 We are live. Okay. So should we start? Go ahead, Amish. Okay. Yes. So just a second. Let me mute my YouTube tab. Yeah. Okay. So hello. Hello. Good morning, everyone. So today is the second Sunday of the month and we will start with our second episode of Steamboat. And in this Steamboat series, in this voyage of Steamboat, what we do is we bring you exciting stories from the world of Steam, which is science, technology, engineering, art, and mathematics. All these are interdisciplinary now and they form very important aspects of our everyday life. And like I said, we meet on second Sunday of every month at 11 a.m. and we share, discuss, and talk about various ideas of Steam. And this session is going to be in English, but we also try to bring out the same content in different languages, different regional languages, like Hindi, Marathi, and many more. So do keep in touch with our YouTube channel so that you are informed about which session comes up and in which language is going to come up. So before starting today's session, let me ask a question. Did you watch today's sunrise? I know it's a Sunday and who wants to wake up before the sun to watch the sunrise, but just put your answer in the chat box and see how many of you were able to see today's sunrise. So I'm having a look at the chats. And so did no one see the sunrise today? Okay, so Advika is saying no. How about others? Okay, Nishita is also saying no. Oh, Vedante is saying yes, he did. Okay, so that's nice. So today we have a nice Jugalbandi of two speakers with us. They are Chaitanya and Varuni. So Varuni has joined us from all the way from Chennai. Right. And Varuni is an outreach associate at Institute of Mathematics in Chennai. And she works on designing and conducting activities that make science communication more interactive. And we also have Chaitanya Ursekar who is a PhD student here at Homibaba Center for Science Education, Mumbai. Very designed science and mathematics activities for students and works on understanding how teachers use those activities in their classrooms. So I'd also like to remind you, please put your questions and answers and doubts if you have any in the chat box so that we can get back to it. And now it's over to you Varuni and Chaitanya. Hi everyone. Yeah, thanks Amish. Okay, so Varuni, so someone sent me this photograph on WhatsApp the other day and these are supposed to be pictures of sunsets from Mumbai. But I always thought that the sun sets in the west and I thought it sets at the same point every day. But this shows something very different. So tell me, does this really happen? So this is quite interesting. So I think some friends in our audience also looked at sunrise or they maybe saw sunset yesterday. So do you think this happens or do you think this is some fake news that's being circulated? What does the audience think? Maybe someone watched the sunset yesterday. So yeah, so some people seem to say no, this doesn't really happen. But I'll tell you it actually does. So the sun doesn't always set exactly in the west. So west is right now, let me just put west onto this so you can see it. So this is west and so because this is west, north is somewhere to this corner on the right, right? So do you see a pattern here? Do you guys see a pattern here, any of you? Yeah, let's just ask the audience. So Varuni is saying that this does really happen. So what seems to be happening to the sunset between March and June? What's happening to that sunset point? Okay, so Vedant is saying that the sun keeps moving towards the north. Yeah, so that's actually exactly what is happening. The sunset point keeps shifting towards the north and yeah. So in fact, if you looked at the sunrise, so I think someone here said that she has seen this with the sunrise as well. So in fact, if you looked at the sunrise point, that would also move in exactly the same way. Oh, so Varuni, do you have pictures of the sunrise also like this? So yeah, let me maybe show you this picture. So this is a picture that was taken in Aman in Jordan and this is a picture of sunrise. So what this person has done is that every once a month, they looked in the same direction and they took a photo. So you can see that in December, the sunrise is sort of, let me also put on, put some directions on here so it's easy for us to see. So we have east over here and now north is to the left. So initially in December, they see that the sun is rising more towards the south and then slowly between December and June, it's moving further and further north and then after June, it seems to come and move back towards the south. Okay, so tell me something. So this is sunrise in Aman in Jordan but the other image that we had was from Mumbai. So does this mean that this pattern of sunrise and sunset is actually the same all over the world? So actually yes, so this is true all over the world. So from December to June, the sunrise point moves from south to north and the sunset point and in June, it reaches some northernmost point and then from June to December, both the sunrise and sunset points move back towards the, from the north to the south and in December, it reaches the southernmost point. So in fact, the southernmost point is coming up soon on 21st December and the northernmost sunrise and sunset is on 21st June. So do you recognize these dates? 21st December and 21st June. Yeah, so is there something special about these dates? Maybe we can see the audience. Do you recognize these dates? Okay, I think I remember this. So I think I've heard of the solstice dates. Are these the solstices, Varunee? Yeah, so they are actually exactly the solstices. Okay, so what you told me so far is that sunrise and sunset, so the southernmost sunrise, sunset happens in on December solstice and northernmost on June solstice. But what I want to do is I want to put all of it together into one thing so that I can imagine it. So I would like to make a drawing. Okay, so can we do that? Sure, let's try that. Yeah, let me draw someone in Mumbai. Okay, so let's call this person Sachin. Okay, he's my favorite cricketer. So now we know that the sunrise and the sunset are actually happening on the horizon. So the horizon is basically the furthest point that one can see in any direction. So to do that, let's draw a circle. So this person's horizon is this circle. And so let's add directions also. Okay, so let's add north, south, east, west. Yeah, like that. Okay. So now on the December solstice, the sunrise is actually the southernmost. So it's south of east. Okay, so it should be at this point here. Now, what about the sunset in December? Where do you all the audience, where do you think it is going to happen in December? You can just type in the chat box and tell us. Okay, so Vedant is saying it will happen to the south. Okay. So yeah, that is actually correct. It will happen. Oh, southeast. We are talking about, we are talking about sunset Bhuvan. So I would say it will happen in the west, I think. So yeah, let's put the sunset in December to