 okay so we are going to use parallax method to devise a strategy to find the distances of heavenly objects like moon or some stars from the earth okay now what happens is that suppose there is let us say there is a star like this okay and I am I want to use parallax method I want to find out the distance of this star from the earth okay now even though we have drawn earth bigger than the star but in reality earth is like a grain of sand in front of the size of the star okay so you know even if you go from this place to that place the star will remain right above you its location will not shift okay in the diagram it is very easy to draw you know you can draw it like this and then you know the distance between these two points or you have this angle and all that but in practical this angle is zero perfect zero okay so there is a different strategy to find the distance of a very very far away star okay but suppose star is close by suppose the star is slightly closer okay then this angle could be you know close to zero but you can still measure it probably one point zero point zero zero one degrees or radiance like that so you can measure it okay how to measure that angle to measure it that angle you look at the very very far away star which will be right above your head because that's for for that star the entire earth is like a point only so star will be right ahead of you right above you so you look at the far away star okay which is this line of sight and then you look at the nearby star you get this angle how much you have to rotate like this will give you this angle okay then you go far away place then again you look at the same very far star which will be again right above you and then you look at the nearby star you get that angle suppose this is theta 1 this is theta 2 this angles will be equal to theta 1 plus theta 2 understood and once you know theta 1 plus theta 2 this should be equal to what this length divided by that length okay you exactly know that how far you have moved yeah so you if you know the angle you'll get to know how far the star is from the earth okay so we will be solving numerical related to this okay suggest that I thought I could introduce what kind of numerical should be there okay and also one more thing is that we are dealing with extremely small angles okay so we need to introduce a smaller unit of angle it will not be comfortable to say that angle is let's say you know 2.3 into 10 is power minus 4 degrees or minus 4 radians so if I introduce a smaller unit for example if you have to talk about let's say distance of hydrogen's electron from the nucleus you'll be talking in terms of Armstrong right suppose you have to talk about distance of very very less you'll be talking in terms of millimeters okay so like that if I have to talk about very very small angles so I need to introduce a smaller you know smaller unit of the angle itself okay makes sense okay so let's try to introduce the smaller units of angle okay so we already know what is one radiance okay there is something called one minute which is one dash okay one minute is 1 by 60th of radiance write it down and one second one by sorry one minute by 60 radiance which happens to be equal to 1 divided by 3600 radiance minutes minutes is for time I understand that okay but for the angle also we are introducing minutes only because we are dividing the radiance into 60 equal parts just a convention there is no as such this thing okay now can you tell me how many radiance one degree has one degree has can you write one degree in terms of radiance how much it is okay try writing this one degree how many radiance calculate it calculate and then you have to tell me you have to calculate and remember also one minute how many radiance one second how many radiance the another name to minute is arc minute another name to second second is our second how to get one degree how many radiance it's a five by one seven four point zero one five radiance is how many degrees one eighty degrees okay so basically you can write like this 180 degrees correspond to pi radiance so one degree will correspond to pi by 180 okay how much is pi by 180 0.0174 okay I'll write it down this is 1.745 into 10 is power minus 2 radiance okay how much is one minute equal to in radiance how much it is 2.910 power minus 4 2.9 into 10 so minus 4 using Calcutta Calcutta 1.66 divide 0.166 0.166 so 1.6 that's wrong it is 1.6 divide by one minute no one minute is 2.9 in terms of degrees okay that's it wait me no he said in terms of radiance this is in legal how can one 60 degree how hmm so how I think it's in terms of degree in terms of degree in terms of 180 to 180 no no wait wait wait one minute one minute is one degree divided by 60 radiance whatever is one degree in terms of radiance have to write that and then divide by 60 so correction guys one minute is one degree divided by 60 okay one degree you are splitting into 60 parts but then so I have to convert one degree in terms of radiance okay and that you write in terms of radiance you can say that 1.745 10 is for minus 2 divided by 60 this is what this is the amount of radiance okay so this will be coming up to be that one degree we have divided into 60 parts all right now can you find one second how much divide that by 60 now how much 4.85 into 10 is to minus 5 10 is so minus 6 yeah yeah yeah okay so these three things if you remember it will be good okay you can use it directly otherwise you can anyway is calculate okay one minute see forget about the units if you split one degree into 60 parts one part is one minute okay now that one part you can write in terms of degrees or in terms of radiance so if you have to convert it in terms of radiance you need to first write how much is one degree in terms of radiance and then divided by 60 all right so that is one all right and when you deal with the distances always use SI units radiance okay don't use degrees right any other any doubt please ask any doubt so see let me see you have this as one degree okay all of you focus here this is suppose one degrees there is one degree angle degree is close to us because we have been using degrees since our childhood but then you know radiance is the SI unit so we need to get familiar with the radiance also okay this is one degree till now we never used or we never have to use anything less than one degree okay but now going forward the angles we are dealing with are very very small so we are introducing a smaller unit than one degree so what we have done is that we have split one degree angle into 60 equal parts okay so how much will be the one part one degree divided by 60 okay so that is the that is the one stop talking that is the one minute okay now that I can write in terms of radiance how can I write in terms of radiance convert one degree in radiance convert one degree in the radiance and then divide by 60 you will get it in radiance understood all right similarly one second is one minute divided by 60 you have not only split one degree into 60 part each part of that you have again divided into 60 so we are dealing with extremely small angle when I say one second okay so one second is one degree divided by 360 in terms of degrees it is one divided by 360 that is in terms of degrees but if you want to write that in terms of radiance you have to first write what is one degree in terms of radiance and divided by 360 this is one divided by 3600 degrees this is in terms of degrees if I have to convert this in radiance I need to write what is one degree in terms of radiance and then divided by 3600 okay so we have introduced very very small unit and at times even this small unit is not sufficient to define the kind of the angles you are dealing with okay any doubts now anything so let us move further you know these kind of things you will learn better when you solve numericals okay