all right now there we go a little bit more I want to say about luminosity and apparent brightness before we move on okay now check this out there we go let's talk about units for a second all right I am I've lost my my my streaming there we go okay so let's talk about units for a moment all right here we go luminosity what's it measured in let me go back to this other page where I wrote the definition if we look right here the definition says the total amount of light energy produced per second so it needs to be energy per second does anybody happen to know what the unit for energy is in most science and you may have heard this you haven't heard this in this class but you may have heard it in some other science class starts with a j starts with a j it's joules joules is the unit of energy okay joules um so here we go I mean let me write that up on my page here we go so luminosity is measured in joules per second but you have seen joules per second before okay its measured in joules per second check this out check this out joules per second is another name for a watt have you guys heard of watts before yes a watt and a Joule per second or the same thing where have you seen watts before where have you seen watts before yes yes light bulbs light bulbs always have their wattage written on them somewhere so remember luminosity is the total light emitted per second which is measured in watts so that means if you have a 200 watt light bulb it's producing 200 joules of light per second and a 300 watt light bulb would be 300 watts sorry 300 joules of energy per second and that's why a higher wattage takes more electricity to run here's the problem though we can't use watts or we could use watts for stars but it's gonna be a pain in the butt right why would watts be a bad thing to use to measure stars like the Sun like we wanted to do the wattage of the Sun why would that be a bad unit to use that's correct stars are too bright and a watt is too small if we were to use watts for the Sun the wattage of the Sun is about 10 to the 33rd watts the wattage of the Sun is 10 to the 33rd watts so yeah even even gigawatts is way too small watts are way too small 10 to the 33 that's a one followed by 33 zeros I don't even know what that number is called okay so instead it takes a lot of lightbulbs to meet equal the Sun yeah yeah so instead what we do is we make the sun's wattage the standard wattage for stars and we call it here we go so this amount of watts is called a solar luminosity and it's written like this this would be one capital l circle docked let me zoom that in there we go so the luminosity of our Sun is called a solar luminosity and we make that the standard wattage for stars so our Sun is one solar luminosity and that way we can deal with very small numbers if there was a star with twice the luminosity of our Sun it would just be two solar luminosities does that make sense two solar luminosities would be twice the brightness of our Sun okay or twice the luminosity of our Sun and with that in mind the brightest stars out there usually don't get above around a thousand solar luminosities usually okay so there are stars that are a lot brighter than our Sun but a thousand is a number that with it's a lot easier to deal with then bajillion Gillian Gillian Gillian Gillian Watts right so yeah so luminosity is usually measured in solar luminosities okay now apparent brightness apparent brightness has a unit that I do not like at all okay and that particular unit is called the magnitude okay the magnitude I really don't like this unit I think it's a little out of date and it's clunky and hard to understand but you it's used so often that I do need to teach you guys about it here's how out of date it is the magnitude system was originally set up by a guy named Hipparchus I might have might only be one P but it doesn't matter based on that name can you tell when this guy was around when did this guy live when did he come up with magnitudes like if I'm Hipparchus when am i around this is an ancient Greek person yes this is an ancient Greek person here so this system for apparent brightness is is very very very it's that hundreds of years old right and technically it's called the apparent magnitude but I frequently just shorten it to magnitude but here's the way it goes ancient Greeks didn't have telescopes they didn't have cameras so they decided how bright stars look just by what they saw with their eyes and Hipparchus got a bunch of his buddies together and they decided to classify the stars based on how bright they looked and the absolute brightest stars in the sky were given a magnitude of one if they were the brightest stars in the sky they were called magnitude one okay now check this out magnitude one was the brightest stars stars that they decided were half as bright as the magnitude ones were called magnitude two so magnitude two stars were half as bright as magnitude one stars and then the stars that were half as bright as the twos were called magnitude three and stars that were half as bright as that where magnitude four and half as bright as that was magnitude five and half as bright as that was magnitude six and then he stopped so here's the question number one why did they stop why did they stop at six why'd they stop at six that's right if they kept going half as bright half as bright half as bright half as bright half as bright sixes are extremely dim and if you went half as bright as that you can't see it with your eyes anymore and that was the only thing the ancient Greeks could use so that means the system stopped at six until we invented telescopes and we're able to go see dimmer right so telescopes are able to see dimmer than your eyes so now we have seven and eight and nine and ten on on up and can anybody see why I hate this what is non-intuitive about this what makes this confusing yes bigger numbers bigger magnitudes mean dimmer stars okay so if I discover let's see if we understand this if I discovered a brand new star and I told you check out this star I found it has an extremely high magnitude what did I just tell you about that star if I told you my new star had an extremely high magnitude what am I telling you about that star so if I say it has a high magnitude I mean that the magnitude is a very high number which means that the star is very dim okay so if I say a high magnitude six is a high magnitude one is a low magnitude so a low magnitude means a bright star and a high magnitude means a dim star it's I don't like it I don't like it it's confusing let's just put like a big frowny face on this Oh No and write the word flipped maybe over here we can write low is bright and high is dim okay I hate it I hate it so much I wish we would get rid of it I also am NOT a super fan of the half half half half thing but you know that's a different issue okay but essentially I'll go ahead and tell you right now that this is going to be one test question about magnitudes okay there's going to be one question about this and it's going to be designed to make sure that you know it's flipped so essentially you're gonna have a situation on the test where there's one object that's bright and one object that's dim and I'm gonna ask two things about it and we got to be careful here okay so imagine Fang a is bright and thing B is dim if I ask you which one has a higher apparent brightness you would say the bright one has a higher apparent brightness okay so the answer to that one would be a but here we go but if I asked you remember a is bright B is dim if I asked you which one has a higher magnitude which one would be the answer which one would have a higher magnitude bright thing a or dim thing B dim thing B that is correct so again if I told you bright thing a and dim thing B you would tell me a the bright thing has a higher apparent brightness but B the dim thing has a higher magnitude okay I'm just telling you right now that's gonna be a test question write it down you'll be good all right okay I think I have a question here somebody is asking if there are intermediate magnitudes there are that's not something you have to worry about for a test but yes there would be a one point five and a one point seven that would be but in between these two brightnesses right here okay in between these each of these magnitudes you can have more of them and by the way the Hubble Space Telescope can see all the way to a magnitude of thirty which doesn't seem like a lot bright a lot sorry a lot dimmer than what your eyes can see but remember every time you go down a number or I should say every time you go up a number you get half as dim and so that's 1/2 times 1/2 times 1/2 times 1/2 times 1/2 30 times to get to a magnitude of 30 and so that means the hubble space telescope can see millions of times dimmer than the human eye that's why every time we invest in a new telescope that can see a higher and higher magnitude every time we add another magnitude to the telescope we're able to see way dimmer objects and we always will be discovering new stars and new galaxies there's a replacement for the Hubble tape space telescope it's going to be going up soon ish probably sometime in the next 10 years and when it does because it will be able to see a much higher magnitude it will almost instantly be discovering millions and millions and millions of new galaxies so look for a bunch of new galaxies to be known very shortly when we get that new telescope up so yeah that's pretty cool all right ok