so what makes the conditions so bad a lot of things but the first one I want to talk about is this do you guys remember what the temperature on mercury was like was mercury hot or cold yeah mercury was hot right mercury was give or take 660 ish degrees during the daytime it gets very very hot on average during the day it does get cold there at night we mentioned that but if we were to make a guess just based on distance from the Sun just based on distance from the Sun should Venus be hotter or colder than mercury just based on surface distance from the Sun well which which planet is closer to the Sun Mercury is closer to the Sun so if we were just going my distance from the Sun mercury should be hotter Venus should be colder but as some of you already know as I can see from some of your comments right now Venus is hotter than mercury in fact Venus is the hottest planet in our solar system by far it is by far the hottest planet on average it is 200 degrees Fahrenheit hotter than mercury is during Mercury's daytime okay so that gives you roughly about 860 degrees Fahrenheit as the average temperature on Venus and what would we expect to happen to the temperature at night on Venus what we expect to happen to the temperature at night yeah we did expect it to get colder just like mercury just like earth we expect it to cool down at least a little bit you know just like on earth but it doesn't it stays 860 degrees at night time even when the Sun is not out right and what would we expect the poles to be like we'd expect the poles to be colder also but on average basically the entire planet of Venus all over it all the time is 860 degrees and there's not really seasons it's it's just hot hot hot all the time all year long so does anybody know why Venus stays hot all the time why is it the hottest planet and why does nighttime or being at the poles not help yeah so we're basically getting it it's because of how the atmosphere of Venus works through through something called the greenhouse effect okay and have you guys heard of the greenhouse effect before what's another planet that has a greenhouse effect let me put it that way what's another planet that has a greenhouse effect happening right now yes the earth has a greenhouse effect before I get into this is the greenhouse effect a bad thing in general is a greenhouse effect a bad thing in general right in general a greenhouse effect is not a bad thing but like a lot of things the greenhouse effect is one of those all things in moderation kind of things it's a good thing that Earth has some greenhouse effect but we don't want to have too much greenhouse effect right what's a good example of a place with too much greenhouse effect I think you guys can guess this one pretty well what's a planet with too much greenhouse effect yeah Venus okay now to understand what well specifically green venus has what we call a runaway greenhouse effect okay which essentially in simple terms is a a greenhouse effect that is gone completely out of control we don't currently have a runaway greenhouse effect on earth but we have to be careful right so Venus is like an extreme case of what a greenhouse effect can do now to understand what I'm talking about I'm gonna real quick explain how a greenhouse effect works okay and then I'll explain explain how it works on earth and then I'll explain how Venus is different okay so let me just flip over to a different device here so I'm gonna try this out I'm not 100% sure that this is gonna work for me um let me flip this over oh and of course it has frozen on me so let me get give me one second to reboot that program the school let me borrow one of their document cams can everybody see my hand right now on the on the cam can everybody see this okay good okay so what I'm gonna do here is I'm going to attempt to use this instead of the the marker board they gave me because you guys probably saw last time holding up that marker board was very awkward so what I'm gonna do is I'm going to draw a picture right here of the greenhouse effect to show you how it works okay so let me get this going I mean bring this down let's say that this is the ground okay that's the ground right there okay and just so you know it's the ground here's a let's give us a little tree right here there's a little tree here's here's you you're hanging out this let's assume this is Earth and not Venus or you'd be dead right here so there's you let's let's make you kind of fancy there we go give you a top hat and a monocle and a cane there we go that's that's you out for a a good night on the town all right now a greenhouse effect happens when you have certain kinds of gas in your atmosphere and there's a lot of different kinds of gases that we call greenhouse gases but what is the one that we're going to be talking about right now what's the one that's relevant for both earth and venus here which greenhouse gas do people talk about all the time yeah we're getting a couple of co2 s here carbon dioxide co2 and carbon dioxide are the same thing it's just two different ways of saying it so essentially in order for a particular gas to be called a greenhouse gas it has to have a certain profile to it now if you remember in lectures we had in class we talked about how every atom so every element and every molecule has a certain fingerprint to it and let me review what I mean by fingerprint there remember every type of substance has certain wavelengths that it really likes that it likes to absorb and other wavelengths that it doesn't care about at all so if you have a gas and you shine something that's part of its fingerprint on it it wants to trap that particular wavelength of light and if you shine a wavelength that that particular gas doesn't care about it will let that particular wavelength pass okay so that's kind of a review of what we talked about like a over a month ago now now it turns out that sub substances like co2 or carbon dioxide have a particular type of fingerprint specifically that fingerprint doesn't contain very much visible light and UV light so in other words co2 doesn't particularly care about visible light and UV light there's a few wavelengths it likes in those ranges but for the most part it will let UV light and visible light pass okay but the fingerprint of a greenhouse gas like co2 does like infrared light okay so let me make sure there's not a question here okay so essentially what's happening in a greenhouse gas is that it real likes infrared doesn't so much care about visible in UV okay now a real quick question before we go further is infrared light a longer wavelength or a shorter wavelength than visible and UV is infrared longer wavelengths or shorter wavelengths than visible and UV just as a review longer it's longer and don't worry of iffy if you've forgotten that it's been a while since we've been able to talk about that so visible and UV are very short wavelengths UV is even shorter than visible and infrared is longer than what we can see so what i'm gonna do is i'm going to put some co2 up in the air here and in real life the co2 is not in a big layer like that it's spread out throughout the atmosphere okay but just imagine it's gonna be easier for me to show you how this works if we sort of pretend it's just a layer like this okay now does anybody know what the main wavelength of light the sun is giving off what are the main types of wavelength the main like the peak types of wavelength that the sun is giving off yeah so we got two of them visible light and UV so there's