A new moderately dark location in the Rhön, Germany, gave us the opportunity to capture several new images including the Cave Nebula shown here. The Cave Nebula, catalogue reference Sh2 155, is an emission nebula in the constellation of Cepheus. It is embedded in a larger region containing emission, reflection and dark nebulae. The brightest part of the nebula has an apparent magnitude of 7.7, being situated about 2400 ly from Earth. The somewhat unusual rendition shown here is derived from 6 filters in total: Hydrogen-alpha, sulphur-II and oxygen-III ultra-fast narrowband filters and g´, i´, and z-s´ photometric filters. The g´ filter (400-550nm) captures nicely the reflection nebula, whilst the i´ (700-845nm) and z-s´ (820-920nm) filters transmit infrared light at different wavelengths. The data from these two filters then needs to be colour-mapped to a visible region of the spectrum.  The following colour mapping has been applied to create this particular image: g´ mid-blue, O-III cyan, Ha yellow, S-II sunset orange, i´ crimson, z-s´ purple. The image is part of the “Colours” showcase.

Celestron RASA11
10Micron GM1000 HPS
SIGMA fp L (monochrome)
H-alpha, S-II and O-III ultra-fast narrowband filters and SLOAN/SDSS g´, i´, z-s´ photometric filters
11,5 hrs, ISO 400, F2.2, 620mm 

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