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Contains:  IC 4601, IC 4592, The star χOph, The star ψOph, The star νSco, The star ω2Sco, The star ω1Sco, The star β2Sco, The star Graffias (β1Sco)
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The Blue Horsehead Nebula, 


            Gabriel R. Santos...
The Blue Horsehead Nebula

The Blue Horsehead Nebula

Technical card

Resolution: 3132x2205

Dates:July 4, 2016Aug. 1, 2019

39x180" ISO1600
38x120" ISO800

Integration: 3.2 hours

Darks: ~25

Flats: ~24

Bias: ~40

Avg. Moon age: 0.24 days

Avg. Moon phase: 0.11%

Bortle Dark-Sky Scale: 2.50

Mean SQM: 21.60

Mean FWHM: 2.90

Temperature: 10.90 job: 2989027

RA center: 243.546 degrees

DEC center: -19.358 degrees

Pixel scale: 6.904 arcsec/pixel

Orientation: 166.914 degrees

Field radius: 3.673 degrees

Data source: Traveller


This complex lies in the constellation Scorpius along the plane of our Milky Way Galaxy. This is a fantastic object to be imaged, although it never rises much above the horizon for Northern imagers. Being at 22ºS, I have a particularly privileged view of this area. The star near the eye of the horse is embedded in blue reflection nebula IC 4592, over 400 light-years away. The horse's gaze seems fixed on Beta Scorpii, also named Graffias. Toward the top right, near the horse's ear, is another striking bluish reflection nebula, IC 4601. The characteristic blue hue of reflection nebulae is caused by the tendency of interstellar dust to more strongly scatter blue starlight. [1]

The famous “Horsehead Nebula”, B33 in Orion is also a stunning nebula. I find both of them to be interesting and beautiful, but this target happens to be a much better match for my equipment than its tiny black brother.

This image is composed of my best two sessions on this beautiful nebula. The first one is actually 3 years old, from 2016. This year, during the 12th Brazilian Astrophotography Meeting (EBA) I managed to capture some more data. The framing was quite similar, so I integrated all of it! Unfortunately, EBA’s conditions were not perfect for this image (some cirrus and imperfect focus), but it contributed positively to the SNR of the integration. Processing this nebula is quite difficult – many field stars, faint nebulosity and subtle colours. It is thus far my best IC4592, but I don’t think it will be my last – next season I’ll try this target with the faster Samyang setup.

Constructive criticism, comments and suggestions are more than welcome in the comments section. Thank you for taking your time to look at this image!

Dates: 04/07/2016 & 01/08/2019
Locations: MG, Brazil and 12th EBA, GO, Brazil. Dark-Rural Skies (Bortle 2-3, calculated SQM ~21.7)
Camera: Canon EOS T4i/650D (stock) at ISO 800 and ISO 1600.
Optics: Tamron 70-200mm f/2.8; operated at 200mm f/3.5
Mount: Sky-Watcher HEQ5, tracking, guided
Exposure Detail: 38x120s + 39x180s, total 193min or 3h13.

[1] APOD 2013/04/02 and APOD 2018/11/05



Gabriel R. Santos...
License: None (All rights reserved)

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The Blue Horsehead Nebula, 


            Gabriel R. Santos...