ASTRO:
     type=Supernova remnant
     const=Gemini
     mag=12
     dist=5000 ly
     size=70 ly
IMAGE:
     location=EB Driveway
     BrtlCls=4
     moon=58% (avg) WxCr
     exposure=DSLR OSC 41x600s (6.8h), ISO3200
EQUIPMENT:
​     optics=ES102CF APO / Stellarvue 0.8x rdcr, FL(eff.)=571mm, f(eff.)/5.6
     camera=Nikon D90 (mod)
     filter=Radian Triad Quad NB
     mount=Celestron AVX EQ
     guiding= Orion 60x240mm, ZWO ASi244MC
SOFTWARE:
     acquisition=Stellarium, APT, PHD2
     processing=DSS, Photoshop (RCAstro), LrC

Sharpless 248 (Sh2-248), also known as the Jellyfish Nebula, and IC 443 is a galactic supernova remnant (SNR) in the constellation Gemini.  It is located near the star Eta Geminorum at a distance of roughly 5,000 light years from Earth.

The Jellyfish may be the remains of a supernova that occurred appx 16,000 years ago. The same supernova event likely created the neutron star that is the collapsed remnant of a stellar core inside the Jellyfish. It is one of the best-studied cases of a supernova remnant (SNR) that is interacting with surrounding molecular clouds.

NASA's WISE (Wide-field Infrared Survey Explorer) spacecraft - an infrared-wavelength astronomical space telescope active from 2009 to 2011, and the predecessor to NEOWISE - a re-purposing of the space telescope for cometary reconnaissance - captured an image of the Jellyfish that provided an improved understanding of the nebula.  It has an angular diameter of appx 50 arc-minutes.  By comparison, the full moon is appx 30 arc-minutes across.  At the estimated distance of 5,000 ly from Earth, it corresponds to a physical size of roughly 70 light years across its widest dimension.

Notably, the Jellyfish's X-ray morphology is centrally peaked.  It is believed there may have actually been at least two (2) supernovas that occurred in this region of space.  The SNR optical and radio morphology is shell-like, consisting of two connected sub-shells with different centers and radii.  A third, larger sub-shell is now recognized as a different and older SNR (by appx 100,000 years). 

Jellyfish's age is still uncertain.  There is some agreement that the more prominent supernova happened appx 16,000 years ago.  Recent Chandra and XMM-Newton observations identified a plerion nebula, close to the remnant southern rim. The point source near the northern apex of the nebula is a neutron star, the remaining relic of the SN explosion.  The nebula's location inside a star forming region, and the presence of a neutron star indicate it is the result of a Type II supernova, being the ultimate fate of a massive star explosion.

220207 - Sh2-248 "Jellyfish" nebula