AST201H1 Lecture Notes - Lecture 22: Elliptical Galaxy, Disc Galaxy, Cosmic Distance Ladder

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Irregular galaxies are a result of a collision of two galaxies (mergers. ) When its finish its star bursts, it will probably another disk galaxy. But if there is no gas or dust left then it will create an elliptical galaxy. To understand how big galaxies are, we need to know how far away it is. Parallax how we measure the distance of stars. This method only works for stars a few thousand light years away. The current instrument that is measuring parallax can only measure the stars within the milky way (though it has done a great job till now. ) Luminosity tells us how bright something is intrinsically. Apparent brightness is how bright something looks to us. The small fraction of light received on earth determines the star"s apparent brightness. The closer a star is to earth, the higher the fraction of its light we receive. The amount of light we receive goes down as the square of the distance.

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