Astronomy Cast

Astronomy Cast takes a fact based journey through the cosmos as it offers listeners weekly discussions on astronomical topics ranging from planets to cosmology.

The observatory

Guidestar-Observatory is located close to the Rhine-Valley on the edge of the town of Weinheim. In 200 meters above sea level there is a fairly good and dark eastern and southeastern sky, to the west is quite a lot of light pollution because of the densely populated Rhine Valley.

Windeck WeinheimThe station with its roll-off-roof is operational since 2003.

For power supply two solar panels are feeding three solar batteries with a capacity of 105 Ah each. The power consumption for a typical night goes up to 60 Ah (for mount, ccd-camera, dew-prevention, focuser and laptop). For almost 3 years now the station is relying solely on solar power

Close to the observatory the old castle Windeck sits on a hilltop overlooking the city. It was built around 1100 and is today a popular destination for tourists and locals alike, with a beautiful view over the Rhine Valley. On days with good weather conditions one is able to see the "Pfälzer Wald" (30 miles) and sometimes even the distant french Vosges mountain range.

The telescope

In late summer 2004 our 8" Vixen VC200-Cassegrain was replaced by a Celestron C14 that is mostly in f/5 config with a 0.5x focal reducer from Optec compressing the focal length to 2100 mm.
Attached to the C14 is a TCF-S motorized focuser also from Optec. The @focus-feature in CCDSoft makes it easy to achieve a precise focus. Together with the CCDSoft-plugin CFWHM it makes life a lot easier.

Roll-off-roofC14 backendCity of WeinheimJupiter risingsolar panelsCastle Windeck

In nights with good seeing we are able to achive FWHM of 1.9". Focus drift due to temperature differences can be compensated by monitoring the optical tube temperature with a probe.
The primary mirror of the C14 is locked with two threaded bolts to minimize the mirror shifting, that is so typical for SC-type telescopes.

The C14 is supported by an Astro-Physics AP1200GTO. This piece is a dream come true. Without to much tweaking of the PEC-curve the periodic error is less than 3 arcseconds. Active guiding with the build-in guidechip of the SBIG ST-8 camera is working very reliable.

PEC of AP1200The graphic shows the raw PE without correction in red (peak to peak 4.6 arc-sec). In blue with enabled PEC. The correction curve was generated with PemPro out of over 500 data points and 5 worm cycles. (Click on graphic to enlarge)

The pointing so far isn't perfect, mostly we achieve an accuracy of about 7' after a 50 degree slew and 15' after a meridian flip - probably still a mirror shift issue. Thats good enough for most of our work. We tried to improve the pointing with Software Bisques TPoint. But there seems to be some unpredictable movement that can not be compensated by software – maybe the dovetail is another weak part in the system and we have to replace it with tube rings.

at home ...

the astrometric program started in 2003 right after the completion of the astro-shed with the 8" Vixen VISAC VC200. Soon I was infected by the "blinking virus" and most of the "shutter-open-time" was devoted to measuring minor planets. Even though the golden age of the 90s was over, when a lot of minor planets where discovered by amateurs, it was and is fun taking part in the follow-up work and supporting the big surveys. The main reason for replacing the 8 inch in 2005 with a 14 inch Schmidt-Cassegrain was pushing the limiting magnitude to 20.7 mag. The only way to stay in the game. And after a long wait we were awarded by our first discoveries in September 2008 (2008 QX19 und 2008 RZ77).

... and abroad

For almost two decades our favorite place for doing astrophotography abroad is the mediterranean region of the Provence in southern France. In the late 1980s we made our first trips to the (in Europe) well know Observatory of Puimichel. With its 1 meter Newton it was then the largest telescope built and operated by an amateur.

In the 90s we discovered a nice little place 90 km west of Puimichel on the Plateau d'Albion. It is located north of the Luberon mountains and a sparsly populated region with an average altitude of 900 m. Lots of images in the gallery were made at this place. Usually good weather is accompanied by strong winds (Mistral). So you can have clear nights with a high degree of transparency and a real dark sky, but struggeling with bad seeing. For those trips the equipment is always with shorter focal length (less than 500 mm) and a good wind shelter is mandatory.