Complex sentence: HD 138573 is G-type main-sequence star in the constellation Serpens, class G5IV-V, roughly 100.8 light years from Earth (30.912 parsecs).
Split into simpler sentences: HD 138573 is G-type star in the constellation Serpens. That means when this star was a main-sequence, class G5IV-V. It is about 100.8 light years from Earth (30.912 parsecs).