Anyone got a transparency predictor?

[almcl]

The last few nights have been clear according to all the forecasting apps I usually use, but the transparency of the air has been rubbish in my Bortle 6/7 corner of Shropshire.  A milky haze suffused the sky and even bright stars were barely visible.  My previously ultra reliable OAG, which has never had any difficulty picking twelve guide stars, struggled to provide even one.

Convinced that this was down to some sort of haze/cloud even though the Met Office, Meteo Blue and Clear Outside were all insisting the sky was clear, (the realtime hi-res infrared image on Meteoradar does shows a hint of haze, but is difficult to interpret over land) I started searching for an atmospheric transparency predictor, and while I found one for North America, (www.astropheric.com) I can't find anything similar for UK/Europe.

Does anybody know of one?

[DaveS]

The "Good to Stargaze" app has transparency and seeing. How accurate they are may be debatable.

[Second Time Around]

I think many of us in the UK have had the same problem in the last week or so.  I record how accurate cloud forecasts are from 7 sites.  For more details go to https://stargazerslounge.com/topic/376745-a-record-of-the-accuracy-of-my-local-cloud-forecasts/

However, none of them has been accurate this last week for exactly the reason that you mentioned.

Then I use Zoom Earth that shows infrared satellite pictures for night time cloud.  It doesn't make forecasts but shows the actual sky at 15 minute intervals and going back some time.  This has been accurate all week.

Go to https://zoom.earth/places/united-kingdom/

[Elp]

Metoffice detailed map view is generally reasonably good, you have to manually change the hours on the slider and it will update accordingly, allowing it to play automatically doesn't give you the time to really scrutinise it. I tend to click backward and forward on the sliders a few times, wait a second and it updates. It's a bit hard to notice as the grey blends into the green land masses but the misty cloud is visible. You are right though, it initially looks clear but it isn't. Clear outside I only use as a general view for the week, metoffice combined with AccuWeather I find useful.

Edited March 25, 2022 by Elp

[almcl]

Thanks all for the thoughts, most helpful!

 

1 hour ago, DaveS said:

The "Good to Stargaze" app has transparency and seeing. How accurate they are may be debatable.

I see what you mean DaveS,  at the moment we have milky haze up to 45° above the horizon but it still says 'good to stargaze'.

1 hour ago, Second Time Around said:

Then I use Zoom Earth that shows infrared satellite pictures for night time cloud.  It doesn't make forecasts but shows the actual sky at 15 minute intervals and going back some time.  This has been accurate all week.

Go to https://zoom.earth/places/united-kingdom/

Thanks for that  link 2ndTime, hadn't seen that one before although I have been following your record of forecasts, which has been interesting. I'll have to give that a bit more study.

 

1 hour ago, Elp said:

Metoffice detailed map view is generally reasonably good, you have to manually change the hours on the slider and it will update accordingly, allowing it to play automatically doesn't give you the time to really scrutinise it.... It's a bit hard to notice as the grey blends into the green land masses but the misty cloud is visible. 

Is that the UK observations map? with the satellite visible and IR options ? (I find their info is pretty good but the website is a bit of a nightmare to navigate.)  

[skybadger]

My sky temperature readings never got lower than -10 due to the mistiness last week. Maybe that can be a proxy for transparency ? -25 or even -30 is typical for a good clear dark sky. 

When the prevailing wind is from the south or east in winter and the sky is clear (ie cloudless) it can still be quite hazy and the sky temp is again elevated. 

[Peter Drew]

I think we are suffering from Sahara sand dust at the moment.  Yesterday the setting Sun was perfectly defined but blood red.     🙂

[vlaiv]

Copernicus has good prediction of aerosol and other things

https://atmosphere.copernicus.eu/charts/cams/aerosol-forecasts

Basic chart gives you AOD at 550nm

You have a legend at the bottom - color coded in AOD magnitudes.

For usage refer to this text:

https://skyandtelescope.org/astronomy-resources/transparency-and-atmospheric-extinction/

Quote

Reduction in visibility due to aerosols is called aerosol optical depth (AOD). Optical depth is the term used by atmospheric scientists for what astronomers call extinction. Both are usually measured on logarithmic scales, but optical depth uses "natural" logs with a base of e (roughly 2.718), while astronomical magnitudes are based on the fifth root of 100 (roughly 2.512). Multiply by 1.086 to convert optical depth to magnitudes.

This allows you to either get the idea of how clear the skies will be on particular night - or to calculate extinction if you need to do some advanced calculations - like SNR/exposure time and so on.

[DaveS]

Sounds about right, a big blob of yellow over me, and visibility is poor, with a blood red sun.

[Elp]

1 hour ago, almcl said:

Is that the UK observations map?

Yes, "detailed weather map", it's linked to on the homepage framed in a sort of black box. By default it's set to show cloud and rain.