the southwest. Okay, so now let's talk about June. So in June, on the June solstice, where should I show the sunrise? Which side of the letter E should I show it? So guys, what do you think? Where will the sunrise be in June? Okay, so in June it will be more towards the north. So let's mark that as well. Okay, so yeah, I think everyone pretty much agrees. So now for the sunset, let's put it at the back. So that should be in the west over there. So Varuni, this is what I know happens in in June and in December. So now can you tell us why this is happening? Okay, so to understand this, let's first imagine the path the sun takes through the sky. So let me draw this big dome, which is your sky that you see above you. And yeah, so let's think about what is the path that the sun takes through this. Okay, that's quite simple. The sun will just go up and then it will come back down. Well, it is, I mean, it does just go, it does go up and come back down, but there's a little bit more to it. So you see in Mumbai, the sun actually goes up and comes down at a small angle. So something like this. Oh, okay. Okay, but so that means that on these dates, so between December and June, this path itself that the sun is taking, is that what is moving? Yeah, so that sun path looks like it's moving, right? So what is going on? Yeah, so let's just state this question clearly before we go forward. So what we're trying to now understand is why does the path of the sun in the sky change over the course of the year? Okay, so let's start from the December solstice or what's going to, what's happening, what's coming up really quickly on the 21st. So this is the path that I showed you for December, right? So this is the path I showed you for December. And to imagine what path the sun is taking through the sky, let's see where the earth is in its orbit around the sun, right? So the earth is going around the sun like this. And at this point, the earth is here, right? And at this point, the southern hemisphere is tilted towards the sun and the northern hemisphere is tilted away from the sun. Okay, so let's find our friend Sachin on this. So where should we put Sachin on this? Is he going to be sort of more towards the north or the south of the globe in Mumbai? Yeah, what do our audience friends think? Where is Sachin going to be? Oh, Vedant is saying he's on the south. Okay, just give a few more minutes because our friends from YouTube can also kind of chime in. Yeah. So I tell you where is Sachin? He's in Mumbai, right? He's in Mumbai, yeah. Okay, so he's in Mumbai. All right. Okay. And Mumbai you've written up there is some 19 degrees N. Yeah, I think there's a hint there. Yeah, so yeah, so I think so let me put him on you. So Sachin's going to be at about 19 degrees north. So that's the N that Arnab was pointing out. So that's somewhere here. Okay, so now let's see what is the sun that Sachin is going to see. So what we're going to do now is we're just going to focus on the earth and the sun and remove everything else so you know, we can just see this. Now imagine that there's a sphere around the earth. So think of it as this ball that's surrounding the earth. This is sometimes called a celestial sphere. Okay. Now imagine what the sun will look like if it's projected onto the surface of this sphere. So what I mean by that is you take a line and you join the center of the sun and the center of the earth. And where that line crosses this ball is what I'm calling this projection. And you can just imagine that as just a sticker that we kind of place on this ball that is surrounding the earth. Okay. And now that we've done this, I'm going to show you how we don't even need to think about the actual sun anymore. We just think of this sticker that we've now put on this celestial sphere, which is the projection of the sun onto this sphere that is surrounding the earth. So let me just pause for a minute to see if you know, can you try to imagine this? Is there anything that needs a little bit more clarification? Maybe I'll go forward and you know, you kind of get used to this idea slowly. So okay, but now what we're trying to understand is what is the path that the sun takes as it moves through the sky. So we know that the sun appears to move through the sky because the earth rotates about its axis, which is this axis. So and the rotation of the earth is in this direction. Okay. So now can you imagine like what how the sun is moving? Yeah, so you know, I'm trying to do that. So I know how the earth rotates, but because of the earth's rotation, how the sun will move, I'm kind of having some difficulty imagining this. Okay, so I don't know if the audience is also able to imagine this. Okay. So maybe, so maybe let me try to do something that you know, may make it easier to imagine. So we know that this, we know that the earth is rotating and the sphere is stationary, but let's kind of look at what, look at it from Sachin's point of view. So he's stationary and for him the earth is stationary and what he sees is the sphere itself rotating around him. Okay. So now let's imagine that, right? So we keep the earth stationary and we imagine that the sphere is rotating. Which direction will the sphere rotate? Yeah, so that I think, can the audience also help me think here how, so the earth is supposed to be stationary, but the sphere is rotating. So are you asking relative to the earth, how will that sphere rotate? Yeah, so yeah, so because you're keeping the earth stationary, you want to see what, what, how this sphere is it going to rotate? Okay. Okay. So in comparison to the arrow about of the earth that you've marked out, so a lot of people are saying east west, then some are saying west to east, some are saying anti-clockwise. So let's like clarify these things also. So to me the earth's rotation that you've marked right now appears to be anti-clockwise. So then should the sphere rotate clockwise or anti-clockwise? That's the question I get. Yeah. Okay. So Bhuvan is saying it should now be going clockwise. Let's just wait and see if others are able to, if others have some ideas. Okay. Advika is also saying clockwise. I actually, I agree with all these people. I think also that the sphere is going to rotate clockwise if the earth is going to be stationary. Yeah. So that's, that's exactly right. So this is, this is, let me just mark, I just mark that on there. So now since we can keep the earth stationary, let's remove this rotation of the earth and we just think of the earth as stationary and this big celestial sphere which has the sun on it is as a, as a projection is kind of moving around you. Right. So now what path will this, will this sticker of the sun, so the sun follow as this celestial sphere is rotating? Okay. So the sun is moving, is rotating because the sphere is rotating. And well, I think it would be, you know, like that, like the rotation is clockwise. So I think this may be an option. No, but you know, wait, I am doubtful because the axis is actually diagonal. So I think maybe