CONTENTS[br] Introduction 594[br] 1. The sun as a whole 595[br] a) Dimensions 596[br] b) Rotation 596[br] c) Radiation 596[br] d) Atmosphere 596[br] 1. Photosphere 596[br] 2. Chromosphere 597[br] 3. Corona 598[br] e) Interior 598[br] 1. Solar neutrinos 599[br] 2. Convection zone 599[br] 2. Phenomena in the solar atmosphere 600 [br] a) Sunspots 600[br] b) Magnetic fields of spots 601[br] c) Faculae 602[br] d) Chromospherie flares 602[br] e) Prominences 603[br] f) Coronal streamers and holes 603[br] g) Centers of activity 604[br] h) Solar magnetic field 604[br] 3. Rotation of the sun 604[br] a) Observational data 604[br] b) Rotation of the solar wind 606[br] c) Oblateness 606[br] d) Hydrodynamics of the differential rotation 607[br] e) Reynolds stresses 608[br] f) Hypothesis of an anisotropic viscosity 609[br] g) Equations for the second moments 610[br] h) Numerical simulations 611[br] 4. The solar cycle 612[br] a) Wolf numbers 612[br] b) Sporer'slaw 612[br] c) Hale-Nicholson laws 613[br] d) Waldmeier eruption hypothesis 613[br] e) Relaxation nature of the solar cycle 613[br] f) Maunder minimum 614[br] g) Babcock model 615[br] h) Leighton's equations 616[br] i) Hydromagnetic dynamos 617[br] References 618[br]