Crescent Nebula, also known as NGC 6888, Caldwell 27 and Sharpless 105, is an emission nebula situated in the constellation of Cygnus roughly 5000Ly away and was discovered by William Herschel in 1792.
The Nebula was formed by the fast stellar wind from the nearby star Wolf-Rayet star WR 136 (HD 192163) which is colliding with the slower moving wind when it recently formed into a red giant approximately 250,000 – 400,000years ago. |
The resulting X-ray emitting stellar wind is a result of two shock waves, one moving in the ward and one moving outward resulting in the inland moving shockwave heating the stellar winds.
This object is faint which requires the minimum O-III and Ha filters for the nebula to be found visually. With Astrophotography the nebula can be photographed, but with minimal success without the required filters..
This object is faint which requires the minimum O-III and Ha filters for the nebula to be found visually. With Astrophotography the nebula can be photographed, but with minimal success without the required filters..
The picture above is an example with no filter using a ZWO Asi 178mc, showing how important it is for Filters to be used with Emission nebulas. Apart from the heavy star bloat (and the Amp glow which will be extreme if you push the data too far in post processing and not enough calibration frames), the data collected is minimal.
Below are several examples with Optolong L-eXtreme filters with varying post processing styles. One shows the more blue OIII with the surrounding Ha nebulosity, and the other prioritising the more Ha over the OIII.
The one on the right, showing more Oxygen-III (OIII), looks more natural, but the left side one shows more hydrogen-alpha (Ha) throughout the crescent and surrounding regions. Both pictures below are 7 hours of exposure at 600-seconds per exposure (10 mins). Stacked in Deepsky stacker and processed in Pixinsight. Both pictures are from the same data collected and just processed differently.
The one on the right, showing more Oxygen-III (OIII), looks more natural, but the left side one shows more hydrogen-alpha (Ha) throughout the crescent and surrounding regions. Both pictures below are 7 hours of exposure at 600-seconds per exposure (10 mins). Stacked in Deepsky stacker and processed in Pixinsight. Both pictures are from the same data collected and just processed differently.
The setup
Scope - Skywatcher 72ed
Mount - Skywatcher eq5 goto
Guide scope – ZWO 30mm
Guide Camera – ZWO Asi 120mm mini
Control box – ZWO ASIAIR Pro
Filter – Optolong L-eXtreme 1.25
Filter drawer next to the camera sensor
Fox Halo 96k power bank
Dew heaters with their own power banks on both guide scope and main scope
All the data was stacked with DeepSkyStacker and Processed in Pixinsight. (Other software is available which is free and will is linked in the equipment used/ software tab)
Scope - Skywatcher 72ed
Mount - Skywatcher eq5 goto
Guide scope – ZWO 30mm
Guide Camera – ZWO Asi 120mm mini
Control box – ZWO ASIAIR Pro
Filter – Optolong L-eXtreme 1.25
Filter drawer next to the camera sensor
Fox Halo 96k power bank
Dew heaters with their own power banks on both guide scope and main scope
All the data was stacked with DeepSkyStacker and Processed in Pixinsight. (Other software is available which is free and will is linked in the equipment used/ software tab)
This was a fun target. it is quite faint, but can be fun processing this target regardless of which way you choose to process it. The amount of detail is staggering in the crescent and surrounding area.
Update
I have recently taken this target again, but this time with my RASA. I assumed I had done this target with the RASA, but clearly, I was wrong. Below are two pictures which are processed slightly differently.
The RASA has been recently replaced due to a faulty mirror which caused half-star halos to round stars, which on the larger stars ruined the picture. I created a solution for this and carried on using the RASA which was a simple fix till the scope was replaced.
Below is 2 hours of total exposure at 60-sec sub-exposures, dithering every 3 frames.
The RASA has been recently replaced due to a faulty mirror which caused half-star halos to round stars, which on the larger stars ruined the picture. I created a solution for this and carried on using the RASA which was a simple fix till the scope was replaced.
Below is 2 hours of total exposure at 60-sec sub-exposures, dithering every 3 frames.
My recent version of the Crescent Nebula was taken on 27/05/23 using the following setup.
Scope – Celestron RASA 11
Mount - Skywatcher EQ6 R Pro
Guide scope – ZWO 30mm
Guide Camera – ZWO ASI 120mm mini
Main Camera – ZWO Asi 533mc Pro
Control box – ZWO ASIAIR Pro
Filter – IDAS NBZ Nebula Booster 2”
Starizona Filter drawer next to the camera sensor
Fox Halo 96k power bank
Dew heater with its own power bank on the guide scope
Main scope Celestron ring dew heater powered though the ASIAir
and consisted of 90 frames at 60 secs for a total of 1hr 30 mins of data.
Scope – Celestron RASA 11
Mount - Skywatcher EQ6 R Pro
Guide scope – ZWO 30mm
Guide Camera – ZWO ASI 120mm mini
Main Camera – ZWO Asi 533mc Pro
Control box – ZWO ASIAIR Pro
Filter – IDAS NBZ Nebula Booster 2”
Starizona Filter drawer next to the camera sensor
Fox Halo 96k power bank
Dew heater with its own power bank on the guide scope
Main scope Celestron ring dew heater powered though the ASIAir
and consisted of 90 frames at 60 secs for a total of 1hr 30 mins of data.