CHART HERE
Names of Nakshatras and something about them to correlate with, dates.
What are Rashis? Let me provide both a simple and detailed explanation. In simple terms, if the entire year is divided into 12 sections, these are called Rashis. The names, dates, hindi names and the planets ruling the essence of these divisions is given below.

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Let us discuss this in detail now.
Ancient Indian Astrology is based on the positions of planets (and other heavenly bodies) at specific times and locations. So naturally there are 2 parts of Ancient Vedic Astrology - first, the calculation of the location (of these planets in the sky) and second, drawing inferences and making predictions based on the position. These are called "Ganit" (which in Sanskrit means "Calculation" or "Mathematics") and Phalit (which literally means "Fruits borne out of the situation"). Let us for a moment, ponder upon the problem of Ganit - how exactly does one go about creating a map / jotting down the location of heavenly bodies (with respect to earth)?
The way this was solved by Ancient Indian sages was to first create a list of easily visible constellations in each of the 12 lunar months. Due to the revolution of the earth around the sun over the backdrop of this (assumed to be fixed) cosmos of constellations, these 12 divisions / constellation-focused lunar months actually form a pie chart of the entire cosmos, as traced via an elliptic path of the earth going around the solar system. This is easily explained via pictures below.
Pic1: Shows the sun and the earth (rotating around itself). The part of the earth facing the sun has day, and the other part, facing away has night. Concept to understand: If you are looking up from earth into the night sky, "where" in the cosmos you will be looking at - is highlighted with an arrow / "Vector".
Pic2: Shows the sun and the earth (revolving around the sun). Shows the orbit / path traced by the earth during the calendar year (abstracted to be a simple ellipse here). Also shows the position of the earth in the orbit at different times of a calendar year. Concept to understand: The "Vector" of the night sky points to different areas of the cosmos during the year. In other words, when we look at the night sky every month we are looking at a different sector of the cosmos - this is highlighted by the arrow.
Pic3: Shows an abstraction of the visible universe / cosmos. Highlights different constellations of the visible cosmos visible over the night sky during different parts of the year. Concept to understand: Since there are innumerable stars spread throughout the night sky, the ancient sages mapped out easily visible constellations in each of these 12 different sectors. These sections are called Rashis.
Pic4: Shows the pic-chart of Rashis over Pic2.
These pics show that the night sky of the 12 months is divided over 12 sections - each called a Rashi. Thus, it became possible to create a "map" of the sky, and able to determine the prime determinant for astrology - to create a map showing the location of heavenly bodies in a way which is understandable.
if the entire cosmos ( as visible from earth) was divided in 12 lunar months,