5 ideas
Jagadananda Roy came to Rabindranath Tagore's attention through science pieces he contributed to Tagore's circle. Tagore brought him in first as a tutor to his children, then as a teacher at the Santiniketan school. Grahanakshatra grew from that teaching: it was written for the specific Bengali teenagers in his classes, so it was shaped by what real students could follow rather than by an imagined general reader.
Students taught science in a foreign language spend their effort decoding words and end up memorizing terms without grasping the phenomena. Explaining the same material in the learner's everyday language removes that barrier, so attention goes to the idea itself. On this view, vernacular science writing is a precondition for real understanding, not a simplified second-best.
The words graha and nakshatra already carried astrological and mythological meanings in Bengali. Roy's approach keeps the familiar words and fills them with physical, observational content. Readers get a foothold in terms they already know, and the old meanings are quietly displaced rather than attacked head-on.
Explanation begins with what a young reader can see directly: the sun's daily path, the moon's phases, and bright wandering planets among fixed stars. It then moves outward to the mechanisms and scales behind those sights.
Astronomical distances and sizes mean nothing as bare numbers to a teenager. Converting them into familiar terms, such as how long a train, a walker or a beam of light would take to cross them, turns an abstraction into something felt. Across a bodily sense of scale, the reader can grasp how small the Earth is and how empty space is.