The term 'sphere start' is composed of two words, 'atmo' and 'hemi'. Atmo is a four-letter word meaning 'ATMOSPHERE', referring to the gaseous envelope surrounding a celestial body. Hemi is also a four-letter word meaning 'HALF', referring to the fact that a sphere is a three-dimensional object with two halves. Together, these two words form the term 'sphere start', which refers to the beginning of a sphere's shape.