Although Abell 21, or Sh2-274, has a large apparent diameter of 10 arcminutes, its surface brightness is so low, with features ranging from magnitude 16-25, that it was not discovered until 1955. It is a planetary nebula lying at a distance of 1,500 light-years in the constellation Gemini, which gives it an estimated diameter of 4 light-years. The parent star, now a white dwarf, is thought to be the deep blue star near the center of the nebula.

RIG1:
ZWO ASI533MC Pro (gain 101, offset 40, -10°C)
ZWO OAG & ASI 120MM for guiding
Skywatcher 130PDS f5 with 1X coma corrector
Optolong L-eNhance filter
RIG2:
Tecnosky 60ED APO
ZWO ASI 715MC (gain 50, offset 40)
Optolong L-eNhance filter

Skywatcher EQM-35 Pro

Pixinsight and Photoshop