LESSON 14 – Properties and Evolution of StarsBasic Properties of starsIn this lesson we're going to look at the properties and evolution of stars. We'll look at theimportant properties of stars and spectroscopic classification – how we classify them intodifferent spectral types. We'll look at something called the Hertzsprung-Russell Diagram,which is a diagram that helps to make sense of different types of stars. And we'll look at theevolution of stars – how stars change over time.Our Sun is one of billions of stars in our Galaxy. How do we make sense of this huge numberof stars? Well, it helps to measure their basic properties, and to look for patterns that help usclassify them.There are three important properties of stars:Mass:A key property is a star's mass – the total amount of material in the star. This turns outto be a difficult property to measure.Luminosity:Another key property is luminosity - the rate of energy production from a staror equivalently, the power the star emits. We call very luminous stars "giant" or even"supergiant" stars. Less luminous stars (like the Sun) are "dwarf" stars.Colour or Temperature:Another property is a star's colour or temperature (which turn outto be related). Red stars are very cool stars, with temperatures of about 3000 K. At hotter andhotter temperatures we go through yellow stars like the Sun (with a temperature of about5800 K), and the hottest white and blue stars with temperatures of 10000 K to 30000 K ormore.Types:Stellar types are then defined by a combination of these properties. You often hearstars referred to with labels like 'red giant' (which is a cool but luminous star); or 'whitedwarf' (which is a hot, but low luminosity, star.)Luminosity and DistanceHow do we measure Luminosity?
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