Hello, all I have just read some foundamental concepts about EM spectrum in astronomy. One thing I don't quite understand is that "Stars with higher temperature or higher pressure shows a broadened line on its absorption spectrum". A breif explanation states that a higher temperature or pressure leads to a greater number of atomic collisions each time. I am not absolutely convinced with the relation between atomic collision and broadening absorption line. An assuption I made is that the KE produced by collisions between atoms or ions does not absolutely fit the certain energy levels of an element (Hydrogen?). So, the broad of an absorption line is due to these random collisions. With higher the temperature or pressure, there should be a greater probabilities of collisions in each instance, which should leads to a broader line. One last thing I can't figure out with is that the area of the absorption line (width times intensity) is always the same (same energy produced) Why???