it can be like this also. So I, I don't know. Can you guys, audience, can you help me out here? Should it be option one or should it be option two? Will it be the upper path or the lower path? Okay. Divyanka is saying it will be option one, the upper path. Okay. Let's just wait for others also to share. Okay. Yeah. Nishtha is saying option two, Vedanta is saying option two. Varuni, why don't you tell us what, what it is, what path will the sun take? So actually, what you were thinking when you drew the second part is, is what is going to be happening. So let me just show you that. Okay. And I think maybe it will help if I also say that, see, this is the, the earth is rotating about this axis. Yeah. So, so that's kind, and I think you, that's what you were thinking when you drew the second path as well. Yeah. So this is the correct path that the sun will follow. Yeah. So I think that one of the questions on the chat from Bhuvan is why is it option two? So basically, I, as I understand it's because that, that axis is tilted, right? So because it has to go around that central line, you know, I guess that the rotation would be like that. So I hope that clarifies it. By the way, there was one question that Arnab had posted, which was, is the celestial sphere the same as the sky? So that is quite interesting and we will come to it just in a minute. Okay. Right. So just that I'm glad that question came up because it helps me go forward. Okay. Okay. So, okay. So now, so now we know what the path, what path the sun is taking on this, on this sphere that we've drawn. Right. Okay. So now let's, now let's see for this person, for our friend Sachin in Mumbai. What is the sky that he sees when he walks out? Right. So this is the sky that he's going to see. So remember the earth is now stationary. Right. So the sky he sees is just whatever he sees above him, which is this. Okay. Right. And this is this, this blue part. Okay. So, yeah. Okay. But you know, I like, I'm having to tilt my head to actually imagine what sky he will see. Can we, can we rotate? Can we like do something about this? Yeah. Yeah. Let me, let me do a rotation, which maybe makes it easier for you to see. Right. Okay. So this is now the sky that Sachin sees when he looks up. Now the sun moves along. So the sun's, sun is moving along this path, right, that we just figured out. Now it enters Sachin's sky at sunrise and it leaves Sachin's sky at sunset. Right. Right. Right. So, so shall we, shall we try to mark sunrise and sunset points on this? Like let's get the audience involved in this as well. So guys, like we have seen, so you know what direction north is and you know what direction the sun is entering and leaving. So, where would the sunrise point be on this? Can you tell us? Will it be at the front part of the back? Okay. So I think, I think it is going to be in the front. Okay. Where, where it actually enters and cuts into the horizon. Okay. And if that is sunrise, then obviously like as the sun goes around to the back, like that should be sunset. Right. Yeah. So, so Bhuvan is asking whether the sun rises and sets in the same place. So no, it doesn't. It rises south of east and it sets south of west. Okay. So as you can see on that path over there, I hope as it, as the path cuts into the horizon, that's where the sun rises and as it cuts out of the horizon, that's where it sets. Okay. So now Varuni, I think I can see how they are, how this sunrise and sunset is happening towards the south. You know, you showed me what you had showed me earlier, what is happening on the December solstice. And we had drawn that diagram as well. So now I see why that is happening. Okay. But now can you tell us why is the path in June different? Why is it towards the north? Okay. So let me try and go through this for June. But before that, I think there's a little bit of a question still about the path that the sun is taking. Right. In the, in this previous thing. Right. So let me just try to clarify that before we go forward. Okay. So these were the two paths that Chaitanya had kind of suggested. Right. And what I ended up telling you is that the second path is the one that is actually what is happening. Right. So the reason that is, is that you need to think of the earth rotating along this axis. Right. So if it's rotating around, so I mean the earth is, sorry, the other stationery, you need to think of the celestial sphere that we just made rotating about this axis. Right. And because it's rotating around that axis, it kind of stays in this circle here. If it was rotating about a different axis that was just going straight up and down, then the first path may have worked. Right. But since it's, it is rotating at this angle about the axis that's at this angle, this is the path that it's tracing out. Right. So I hope that helps. I think there was a little bit of confusion. So this is, this is the path. Right. Yeah. So we, you know, saw the sky and then we kind of saw like east and west. Yeah. So Nishita is asking, so, so next day the sun will also rise and set at the same point up. We shall see. So let me go to June and show you what happens in June and then we'll come back to this question. Okay. So, and this is, so this is the path that I showed you initially. So now what's happening in June before, let me just recap for the story so far. Right. So this is, this is what I showed you for the path that the sun is taking in December and we saw why the sunrise and sunset points us south of east by looking at the position the sun is in its, in its orbit around the position the earth is in its orbit around the sun. And then we did this thing of like we drew this celestial sphere and then we marked out the path. So is this, is this kind of okay with everyone for now? And then we'll go forward. Okay. It looks like it's okay. Okay. So, so this is, this is the path that I showed you for June. So now the earth has kind of moved. So this is six months later. So the earth is now in this position in its orbit. Right. And what we want to do now is we want to draw this, do this same celestial sphere thing. So this is the sphere and I basically if you draw, we're going to do the same kind of projection. So I'm taking the center of the sun drawing a line to the center of the earth and where the, where the sun is falling on, where the sun, where this line crosses the celestial sphere is, is where we're going to do this projection. So now does someone want to, do someone want to kind of think about what the path would be? So we just kind of, I just worked out the path for you on this by saying that the rotation is happening along this axis. So here the rotation is going to be along this axis. So how do you think this sun is going to move? So let's, let's get the audience involved in this as well. So now we know that the sun is still going to rotate around this sphere. Okay. So Divyank is saying it will go towards the west. Yeah, okay. Varunee, I think the question is like, so will the path in June appear to be the same as in