This star belongs to its own eponymous S Doradus class of variable stars, also designated as luminous blue variables or LBVs.
LBVs exhibit long slow changes in brightness, punctuated by occasional outbursts.
 S Doradus is typically a magnitude 9 star, varying by a few tenths of a magnitude on timescales of a few months, superimposed on variations of about a magnitude taking several years.
The extreme range of these variations is from about visual magnitude 8.6 – 10.4.
 Every few decades it shows a more dramatic decrease in brightness, to as low as magnitude 11.5.
The nature of the variation is somewhat unusual for an LBV; S Doradus is typically in an outburst state, with only occasional fades to the quiescent state that is typical of most stars in the class.

The colour of S Doradus changes as its brightness varies, being bluest when the star is faintest.
 At the same time, the spectrum shows dramatic changes.
 It is typically an extreme mid A supergiant with P Cygni profiles on many lines (e.g. A5eq or A2/3Ia⁺e).
 At maximum brightness, the spectrum can become as cool as an F supergiant, with strong ionised metal lines and almost no emission components.
 At minimum brightness, the spectrum is dominated by emission, particularly forbidden lines of Feii but also helium and other metals.
 At the deep minima these features are even more pronounced, and Feiii emission also appears.

Attempts to identify regularity in the unpredictable changes of brightness suggest a period of around 100 days for the small amplitude variations near maximum brightness.
 At minimum brightness, these microvariations are considered to occur with periods as long as 195 days.
 The slower variations have been characterised with a period of 6.8 years, with an interval of 35–40 years between deep minima.
 The microvariations are similar to the brightness changes shown by α Cygni variables, which are less luminous hot supergiants.
This star belongs to its own eponymous S Doradus class of variable stars, also designated as luminous blue variables or LBVs. LBVs exhibit long slow changes in brightness, punctuated by occasional outbursts.  S Doradus is typically a magnitude 9 star, varying by a few tenths of a magnitude on timescales of a few months, superimposed on variations of about a magnitude taking several years. The extreme range of these variations is from about visual magnitude 8.6 – 10.4.  Every few decades it shows a more dramatic decrease in brightness, to as low as magnitude 11.5. The nature of the variation is somewhat unusual for an LBV; S Doradus is typically in an outburst state, with only occasional fades to the quiescent state that is typical of most stars in the class.
The colour of S Doradus changes as its brightness varies, being bluest when the star is faintest.  At the same time, the spectrum shows dramatic changes.  It is typically an extreme mid A supergiant with P Cygni profiles on many lines (e.g. A5eq or A2/3Ia⁺e).  At maximum brightness, the spectrum can become as cool as an F supergiant, with strong ionised metal lines and almost no emission components.  At minimum brightness, the spectrum is dominated by emission, particularly forbidden lines of Feii but also helium and other metals.  At the deep minima these features are even more pronounced, and Feiii emission also appears.
Attempts to identify regularity in the unpredictable changes of brightness suggest a period of around 100 days for the small amplitude variations near maximum brightness.  At minimum brightness, these microvariations are considered to occur with periods as long as 195 days.  The slower variations have been characterised with a period of 6.8 years, with an interval of 35–40 years between deep minima.  The microvariations are similar to the brightness changes shown by α Cygni variables, which are less luminous hot supergiants.
S Doradus