太阳基本数据.ppt

Measuring Star Colours Stars have different colours ! Colours depend on surface temperature Hot stars appear to be blue Cooler stars appear to be red ‘Measure’ colours by filters Prisms disperse light into its component colors Two opposing views Light consists of particles Newton (c.1670) Light as waves Christiaan Huygens (1678) Seemingly a ‘either – or’ situation Particles cannot behave like waves Waves cannot behave like particles The wave picture gets a boost 1801 Thomas Young Double-slit experiment Include graphic Demonstrates wave nature of light, rejects particle picture A slight problem In what medium do light waves travel ? Concept of ether (check spelling !!) Concept of fields An unexpected solution : Complete theory of electricity and magnetism by James Clerk Maxwell (c.1860) allows for electro-magnetic waves to travel in vacuum with speed of light Measuring Waves Waves are described by two numbers: Wavelength (?): Distance between wave crests. Frequency (f): Number of wave crests passing per second. The wave speed, c, is the product of these: c = ? f Examples of Waves Ocean waves: ? = 100 m, f = 0.1/second; wave speed: c = 10 m/second (36 km/hr) Speed depends on water depth, salinity, etc. Sound waves (A 440): ? = 0.73 m, f = 440/second; wave speed: c = 320 m/second (1150 km/hr) For sound, “frequency” = “pitch”. Light as electromagnetic waves Can treat light as an Electromagnetic Wave Fluctuation(波动) in the intensity of electric and magnetic fields. Travels through a vacuum at the speed of light. Doesn’t need a medium to “wave” in. Speed of light is a constant for all light waves: c = 300,000 km/sec Independent of wavelength or frequency. Electromagnetic Wave Visible Light Waves Wavelengths: 400 – 700 nanometers (nm) 1 nm = 10-9 meters Frequencies: 7.5?1014–4.3?1014 waves/second Visible Spectrum: Red Orange Yellow Green Blue Indigo Violet 700 nm ------------- 550 nm ------------ 400 nm R O Y G. B I V 电磁辐射是以变化的电磁场传递能量、具有特定波长和强度的波（波动性）。 波长范围：＜0.