December? I suppose like that, that's what I'm thinking of right now. What do you guys think? Okay, Nishtha is saying it will be the same. Divyank is also saying it will be the same. Vedanta is saying it will be towards the east. So maybe let me, let me give you a hint or point or something. So when we projected the sun in December, we took the sun and we projected it onto the celestial sphere and it showed up somewhere here, right? Which is the southern part of the celestial sphere. So then when we rotated the celestial sphere, this path showed up in the southern half of this, right? So now when we are projecting it onto the celestial sphere in June, it is showing up a little bit north, right? Like it's not, so it's towards the top half or the north half of the celestial sphere. So when it goes around, is that path going to be in the southern half or the northern half? Yeah, I think it's going to be towards the north. Yeah, so I think other people are also kind of agreeing with this. So in fact, that is the path that it takes. So in June, on the celestial sphere, the path that the sun is taking is towards the northern half of this. Okay, so now let's do the same thing, where is the sky, right? So our friend Sachin is over here, right? So this is the sky that he sees. Let me do, I mean, yeah, so let's not break all of our mix. So I'll just rotate it for you so you can see the sun, the sky above and the sun moving through it. So just let's reorient ourselves because I think there's a bit of, just to make sure everyone's on the same page. So let's mark out east and west on this. Where is east going to be? Is it going to be to the front of this or to the back of this? Okay, so I think east is going to be to the front, that's what everyone is saying. Okay, perfect. So is it? So, sorry. Yeah, I think east is not in the front, right? Because everyone, everyone thought that, so I think the previous image that we had, okay, in that north was to the right, and that's why east was in the front. But in this image, north is to the left. So now, actually the comparison is not the same, right? Okay. Yeah. So, sorry, just let me cut in. I think like some of the, there's some debate here about whether east will be in the front or the back. Advica is I think very certain that east has to be in the front. But look at where north is. Okay, if north is north is now towards the left hand side, okay, east would have to be towards the back, and west would now have to be towards the front, right? So yeah, can you show the previous picture once? I think Varuni, if you just switch to that slide and show it, it will help. Yeah, so you see in this north has, yeah, so because north is towards the right, east and west like the directions have got switched. Yeah, so does this? Maybe what we can do is, so we were going to show people how that thing changes back to the correct, to the, to our previous orientation. Oh, Nisha got it, great. Okay, so I think you were going to show how to fix it and like make it towards the right anyway. Yeah. So why don't you go ahead and do that? Yeah, okay, so we marked out east and west on this. And so now what we had if you remember the previous image was north was to the right and here we have north to the left. So to be able to compare it, what I'm going to try and do is I'm going to rotate it. So I'm going to take the north which is on the left side and just rotate the whole globe and bring it to the right side. So this is kind of what happens. Okay. I'll give people a second to kind of see this rotation. You can just switch back and forth between them. I think. Yeah, so this was what it was. And then I rotated it so that the north moves to the other side. Okay. Yeah, it's a bit tricky. It's like if you have to imagine all of this like, you know, moving around and so on. But I think if we can settle on this image, I think like people also are starting to get it. So if we can settle on this, you know, let's mark sunrise and sunset on this as well. So again, wherever it enters, will be the sunrise point. So that is towards the east. And then sunset will be where the sun path exists. So that should be towards the west, but both in this case are on the northern side. Right? So that I see how it looks like what we had before. How does the path for June seem to change? So shall we try to put all of this together, like into one, like just make sense of it? Yeah, so that may be a good idea. We can sort of put it all. Yeah, so let me just put this out as what you had earlier. So this is Sachin in Mumbai. And this is the sky that he sees. Right? And so now the path that the sun takes in the sky in December is towards the south. So that will be like this. And then that is that on the December solstice, that is the southernmost sunrise and sunset. And what we know is that in June, it moves off towards the north. And on the June solstice, it's the northernmost sunrise and sunset. And because we looked at this celestial sphere just now, we have some better understanding. We can imagine why this is happening also. Okay. But so now folks, what do you think is happening to this path between December and June? So I think between December and June, it will seem to be moving north. Okay. And Nishita actually has a question. He next day, will the sun rise and set and on the same point? So Nishita now, maybe you can only tell us like if the path is moving over the course of the year, do you think the sun is going to rise and set on the same point on the next day exactly on the same point? What does everyone else also think? Do you think the next day the sun will rise and set exactly in the same point? It is moving northward. Okay. So is my screen only partially visible for some reason? I can see it in full. It's fine. It looks fine. Okay. I think someone seems to be having a issue. Okay. Okay. So Nishita seems to also kind of agree that it will move. Yeah. Right. So what I think Chaitanya is saying is that he's saying that it from December to June, it's moving northwards. Yes. So this, you may have actually heard of, you guys may have actually heard of this. So this is what is also called Uttaraya. Right. And so from June, Uttar as in north. So from December to June, the path of the sun is kind of moving further and further north. Okay. So then if from December to June, it is moving like that. Then from June to December, it has to go back towards the south. Right. What does the audience think? From June to December, it makes sense to me at least that it goes back towards the south. Yeah. Okay. So I think people tend to agree. Okay. This also is maybe something that you have heard of. Yeah. So Bhuvan has this, so yeah, just one second. And so this is actually what you may have heard of is Dakshinay. So Dakshin as in south. So as the sun, the path of the sun is moving further and further south between June and December, this is called Dakshinay. So okay. So the question, I think there's a question from Bhuvan about, so the sunset is opposite of sunrise. So if by