Tech – Motorized main mirror cover

Over the winter it was not possible to work at the KRO site to finish electrics and other building related stuff due to heavy snowfall (Read in an upcoming post more about the weather conditions at the KRO site).

However, due to this circumstances we had time to dismantle the telescope in Davidschlag (Want to know more?) and start with the technical updates we have planned for it.

One of these updates is building a main mirror cover to prevent the mirror from gathering dust when not used.

For this we had to develop a light weight motorized construction, which we can add to the mirror box.

We came up with a light aluminum frame (split into two flaps) which is powered by a 12V Motor.

The frame now looks like this (without flap cover):

The finished main mirror cover frame with the small 12V motor on the right, powering both cover flaps. (Photo by Günther Truhlar, 07.02.2019)

The following video shows the frame in action:



Tech – Dismantling the telescope

Since the winter was/is very hard in the alps, at least on the top of the mountains, and we couldn’t work at the observatory site, we had some time to work on the telescope. To be able to do so, the first thing was, dismantling the telescope at its current location, Davidschlag.

A last picture of the old telescope on its original location. Next time when it is back there, it will be highly updated and initial testing can begin. (Photo Erich Meyer, Erwin Obermair, 1999)

We found a day where we didn’t had any snow and the weather was fine enough to.

So we organized some transport capabilities and some aid to handle the fairly heavy telescope parts and start dismantling it. Luckily we didn’t had big problems, it all went quit well and so the telescope was in pieces and packed after a few hours. The following pictures show the process.



We have also made a timelapse video of the whole day:


We temporarily stored the telescope in a garage of an observatory colleague and we started working on improving the tech, namely the encoders and the motorized main mirror cover.

Tech – LBB (Biss-C protocol converter)

As mentioned in several prior blog posts (Tech – The Telescope Mount, Tech – First Hardware/Software Test, Tech – Alignment & Guiding (Take 3) – Fail, Tech – Telescope Control (Part 2) and Tech – Using Renishaw Absolute Encoder) we plan to use absolute encoders on our telescope mount.

As we found out, the Sidereal Technology SiTech Servo II supports absolute encoder we decided to go for it. To be able to connect the 26bit Biss-C compatible Renishaw Resolute read heads to the SiTech Servo II (which speaks RS232 and not Biss-C) we needed to obtain a small interface box provided by Sidereal Technology: the so called LBB (Little black box).


Essentially it is a prtocol converter which converts the Biss-C protocol electrically and logically to the RS232 interface of the SiTech controller.

Therefore you find some level converters and a small microcontroller inside this box.


So what’s next?

We now have to order the correct sized encoder rings and read heads (in our case the 413mm diameter ring for the RA and the 200mm diameter ring for the DEC axis) and once we got them adapt the mount to be able to mount the rings to it. The main problem here will be to find a suitable and easily adjustable read head mount (the tolerances here are quite narrow). But let us discuss this in another post.


Tech – Dome Improvements

As mentioned in Tech – The Dome and Under Construction – The Dome, we are using a ScopeDome 4m dome to house our telescope.

The stock dome itself is quite well made, but we identified some points to need some improvement – mostly related to the harsh conditions we face in the winter (high snow, fast winds and low temperatures).

The first issue we will solve is related to the shutter mechanism. This was identified through a small incident: we had some very strong winds a few weeks ago, and the wind managed to lift the shutter a little bit so that the drive gear jumped out of the gear rack.

The detached gear. (Photo by Rudi Dobesberger)

We are currently investigating on how to improve this situation. The Problem is, that the shutter has too much play, and therefore it is possible that the gear jumps out of the gear rack.

We think that in this case the wind entered the dome through the several gaps at the shutter and at the gear rim.

To prevent that the wind pull through the dome in the future and to prevent drift snow to enter the dome, we installed a rubber lip at the shutter.

The ready installed rubber lip, which should prevent drift snow and wind inside the dome. (Photo by Joe Stübler, 17.11.2018)
Detail photo of the installed rubber lip. (Photo by Joe Stübler, 17.11.2018)
The right hand part of the rubber lip. (Photo by Joe Stübler, 17.11.2018)

We also plan to install similar lips inside and outside the gear rim, to prevent that insects have easy play when entering the dome.

