"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy." This quote from Hamlet (Act I) may be addressing the shortcomings of rationality, but I am using it to point to our habit of not looking deeply into things. Certainly, in the case of this image, not looking deeper can leave you with only a shallow, visual experience.

In the most general sense, there are two areas of nebulosity in the image: Sh2-248 (IC443) and Sh2-249 (IC444). Sh2-248, also called the Jellyfish Nebula (but not by me), is a Supernova Remnant (SNR). Sh2-249, on the other hand, is an HII (ionized) region. 

The SNR in itself is worthy of extensive study, but here are the basics. The explosion happened 10000 to 30000 years ago when one of the Type O supergiants of the Gem OB1 Stellar Association reached the end of its life. All that is left of that star are these remnant shells and a neutron star, the latter moving away from the explosion site at nearly 1 million km/hr (622000 m/hr). I've labeled the location of the neutron star in Revision B. If you look at the structure with the location of the neutron star in mind, a different structure may appear before your eyes. More can be said: the differing geometries of the parts of the SNR are an indication of the blast wave's interaction with varying densities of surrounding molecular clouds. The most dense wall of hydrogen confronting the shock wave is where you see the brightest surface of the SNR.

The relationship between Sh2-148 and Sh2-149 is a bit unclear. They are both seated in the greater molecular cloud of the Gem OB1 Association, but Sh2-149 is probably 'behind' Sh2-148. An interesting article by Donati-Falchi & Tofani seems to prove this. You can read the abstract here. There are three stars responsible for the ionization of Sh2-249. You would be forgiven for thinking that 10 Gem, 11 Gem, and 12 Gem were somehow involved in this ionization; after all, they "look close", but our 2D images simply cannot give us the proper perspective! In actuality, only two of the ionizing stars are in the frame of the image (one being 11 Gem, also designated HD43818 ). The location of both are identified in Revision C; 11 Gem being the unlabeled star. 

There's more. Looking at the plate-solved image you will also see various LBN and LDN notations. These are bright nebulae and dark nebulae from Lynds' catalogs. Lynds refers to Beverly Turner Lynds, a UC Berkeley graduate who went on to work primarily at University of Arizona and Kitt Peak. Her two catalogs were accomplished early in her career. Her seminal work was the result hours of study of the Palomar Observatory Sky Atlas prints in the early 1960s. You can ready the original LDN article here and the LBN article here.  These areas form a subset of the larger Sharpless regions and are wonderful targets for longer focal length scopes. There are some intricate and beautiful structures in these catalogs. Thank you Dr. Lynds for the bountiful supply of targets. Happy International Women's Day to Beverly Turner Lynds!

There's still more! There are two conspicuous stars in the image that are troublesome to the astrophotographer: 7 Eta Gem (η Geminorum, formerly Propus) and 13 Mu Gem (μ Geminorum, formerly Tejat). The former is an M2III red and rather cool giant star, 314 R☉, and part of a triple star system. The later is also an M class (M3III) star, a long period variable, and also much larger than the sun at 80 R☉. When imaged both should appear orange. Neither of these two stars has anything to do with H2 region or the SNR, but are both visible in the night sky as Castor's foot, if you imagine such things . 

A picture may be worth a thousand words, but sometimes it takes a thousand words to reveal what a picture is actually showing us! In the case of this image, there is still more to do, but my summary is done and I leave the rest to you. If you've read this far, then I thank you heartily and wish you clear skies until next time!