Planet observation with near
infrared light

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Projectmanager/Author: Silvia Kowollik
Page 2
Update: 10.05.2008


Optical planet observation usually is done during the night. An exception of this rule is the observation in the near infra red between 665 and 1050 nm. This also can be done during daytime. Apart from a longer observation possibility over the year, two further advantages arise as a result of the larger wavelength of the electromagnetic radiation: Turbulences in the terrestrial atmosphere obstruct the resolving power in IR not as much as in the visual range and with ir one can look deeper into the atmosphere layers of the other planets of our solar system.

For a successful observation within the near ir range with the 80 cm mirror telescope of the observatory extensive searches and tests are necessary in front of the observation  relative :

- the selection of a suitable filter
- the selection of a camera, which is sensitive enough in the planned wavelength coverage, in order to catch the weak light with high contrast.

At present the following filters are available:

  665 nm Longpass from Astronomik, based on Schott RG 665
     
  800 nm Longpass from B+W # 93
     
  890 nm Methanebandfilter (Bandpass, FWHM = 12 nm)
     

Graph at present not available

  1000 nm Longpass from Edmond Optics
     
  Spectral sensitivity characteristics of  DMK 21AF04.AS

With the selection of the camera, one has to make certain, that the camera contains a b/w chip, cameras with Colour-Chips are unsuitable.

With the DMK 21AF04.AS from the company "The Imaging SOURCE" was found a suitable camera. 640 x  480 square pixels with 5,6 x 5.6 my provide for a sufficient sensitivity, the selection rate of up to 60 pictures per sec. as well as the possibility fof longterm exposure up to 60 minutes per picture are ideal for planet photography with various filters.

After the selection of filter and camera on june 07th 2006 a first test with the 665 nm IR-Longpassfilter, RGB Filter (Astronomik) and the methanebandfilter on planet Mars and Saturn was done with the 80 cm mirror telescope. The test served for the examination of the theoretical initial considerations.

  Mars on 23.02.2008

Albedostruktures on the surface of Mars with several filters.

   
   

Saturn on 23.02.2008, Image captured with DMK 21 AF04.AS and 665 nm Longpassfilter at the 80 cm mirror telescope (f/10).
 

   

   

Saturn on 19.04.2008, Image captured with Webcam 740 Pro and UV-IR-Cut Filter at the 80 cm mirror telescope (f/10).

The bright spot at STrZ (upper right of planetary disc) near the central meridian is a huge hurricane in the atmosphere of Saturn.

   

 

Saturn on 19.04.2008, captured with DMK 21AF04.AS and 665 nm IR-Longpassfilter at the 80 cm mirror telescope (f/10).

With 665 nm IR-Longpassfilter the hurricane is not visible.

 

       

The treatment of the pictures was divided into 3 steps:

- subpixelexact averaging
- contrast rise
- sharpening

These first tests with the 665 nm IR-Longpassfilter at the 80 cm mirror telescope showed that the filters fulfill our expectations. The light of the planet atmosphere is effectively weakened. Particularly with deeply standing planets and during daytime sharper pictures than within the visual range have been captured

With suitable weather conditions further tests with other IR-Filters are accomplished in may and june 2008 at the observatory.

In September 2008 Uranus will be seen at the night sky and we will observe Uranus during the following month to detect clouds on the planetray disk.

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