• Yellow -> surface temperature is about 6000K
• angular diameter is about 1/2 degree
• dark spots move around in about 25 days (slower at poles)
• brightness = 1400 W/m²
• absorption lines -> H, He, C, N, O, Fe
• Dopper shift -> rotation, surface convection, ringing

Once we know the DISTANCE, we can measure

• distance + angular size -> radius = 7x10⁵km
• distance + period + Newton -> mass = 2x10³⁰kg
• distance + brightness -> luminosity = 4x10²⁶W