[12] It was later listed as a spectral standard G4 0-Ia, indicating a highly luminous star type now known as a hypergiant.

[16] High resolution spectroscopic studies and modern space-based observations have revealed an unusual chemical makeup and a hollow spherical dust shell, but haven't fully resolved whether HD 179821 is a highly luminous yellow hypergiant or a dimmer, lower-mass post-AGB star.

[10] HD 179821 has a cold detached dust shell that has been studied with the help of the Hubble Space Telescope.

The current mass loss is low, but during the formation of the shell it is estimated to have been 4×10−4 M☉/yr, an exceptionally high rate being comparable to that of the archetypical OH/IR red supergiant, VY Canis Majoris.

[17] Like its constellation neighbor and also hypergiant star IRC +10420, it is surrounded by an extended reflection nebula.

These molecules may result from an active photochemistry, generated by UV photons emitted by the central star as it warms up, or can be produced in shocks.

[11][10] This discrepancy arises because its distance was too great to be measured by parallax before the Gaia mission and it has some properties of both a yellow hypergiant and a protoplanetary nebula/Post-AGB star.