We study the nematic-smectic phase transition of a thermotropic liquid crystal confined to a spherical shell. Far from the nematic-smectic phase transition temperature, ${T}_{\mathrm{NS}}$, we observe a configuration with four $+1/2$ defects, as predicted by theory. Since in this case ${K}_{1}\ensuremath{\approx}{K}_{3}$, the four defects are confined at the thinnest part of the shell to minimize the energy associated with the defect cores. By contrast, near ${T}_{\mathrm{NS}}$, where ${K}_{3}\ensuremath{\gg}{K}_{1}$, bend distortions become prohibited and the defects organize themselves along a great circle of the sphere, confirming recent theoretical and simulation results. During this structural change, the defects associate in two pairs that behave independently. In the smectic phase, we observe a new configuration displaying curvature walls.
