i'm sorry we're getting there we're getting there there's one last thing we need to add in and then we'll uh we'll have everything you need for test two coming up so check this out here we go back to our list the last thing we need to add to the list is mass the amount of material in that star is that our final direct one or our final indirect one is mass the amount of material in that star direct or indirect indirect here we go indirect here we go let's pop it in there it's indirect we can't see inside the star so we can't know it directly here we go so how do we figure it out how do we indirectly define the mass of a star we find it indirectly okay we find it indirectly um what would the way to indirectly find it what does mass cause if a star has more mass that means it's also going to have more what what does increased mass give a star more gravity correct so by watching how nearby objects are affected by the gravity of a star we can figure out what its mass is okay and what we've learned is that for almost all stars all of the other properties other than distance are tied to the mass okay all of the other properties for most stars is tied to the mass so here's what we can do to make everything easier and bring it all together here we go i'm just gonna turn this over here check this out let's say we're looking at a star like our sun and we increased the mass all right let's bring it on home if we increase the mass of this of a star what probably happens to the size what probably happens to the size it gets bigger okay more mass means a bigger star okay and as you guys said more mass means more gravity so that means a star with a higher mass will squeeze itself more tightly not enough to shrink the star it's still going to be bigger but if it's squeezed more tightly what does that do to the temperature if this star squeezes its core more tightly what's that going to do to the temperature of that core would it go up or down it would get higher that's something we talked about way back when we were talking about meteorites right so what does that mean that means that uh if a star has a bigger mass for most stars that's going to mean it's also going to have a higher surface temperature so increasing the mass of a star looking at bigger masses means bigger sizes and bigger temperatures what is that going to do check this out if the core and the surface are hotter that's going to affect the fusion inside would making it hotter make fusion happen more or less often would higher temperatures inside the star make the fusion happen more or less more it would happen more okay more it would happen more um so here we go that means if the star fuses more its luminosity is going to go up okay now here's the thing this means for most stars most stars increa the higher the masses the higher all of the major properties are okay the higher the mass is the higher all of the major properties of now i said most stars uh that's because there are some stars that don't follow this pattern okay the this is for stars like our sun which we actually call here we go main sequence stars this is just the name that we give to stars like our sun in other words stars that haven't started to die yet stars that are still fusing hydrogen in their cores so for most stars it's like this let me just bring it all together in the final part here we go let me bring my spectral types back in now remember for main sequence stars which is almost all the stars out there almost all the living stars all of the properties increase together okay so here we go we said for these spectral types let me pop myself under here for these spectral types o's are hot m's are cold stars that are g's like our sun are kind of medium but if we're talking about main sequence stars like our sun let's see if we can figure this out which of these two types has a higher mass b or g which of them has a higher mass for main sequence stars like our sun and keep in mind when you're answering this remember all of the properties increase together four main sequence stars it's the bees it's the bees right so if b's are hotter than g's then for main sequence stars that means they are bigger than g's as well okay what is um what's what's uh what's a bigger mass f or k what's a bigger mass f so let me put some extra notes on here and this will help you out for anybody who's not quite getting it so for all stars hot is the o side and cold is the m side but for main sequence stars like our sun we also get this side being high mass big size and high luminosity because all of the properties go together right so for main sequence stars this is not just hot it's also high mass high big size high luminosity whereas on this side for the cold side for main sequence these are also going to be low mass small size and low luminosity okay so basically there's gonna be a bunch of test questions like this on test number two um i will just have a a a list of letters they won't be in order you need to know the order okay but i'll say something like okay you've got uh an a an f and a k and it could be more than that but let's say we had an a an f and a k and i could ask okay which one of those is the biggest size and what would the answer be for a f and k what would be the biggest size for main sequence a because it's closer to that list right which one would have the lowest luminosity k because it's closest to that list right so the closer you are to this side the more like this you are right and the closer you are to that side of the list the more like that list you are okay let's put the final type of question here we go last bit of info these things there's billions of all of them out there but they're not all just as common which side would you expect to be more common m stars the small cold ones the small dim cold ones or the big hot bright ones like the o's which one would we expect to be more common yes so ms would be more common there's way more little boring ones than big hot bright ones these would be easier to see but there's way less of them does that make sense so it's just here's a way to remember that it's just like people what is more common out there in the world boring and small or hot and bright just saying it's just like people the cold small boring ones are way more common than the hot bright ones right so the stars are like that uh it's just the way it is we can't all be o's most of us are m's okay uh you decide which one you are all right um yeah so that that's it that's the uh that's the whole uh that's everything that we're gonna be doing for the for this semester somebody's asking about dark matter i will have a lecture on dark matter over the summer so stay tuned i can teach you all about dark matter if you pay attention to that