Have you ever wondered, those who believe in Sun Sign Horoscope, why the signs of Horoscope have a month in it? And more specifically, why they don't start from first day of the month? Why Aries starts with 21st of March and not with 1st January?
Let me answer these questions one-by-one, again, as per "my" study/thoughts. To answer these, we need to think upon some Geographical facts, we observe, in reference to the Sun.
Everyone knows there are mainly 2 seasons, viz. Summer and Winter, in the world except few countries, such as India, Brazil and other lying in same latitudes, which have an extra Monsoon season. Most of us know that, these seasons are because of presence of the Sun in particular hemisphere of the Earth.
e.g.: If the Sun is at Northern Hemisphere, then the countries/continents lying to the North of an Equator, such as North America, Europe, large part of Asia etc., will experience Summer while, at the same time, Southern countries/continents, such as Australia, South America, Antarctica etc, will experience Winter.
Latitudes and Longitudes are the imaginary lines drawn on the Earth surface/map, which divide the Earth in North-South and East-West quadrants, respectively.
Now, the question is, why the Sun moves in Northern and Southern Hemisphere of the Earth?
Simple answer is that, it is not the Sun but, the Earth, which is rotating around the Sun (which results a year) with revolving around its own axis (which results day and night) in West to East direction (which results the Sun to rise in the East and sets in the West) with axis of Rotation in North-South direction, has little tilted axis of rotation. Simply, the Earth does not have axis of rotation (around own) in exact North-South direction. This tilted axis of rotation causes the Earth to bend and lean back vertically (North-South direction) in front of the Sun to maintain the orbit of rotation around the Sun. Otherwise, the Earth will loose its orbit and may collide with other planets or the Sun. In result of this balance making act of the Earth, we see the movement of the Sun in different hemisphere of the Earth.
So, on March 21st of every year, the Sun appears to be in front of an Equator, 0 degrees latitude, showing exact 12 hrs. of day (time between Sunrise and Sunset) and 12 hrs. of night on the Earth, and from next day onward, the movement of the Sun is appeared to be in the Northern hemisphere. The Sun will continue to move in Northern hemisphere, till it reaches 23(1/2) degrees North latitude, which is popularly known as "Tropic of Cancer", and this happens to be on 21st of June. So, 21st of June is Big/Longest Day in Northern hemisphere. This journey is of 3 months. And causes complete Dark at extreme Southern hemisphere and a day of 24 hrs. on North pole. This means, the Sun does not rise on South Pole and does not set on North Pole for that day (and nearby days as well).
From next day onward, again, the Sun starts moving in South direction and on 22 September, it again reaches to Equator. From this day, the Sun starts moving in Southern hemisphere. This journey is of again 3 months to reach out 23(1/2) degrees South latitude, which is popularly known as "Tropic of Capricorn", i.e. on 22 December. This causes complete Dark on extreme Northern hemisphere and a day of 24 hrs. on South pole.
From 23 December, again the Sun starts its Northern journey of 3 months which completes on 21st March. And this completes a journey of 12 months i.e. a calendar year.
Now, if you observe, the zodiac signs are 12 and also, time required for the Sun to make "visit" every part of the World/Earth is also 12 months. So, we can divide the Space, where the Sun appears to be moving, into 12 equal parts in which we can see the Sun at same location (or Part of Space), on particular day, every year. Those parts are named with Zodiac Signs. So, in a way, the Sun can visit every zodiac sign (actually part) for an entire month. This gives the logical answer of "Why the signs of Horoscope have a month in it?"
Now, the question is, "Why not 1st of January?"
Of course, on 1st of January the Sun is in front of some specific latitude every year, but, it is not the Equator which is supposed to be Zero degrees i.e. at the center of the Earth Surface and which divides Earth into two equal hemisphere viz. North and South.
But, the Sun is at Equator for two dates 21st March and 22 September. Then why only 21st March is considered as a start and not 22 September?
Yes, quite a valid and logical question. Now, as per me there are 3 answers for this question.
1. If you observe the map of the Earth, you will find, most of the countries and hence most of the World population, lies in Northern hemisphere. And hence, we might have considered Northern movement of the Sun first than Southern.
2. If you carefully observe the names we have given to 23(1/2) degrees North and 23(1/2) degrees South, then they appear to be "Tropic of Cancer" and "Tropic of Capricorn" respectively. And Horoscope of sign Cancer starts from 21st June while that of Capricorn is 22 December, which are as per our above observations of movement of the Sun in different hemisphere of the Earth. I really have no idea what comes first, Horoscope or Tropic Names. 😉😉
3. And most important and more appropriate reason is constellation (Nakshatras). Actually, my above description is just to clarify the movement of the Sun in the sky. If we look at the clear sky in the dark night, like I said before, in the parts of the sky (where the Sun appears to be moving and which are named as Zodiac signs), we can see different constellations form a particular symbol. And those symbols are nothing but Zodiac symbols. Moreover, the Zodiac signs are named as per these symbols only.
e.g.: On 21st March night (till 20th April), if we look at the sky, in the region of the Sun, we should see the Aries shape and so on.
I used to see sky every night, but, due to my lack of imagination or not having clear sky, being in the city, I don't see such shapes. But, it is said that, at country-side, we can see these miracle in the sky.
But, this (Constellation explanation) is not matching exactly with Vaidik Jyostish, which is popularly known as Patrika or Kundli, that actually works on Constellation positions. The dates are not exact.
e.g.: My birth date is 27th May. So, the Sun in my Kundli must be in Gemini as per Horoscope and our above Sun transit explanations. But, it is situated in Taurus.
This Sun transition is on 14th of every month, as per Kundli. I need to study it a bit more. But, our Sun transition explanation and month in Horoscope is still valid. Just few correction/assumptions to match with Vaidik Jyotish is needed.
These constellations are not only used by Astrologers, but also, Astronomers to identify the location of different stars or astronomical objects in the universe.
Hope this would have given the rough idea of "Why Horoscope has months in it?"
Moreover, if you closely look at the Indian Solar/Marathi calendar, which has a start of New Year, popularly named "Gudi-Padwa", nearer to 21st March, except few years which are, I guess, next to "Adhik-Maas".
***Adhik-Maas : In English calendar, we have an extra day in every leap year (29 February). But, all Marathi months are of 30 days and we have an extra month of 30 days after every 3 years, which is popularly known as, "Adhik-Maas" or "Mal-Maas" or "Dhondaa Mahinaa"
In the end, again, I'm mentioning that, the above explanation of "Month in a Horoscope" is purely my thoughts/conclusion. Here, I tried to bind Geographical/Astronomical facts with Astrology/Horoscope. The original reason may be different. Also, I don't want to boost any kind of Superstitions.
