Guys, we have started to look at What’s Up there in the deep dark skies. However this is like playing a game so that we can enjoy it. So like all games have some basic rules, so stargazing also does have. The rules were taught to us in school days as a part of Geography, where we all knew that we should know the “position” of POLE STAR! The only prominent point on the which underline the NORTH direction!! Right?? But how we will know which is the Pole star in the crowd of stars?? So something we know as a bunch of seven stars also called as Saptarshi or Great Bear with help of it we can spot the pole star. .. But guys, there are more (logical) rules derived by our ancestors.
Before we jump into finding pole star or deciding directions, we should attempt to know the things which we experience daily, annually! Now here where the imagination plays a vital role.
Imagine you are standing in a ground with a clear horizon on all sides. The imagine a complete sky above you as a half globe or done, the other half is below your feet or ground which you can’t see. Now as day begins, the sun rises, it goes up & up in the sky. At some point of time it comes or may not come exactly overhead and then it starts to set down. So imagine if you observe the same rising & setting of the Sun for days, weeks, months & a year, you will come across a very fascinating conclusion that the sun’s movement is not the same at all throughout the year, it varies from one point to other point. This unusual movement of the Sun is because of the “orientation” of the earth around its “rotational Axis”. Conversely & truly speaking the sun isn’t moving around earth. But the earth moves around the Sun & it itself tilted! So because of this we experience the beautiful seasons! So concluding the sun has a specific path in the sky as seen from earth and this path is called as an “Ecliptic!” I always say that the sun’s movement is like the paths of a local train which has definate track. And now imagine you are standing on the ground which lies on the “Equator” of earth, if you expand this equator in all directions into the space then it cuts the dome of sky into 2 parts, the northern hemisphere & southern hemisphere. This big circle is called as CELESTIAL EQUATOR!
Now, you got two big Circles, the one is the Celestial Equator & other is Ecliptic. These circles coinciding each other at two points… Those are the points of interest, because the actual game of season starts on one f the point. Now winters is going on (in Northern hemisphere of earth). So you might have observed that the nights are bigger than the day or night comes earlier. To simplify this, you know that sun rises on East and sets on West (that’s because earth rotates from West to East or anti – clockwise). So if we consider today’s date (23 January) the duration of the day time increases and night reduces. And as we approach March it becomes almost 50-50 day-night! Also the position of the rising sun also slightly changes but remains on East only. So on 23 March the sun rises “exactly” on East and sets in west. So if you observe carefully, you will notice that today’s position of rising sun was South with respect to that on 23 March. Hence on 23 March we have equal day & night. Hence it’s called as Vernal Equinox day. ( Equinox mean equal day-night).
From 23 March, the sun tends to move higher towards north of Vernal Equinox. On 21 June , sun reaches highest point of North causing bigger day than night. This is called as Summer Solstice for northern hemisphere.
Now sun will move towards south and again we will have equal day-night situation on 23 September, called as Autumnal Equinox!
From here onwards, sun will move south most point on 21 December and we will have chilling winters on Northern hemisphere. With longest night on the same day. This is termed as Winter Solstice!
This cycle of circles will go on & on…
So sun’s apparent movements on sky causes Vernal Equinox, Summer Solstice, Autumnal Equinox, Winter Solstice are the 4 points of interest & intersection of great circles. This all happens because of the tilt of earth’s axis at 23.5 degrees .
Just imagine if earth wasn’t tilted, then we couldn’t have the seasons to experience, diversity of life on earth etc etc.
We will continue for the next rules in next session. This will take time for you to digest. So that we can have break to understand it well.
©️ Ambarish Pawar 🌐