opposite, you mean that it's east versus west? Yes. So on any given day, on any given day, the sun rises maybe south of east, south of east and set or north of east and sets south of west. Yeah. Okay. So yeah. So is that, does that help Bhuvan? Yeah. Okay. So it's, in fact, the sunrise and sunset points are equally either east or west are equally north or south of east on any given day. Okay. So yeah. So there are a couple of questions here, which I will just come to. Nishtha is asking something about 21st December. But one thing I want to ask is, so Nishtha is asking whether 21st December is the shortest day of the year. So that is correct. And in fact, that is interesting because that is something we'll come to in a bit. So Varuni, in between, so if it's moving north-south in between at some point of time, there should be some day on which it rises and set exactly, rises exactly in the east and sets exactly in the west. Yeah. So that's an interesting observation. So that should happen because it's moving from, you know, a southern point to a northern point and back, right? So do you want to guess like when it's going to kind of rise in the east and set in the west? So since the northernmost and southernmost are on December and June solstices, I'm wondering whether this exactly east and exactly west is also on some special day in the year. Yeah. So let me tell you, so those when it's rising, the days on which the sun rises exactly in the east and sets exactly in the west are actually the days of the equinox. So it will kind of look like this on the equinox days, right? So this happens once between December and June. So as it's going in this direction, so that is in March, around March 21st also. And then it's going to go back, remember, it's going to go back from the northern side to the southern side. So again, it's going to cross this point in the middle. So that's going to happen in September, around 21st or 22nd September. So these are, you know, on the equinox days are the only days that the sun will actually rise exactly in the east and set exactly in the west. So let's just go back to why this is, I mean, because we had kind of framed the question as why is this happening? So what we see is that, so this is something that we see in the sky, but what I understood is that the root cause of it is that the earth is moving around the sun. Yeah, it's so exactly. So the position of the earth in its orbit around the sun makes this sun path different at different times of the year. Okay. So this is what we also saw in those photos that initially you had shared. Yeah, so then Varuni, I actually have a question since and Nishtha was also asking and Bhuvan is also asking this. Okay, so Nishtha was asking 21st December is the shortest day of the year and 21st June is the longest day of the year that's what Bhuvan is saying. Okay, but you know, that's true. And for example, in 21st December, I know that it's the shortest day and the longest night. But you know, I was watching this test match in Australia. And over there, it seems to be the other way around. You know, for example, in Mumbai, sunset in December seems to happen at around 6pm. But if you look at some place in the southern hemisphere, on this same day, sunset like at 536pm, these people are playing cricket. So it's like bright and sunny. So how does this happen? Does this also have something to do with that sun path? So in fact, your guess is right on target. So yeah, so now we have this new question now. So the new question is why are there longer days in the southern hemisphere when there are shorter days in the northern hemisphere? So this is because the path that the sun takes in the sky is different between locations. So let's try and see how we can work that out. So this is what we worked out in terms of what is happening in Mumbai. So remember, I drew these at a small angle. So these angles. So this angle actually changes from location to location. And if we figure out these angles, that will help us tell these the number of hours in day and night. And for this, we can go back to our old friend, the Celestial Institute. So this is what we had already for Mumbai. So let me do that rotation so people don't have to tilt their head. So let me also remove all of this other stuff so we can just focus on the full sun path. So how long is this full sun path going to take? The whole path. So the sun is kind of going in this path. This is the sky that Sachin sees. So how long is it going to take? So 24 hours. So that's the amount of time this takes. So now what you see above this plane, so the blue is the sky that Sachin has seen during the day. And like I told you earlier, the sun enters into his sky at around sunrise and then exits the sky at sunset. And after that, he can't see the sun. The sun is kind of on the other side. He can't see the sun. He has night. So then can I trace this out? So the part where he can see the sun is the part during the day. So that's what it would look like. So I've colored it yellow. And then the part where he can't see the sun, the part of the path where it is night. So let's color that in blue. So now what we were talking about was which is longer, is day longer or night longer? And this is happening on 21st December, the December solstice. So December solstice, like just by looking at this audience, can you tell which one is longer and which one is shorter? Okay, Azvika is saying that night is, night is what? Is it longer or shorter? Night is longer, day is shorter. Yeah, so a lot of people are just, so I know that it's supposed to be that the day is shorter and the night is longer. Okay, but you know, this, it does seem slightly shorter, but the difference is very small here. It's not very obvious. Yeah, so the sun path during the day is in fact shorter, but only by a little bit. So maybe let me show you a more extreme example to help this become clearer. So let's work out day and night paths for somewhere far in the southern hemisphere. Swar Sachin, who's in Mumbai, he decides he wants to see what sun paths and what the sun looks like in Chile. So he goes to this southern part of Chile, to this national park and this is, so now we can try and work out in our celestial sphere what, how this is going to look for him. Okay, so let's move him on the globe. So here he is in Mumbai and so I'm going to move him far south, right? So 50 degrees south. So notice that the sun path I haven't changed because the sun is in the same, the sun is in the same position, the earth is in the same position and so it's drawing out the same path in the celestial sphere. So now what is the sky that he sees here? So this is the sky, right? And I'll do this rotation, I mean you'll have to do like some crazy gymnastics to actually see this. So let me rotate it so the sky is above. So remember now he's at 50 degrees south in Chile and this is the sky that he sees when he's looking up. So and I'll finally do this last thing where I can remove all the other stuff so you can see what's going