What you’ll learn4 learning objectivesChoose one objective for a focused lesson, or study the complete topic.25.1.1The term luminosity as the total power of radiation emitted by a star• understand the term luminosity as the total power of radiation emitted by a starSyllabus objective25.1.2The inverse square law for radiant flux intensity F• recall and use the inverse square law for radiant flux intensity F in terms of the luminosity L of the source F = L / (4πd 2)Syllabus objective25.1.3An object of known luminosity is called a standard candle• understand that an object of known luminosity is called a standard candleSyllabus objective25.1.4The use of standard candles to determine distances to galaxies• understand the use of standard candles to determine distances to galaxiesSyllabus objective