This is comet Neowise, a phenomenon more visible to the camera than the eye. I'm happy I got this photo last night but I see hints of star trails. If tonight is clear I'll re-shoot at a shorter exposure. I see by my notes, which I failed to consult prior to this shot, that the rule for avoiding star trails is to leave the shutter open for no longer than 600 sec-mm / focal length in mm. That's for full frame; use 300 sec-mm / mm for APS-C. So I would be better off at 6 sec (600 sec-mm/105 mm => 6 sec), not the 15 sec I used.