Located in the southwest corner of the constellation Cepheus is the large emission nebula Sharpless 2-142 and its’ embedded open cluster NGC 7380. NGC 7380 was first described by Caroline Herschel in 1787 and is approximately 7,500 to 8,000 light years distant. NGC 7380 is believed to be an open cluster that is presently in its formation stage and which has not yet dissipated the dust and gas cloud in which it has formed (Sharpless 2-142). Sharpless 2-142 is believed to be illuminated by the ionising radiation of the spectroscopic double star DH Cephei.
NGC 7380 is a fairly easy object for amateur telescopes under moderately dark skies. Sharpless 2-142 is a much more difficult object which requires an O-III filter and dark skies to see.
The image above is a color image taken with red, green and blue filters which are combined to create a color image. The many, many foreground and background stars in this field make it difficult to fully visualize the extent of the Sharpless 2-142 nebula and other objects in the field. The image below has been taken with a narrow band filter which blocks out all light except for a narrow window centered on the hydrogen-alpha emission line at 656.2 nm. Using a “narrow band” filter such as a hydrogen-alpha filter attenuates the stars and allows us to see that much of this field is filled with faintly glowing hydrogen gas. [Click on the image for a higher resolution version.]
Below is an annotated copy of the hydrogen-alpha band image which identifies some of the more prominent objects in the field. Sharpless 2-142 and NGC 7380 are labeled as is DH Cephei which is the star whose ionising radiation is causing the Sh2-142 nebula to glow. Also seen in the frame are the prominent dark nebulae LDN 1200 and LDN 1197; the open clusters King 10, King 18 and NGC 7423; and the smaller emission nebulae SH2-148, 149, Sh2-143 and Sh2-139. [Click on the image to see a higher resolution version.]
The next image below has had the stars removed using mono_starnet++ and shows more structure in the background hydrogen gas that fills the frame.
Acquisition Date: color image – August 28-29, 2019
h-alpha image – August 31 – September 1, 2019
Location: Tierra del Sol, San Diego County, California
• Imaging Scope – Takahashi FSQ-106 EDX IV
• Imaging Camera – ZWO ASI1600MM-C with EFW2
• Filters – Baader 36mm unmounted red, green and blue filters, Baader 36mm unmounted 7.5nm hydrogen alpha filter
• Guiding – Borg 77ED with ZWO ASI120MM-S
• Mount – Astro-Physics 900GTO
Camera Control – Sequence Generator Pro
Guider control – PHD2
color image –> gain 76, offset 15 – cooled to -15
h-alpha image –> gain 200, offset 50 – cooled to -15
color image – 40 x 120s for each of the red, green and blue filters
h-alpha image – 65 x 240 s
A larger view of the color image can be seen by clicking on the image below.