Historically this star was used as a luminosity standard to compare with other stars to check for variability, but it was later discovered that Bellatrix itself is an eruptive variable, changing in luminosity by a few percent over time.
Historically this star was used as a luminosity standard. This was to compare with other stars to check for variability. Bellatrix itself is an eruptive variable. Bellatrix itself is changing in luminosity by a few percent over time. This was later discovered.