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 Post subject: Atmospheric transparency
PostPosted: Fri Jan 04, 2019 8:35 am 
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Joined: Sun May 11, 2008 6:11 pm
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Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
Thursday (yesterday) was another grey and gloomy day. I was at the Foredown Tower but from the Viewing Gallery, surprisingly, the transparency was superb! The sea horizon, during the day, was razor-sharp and Isle of Wight, over 40 miles away, was obvious to the unaided eye and showed well in the spotting scopes set up there for use of visitors ( and me!) - these are nothing fancy, just old ones of mine on tripods. Scanning the top of the grey shadowy hump of the island, in silhouette, two masts or pylons could be easily seen. The greyness of the day was brighten and spirits raised when a small flock of (14 or15) Goldfinches, in their gold and red livery and smart black and white closed wingtips, joined us for a while, flittering around the bushes and tree in the garden. A joy to behold. As for anything astronomical , nothing to report! Regards maf.


Last edited by mike a feist on Fri Jan 04, 2019 2:18 pm, edited 1 time in total.

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PostPosted: Fri Jan 04, 2019 10:16 am 
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Location: Lancashire
Goldfinches are exquisite little birds. I once saw half-a-dozen or so of them drinking from a puddle on a path. Thistle seeds are the Goldfinch's speciality.

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PostPosted: Mon Jan 07, 2019 7:59 am 
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Location: Galloway, SW Scotland
We get quite a few goldfinches....lovely birds!

Looking at the forecast, it would seem that this evening holds the possibility of transparency all the way to the stars.....

But I whispered that.....! :wink:


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PostPosted: Mon Jan 07, 2019 6:29 pm 
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Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
I hold my breath in silent anticipation... although maybe this will not occur here in the south as well as your location. Regards maf.


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PostPosted: Tue Jan 08, 2019 7:27 am 
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Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
Did see beyond the clouds this morning, Tuesday 8/1/19 at 0500 had a view of R Leonid again in 10x50 binocular. Bands of cirrus a bit intrusive. Looked at Venus at 0725 UT and was able to follow Venus into daylight and did so till 0900 UT using a secondhand Bresser 10x50 binocular on a tripod from the garden. Then I left for the Foredown Tower. Lots of high ripple clouds, spread-out contrails and very cold wind. Regards maf.


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PostPosted: Tue Jan 08, 2019 10:18 am 
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Location: New Farnley, Leeds lat 53.8N long 1.6W
First clear morning in a while Mike, managed my first solar observation since the 2nd of Jan. Glad you managed to get out. Bob


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PostPosted: Thu Jan 24, 2019 11:32 am 
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Location: Surrey
If you are interested in forecasts of sky transparency I have a page on my website at http://www.johnmurrell.org.uk/sky%20transparency.htm. The subject is a bit confusing as meteorologists & climate scientists tend to speak about AOD or Aerosol Optical Depth. While Mike's observation was near horizontal the AOD measurements are vertical.

Note also that transparency is not related to what we as astronomers call 'seeing' .

The best surface transparency I remember was in the week after the 1987 'Hurricane'. I was sailing from France towards the East End of the Isle of Wight overnight. We got part way and noticed we could see lights from the Isle of Wight including cars through binoculars. This being in the days before GPS we were a little confused as to where we were - we could not get be that close to the island at the speed we were going. We then decided that if we were that close to the IoW we should be able to see the lighthouse on St Catherine’s Point. While we were thinking about this I noticed that the beam of the lighthouse was illuminating the top of our sail ! This indicated it was over our horizon. An estimate of the height of the light beam on our sail combined with the known height of St Cathererine's Lighthouse enabled us to calculate our position which was pretty much where we expected to be. I can't remember the exact distance but we were seeing the car, street and house lights at bettween 30 to 50 miles.

John

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PostPosted: Thu Jan 24, 2019 3:12 pm 
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Sicily can be seen from Malta and vice versa. More than 60 miles.
Buildings and a church spire on Sicily could be seen in a 2.5 inch refractor.
The wide panorama photo at night shows lights over 70 miles away on Sicily.
My T.V. antenna man is from Sicily and he told me this originally.

The record seems to be in the mountains of South America, I cannot remember the country but over 500 km, i.e. more than 300 miles.

I frequently saw Estonia from Finland. More than 45 miles.
An island 5 miles away, I thought was 1 mile away on one transparent day. I could not believe how much I saw in my 150mm Maksutov.
Mirages were also very common with upside down ships on top of the real ships in the Baltic.

From Helsinki we saw a bright star that was on or below the horizon. 60.5 degree north latitude. Star minus 30 degrees declination.

Regards,
David


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PostPosted: Thu Jan 24, 2019 4:40 pm 
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David,

I remember sailing from Tenerife to La Palma for the first time and deciding we needed to work out a course to steer much like crossing the English Channel from Deven to Cherbourg. I was quite suprised to see La Palma on the horizon as soon as we left. Quite difficult to get the crew to sail the calculated course which allowed for the NE wind and the current from the same direction - they kept on wanting to point the yacht at the island instead of to the right of it !

Visibility in Iceland is quite exceptional as well (volcanoes permitting) - I have started walking to a feature I thought quite near and after an hour it looked no closer. It makes you realise just how much muck there is in the air here hence the AOD charts in the link I gave above. Of course some of the much is natural normally sea salt but a lot is anthropogenic.

It will be interesting to see what happens post Brexit when we will no longer be allowed to export pollution to Europe and they will no longer be allowed to send it to us !

John

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PostPosted: Thu Jan 24, 2019 4:52 pm 
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Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
The best mirage effect I have seen occured as we were leaving the Foredown Tower one May afternoon (year uncertain). This was a 'fata morgana'. "The Isle of Wight ;appeared to be split into about six pieces with the southern part of the island looking like the open mouth of a snake".When viewed in optical equipment it really was spectacular. (Description from a lose note recently found in a book). Regards maf.


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PostPosted: Thu Jan 24, 2019 5:36 pm 
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I remember in the early 1950s, maybe 1952? trying to get home from school.
We lived on a slight hill, 250ft elevation above sea level.
The neighbouring roads probably 50 ft lower.

There was thick smog and I could just see my feet, but as I got nearer home I could barely see my outstretched hand.

I had to feel my way along the walls and hedges until I arrived home.
Unfortunately, I miscalculated and was at a neighbour's house two doors away.
Eventually, I got home.

That year I think that the smog killed thousands and the clean air act was brought in.

Regards,
David


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