"Imaging" the sky

Shoot a high-powered pulsed laser at it, and do a time resolved measurement of how much comes back, and when. The pulse won't get far into dense cloud.

Sending up a small fleet of dirigible balloons could give you more complete information, but would be even more expensive.

Yes, that should work. But just by having constant or controlled exposure, you can pretty easily determine if there are 'some dots' visible in a given sky segment. This would get rid of alignment issues and should give good enough result for most purposes.

-- mikko

Now I am beginning to get a feel for what you want to do I think your best bet is an off the shelf cheap HD dashcam with 170 degree FOV (£24).

You would have to align the long axis of 16:9 FOV with the local prevailing wind for best weather predicting purposes.

IDK if they allow single shot modes or not. You may have to settle for grabbing a video and registax or an equivalent implementation to get enough sensitivity for stars. My instinct is that they will just about see the brightest stars if you are lucky.

The latest models now are a lot more difficult to modify. And I think some of the prime movers in QUIAG are sadly no longer active.

Yes, but for initial proof of concept you can probably go a long way down this line to see how practical it is with really cheap parts.

I have been thinking about that - you could probably do a simple occulting disk that moves around the camera on a 24 hour clock. Or just ignore the problem initially and have a spare camera in case the first one gets CCD burn problems from the sun.

Edwards Optics might have something suitable but they are a bit pricey.

I think it was a big thing when really cheap webcams became available - the combination of continuous high resolution video and "lucky seeing" made it possible for amateurs to get planetary images as good as or better than big professional scopes! Basically the big scopes suffer from image distortion because the phase screen is so irregular.

One modest sized scopes the image stays in focus but moves around too quickly for the eye to follow but well within video frame rate. The trick is to take that fast video align the frames and sum. And simply throw away any bad frames that don't have decent contrast.

Side effect has been that we see many more impacts of things onto Jupiter and the moon since both are routinely imaged 24/7 now.

I was referring to measuring the brightness of a certain star at given time, which required careful alignment and distortion correction. Your needed level of alignment is easy to do.

The suggested cameras and fisheye lenses in the Indi Allsky project are very sensitive and also sunlight tolerant, so this should be easy - if you can do some simple image analysis (AI can help you to code this!)

-- mikko

We do see meteor showers clearly at least when the clouds permit... > As it is such an arid climate, cloud cover is relatively rare (though we > got screwed last week as we had one of our infrequent storms coincident > with the Leonids). The huge expanses of "empty" (desert) land also > help maintain that level of darkness. There is a reason why optical observatories like high desert locations. > My intent is just to integrate "light" for some period at some direction at > some time. And, correlate this with other observations "this date, last > year", > "yesterday", etc. to get a feel for what the skies look like. One thing that may be useful to know is that yesterday 4 minutes later than clock time now the sky should look identical to today (AOTBE). Strictly 3m 56s. Sidereal day is 3m 56s shorter than mean solar time. > Much like a regular Joe would do: "It's cloudy tonight. No need to > protect > the cold sensitive plants as it likely won't get very cold." His knowledge > of the past/future isn't anywhere near as specific as that of a machine > -- yet, > serves him well (enough). For that you probably want windspeed and a simple skyward and ground facing thermocouple pair. Rapid cooling of the skyward one means real risk of frost.

Preferably coated with something having a high emissivity in the far infra-red. A small piece of Kapton tape folded over each junction would be fine for initial testing. John

. Rapid cooling of the skyward one means real

Any pigment carbon black paint will do. Even white paint is black in the thermal infrared band. For this reason modern observatory domes are now painted with a hybrid aluminium/white pigment so that after dark the dome surface does not supercool and cause cold air to drip in through the dome slit creating avoidable turbulence.

The idea is to have a two pixel imaging system consisting of a pair of thermometers with low thermal inertia one facing upwards shielded from the ground and another that is ground facing and shielded from the sky.

The temperature difference and its rate of change gives you the extent to which the situation is likely to allow a frost and/of fog to form.

You also need windspeed and relative humidity. This is probably the simplest kit configuration to predict risk of frost of fog.

Dew point was always very important to astronomers and highway traffic monitors so you can get purpose built kit for this sort of thing.

It is essentially a fairly pure measurement of radiative heat loss to the sky which will under most circumstances be a very good guide.

Once you have a few temperature curves for typical conditions that's good enough. High cirrus can make quite a difference to thermal losses to the sky although nothing like as much thick low cloud does.

We were mainly concerned with not getting condensation onto the optics or mast head amplifier depending on the type of receiver/sensor.

I think what we have proposed might be OK for that and fairly robust minimal & cheap too.