AST 248 Lecture Notes - Lecture 3: Inverse-Square Law, Photon Energy, Photon

• School: Stony Brook University
• Department: Astronomy
• Course: AST 248
• Professor: James Lattimer

Document Summary

Speed is c = 3 1010 cm/s = 186,000 mi/s = 6. 7 108 mph. Distance traversed in 1 year is called a light-year. Has properties characteristic of both waves and particles. Wa(cid:448)e (cid:374)atu(cid:396)e: wa(cid:448)ele(cid:374)gth f(cid:396)e(cid:395)ue(cid:374)(cid:272)y = (cid:272) (cid:894)speed(cid:895) = (cid:272) Visible light is optical radiation, 3 10. 13 (cid:272)(cid:373)(cid:895) to (cid:396)adio (cid:894) 103 cm). Particle nature: smallest unit of radiation is a photon. Photo(cid:374) e(cid:374)e(cid:396)gy is p(cid:396)opo(cid:396)tio(cid:374)al to f(cid:396)e(cid:395)ue(cid:374)(cid:272)y e = h h is pla(cid:374)(cid:272)k"s (cid:272)o(cid:374)sta(cid:374)t, (cid:1010). (cid:1010) (cid:1005)(cid:1004) Brightness (b) or intensity (i) is apparent flux from an object while luminosity (l) is the intrinsic or absolute power output. Inverse square law of brightness brightness (intensity) diminishes as distance squared: b = l/d2. Radiation from a luminous object is emitted at virtually all wavelengths, but peak wavelength of dist(cid:396)i(cid:271)utio(cid:374) is i(cid:374)(cid:448)e(cid:396)sely p(cid:396)opo(cid:396)tio(cid:374)al to te(cid:373)pe(cid:396)atu(cid:396)e = (cid:1004). (cid:1006)9 (cid:272)(cid:373)/t k aka wien"s law. Therefore the color of a star is a measure of its temperature.