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Comparison of Filtering without Filtering

Scans across the Jovian disk including 2 Satellites (IO and EUROPA).

Images were recorded using a 280 mm diameter Schmidt-Cassegrain telescope with a QHY6 camera equipped with a ICX255 chip. Images were taken on the 14th of July 2009, around 0h 30min UTC.

Exposure times were 10 msec for the images without filter ('none') and 1000 msec for images with filters (either 17nm, the "new" one or 21nm (the "old" one).

Two different filters have been compared, the "OLD" filter from a charge made in 1996 with 21nm FWHM and the "NEW" one, made recently, with a FWHM of 17nm.

No Filter
10 msec

Old filter
1000 msec

New Filter
1000 msec



For the following intensity values, comparing the Jovian satellites with HIP 107302, other images have been taken on the 25th of August around 23h 55min with the 17nm methane band filter and the QHY6 camera with a ICX255AL chip. Images were again taken using a 270mm SCT with 2800 mm focal length.

Here is a table of the total intensities of the Jovian satellites and 45 CAP, as measured from these images. A 17 nm bandwidth (FWHM) methane band filter centered around 890nm has been used.



Used pixel size (1x2 binning)
 9.8 µm  [in x direction]
 12.6 µm  [in y direction]
Pixel size in arcsec:
0.72''
0.93''
Area of one pixel in the sky
0.67 arcsec²


Total intensity of IO   (normalized to 1)
1.00


Total intensity of Europa     (rel. to IO)
0.81


Total intensity of 45 CAP    (rel. to IO)
0.27


Intensity of Jupiter near to   (rel. to IO)
the dis- and reappearance point
per pixel:

0.02




Everything depends now on the image quality. If the star has a disk of 2 arcesec in diameter, it covers about 4/0.67 = 6 pixels. This results in an intensity of 45 CAP per pixel of 0.27 / 6 = 0.045 units, which is still more than the 0.024 units per pixel of the Jovian disk.

Interesting informations and graphics you can find on the special webpage for this event made by Gerhard Dangl.

By monitoring disappearances and reappearances of Jovian satellites behind the Jovian limb, you can get an idea, what you have to expect.



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