Measuring the seeing in the UK

[FraserClarke]

Hi All,

I have a small research project brewing in the back of my head to measure the seeing in the UK in a quantitive sense by using a differential image motion (DIMM) on a set of telescopes. This measure, used at almost all professional observatories, allows you to decouple the atmospheric seeing from other effects such as focus, telescope optics, mount jitter, etc. It also gives a quantitive measure of the seeing in arcseconds, rather than a qualitative measure such as a Pickering '8/10'. All you need to do it is a telescope, a webcam, an aperture mask (bit of cardboard with holes in it!), and some software to analyse the images.

I'd like to involve as many astronomers as possible across the country to turn their telescopes into a DIMM for a few hours per night, or a few nights per year -- as much as you are interested. We'd develop a free implementation of the DIMM analysis software, which would give you a quantitive measure of your site's true seeing. All the results would be collected in a central database, and we can analyse how good/bad the UK really is for seeing. It should be possible to draw correlations between weather forecasts and seeing conditions, with real measures of seeing to calibrate it all. I think the results could be very interesting!

Is this something that would interest people? Would you be willing to be involved? It would help me immensely when I ask for the money for the project to know that there is a group of people ready to put their telescopes to work to get the data! I think the requirements would be;

+ Telescope >20cm (8") aperture, capable of tracking and guiding

+ CCD or webcam

+ Willingness to spend some of your valuable imaging time taking the data!

I've put the thread in here, as I think this kind of measurement is of most interest to those doing astro-imaging -- and of course you're the most likely to have the necessary equipment!

Do please post here, or PM me, if you're interested.

[Revs]

Sounds like a great project! I wish I had the equipment to help

[pete_l]

Yes, I was very intersted in the idea until I saw

Telescope >20cm (8") aperture, capable of tracking and guiding

and that's gonna be a killer for me

[FraserClarke]

Yes, I'm afraid the 8-inch minimum size is a limitation of this technique; it just doesn't work with smaller apertures.

[Zoeff]

Sign me up! I do however live in the netherlands so it'll be a point of reference for...somebody on the mainland I guess?

I already have a few avi's of bad seeing with exact time and date made with my 8" SCT at f/30. Is that what is needed for this?

[FraserClarke]

Hi Zoeff, Yes of course you are more than welcome! I only put 'UK' in the title as this seems to be a UK-centred forum (and I'll try to get some funding from a UK organisation). Anyone anywhere is welcome to join in.

The data needs to be taken with an aperture mask, but the process is probably very similar to what you've already done for your AVIs.

[Zoeff]

Oh right, you mentioned that in your original post...

So.. where is this aperture mask? I'd like to make one as soon as possible.

[FraserClarke]

Hi Zoeff,

One of the initial goals of the project will be to work out the optimum aperture mask size and shape. In the meantime, you could probably start with a mask with two ~40mm holes, separated by as much as you can (160mm in your case). This goes on the front of the telescope, over the schmidt plate for an SCT. Then defocus the telescope a little bit, and you should see two star like points on the detector. It's the relative motion of these that gives a measure of the seeing.

[Zoeff]

That sounds very intuitive, I'll wait for you to finalize the design.