Of the approximately half-million stars in Keplers field of view, around 150,000 stars were selected for observation, and they are observed simultaneously, with the spacecraft measuring variations in their brightness every thirty minutes.
Stars were selected for observation. This was around 150,000. This was of the approximately half-million stars in "Keplers field of view. They are observed simultaneously. This was with the spacecraft. This was of the approximately half-million stars in" Keplers field of view. This spacecraft is measuring variations in their brightness every thirty minutes.