It comes from the time when we were born. Ask your Mom or get your birth certificate or hospital records, it should have your time of birth. How is that important? Let us see.
We all know that the earth has this funny movement of spinning around and shifting to the right. It is almost like a dance.
Now, the earth moves through the 12 zodiacs while rotating that is during the day and again as she revolves around the Sun.
The shift through the zodiacs during the day (while she rotates in her axis ) gives our Lagna and shifting through the zodiacs while revolving gives our Sun sign.
So, how do we get our lagna?
It is a wee bit mathematical. Nothing complicated!
if the Universe is all around us that would translate to 360 degrees, and a day lasts for 24 hours, then the earth moves through (360/24 = 15 degrees) of the Universe, in one hour.
Again, if there are 12 zodiacs and total degrees are 360. Each zodiac rules (360 / 12 = 30 degrees. )
So combining the two logic we get earth stays in one zodiac while rotating around its axis for about 2 hours. Hence, the number of hours ahead or later from sunrise determines how many degrees we have moved away or are yet to travel to the Zodiac in which the Sun rises; and that becomes our lagna.
So if we are born on 15 July say..when the Sun is in Cancer, meaning the zodiac Cancer rises in the east at 6:30 am sunrise time (you have to find the sunrise time either from the almanac or Google it up.), then if anyone is born at 6:30 their lagna would be Cancer. If they are born at 6:00, which is 1/2 hours before sunrise then their lagna would be the zodiac before Cancer i.e., Gemini. Similarly, someone born 4 hours, say, after sunrise will have a lagna that is in the zodiac that is 2 places later from Cancer, which would be Virgo.
Yes, the Sun is our base for every possible calculation. Even for those who use the Moon sign to predict. The calculations always take Sun as the basis. It forms the centre of the Solar System, so it makes sense, right?
This is our stepping stone… our starting point …our level zero.
It is a bit of physics, geometry, and mathematics at this moment. Mull over this before we move on to what the lagna signifies.