The crossword solutions for the term START FOR 'SPHERE' are ATMO (4 letters), HEMI (4 letters), and IONO (4 letters). ATMO stands for atmosphere, which is the layer of gases surrounding a planet or other celestial body. HEMI stands for hemisphere, which is half of a sphere or globe, divided by a plane passing through its center. IONO stands for ionosphere, which is a region of Earth's upper atmosphere that is ionized by solar radiation.