Be careful not to overcommit at first. But, do follow through by keeping in touch with your partner teacher or astronomer. It's also important to communicate clearly and openly about any concerns, needs, or suggestions you may have. Teachers and astronomers should enter the partnership as equal, but differently skilled, partners. Teachers are likely to be more knowledgeable about how students learn, what students need to know, and about how to structure and manage a classroom activity.
Astronomers are likely to know more about astronomy and technology.
Your partnership will be more successful if you enter it with respect and an expectation of equality. But don't expect your partner to know everything or to do everything perfectly the first time. Let your partnership and your own skills develop as you get to know each others' strengths. Provide adequate time for planning and follow-up. An initial planning meeting or two will help you understand each others' needs and interests.