Black Body

Black Body
https://en.wikipedia.org/wiki/Black_body
"An ideal body is now defined, called a blackbody. A blackbody allows all incident radiation to pass into it (no reflected energy) and internally absorbs all the incident radiation (no energy transmitted through the body). This is true for radiation of all wavelengths and for all angles of incidence. Hence the blackbody is a perfect absorber for all incident radiation.[10]"

A star or planet often is modeled as a black body, and electromagnetic radiation emitted from these bodies as black-body radiation.

My question is as follow:
Can we assume that any star, planet, moon would be considered as a black body, even if it is a simple gas star? In other words, is there any limit in its size or its radiation/energy density in order to be considered as black body?