Occultation of star Aldebaran by the Earthmoon
December 23, 2015

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Report from Nonndorf in Austria (15.2356 E, 48.7871 N)
The bright star Aldebaran (Alpha Tauri) in the constellation Taurus is occulted several times in the years 2015-2018 by the Moon. In addition to these occultations during this period several close encounters will happen in the sky. These events take place in the daytime and in the night sky. In the evening of December 23, 2015, there was an occultation of Aldebaran by the Earthmoon which was observable on the southeast sky in northern Austria. The begin and the end of this occultation was captured on videos with GPS time insertion in Nonndorf. Sadly, the sky was mostly covered by clouds. Often only the moon was visible through the clouds. Mostly the bright star Aldebaran was invisible with the naked eye. Because of its spectral class K5 III the star Aldebaran emits a large amount of light in the long wavelength redish range. So I tried recordings with infrared filters on the cloudy sky. The filter used for occultation begin was a Planet IR Pro 807 from Astronomik. The relatively steep transmission curve of this filter ensures that wavelengths are blocked below about 775nm and only longer-wave lenghts can reach the CCD of the video camera. At the occultation end the cloud layer density has decreased. So I had to use a IR-pass filter RG850 from Edmund Optics to avoid overexposure. This filter blocks wavelenghts below 700nm, reaches a transmission of 50% at 850nm and a transmission of 90% at 950nm. The Sony ICX419ALL CCD used in the video camera WAT-120N still has a relative sensitivity of 37% at 775nm but reaches only 7% at 950nm. Thus, this camera is also very well suited for recording in optical infrared. With this IR filters the scattered light caused by the clouds could be clearly decreased.

The telescope used was a 10 inch Newtonian mit a focal length of 1200mm. The video camera used was a WAT-120N CCIR in none integrating mode. The used infrared filter was placed in a filter slider. The video time inserter uesd was a KIWI-OSD. The mount Skywatcher EQ8 was controlled by the notebook via EQMOD and Guide9.