on, right? So now can you tell if the day path or night path is longer? So now with this, what does the audience think? Like the part which he can see in the sky is the day, right? And then the part which is below is the night. So now can we be, which one is going to be longer? Is it day or night? Okay Vedanta is saying day path is longer. Okay, day is longer than night. Yeah, I also agree with this. So let's trace out the day and the night path again like we did before. So the day part is going to be like this. So let's trace that in yellow again. And then the night is going to be like just a small all the way over here. So let's make that in blue. So yeah, we can very clearly see that the day is much longer when you are in Chile. And the audience also definitely agrees, like everyone is saying day is longer. Okay. So here it's more obvious. So let me, maybe we can look at this slide and I mean we can look at putting it all together again like we did before. So what we have is, so let's see. So that was the path in, so let me draw for Mumbai first. Okay, so for Mumbai that is what happens during the day. But, and that's what you had shown me. But then to draw the night path, let's draw that dome below as well. And then let's draw the night sun path also in Mumbai. Okay. And then for just imagining like on the same diagram, let's do it for Chile as well. So the day path for Chile will be like that towards, yeah, that it was much longer. And then the night path will be continuing on from there and coming back and that will be much shorter. Okay. So that is what I have understood so far from this. Okay. But you know, now I can see some kind of pattern over here. Okay. So what, so something seems to be happening to the past as we go from from Mumbai to Chile. So what is happening to that? So do you, maybe it helps to think about or do you want to try and think about what is happening at the equator? Okay. At the equator, is it? Yeah, I have a guess. I think I can guess, but maybe the audience can also help me out. And Maruni, it might help if you label this as well. Yeah. Okay. So now this is the path that we saw in Mumbai. This is the path in Chile. Now, if Chaitanya wants to draw the path for the equator, do you, does the audience think, is it going to be more tilted, less tilted, tilted to which side? So first of all, let's see, yeah, is it going to be more or less tilted? And then we can decide to which side. Yeah. Vedant is saying that days and nights take the same amount of time. Is that in the equator Vedant? Is that what you're saying? Okay. So can you imagine how that path, like what path will the sun take if you are standing at the equator? Like, compared to Mumbai, for example, is it going to be tilted towards the north? Is it going to be tilted towards the south? So can you imagine the path at the equator? Okay. This is, I think it's a bit tricky. You know what? I am going to make a guess, Maruni. So let me just make this lighter so that maybe, yeah, you can, why don't you guess and then we can try and see whether the audience is kind of with us. Yeah. Sure. So what I think is that at the equator, the path is actually going to go straight up and some straight back down. Okay. So I think it's going to be like that. And I think that's going to happen. Yeah. So Vedant is saying it will go exactly north to south. In fact, I am saying I think it will go exactly, yeah, like that. Yeah. So I think the reason this is happening is, you know, as you go from 19 north to, so equator is between 19 north and 50 south. So the path should be somewhere in between them as well. So that's why I think, and you know, it's 90 degrees. So I thought it's something special. So maybe it will go straight up and come back down. Yeah. I mean, so your guess was kind of correct. So maybe I'll try, let me put this on a separate, separate all these paths and maybe you can see the pattern for, you know, the full pattern of what's going on. Okay. So first, so this was our friend Sachin who was in Mumbai. Right. And in December, let me add four of his friends who are in different places on the earth. Right. And then just rotate it so that, you know, our north is always on the right side. Right. So now what we've drawn out is, you know, what was happening in Mumbai. Right. We drew out what he saw in Chile. And then Chaitanya had a guess for zero degrees for the equator. Yeah. So does the audience sort of start to see a pattern here in terms of what's going on? Shall we try to see maybe what is going to happen in 20 south? So this is what is happening around 20 north. This is what's happening around 50 south. And this is the equator. So in between? Yeah, in between these two. Should I tilt it? So first of all, should it be tilted? Let me ask that. So at this equator, we decided it was just going straight up and down. So let me first ask if you think it should be tilted at all. Yeah. Audience, audience, Nishita doesn't think it should be tilted. Okay. Okay. So whether you want me to tilt it to the left or to the right? Like, is it going to be tilted more towards this side or more towards this side? So in fact, yeah. So let me put this on. So it's going to be tilted like this. So from zero degrees as you go further, as you go further towards the south, it's tilting more and more to the right. So now, what? Sorry, I think Varuni's sound has cut off. Her video looks frozen. Okay. Varuni, Chaitanya, just go ahead and Yeah. Okay. So I'll continue this. The thing is the slides are with her. Okay. Do you have a copy of them to share if you can? Yeah, I do have a copy to share. Shall I do that? Maybe that's the best thing to do. Okay. Let me do that. Okay. So Okay. I will allow you to share. Yeah. Okay. So we were... Okay. Varuni is back. I think Varuni is back. Okay. Okay. I'm on a hot spot. So maybe I should just... So should Chaitanya do the screen share? Yeah. I can do that. Yeah. I think that's better. Yeah. So Chaitanya, I have given you permission to share your host anyway. Okay. So here we are. Just a second. Sorry, audience. We just hold on. We've had a little glitch. We will be back with the presentation. Okay. So let me just... Yeah. Okay. Can you see my screen now? Is it clear? Yes. Yes. Okay. So where were we on this? We had already finished the guy at North and we were doing the 50 South or 50 North. Yeah. So 50 North. So what's... So this is now 50 degrees North. So what's going to happen here? So Varuni, take it away. Yeah. So yeah. So now what I was asking you was what is going to be happening at 50 North, right? So is it... First of all, is it going to... Is the path going to be tilted? So I think Bhuvan is saying yes. Okay. Now is it going to be tilted? Which direction is it going to be tilted? Towards the left or towards the right? Yeah. So Vedant is saying it will tilt towards the left. Okay. So that's in fact right. So it's going to tilt. And okay. So the pattern that I see is right. That if I start from the equator, okay, if I start from the equator, that is at