud (dust, smoke, humidity) the less faint things you can see: nebula and galaxies.

Seeing can also be referred to as steadiness. You can have crystal clear skies, but if the jet stream is screaming overhead, the image will be all jumbled like the air over hot asphalt. The steadier the image, the better for planetary and/or double stars.

The effects of transperancy can be negated by light pollution or the moon; however, seeing isn't. But good seeing can be negated by doing something silly like looking over the roof of your house in the middle of a cold night.

Hope those links and thought help!

[gaa_ian]

Oh ... now I understand :shrug:
Thanks for the links, though :thumbsup:

[asimov]

Yeah, these days I use the good old 'how much is a star twinkling @ 45 deg above the horizon' to ascertain weather I bother setting up or not. Good explaination rapid. I was too lazy to type all that, lol.

[ballaratdragons]

Um, yep.

Glad I'm not the only one who doesn't know the difference!

[asimov]

Seeing it's been raining here for 2 days straight & washed all the crap/dust etc. out & now it's clear....I have 7 outa 7 transparency!!

[RapidEye]

No problem fellas.

I just had one more thought....
Tube currents in your scope can easily be confused for unsteady skies (poor seeing).

G'Luck!!!

[h0ughy]

You are quite correct Ken, you and I don't know any different :shrug: , Except you have a very large signature that is riduculous :D :poke: :poke:

[h0ughy]

Thanks Rapid Eye :thumbsup:

[janoskiss]

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

[RAJAH235]

Ahh Steve. KISS, eh? :P :thumbsup: :D L.

[RapidEye]

And a picture is worth a thousand words :D

[xstream]

This is a good link for seeing

http://uk.geocities.com/dpeach_78/pickering.htm

[ving]

interesting topic. of course i am brilliant and knew it all already.
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.
:D
its all good!
some times i post for the sake of it :ashamed:

[janoskiss]

:rofl:

[asimov]

99 to go vingster...

[ving]

98! :ashamed:
dont encourage me asimov! :P

[Dave47tuc]

:rofl: :rofl: I'm a bit late on this but I liked this comment. Very well said. ;)

[ballaratdragons]

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


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]

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]

Huh! :shrug:

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]

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]

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]

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

[asimov]

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]

seeing = quantity
transparency = quality
(of light)

:shrug:

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

[ballaratdragons]

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]

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

[ballaratdragons]

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' :thumbsup:

[janoskiss]

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. :D

[ballaratdragons]

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]

In a bigger nut shell :whistle:

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. :shrug:

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? :D

[janoskiss]

Dave, it sounds like a quantity-quality set of measures you be describing you mighty knight of the skies. :D (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]

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

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

[ballaratdragons]

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]

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

[Stu]

Our seeing (in Melb) is usually pretty good because we don't get the jet stream and it rains about one a day for 5mins...here and there, then gets sunny, then cloudy, then hot, then cold, then dark, then clear, then rainy, then clear, then freezing, then hot again...no wait, make that cold...

[ballaratdragons]

LOL! That's Melbourne exactly.

Reminds me of that old Melbourne saying "if you don't like the weather, wait 5 minutes".

Not much different to up here in the hills except for the summer months when it's hot, hot & hot all day and hot & muggy all night.

[cahullian]

yeh Ken but how is the seeing and transparency on those nights??? lol

[RapidEye]

LOL :rofl: You guys are overthinking it =-)

Go back to the begining of the thread: the transperancy and seeing (steadiness) are seperate measurements of the sky quality. Sort of like temperature and humidity of the air outside. They are related, but are independant measurements.

If it is cloudy, yes transperancy is nil; and seeing is irrelevant because there is no way to determine it 'cause you can't see past the bottom of the clouds.

Here in the SE US, it isn't uncommon to have very poor tansperancy from all of the humidity; however, usually when the air is like that, it tends to be very stable. I've had some great planetary viewing sessions when you could hardly see the planets naked eye from all of the gunk - but they are bright enough that it punched through the haze and the steady air made for very stable disks.

When transperancy is poor - DSO's viewing suffers
When seeing (steadiness) is poor - Planetary and Doubles viewing suffers
When both are poor - watch a good ball game on TV instead. :thumbsup:

The real irony of it is - typically the conditions that make for great transperancy usually make for poor seeing and vice versa. Having a night of exceptional transperancy AND seeing is pretty uncommon, and if you are lucky enough to get that when there is no moon, don't go to bed: you've just hit the astronomy version of the Lottory :scared2: At least that is the case here in the US...

[ving]

I'd have said the other way around...

transparency = quantity = cloud cover, dust, pollution, etc which will blot stars out

seeing = quality = atmospheric conditions that determine how well you can see the objects
?
no?
I too am making it up :P
makes sence tho. except bad seeing will also make fainter objs hard to see.

[janoskiss]

Of course you're right David. That's what I meant. :D Which is why I wrote the opposite. :rofl: Makes perfect sense if you forget about logic. :rofl:

[rumples riot]

Ok heres my take on both.

Seeing should actually be measure on a 1-10 scale. Seeing is most commonly vital for planetary work and close doubles. When seeing is at 1/10 little if any detail can be seen of any planet. In fact the image will dance around like it is in a washing machine. Little if any detail can be seen at all. When seeing is very good say from 7-10/10 the image of the planet will not move, it will be steady and lots of detail can be seen. This is even when transparency is around 5.

As to transparency this relates more to observations made of DSO's. Typically high cloud and dust particles will affect transparency. Fine detail of nebula and galaxies will be lost due to poor tranparency. Scale again is 1-10. You can still have good seeing even when transparency is very low. Light pollution will also be affected by transparency. In fact they are inter-related. If the sky has lots of dust particles in it, and you live in a city then the light pollution have a greater effect. The light bounces off all the crystals of dust or cloud and increases the light pollution. The best time for good transparency is usually after a big rain period. The sky will be crystal clear because the atmosphere has had a wash. This does not mean that seeing will be best either, that is because upper atmosphere winds can and do effect seeing.

A good example of what I mean is this. I live on the sound side of Adelaide. Most nights the light from the city will effect any viewing to the north. Being a city there is a lot of dust in the air, when the dust is really bad or there is high sirius cloud the transparency will be lousy typically around 4/10 and this will extend overhead and to the south. However even on nights like this I can sometimes get great seeing for planetary imaging. This is because the jet stream is calm overhead and local conditions are very clam. In addition even on nights when the sky is crytal clear the jet stream can make the sky twinkle and planetary work impossible.

So seeing is related to the air currents and transparency is related to things like dust, cloud and pollution. The two are not related to each other and are caused by different influences.

Hope that makes sense.

[ballaratdragons]

From that Paul, a way I can remember which is which is to play 'word association' games in my head.

I will look up at the sky next time and if I am 'seeing' the sky shiver, distort or move in any way I will rate the 'seeing'.

I will then look at whether I am looking through 'Transparent', Translucent or Opaque air and rate the 'Transparency'.

Makes sense to me that way!

I will look at seeing if there is any movement and also find out if the sky is transparent enough to see through! :thumbsup: