We present the first detailed quantitative study of the stellar populations of the Sagittarius ( Sgr ) streams within the Stripe 82 region , using photometric and spectroscopic observations from the Sloan Digital Sky Survey ( SDSS ) .
The star formation history ( SFH ) is determined separately for the bright and faint Sgr streams , to establish whether both components consist of a similar stellar population mix or have a distinct origin .

Best fit SFH solutions are characterised by a well-defined , tight sequence in age-metallicity space , indicating that star formation occurred within a well-mixed , homogeneously enriched medium .
Star formation rates dropped sharply at an age of \approx 5-7 Gyr , possibly related to the accretion of Sgr by the MW .
Finally , the Sgr sequence displays a change of slope in age-metallicity space at an age between 11-13 Gyr consistent with the Sgr \alpha -element knee , indicating that supernovae type Ia started contributing to the abundance pattern \approx 1-3 Gyr after the start of star formation .

Results for both streams are consistent with being drawn from the parent Sgr population mix , but at different epochs .
The SFH of the bright stream starts from old , metal-poor populations and extends to a metallicity of [ Fe/H ] \approx - 0.7 , with peaks at \approx 7 and 11 Gyr .
The faint SFH samples the older , more metal-poor part of the Sgr sequence , with a peak at ancient ages and stars mostly with [ Fe/H ] < - 1.3 and age > 9 Gyr .
Therefore , we argue in favour of a scenario where the faint stream consists of material stripped i ) earlier , and ii ) from the outskirts of the Sgr dwarf .