a reason I brought up those two types of lights specifically our Sun is giving off mainly UV and visible light the peak is right around it's the peak is invisible but it gives off a lot of UV as well now that doesn't mean it's not giving off other kinds of light but that's just what the peak light is so let's imagine that the sunlight is coming down in the form of visible and UV so let me get some sunlight coming in from the top here sorry about my sloppy wavelength here this is visible and UV light now notice the visible and UV light went right through the co2 why does the co2 let the visible and UV light through why does it let it through what did I just say about it a second ago somebody just said it doesn't like them and that's basically the answer remember if if a particular wavelength is part of its fingerprint it likes it and it wants that light and if it's not part of the fingerprint it doesn't like that kind of light and doesn't care so what's happened here is that the the light has been allowed to go through because co2 does not have a very significant visible and UV component to its fingerprint now when that's light gets to the ground there's two things that could happen what two things could happen to that light when it hits the ground right it can be absorbed or it can be bounced back up into the sky so it's either gonna reflect off the ground or get absorbed and some of the light will get absorbed and some of it will get bounced back into the sky so some of it will come right back up okay and some of it will get absorbed I can't really draw absorption so I'm gonna just kind of do that that's that's absorption right there if you're drawing along with me maybe you want to mark that as absorption right there okay so here's my quick question which one of those two things is going to actually heat the ground up is it a the absorption that's gonna heat the ground up or the reflection that's gonna heat the ground up oh we're getting a couple of answers right now that is correct it's the absorption so the ground really only gets heated when the light gets absorbed if this light bounces off the ground it actually takes the heat with it okay but this is still visible in UV light and co2 does not care about it so what's gonna happen when that light gets right here is it's just gonna go right back through it again and go to space and this is not 100% perfect a little bit of it gets blocked on the way in and on the way out because there you get what I'm saying but for the most part it's gonna let the UV in on the way in and it's gonna let it out on the way out and if this were the entire story this would mean there's no greenhouse effect and earth's temperature would be a lot colder than it is okay if this was the whole story of how light worked on our planet the Earth's average temperature would be below freezing and that would be a very bad thing for us we wouldn't want our average temperature to be below freezing okay so now here's what we got to do we're almost done with this picture if the ground heats up does it want to hold on to this heat no it wants to get rid of it but is the ground gonna heat up enough to give off visible light in other words is the ground on the earth gonna heat up enough to be as hot as a light bulb yes or no no it doesn't get as hot as a lightbulb it doesn't get as hot as a as the Sun but it does get hot right and hot things tend to give off light and if you remember the hotter something is the shorter the wavelength that wants to get off or give back off so since the ground doesn't get that hot would we expect it to give off a longer wavelength than visible light or a shorter wavelength in visible light okay so like I just said the hotter something is the shorter its wavelength is gonna be so since the earth doesn't get as hot as the Sun its wavelength will be longer than in visible light okay and what type of light is just a little bit longer than visible light it's infrared like we were saying before so essentially the earth tries to get rid of the heat it absorbed by giving off infrared light so here's infrared light coming back out so this is IR I'll put IR here and put a V and UV here okay now what's gonna happen to this infrared when it gets to the co2 though when this infrared hits the co2 what's the co2 gonna say what's it gonna do that's correct the co2 essentially blocks the infrared by absorbing it so because the co2 does have infrared in its in its fingerprint a lot of infrared wavelengths in its fingerprint it's going to take that co2 absorb it and essentially trap it here on the earth for us and it does reom of it goes off into space but a lot of it is going to end up coming back down where it will just get reabsorbed or reflect but it's still infrared at that point so it just keeps getting blocked when it tries to leave so a lot of times people say that the greenhouse effect is trapping sunlight it's not really the right way to think of it because the sunlight is allowed in and out what it does trap is the infrared light that the earth tries to get rid of when it gets heated up by the Sun okay now here's my next question there is co2 in the air on earth but is the proportion of co2 in our air very high is the amount of co2 in the air on earth a very large percent of our atmosphere does yes or no it's a low percent it's a low percent so our atmosphere if you remember is mostly nitrogen and oxygen with a less than one percent co2 give or take and that amount of co2 is able to trap enough infrared light to heat our planet about 50 50 to 60 degrees Fahrenheit which is enough to keep us from freezing but that shows you that a little bit of co2 goes a long way in terms of being able to trap heat okay now it looks like we're getting a question here so let me pause for just a second for that question or maybe not okay so now why is Venus different okay what makes things different on Venus so here we go there's gonna be a little bit of a long walk the amount of co2 in the air is what determines how well it traps heat oh by the way why do we call this a greenhouse effect why is this called the greenhouse effect yeah because it works pretty much exactly like a greenhouse greenhouses are covered in glass their walls and ceilings are made out of mostly glass and it turns out that glass works very much similarly to a greenhouse gas in this case in that it lets visible light through but glass tends to block infrared light so sunlight is able to get into the greenhouse but when the plants and ground and material inside the greenhouse tries to get rid of that heat in the form of infrared that infrared light gets trapped by the glass so it works just the same as this okay you probably have experienced that have you ever parked your car on a sunny day in the parking lot and then get into your car what is it like what's it like inside of your car if you had your windows up on a sunny day yeah it's exactly it is very very very hot it is hot as death in your car even if it's hot that day if you get into that car it's gonna be very hot because you're hot your car is like a miniature version of the greenhouse effect in that case so if if you park your car on a sunny day the sunlight is able to come into your car in the form of visible light and UV light but then the glass of your windows prevents the infrared light from escaping and that's why also if you leave a little crack in the windows it provides a an area for the co2 sorry the the infrared light to escape out your windows and it doesn't get as hot okay