Over the course of one year in 1936 to 1937 a star in the Orion constellation became 250 times brighter, increasing from a magnitude of 16 to a magnitude of 10. In one three month period the star became 100 times brighter.
The star is FU Orionis and is the first star to be observed going through this phase of growth.
Quoting Joel Green of the Space Telescope Science Institute:
“By studying FU Orionis, we’re seeing the absolute baby years of a solar system. Our own sun may have gone through a similar brightening, which would have been a crucial step in the formation of Earth and other planets in our solar system.”