Final answer:
The most effective activity for sixth-grade ESL students studying astronomy would be the Voyagers in Astronomy feature, which presents biographies of significant contributors to the field.
Step-by-step explanation:
Based on the given information, the most effective activity related to the unit on astronomy for a sixth-grade ESL class would be the Voyagers in Astronomy feature.
This feature presents brief and engaging biographies of the people behind historically significant discoveries, which aligns with the TEKS objective of telling important events gleaned from various sources.
By learning about the individuals who made significant contributions to the field of astronomy, students can understand the important events and ideas related to the subject.