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# Astronomy 102 October 11th.docx

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School
Department
Astronomy
Course
CAS AS 102
Professor
Merav Opher
Semester
Fall

Description
Stars have atmospheres as well as planets When an electron breaks free of an atom due to too much energy, it is called ionizing the electron Some light leaving a star is absorbed by atoms in the star’s atmosphere Hotter stars have hotter atmospheres, cooler stars have cooler atmospheres All stars are mostly hydrogen and helium Absorption lines increase in colder stars Annie Jump Cannon came up with a system of classification for stars She did it based on surface temperature of the stars Stars names O B A F G K M THe hottest stars are called O stars, those are the hot blue stars They have a temperature of 30k Kelvin The coolest stars are called M stars, those are the small red stars They have a temperature of 2800K The sun is a g star Sun is a type G2 star Letters have numbers next to them 0-5 Lower numbers mean the hottest stars and vice versa When two objects in orbit are very massive, they are going to orbit around the center of mass A less massive star movies faster on larger orbit v1/v2=m2/m1 Spectroscopic binary: spectral lines of the two stars show periodic changes Radial speed is measured through Doppler shift HR diagram is a life story of stars, telling us not just how they were created or how they died, but everything about them Stars move around the HR Diagram as they age Most stars are on the main sequence Aless massive star moves faster on larger orbit Hippacos Satellite: Measures nearby distances using parallax Luminosity of the sun is one solar luminosity You can determine if a star is in the main sequence star by looking at its absorption lines in its spectrum You can measure temperature just by looking at a star By playing the star in the main sequence, you find out the luminosity of the star 22 By finding out a star’s luminosity, we can find out its distance Stars in the main sequence are also distributed differently according to their masses If we know a star’s mass, we know where in the main sequence it is located Not all stars are in the main sequence Some stars that are not in the main sequence are very luminous, cold, giant stars If the sun were such a star it would have swallowed the planets Others stars that are not in the main sequence are very hot, low luminosity, and small, they are called white dwarfs HR diagram has several classes, they are classes 1-5, with Class 5 being the main sequence Chapter 14: The Sun The mass of the sun is 300,000 time that of Earth The radius of the sun is 100 times that of Earth Active regions, the parts of the Sun where there is a lot of activity Aflare is a piece of the atmosphere of the Sun that the Sun is ejecting War inside of a star is gravity vs the energy released by nuclear reactions This energy is called fusion Standard Theory of the Sun:Atheory or a model that people developed based on everything that has been found out about the Sun For a star to be in equilibrium, the force of gravity has to be equal to the force of the energy released by fusion Hydrostatic equilibrium: Nothing is moving, every
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