Ever since I learned about the solar system and the universe, I was intrigued by it. Since my childhood I wanted to be an astronaut.
These two ideas are very very close and I feel you should combine both of them and make one sentence.
I remember convincing my father to buy me a telescope when I was young so that I can look at the moon and the stars and pretend to be a young scientist.
In fact I feel this would provide you a better hook for this response. Why not begin with this sentence? It speaks of your interest in astronomy so well :)
I think you should talk more about your experience in this field and future goals. You talk a lot about your passion, but it is also important to tell them what you did to pursue your passion and what you intend to reach at the end.