let's go back to our other motions they the other two motions have much more of an effect on us we're probably gonna talk about orbit next time so for this time let's talk about just rotation what did we say rotation gives to us what is rotation give us okay rotation gives us how does it affect us it's the spin that's correct that gives us the day and night cycle right it gives us the day and night cycle so a day is defined based on the rotation of the earth okay so you can say that a day is one rotation of the earth okay one rotation of the earth up it froze on me again sorry about that restart so you could say again that a day is one rotation of the earth okay and in fact if you um hey if you define a day in that way there's a special name for the day that's called a side aerial day it's spelled like sidereal and this is supposed to be two words sight side aerial day side aerial is one word and day is another word but site D one side aerial day is one rotation of the earth that said it's very very difficult for a human being to tell when the earth has completed one rotation why why is it hard for you to know when one rotation has finished why would that be hard to do because of where you are right where are you where are you right now oh did all our guesses leave where you stand in your standing on the ground you're standing on the earth right you're on the earth and because you're on the earth we're rotating with it so because we're rotating it with it it's hard to tell when run rotation is done so instead of using the earth itself to define a day what else could you use instead instead of using the earth to tell when a day is over what else could you use that would be much easier for you to see the Sun that's correct if you wanted to define a day based on the Sun we actually give it a different definition okay we call it an apparent solar day wait my spelling is bad parents two peas right honey still a parent somebody help me out please I'm terrible at spelling how do you spell a parent somebody give it to me at the discord my brain is blanking this is right this is right a pair of as two peas right yeah that's that's right okay here we go I knew I knew something looked a little wrong there thanks guys see it's so totally okay to be wrong sometimes zel right there we go I'm pretty sure that that's right okay so the apparent solar day is a day based on the Sun okay yeah I'm tired too it's okay so the append on the rotation of the earth it's called a sidereal day and if you base it on the position of the Sun in the sky it's gonna be the apparent solar day now we need to pick a time of day to track the Sun end okay and we're not talking about the daylight here we're talking about one 24-hour day would it make sense to define the apparent solar day as the time between sunrise today and sunrise tomorrow would that be a good time to piss sunrise a good time to pick to be what you track a day based on actually no sunrise to sunrise is not actually a good time I'm kind of tricking you there I kind of led you in that direction that's okay why is it that sunrise to sunrise is not gonna be good for 24 hours okay why is sunrise to sunrise not gonna be a good time to define 24 hours based on there's something that happens to sunrise every day think you guys can figure it out it doesn't always happen at the same time right so for example in the summer Sun rises earlier in the day and then as you go towards winter the sunrise will be a little bit later every day until it's really late in the winter so we can't use sunrise to sunrise and for the same reason we can't use sunset to sunset but there is a time of day where the Sun is always in the same part of the sky what time of day am I talking about what time of day would be a good time to use any guesses noon that's it noon that's correct you guys oh you're all getting it boom new new new new new good job guys noon is good because it doesn't matter and we're ignoring stupid old daylight savings time I'm not even gonna get into daylight savings time but it's dumb we should get rid of it look it up if there were no daylight savings time then where's the Sun gonna be at noon every day it's gonna be highest in the sky and it's always gonna be hitting the halfway point of the sky at noon no matter when sunrise and sunset is it's always hitting above your head at noon okay so we're almost to a definition for a parent solar day what do we call that place directly over your head what's that place over your head cold we actually already asked this earlier so maybe we can get it again what's this place called Zenith so that's correct good job guys so we could try to say that an apparent solar day is the time it takes the Sun to go from our Zenith all the way around and back to our Zenith okay the time it takes the Sun to go from our Zenith all the way around the sky and back to our Zenith but that won't work where I'm living okay that won't work for most people in the earth it might be different for some of you I don't know where all of you are but for me I'm in Florida I'm in North Florida right I'm in North Florida and the Sun will never hit my Zenith okay the Sun will never hit my sinneth can anybody figure out why why can the Sun never hit my Zenith up here in North Florida yeah I could see that somebody's getting the idea here here's a picture of the earth and imagine that the Sun is somewhere way over here on this side of the page so that the Sun lights coming in like this if the Sun is right here not to scale it's okay but it's the worst looking Sun that I've drawn in a long time but whatever here we go if the sun's right here you have to be pretty close to the equator to be standing directly under it okay you have to be very close to the equator to be standing directly under the Sun where I am in North Florida we're tilted too far away from the Sun because of the of my distance