Another improvement dedicated to the gear rim, was to exchange all screws with stainless steel screws. We also reworked all gear rim mounting holes to make sure, the rim is 100% even and therefore the dome can run very smooth and the driving gear doesn’t get detached from the gear rim.


Star Park Hohe Dirn – Impressions 2

On November the 10th 2018, we had another work project to do (Under Construction – Electrics (Part 2) ) at the KRO. So we left the fog in the valleys behind us and enjoyed the perfect weather on the mountain tops.

Below you’ll find some impressions of this day.

At such days the peak of the Hohe Dirn is quite crowded and it was quite difficult to take some shots without hikers on the road. Another side effect is, that we have to constantly explain to tourists what we are doing here.

Under Construction – Electrics (Part 2)

As installing all the electrics is quite some effort, we had to spend another day installing them.

This day was entirely dedicated to install all power sockets in the engineering room and the dome itself.

Installing the power sockets in the engineering room. (Photo by Robert Mayrhofer, 10.11.2018)
Installing the power sockets in the dome. (Photo by Robert Mayrhofer, 10.11.2018)

There are still a lot of things open, we have to do in the near future:

  • installing all switches
  • finalizing the switchboard
  •  installing the lights

Some of the tasks are currently blocked by the carpenter. He has to finish the ceiling and the staircase to the dome. After this, we can install the lights and switches (some of them will be mounted directly on the staircase).

But these things are subject matter for another post, and day, dedicated to electrical installation.

General – Lets Talk about light pollution

Light pollution – a global problem

80%¹ of  earths human population suffers from light pollution, in Europe and the USA even 99%¹. The animal wild life suffers even more, and also plants are reported to be influenced by light pollution¹.

But what is light pollution? In the past this term was only known by the group of persons which are directly affected by it: astronomers and biologists. But the greater public didn’t know the term. But in the last few years, the problem has grown so big, it has even broached in mainstream media.

Light polluted sky over Linz. Taken 30 km south of Linz near Aschach an der Steyr on 12.04.2013. The light pollution increased since. (Photo by Sternfreunde Steyr, Infos about light pollution and the original image can be found here)

Light pollution basically is the presence of anthropogenic light in the night environment². It is created by extensive use of artificial light, such as street lamps, building illumination, etc.

And what are the negative effects of light pollution?

First of all, the lit night sky affects our very own metabolism and psychology². But not only humans suffer from light pollution, so do the animals. And here foremost the insects. You only have to look at a street lamp — you immediately see myriads of insects buzzing around the light. They get trapped in the light, or burned by the very hot light source or just forget to feed and mate. Another less known fact is, that light pollution also has an effect on plants. Plants also rely heavily on the natural day-night cycle which is interfered by the artificial lights.

And of course we astronomers suffer from it, because the free sight to the stars is taken away from us. The artificial light is so powerful that it easy outshines the very faint objects in the sky. In densely populated areas, it is even so strong, that you struggle to see any star at all!

Star Park Hohe Dirn – a perfect sky

The Star Park Hohe Dirn, the location of the KRO, is luckily (yet) a whole other story. We have all major cities in the north and shielded by a small rising ground behind the observatory. So Linz, Steyr, Wels, etc. are well shielded.

The other thing is the south: There are basically two national parks, the national park Kalkalpen³ and the national park Gesäuse³. So in the south there are just mountains and forests for about 120km (Graz). On the east we also have more or less hills and mountains until Vienna comes up in about 150km.

This geographical specialty can now be seen in a light pollution map of the region:

Light pollution map of Austria. The red circle marks the approximate location of the KRO. You can see, it is at the northern border of the very dark area. (Source:, original map can be found here)

Due to this circumstance we have chosen the spot for our star park and for the observatory.
Another lucky circumstance is the local seeing. Our visual observers with their huge dobsonian newton telescopes (> 20″) have reported seeing values from well below 0.5″! And this not just once in a lifetime — these values are achieved several times in a year.

¹Lichtverschmutzung –
²Light pollution –
³Detailed information on the national park Kalkalpen and Gesäuse can be found on the german Wikipedia pages of Nationalpark Kalkalpen and Nationalpark Gesäuse.