When good teaching is combined with good writing, the result is good news in non-fiction for readers, librarians and teachers alike. Although this book's vocabulary is within the grasp of second and third grade readers, it is so pre-eminently suitable as a read aloud item for youngsters-- so necessary for a foundation of knowledge that will match their sophisticated space-chat (picked up from their cradle to kindergarten exposure to the electronic media)-- that we purposely put it in this category, where the gaps outnumber the fillers. Mr. Schwartz does not back away from the dizzying power and enormity of earth-in- space. Each fundamental aspect-- gravity, axis, orbit, the conditions that support life on earth-- is likened to a familiar object. (The earth is a space ship; the earth turns like a merry-go-round.) Without any obtrusive technicalities, the concepts are here for the gaining. The text is arranged like vers libre and the pictures by Caldecott-winner Simont are active, colorful and impressionistic. Their spoofing quality brings the sheer size of the subject down to digestible proportions.