Hα map of the Orion-Eridanus superbubble (Reynolds & Ogden 1979, same region as in Fig. 7). The colour scale is linear and in units of Rayleigh (4π × 10^-4 photons cm^-2 s^-1 sr^-1). A galactic coordinate system is indicated with degree labels in green. The projection is area-conserving and centred on the Galactic anti-centre. The two bright regions near (l,b) = ( − 208, − 18) are the Orion clouds. The bright arc towards the top left of the Orion clouds is Barnard’s loop, probably a shell due energy injection from the Orion clouds. It delineates the extent of the superbubble towards the Galactic plane. The arc-like features towards the bottom of the map may also be related to the shell and delimit the X-ray emission (compare Fig. 7). The shell is also traced in HI (Brown et al. 1995).