the center here, and if I go into the southern hemisphere, okay, then the path seems to be tilting more and more towards the north. Okay. So if I go south, the path tilts to the north. But from the equator, if I go towards the north, then the path tilts towards the south. Okay. So is that pattern correct? Yeah. So that is kind of what is happening. Do others, does the audience also kind of notice this pattern? Yeah. I mean, it might be easier to think of it in terms of right-left also, but I think mostly the audience seems to agree. Okay. So this pattern is about right. But remember, your original question was actually about day and night length. So notice that at the equator, I think someone had just pointed it out. So notice that at the equator, the day and night paths are of equal length. Right. So at the equator, you have equal day and equal night. And then as you change the angle, so as you go further south from the equator, so as you go towards the south from the equator, the portion of day increases and as you go further north from the equator, the portion of night increases. Right. And this is all happening on the same day. So this is true for the December solstice. Right. Right. Exactly. Okay. So but now I have another question. So, you know, right now we have gone to 50 degrees south. So what happens if you go even further south? So for example, on December solstice, if you go to Antarctica, what will happen? This is a nice question. So does the audience want to try? So let me help you out a little bit. So I'll just move all these things to the side, these globes that these positions we drew. And I'm going to show you the sun path at say 70 degrees south, which is near the equator. So that is, yeah. Okay. So that's the path. So now I'm wondering, you know, given that this is the path, I'm wondering what it will look like. So this is Antarctica, right? So audience, what do you think, if the sun path is like this, what do you think is going to happen? Can you imagine what it's going to look like? The audience, I think Nisha is asking when it's the longest day in the northern part, that time in the south, it's the shortest. That's correct. That is what's going on. Yeah. But if we look at this image, what will happen actually in Antarctica? So maybe Varuni, can you just show us the photo? Okay. So there will be no night. Interesting. So this is actually a picture that was taken by the, by some, by an expedition in Antarctica. And this you can imagine as kind of a panoramic view. So they've just taken photos going all the way around. So the sun just kind of goes around you. So that means that here, even when I'm at 12 am at night, okay, people can, that I can see the sun. So that's unheard of. So Nisha is saying that there will be no night. Yeah, you're correct. There's no night as there's no darkness. Maybe that's the better way to put it. So my current is back if you want me to share, if we want to switch back. So now let me just, so remember the question again was this question of why? So why are the days longer in the Southern Hemisphere when they are shorter in the Northern Hemisphere? And I think someone already said, yeah, when it's longest day in the Northern Hemisphere, it's actually the shortest day in the Southern Hemisphere and the other way around. So let's go back to like sort of why is this happening? So in December, the Southern Hemisphere, the angle is such that there's more daylight and the sun is visible in the sky for a longer period of time. So at the same time, the angle in the Northern Hemisphere is such that the sun is visible in the sky for a shorter period of time. Okay. So Varuni, you know, like just to close off, like I was, I was wondering, you know, these images that you showed us, they're very beautiful, you know, like the Antarctica sun and the time lap that a lot of people have taken. So I was just thinking, how can we observe such things? Can we take photographs like this? So yeah, so I mean, you can. So let me just shift a little bit and tell you how, how can you see the sun path and its motion and take some of these really cool kind of images, which is I guess our arts part of the steam show. So this was the initial image. Let me just pull up the initial image that I had shown you. This was from Aman Jordan, remember. So you can do a couple of things. So the first thing is to find a spot where you have a clear view of sunrise or sunset. Okay. It also helps to have some objects close to your horizon, just so that you can have some reference points. So here, there's a little bit of a monument on the right side and then there's some hills on the left. So that helps. Use the compass and face directly east or directly west, depending on if you're looking at sunrise or sunset. And then just, you know, take an image standing in exactly the same place once a month. Okay. So I see. So this is something we can see all over the year. So I was just thinking, is it also possible to see the, we talked about the sun path as having an angle, right? So I was wondering if we can see that as well. So yeah, so actually there are people who've taken some lovely images of this also. So let me show you this. So the picture on the left is from Italy. So this is the sunrise, the sunset over the Mediterranean, I think. And the image on the right is taken by a colleague of ours, Alok from Bhopal. So what you do is you stand in the same place and have your camera in exactly the same position. And every two minutes you kind of take a picture and then you can put it into a collage like this. There are a lot of programs that can help you do this. It's quite easy to do if you have these pictures. So this helps you see that angle. So maybe I want to also point out that, you know, if you look at the angle here of the sunset in Bhopal and the sunset in Italy, you can see that there's a big difference in the angle the sun is taking. So this angle, right? Yeah. Okay. So but people do really cool stuff with this. So they actually also put both of these things together. So this is an image from Canada. So this person has taken pictures from the same spot over the course of the day as to watch sunset. And he's watched this over different times of the year. And they've put all of this into one image which you see here. So you can see like west. So this is sunset. And you can see like, you know, the whole spectrum of this. Okay. So there's, and people do a lot of really cool things with this. So there is also this, there's also this thing called solar graphene. So what you do is you take a sort of pinhole camera and you have, you have photographic paper inside and you just have it be exposed for the whole day. So you can trace out the full path of the sun over the day. So this was a series that was done in Scotland, where they use 27 of these pinhole cameras. And inside they had this photographic paper and you know, you can you can get these full paths. So this is over six months between solstice to solstice. Okay, this is this is quite an amazing