The intended meaning is "very large" in terms of angular scale in the visual field from earth, i.e., apparent size rather than actual physical extent.
TODO: gather largest visual objects across Dutra and Bica (rifts and molecular clouds), Milky Way star clusters (OB associations), Green's SNR, Cederblad, Melotte (Coma cluster, Hyades (no longer classed a cluster)), Gum, Sharpless 2
Define a cutoff for "very large scale." Andromeda is 3° to 5° depending on depth of image signal. Cutoff at or around 4° would exclude 90% or more of nebulae, galaxy and star clusters in historical catalogs.
The intended meaning is "very large" in terms of angular scale in the visual field from earth, i.e., apparent size rather than actual physical extent.
TODO: gather largest visual objects across Dutra and Bica (rifts and molecular clouds), Milky Way star clusters (OB associations), Green's SNR, Cederblad, Melotte (Coma cluster, Hyades (no longer classed a cluster)), Gum, Sharpless 2
Define a cutoff for "very large scale." Andromeda is 3° to 5° depending on depth of image signal. Cutoff at or around 4° would exclude 90% or more of nebulae, galaxy and star clusters in historical catalogs.