大熊座移動星群
Based on the numbers of its constituent stars, the Ursa Major Moving Group is believed to have once been an open cluster, having formed from a protostellar nebula approximately 500 million years ago. Since then, the sparse group has scattered over a region about 30 by 18 light-years, whose center is currently about 80 light-years away, making it the closest cluster-like object to Earth.