Okay kiddo, let me explain the astronomical basis of the Hindu calendar in a way that even a 5-year-old can understand.
The Hindu calendar is based on the position of the sun and the moon in the sky. This means that it takes into account the movement of the earth around the sun, the rotation of the earth on its axis, and the movement of the moon around the earth.
You see, the earth rotates around its axis every 24 hours, which creates day and night. While the earth is rotating, it also revolves around the sun. This revolution takes around 365.24 days to complete, which is why we have a leap year every four years.
Now, the movement of the moon around the earth is also very important for the Hindu calendar. The lunar cycle takes around 29.5 days to complete, which means that every month has either 29 or 30 days.
The Hindu calendar has 12 months, and each month begins with the new moon. This means that the first day of the month is called amavasya, and the full moon day is called poornima.
The length of the Hindu year is calculated using the position of the sun and the moon. The calendar follows a 60-year cycle, and each cycle is divided into five groups of 12 years each.
Overall, the astronomical basis of the Hindu calendar is a complex system that takes into account the movements of the sun, moon, and earth to create a system for tracking time that has been used for thousands of years.