photograph. So maybe before we go to, so I have some resources and things like that to kind of share with you. But maybe at this point, we can take some questions before, before that. Let me just look at the questions coming from elsewhere as well. Sure. So I think like, just before we close off, let's just say thanks to, to the steamboat team and to all of you guys for listening to us. So this photo in fact was taken just this morning by by Arnab from the Gateway of India. So they are all like, they've been very enthusiastic about like, just capturing sunrise and we are hoping that you guys are also now inspired to go out and look at the sun. And if you want to connect with us, well, this is these are all our social media handles. So you can like this reach out to us here. We'd be very happy to hear from you. If you take photographs, like just put them up here and tag us. It would be wonderful. So we'll maybe take a few questions now before we give you some resources to look at. Yeah, so I think Ajit, is it someone had a question about, someone had a question about what kind about sundials? Okay. I can tell you maybe a little bit about sundials. So if you go down to maybe slide 40 or something. Okay. So sundials are actually quite old. So this is one of the oldest sundials that was found. This is from the Egypt's Valley of Kings and it's from 1500 BC. But if you go to 42, if you go to 42, there are some pictures of sundials that you may have seen. So this is on the left, you have Jantar Mantar in Jaipur. So and on the right is another one of these that Jantar is that is in Ayukha in Pune. So correction with location. Yes, yes, yes. So the thing is that what, so these are constructed to tell time. But if you notice, if you look carefully, there are these angles. So these are constructed so that this angle is correct for the location you're at or the location the sundial is at. So this is constructed so that this angle that the sundial is at is sort of perpendicular to the sun path that's going around. Because that sun path, you remember that angle stays the same. It's just the sun path itself that moves back and forth. I mean, this is roughly what happens. Yeah, there's a little bit of a complication that happens between the tropics, but maybe I won't go into that because that gets quite complicated. Yeah. So yeah, I mean, maybe I should also clarify that the sundial is going to tell you your local time, right? So it's telling you in some sense solar time. So the time that is determined by where the sun is in your sky. Now, you may know that, you know, IST is kind of determined with the central longitude. So which is somewhere near Allahabad 82.5. So, you know, your time that maybe you measure with a sundial may be different from IST, which is what your watch is telling you. But if you have a sundial in Allahabad, it should tell you the same time that's on your watch. I mean, close enough. Okay. What are the other kind of questions? So let me just go through a few resources maybe and then just for a minute and then we can kind of close up. I think let's just wait for questions right now. Amish, I think is saying something. Yeah. So do we have any questions listeners on YouTube as well? On Zoom as well? I'm monitoring YouTube. No questions there as of yet. We'll wait for a minute or two for them to put down their questions. And Arnab sir has shared the email ID steamboat at the redhbcsc.tifr.res.in. So if you have any questions or doubts or if you have any topics on which you would like us to, you know, make an episode out of, you can definitely write to us over there. So no questions on your YouTube as well. Maybe you want to just go back to the contact slide, the Steamboat contact slide. Yes. Yeah, this is us. Yes. So write to us over here and also don't forget to get subscribed to our channel so that you can get regular updates of various events and we'll be putting this in different languages as well. Maybe Hindi, Marathi, Tamil. So stay tuned to it. And yes, so no questions on YouTube as of now. Maybe in 30 seconds or so, you can go to the references which Varunee was talking about. Yeah. Nishita was asking how to join the session the next time when it comes. Nishita, I just, you just have to keep, just follow us on these and the links and all will be posted there. In fact, if you subscribe to HTC TIFR Mumbai YouTube channel, you can just be notified when it's live. Yes, Nishita. So this is going to be on second Sunday of every month at 11 a.m. So that is for sure, but there will be other sessions and other languages as well. So you can subscribe to our YouTube channel and also keep checking the Steamboat website and you can always write to us if you have any, if you have any doubts or any queries. Okay, Varunee, let's have a look at the references which you were talking about. Yes. So this is just to give you some idea of like, you know, we want you to look at, take these nice pictures and like observe it and, you know, kind of put together these beautiful collages, some of which you've seen. So a lot of our pictures today were taken from NASA's astronomy picture of the day. So they have these archives. So if you want, if you want some ideas of what to do or if you want to see what other people have done, this is one place to go. The other thing is there's this app called Zero Shadow Day which is quite helpful to, so we went through all these visualizations today. So this app kind of will tell you, will let you go through it, you know, you can move around the sun and the dates and see what's happening. So it's quite, it's quite a nice app and has a lot of different features. So just check it out. And finally, I'll also tell you to check out the ASI page. So the Astronomical Society of India, they have a public outreach and education committee. So they do a lot of things. So they, for example, they have regular talks and also in multiple languages. Yeah, so then we also do observation drives. So we recently did one to do with the equinox. There should be one coming up for the solstice. And they also have these, regularly they have these photo, photo contests. So you can check that out. And then they have other activities that you can do related to the sun or related to observing other astronomical phenomena. So they have a lot of stuff. So you should check them out and get in touch with them as well. They have amateur astronomer groups as well. So yeah, I just wanted to give you these so that you have the room to kind of share. I will put these into the chat box as well. So let me just do that. Yes, that helps. So yeah. So I think that's it from our side. So we can sort of close. Okay. And listeners, we will also put this resources on our YouTube videos description if you want to check it out later. So yes, we are done. Okay. Yeah. Let her put all the resources and then we can end. So yeah, thank you guys. Okay. Yes. Thank you. Thank you everyone for coming and we'll see you next time in this voyage of Steamboat. Yeah. Thanks a lot. Yeah. Bye.