The pulsations of Mira variables cause the star to expand and contract, but also to change its temperature.
The temperature is highest slightly after the visual maximum, and lowest slightly before minimum.
Bouillaud's measurement may not have been erroneous: Mira is known to vary slightly in period, and may even be slowly changing over time.
The star is estimated to be a 6-billion-year-old red giant.
Observations of Mira A in the ultraviolet band by the Hubble Space Telescope have shown a plume-like feature pointing toward the companion star.
are all red giants whose surfaces pulsate in such a way as to increase and decrease in brightness over periods ranging from about 80 to more than 1000 days.
The shape of its light curve is of an increase over about 100 days, and the return to minimum taking twice as long.From northern temperate latitudes, Mira is generally not visible between late March and June due to its proximity to the Sun.This means that at times several years can pass without it appearing as a naked-eye object.In the particular case of Mira, its increases in brightness take it up to about magnitude 3.5 on average, placing it among the brighter stars in the Cetus constellation.Individual cycles vary too; well-attested maxima go as high as magnitude 2.0 in brightness and as low as 4.9, a range almost 15 times in brightness, and there are historical suggestions that the real spread may be three times this or more.