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Contains:  Extremely wide field
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Faint Galactic Cirrus in Apus - Jacob's Ladder, 





    
        

            Gabriel R. Santos...
Faint Galactic Cirrus in Apus - Jacob's Ladder

Faint Galactic Cirrus in Apus - Jacob's Ladder

Technical card

Resolution: 3600x2400

Dates:Aug. 10, 2018

Frames: 40x120" ISO800

Integration: 1.3 hours

Darks: ~20

Flats: ~20

Bias: ~30

Avg. Moon age: 28.46 days

Avg. Moon phase: 1.28%

Bortle Dark-Sky Scale: 4.00

Mean SQM: 21.30

Mean FWHM: 3.20

Temperature: 3.30

Astrometry.net job: 2517807

RA center: 263.763 degrees

DEC center: -78.560 degrees

Pixel scale: 9.882 arcsec/pixel

Orientation: 47.846 degrees

Field radius: 5.938 degrees

Data source: Traveller

Description

Across the southern Constellation Apus, the Bird of Paradise, lies a field of very faint rarely imaged clouds - part of the Galactic Cirrus. In this wide field (20 full moons across), a beautiful region of filamentary structures can be seen. There are objects from many catalogs in this image, especially PGGC (Planck Catalogue of Galactic Cold Clumps) and IRAS. The amateur name of the region is Jacob's Ladder, a reference to the biblical ladder that led to heaven, featured in a dream Jacob had in the Book of Genesis.

Galactic Cirrus are veils that surround our own galaxy – made of dust and gas in the interstellar space. [1] It was first noticed on optical glass plates recorded at Palomar Observatory and subsequently cataloged by B. T. Lynds, in 1965. In the 2000s, Steve Mandel noticed faint cirrus in deep, wide field photographs near the North Celestial Pole, and labelled the nebulosity as the IFN, or the Integrated Flux Nebula. [1] This dust however is not only strongly present at the North Celestial Pole, but also near the South. The Southern region is however much less frequently imaged.

Nested in the field of nebulosity lies a much further away galaxy - IC 4633 - some 120 million light years away [2] IC 4635 is also in the middle of the cirrus. The very south declination (-77º) makes imaging this object a challenge and to most northern imagers it is permanently below the horizon.
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Photographing this object is not an easy task. Long integrations and exceptionally dark skies are paramount. Despite being at 22ºS latitude, this region never rises more than 35 degrees, so I had to deal with some light pollution from nearby cities. Unfortunately, a bit of relative brightness fidelity is lost: the field is so busy with very faint nebulosity that finding true sky background to model the gradients is a challenge. I personally fing the main nebula, Jacob's Ladder, to greatly resembles a giant ant. What do you think?

I also had some problems with the stars. As my 135mm lens is quite heavy, it flexes a bit on the camera bayonet, especially when the camera is pointed almost horizontally (objects low in the sky). Therefore, star quality suffered a bit of tilt - the upper left corner looks good, while the lower right had some pretty noticiable defocus and cyan fringes. I have now built a support ring (completely DIYed) that will address this issue. Finaly, my fast f/2.4 focal ratio helped substatially, but I wish I had more than only 80' of data. I look forward reshooting this target this year, as I absolutely love faint IFN/cirrus clouds.

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

Date and Time: August 10, 2018
Location: MG, Brazil. Rural Skies (Bortle 3-4, SQM ~21.3*calculated)
Camera: Canon EOS 80D (unmodded), at ISO 800
Lens: Samyang 135mm f/2, operated at f/2.4
Mount: Sky-Watcher HEQ5, tracking, unguided
Exposure Detail: 40x120s; total 80 min.

[1] R. Jay. GaBany cosmotography.com/images/galactic_cirrus.html ; [2] OpenNGC (Mattia Verga)

Comments

Author

grsotnas
Gabriel R. Santos...
License: None (All rights reserved)
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Faint Galactic Cirrus in Apus - Jacob's Ladder, 





    
        

            Gabriel R. Santos...