away from the equator I am never going to be directly under the Sun okay so the Sun will go close to my Zenith but it will never go perfectly to my Zenith okay if you're standing on the equator the Sun hits your zenith at least one day during the year and there's actually a whole region around the equator it's a whole region of the earth around the equator where the Sun will hit your Zenith at least one day during the year right you're close enough to the equator does anybody happen to know what that part of the planet is called the part of the planet that's near the equator that's around the equator here I'll give you a hint if there are islands in that part of the of the planet they're called tropical islands because of where they are what is this region around the equator called there's a reason there are tropical islands yes yes it's called the tropics and it turns out that if you are outside of the tropics so if you're too far north or too far south then the Sun will never be directly over your head does that make sense it can be close if you're close to the tropics so where I am in North Florida is pretty close to the tropics so the Sun gets pretty close to my Zenith but it's actually always going to be south of me it's always gonna be a little bit south of my Zenith so I can't say Zenit is in it but I wanted to point that out because it turns out that the tropics the part of the planet called the tropics is defined based on astronomy it's defined based on this so specifically the tropics are the part of the planet where you're where the Sun hits your Zenith at least one day during the year okay so let's figure this out if we can't say that a day is Zenith to Zenith for the Sun what can we do here's what we're gonna do okay for this discussion looking at me let's all pretend I know we're all facing different directions let's pretend the North Pole is over here okay let's pretend the North Pole is that direction and that the South Pole is that direction so North Pole is that way South Pole is that way okay so here's what I want everybody to do real quick everybody put one hand up to your Zenith okay put one hand up to your Zenith boom point it yours in it all right now now let's all point to the North Pole okay so here's your Zenith now point to the North Pole now back to your Zenith now to the South Pole now back to yours in earth now back to the North Pole and so just do a little bit of this okay is everybody doing this don't make me do it by myself okay now I want you to notice something if you look up while you're doing this you're tracing out a line okay trace out you just wave your hands like you just don't care right and if you're doing this you're tracing out a line across the sky okay and that particular line you just traced out is connecting your zenith to the poles okay I actually have a picture I think I have a picture of this from the book uh-oh it logged me out okay give me one second I'm gonna bring up a book here a picture from the book so yeah that line that connects your zenith to the two poles has a name it's called your meridian okay and I'll have a picture here with the name on it sorry for the technical difficulties where did it go here we go we're almost done for today boom there we go so for this person again if they pointed straight up they'd be pointing to their Zenith and then if you connected that with a line to the North Pole and the South Pole you've got this sort of pinkish purplish magenta ish line that they've traced out here called the meridian okay and check this out here we go for the Meridian right here that Meridian is cutting the sky in half okay because it cuts the sky in half from the North Pole to the South Pole that means it cuts the sky in half into the western sky and the eastern sky okay and here's my next question which direction does the Sun Rise from every day the Sun rises in the east west north south which direction are we tell and which direction does the Sun Rise from from the east so if we check this out over here imagine this person is watching a sunrise it rises in the east and which direction does it set in okay if it rises over here where's it gonna set which direction will it set in in the West that's correct in the West that's good good job so that means every single day the Sun will go from here to here and if it goes from east to west across the sky what will the Sun have to cross through it doesn't necessarily have to go through your zenith but what will it have to pass through and I've been kind of building up to this right what will the Sun have to pass through on its way across the sky this meridian if it's gonna go from here to here it has to pass through this line across this person's head so it has to go through the meridian and it's always going to hit the meridian halfway across the sky okay halfway across the sky it hits the meridian so let's put it all together what time would the Sun hit your meridian what time of day if it's the halfway point of its path across the sky what time will it hit the meridian yes it's gonna hit it at noon so if you were in the tropics the Sun could actually perfectly go straight over your head and hit your Zenith at noon but where I am I'm too far north right I'm too far north actually this green shirt's kind of work it out right here and so that means that the Sun is always south of my Zenith but it still is gonna hit my Meridian at noon and if you live down in Australia or if you're living in like in Chile or Argentina then the Sun is going to always hit your meridian to the north of your Zenith okay but for everybody it hits the meridian at noon so we could say that the apparent solar day is the time it takes the Sun to hit the meridian twice okay an apparent solar day is the time it takes the Sun to hit the meridian twice so when it hits it today and when it hits it again tomorrow that's an apparent solar day