The printer has upgraded all publications to a heaver paper stock. The new paper only allows a maximum book size of 310 pages at the 8.5 x 11 paper size. Since, the 8.5 x 11 format is easier to read than the 6 x 9 size, we have split the Terrestrial volume into parts 1 and 2. The total retail price of the two volumes will remain the same.