Learned something new

[Tweedledee]

I have just had a most relaxing day with my wife at Eden Hall Spa After all the water, sauna, steam and massage experiences, I did some reading over coffee and cakes

Reading through some very interesting Webb Society DSO observing reports, I came across some terminology I wasn't familiar with. People seeing things at AV1 and AV2 levels. I gathered it was something to do with averted vision. After a bit of googling, it all became clear, so I though I would pass on the explanation for anyone who is in the dark as much as I was (pun intended)

Seems like AV5 is bordering on hallucination ...

Averted Vision Scale

Averted Vision Scale Developed by Ron Morales of the Sonoran Desert Observatory

AV1 - Object can be seen with averted vision but once found, the object can occasionally be seen with direct vision. If an object is first noticed with averted vision but once found this object can then be seen steadily with direct vision it is considered a direct vision object as opposed to an averted vision object.

AV2 - Object can be seen only with averted vision but it is held steady. Here the sweep of one's vision makes the object detectable.

AV3 - Object can only occasionally be seen with averted vision as it "comes & goes" with the seeing conditions. In this case the object is seen more than 50 % of the time.

AV4 - Object can only occasionally be seen with averted vision as it "comes & goes" with the seeing conditions. In this case the object is seen less than 50 % of the time.

AV5 - Object can only be glimpsed with averted vision after a continuously viewing the field for a few minutes or more. This level of averted vision usually occurs when one carefully observes a field for a lengthy period of time. This might occur within the first 3 to 5 minutes of viewing the field. In this level it is important that the observer has no knowledge of the exact location of a possible object. Having such knowledge prior to viewing could mislead some observers into believing that they saw something they did not actually see. One problem associated with viewing extremely faint galaxies it that sometimes an extremely faint star could be misidentified as an extremely faint galaxy. For this level of averted vision it is suggested that the observer make a field sketch showing faint stars as well as the object in question. This field sketch can then, at a later time, be compared to an actual photograph or chart. At this level of detection are you seeing or just detecting the presence of an object.

[Daz Type-R]

Interesting find Pete, thanks for that.

 

I think I might design a TB rating (Totally blind) in which TB1 is where you cant see much, even when other people tell you its there..... 

[Tweedledee]

Cheers Darren.

Your TB rating might be more useful, for us lot who don't quite have Sonoran Desert skies

[Doc]

As you say this only really works in pristine skies but it's a good thought.

 

 

[Guest zidder]

Interesting find Pete, thanks for that.

 

I think I might design a TB rating (Totally blind) in which TB1 is where you cant see much, even when other people tell you its there..... 

I think I def. qualify for TB1

[BAZ]

Stellarium in braille!

[Tweedledee]

It makes you think just how much visual astronomers can push the limits of their night vision with experience and dedication. I knew visual astronomers did that, but this scale is going towards extremes that I'd never really thought too much about. We all know that averted vision helps us see really faint stuff, but to break that down further on a scale of 1 to 5 is really going some. Most people, especially the ones who like automatic dusk till dawn lamps, never experience any sort of dark adaptation whatsoever, nevermind such extremely low light and contrast levels. In fact going to the other extreme, I've found over the years that more people than you would think are actually afraid of the dark!

Just pondering

[BAZ]

I have to be honest and admit there are times I have spooked myself. I know that there is nothing scarier than a cat, hedgehog or occasional fox in my garden, but now and then the hairs on your neck start to stand up, and the irrational side tales over.

We can find things that are not there as well, your brain will try and make sense of things and come up with something that is very convincing, but isn't actually there.

 

It's just a weird side of the brain which actually makes stuff up, maybe some ancient survival technique. It's called Pareidolia.

http://en.wikipedia.org/wiki/Pareidolia

 

I try to ignore this now, and if need be will check it out with a red light torch, but it's scary at the time when your mind says run, and you know it's not zombies.

 

I wonder if we can train ourselves to get better at using averted vision? Maybe practise trying to make out shapes in the dark and see how good we can get.

If it goes eerrgggh arrgghh, run. (Buffy, for those who remember 

 

[Tweedledee]

That is interesting Martyn.

I have never heard of Pareidolia before and predictive text had a field day with it

Seen it happen to others many times, mostly watching "Most Haunted" and had a right giggle at them scaring themselves half to death at the slightest creak of a floorboard

I don't normally suffer from it, but have had the hairs on my neck stand up when some spiral arms started coming into view at AV2

I'm sure we can train ourselves to improve our skills with averted vision. I know some beginners just can't get it at all at first, or are trying to do it without effect after little or no dark adaptation.

[tuckstar]

Pareidolia tends to poke it's head up all to often in the fringes of astronomy where the conspiracy theories about bases on Mars and things like the face on Mars spring up from. We all know there's no such thing but the human mind will always look for something it recognises, especially patterns even when they are not there.

[BAZ]

Look at Percival Lowell, and his observations of the canals on Mars, a professional trained astronomer, he royally got it wrong.

Read the last line of the "Venus Spokes" here, that might provide a clue.

 

http://en.wikipedia.org/wiki/Percival_Lowell

[philjay]

Interesting, never knew there was a scale for averted vision. So that's , magnitude, sky quality, seeing conditions and now averted vision index we have to remember, its getting complicated this astromony 

 

The history of observational astronomy is full of incidents like Percival Lowell and Martian canals.

One of the interesting things about martian canals is if it wasn't for Schiaparelli in 1877 calling these straightish line features grooves or channels which in italiian is Canali. The translation into English of this word is Canal and hence the myth was born before Lowell started his observations. I wonder if Schiaparelli had called these features something else would the martian canal controversy have ever come to be?