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Review: Aurora Cloud Sensor


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I've had this for around a year now so I've had a long time to get to know it. I was holding back on posting up a review as I've been waiting on a new release of software which is still to materialize. So, I will add a note for the things that I believe are about to get fixed..


If you have ever tried to catch a clear spell or ran an imaging session unattended, you will know how critical it is to have good info on two things: cloud cover and rain detection. There are many ways to do this, ranging from the very cheap DIY / Arduino projects right up to the Boltwood Cloud Sensor stretching up to the thousands of pounds. The Aurora, at £173, sits at a price point that is still within the reach of a lot of observers / imagers, but is it any good?


The Aurora splits into two sections, a bottom piece that allows it to be mounted, then a removable top section containing the electronics. The external sensors are nicely mounted in a PCB. The top section with the sensors holds a light sensor, rain sensor and sky / ambient temperature sensor.


A great little feature of the detachable top is that I was able to buy a second box and phoenix connector for quite cheap. This means I can detach the electronics part, replace it with a blank top, and use the leftover base part to make it into a portable sensor that can be taken to star parties. They should really mention this as a feature and offer secondary kits as this is extremely useful.


One of the reasons I never went down the DIY route was to avoid the complications that can arise with mounting electronics to the exterior of an IP rated box. One year down the line, and having taken a barrage of abuse from the weather, everything is still happy inside and outside the Aurora.


The Aurora connects to a PC via RS232. There is a fairly generous 10m cable with it, but this is easily extended and you should get 30m fairly easily as it runs at quite a low baud rate. Wrapped up in the cable is the power that goes to a DC power supply, and a relay output that can be wired to something to cause an alarm on certain conditions.

The software is really easy to use, it gives a few different tabs. The main one is a quick-look colour coded representation of what the conditions are. The second is a setup page that lets you tweak the values for all the different states. The third is a real-time graph of the data, select-able in 1, 2, 24, and 48 hour graphs. My data seems to drop away at 24 hours, even though it's all recorded in a text file, something I was hoping to see fixed in the new software.


Note: There are a few spikes now and again in my data, this is a bit of an irregularity that is supposedly getting fixed in the new version of software.

One thing I should mention that isn't obvious when you start to get into cloud sensing is just how good it is. You can see in the graph above there is a clear patch around 2-4am. This shows as a flat line a -10c. The IR sensor can actually detect slight fluctuations in temperature that caused by really thin cloud, even when you could be standing outside and it looks completely clear. This is great for monitoring how good the conditions are, and you can see it reflected in subs. It's great for selecting data when stacking.

I was able to split off the RS232 and also feed it to an AMX system, this means I can get a nice graphical representation using Mobai through the iPad. This also gives me the ability to use the Aurora without the PC and have alerts & alarms still work even if the PC fails, a great reliability feature.



For the money, I think the Aurora is a fantastic product. I fail to see what extras you could get from one of the more expensive products. It's really easy to use the incoming data from the Aurora to manipulate a Boltwood text file, this allows it to mimic it's use and be compatible with all the usual automation programs, I use it with CCD Commander.

As an observer looking for the odd clear spell, or as an imager wanting to keep an eye on conditions, you will see huge benefits from buying one of these units.

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Would it detect snow cloud, or in other words how well does it work at the extreme low end of the temp range? I had a near disater this winter when I left the obsy open cameras running etc, nipped inside for a warm up and a brew. When I came back to check things 20 mins later there was a inch of snow in the obsy.

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Would it detect snow cloud, or in other words how well does it work at the extreme low end of the temp range?

Yes, you will see around +10-20c jump in any cloud. This varies obviously depending on season, in the winter I think the sky temperature was around -20c, with the sky around 0c.

I had a near disater this winter when I left the obsy open cameras running etc, nipped inside for a warm up and a brew. When I came back to check things 20 mins later there was a inch of snow in the obsy.

Glad you pointed this out, I forgot to mention it.

The rain sensor itself is heated. This gives two advantages. Firstly, it evaporates rain droplets quite quickly. This means the rain level you see from it is a better reading of actual rainfall, rather than just how wet the sensor is. Secondly, it melts snowflakes really quickly, although they should trigger the rain sensor anyway, this gives an added reassurance that it will catch it.

