Hemisphere:  Southern  ·  Constellation: Monoceros (Mon)  ·  Contains:  19 Mon  ·  20 Mon  ·  IC466  ·  NGC 2311  ·  NGC2311  ·  Sh2-286  ·  Sh2-287  ·  Sh2-288  ·  The star 19Mon  ·  The star 20Mon
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Sivan 5 and 6: First Time Ever Imaged?, 


            Jeffrey K Lovelace
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Sivan 5 and 6: First Time Ever Imaged?

Imaging telescopes or lenses: Takahashi FSQ106 EDX4

Imaging cameras: FLI ML-16070M

Mounts: Software Bisque Paramount MyT

Guiding telescopes or lenses: Stellarvue F50

Guiding cameras: ZWO ASI174mm Mini

Focal reducers: Takahashi 645 QE 0.72x Reducer for FSQ106

Software: Sequence Generator Pro V3.0  ·  Photoshop CC  ·  Starnet ++  ·  PixInsight Processing Software  ·  Open PHD Guiding PHD2 Guiding  ·  The SkyX

Filters: Astrodon Hα 50mm round 5nm  ·  Astrodon B 50mm square E Series  ·  Astrodon G 50mm square E Series  ·  Astrodon R 50mm square E Series  ·  Astrodon O-III 50mm square 3nm  ·  Astrodon S-II 50mm Square 3nm

Accessory: Optec Gemini Focusing Rotator

Dates:Jan. 13, 2021

Astrodon B 50mm square E Series: 37x60" -25C bin 1x1
Astrodon G 50mm square E Series: 37x60" -25C bin 1x1
Astrodon Hα 50mm round 5nm: 52x1800" -25C bin 1x1
Astrodon O-III 50mm square 3nm: 50x1800" -25C bin 1x1
Astrodon R 50mm square E Series: 38x60" -25C bin 1x1
Astrodon S-II 50mm Square 3nm: 46x1800" -25C bin 1x1

Integration: 75.9 hours

Darks: ~23

Flats: ~25

Bias: ~50

Avg. Moon age: 0.32 days

Avg. Moon phase: 0.12%

Astrometry.net job: 4271813

RA center: 7h 0' 41"

DEC center: -3° 49' 37"

Pixel scale: 4.894 arcsec/pixel

Orientation: 0.135 degrees

Field radius: 3.132 degrees

Resolution: 3840x2556

Locations: Sierra Remote Observatories, Auberry, CA, United States

Data source: Own remote observatory

Remote source: Sierra Remote Observatories


Data Acquisition from 2020-10-17 until 2021-01-13
DSO Color Mapping: SH-HO-O with RGB stars
Original Image (Pix) Scale: 4.00

I believe this is the first successful color image of the nebulae Sivan 5 and Sivan 6. Siv 5 is the larger one at the top. Siv 6 lies beneath it and includes Sh2-287, the bright section bottom center. The swooping HII wisp that stretches from left to right and looks like a ship’s hull isn’t officially part of either nebula, and is probably just part of the interstellar medium.

Astronomer J.P. Sivan and his associates identified these nebulae in 1974 from an Hα survey of the Milky Way in which they appeared as a couple of tiny, irregular blots. Apparently, no one has bothered with them since.

Sivan Nebulae are large and exceedingly faint: this image spans over 5° of the constellation Monoceros and uses 74 hours of narrowband data. For 74 hours I got good Hα, adequate SII, and faint but usable OIII. The shorter exposures I’ve seen of this region scarcely reveal these Sivan objects at all. Even the three Sharpless objects here barely appear. If you find any images that clearly show these Sivan nebulae, please let me know and I will update this page.

As this is a potential first, I wanted to keep the colors close to true. This is an SH-HO-O treatment with only a little of the Hα in the green channel. The stars are RGB.

...Speaking of blots, in the cosmic Rorschach ink blot test that is interstellar space, to me this looks like a dog (or seal) sitting in a boat with a single sail. So, I call this the Seadog Nebula.