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Eta Car is one of the most luminous and massive stars in our Galaxy and isthe brightest mid-infrared (mid-IR) source in the sky, outside our solarsystem. Since the late 1990s the central source has dramatically brightened atultraviolet and optical wavelengths. This might be explained by a decrease incircumstellar dust extinction. We aim to establish the mid-IR flux evolutionand further our understanding of the star's ultraviolet and opticalbrightening. Mid-IR images from $8-20~\mu$m were obtained in 2018 with VISIR atthe Very Large Telescope. Archival data from 2003 and 2005 are retrieved fromthe ESO Science Archive Facility and historical records are collected frompublications. We present the highest angular resolution mid-IR images of $\eta$Car to date at the corresponding wavelengths ($\geq 0.22''$). We reconstructthe mid-IR evolution of the spectral energy distribution of the spatiallyintegrated Homunculus nebula from 1968 to 2018 and find no long-term changes.Eta Car's bolometric luminosity has been stable over the past five decades. Wedo not observe a long-term decrease in the mid-IR flux densities that could beassociated with the brightening at ultraviolet and optical wavelengths, butcircumstellar dust must be declining in our line-of-sight only. Short-term fluxvariations within about 25% of the mean levels could be present.

Mid-infrared evolution of eta Car from 1968 to 2018