I've never actually timed how long it takes to trigger during snowfall, but the sensor does pick up very small water droplets, depending on the severity of the oncoming rain it should trigger before any real damage is done to optics. A good test I found was to wet a toothbrush and hold it just away from the sensor, then brush your finger along the wet brushes, this will produce a really fine mist of water droplets. Just a few of these on the sensor is enough to make a difference, it's fairly sensitive.

The heating of the rain sensor does skew the ambient temperature reading as this this is taken from the chassis of the IR sensor (in the picture above it reads 22c when in fact it's about 15c), but this is the least relevant bit of information, and is only really shown as it's part of the IR sensor anyway. If you want real temperature recording you would need a separate unit. I bought a little USB temperature sensor from eBay that is quite cheap, it can be put anywhere in the obs on a long USB lead.

Edited by Euan
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the rain sensor heater will provide enough heating to stop dew forming on the ir sensor.

thats the problem i have with my home made unit as i havent fitted the rainsensor yet so the ir stops working due to dew.

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  • 6 months later...

I too have been impressed with this cloud sensor. Since there is so little decent weather for observing I sometimes leave my observatory running under the control of CCDAutopliot5 now that Aurora have produced new software that produces a Clarity data file that CCDAP5 can read. I have been very cautious so far as it was only a Clarity I file and the rain reporting was suspect. On a few occasions however the cloud sensing has correctly prompted scope parking followed by roll-off roof closure. On others I have checked the Met Office Radar and shut down remotely from the house seeing showers approaching. I have used the relay output to light a warning red LED in the attached warm room for when I am imaging 'manually'.

However there is now a new ALPHA version that generates Clarity I and Clarity II data files that can be read by both CCDAP5 and CCDCommander. It seems quite stable and has been running all night so I can check it out. I do notice the default value in settings for Rain is 10, whereas 1 would correspond to the current Cornish light mizzle. However this can be altered to suit - better a false positive than the other way round.

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  • 5 months later...


sorry for bringing this old thread up, but this seems to be the only one about Aurora Cloud Sensor I've been able to find.

There's a few questions I'd like to ask, but first a bit of background, so you know my wants/needs, budget, etc.

I'm currently working for a finnish observatory and researching different ideas and possibilities for their particular needs, one of which is a cloud/rain detection. As you might know, the temperature differences between winter and summer in Finland tend to be around 50-70 degrees centigrade at worst from +35 in summer (in the sun, not in the shade) to -35 in winter. This means the equipment used outside need to be very sturdy and weatherproof. Since the equipment will be paid by the observatory rather than a single person, the prize isn't the first priority in the choosing process. Still, this doesn't mean I would go straight for the weather stations/cloud sensors costing more than £1000-£1500, if there's something that suits their needs for a £100-£200.

So what I would like to know is:

  • do you think, with the exprience you have from using the Aurora product, that it could handle the intense temperature changes and endure all sorts of weather from sleet to hails?
  • does the product send any sort of wireless signals? This would be a problem, because the obseravory has a radio telescope, and all sort of data transfer should happen via cables (ie. GSM, 3G, wlan, bluetooth and the sort are out of question). Even the usage of microwave ovens is prohibited while they're doing observations.
  • I noticed the software has an alert tab, but is there an option to run a script triggered by the alert? What sort of alerts does the software actually have embedded (email, sms, executing a script and so on) ?

That's all for now, thanks in advance. I might add some further questions as I keep researching these things.

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  • 10 months later...


I have just bought one of these little additions as a relatively cost effcetive solution in my quest for full automation of my dome. Certainly at present the installation was flawless and it was up and running in under 5 minutes, another 5 minutes to do the set-up and data starts streaming. All I have to do now is to try to understand what it is telling me!! Will let you know how I get on but a bit more help in the user guide would help.



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Wow, I didn't know devices like that existed.

How sturdy is it? I.e. could it be permanently mounted outside, to let you know that after a week of cloud, there's now an opportunity to catch some stars?

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It is a standard type of device for any remote or otherwise unattended observatory. Both CCD Autopilot and ACP support them and open roof/dome upon clear condition and aborts the imaging with a dome/roof shut when he clouds roll in or a raindrop hits. Works wonders.

They are always housed in at least IP65 classed enclosures and are built to last in the outdoors. I have had my AAG Cloudwatcher for a year and a half now with no hickups.


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  • 2 months later...

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