Complex sentence: The Sigma Ori open cluster has been the focus of Osorio's team observations due to the age of the cluster which is approximately 3 to 8 million years, it also has little extinctions, its distance and it is observed to be rich and dense.
Split into simpler sentences: The Sigma Ori open cluster has been the focus of Osorio's team observations due to the age of the cluster (approximately 3 to 8 million years). The cluster also has few extinctions, its distance is convenient, and it is observed to be rich and dense.