In the Mahābhārata (Virata Parva, Section 44) Arjuna explains his many names to his daughter in law, Uttarā. In text 14 he explains why he has the name Phālguna.
उत्तराभ्यं च पूर्वाभ्यं फल्गुनीभ्याम् अहम् दिवा
जातो हिमवतः प्रेस्ष्ठ तेन माम् फल्गुनं विधुः
uttarābhyaṁ ca pūrvābhyaṁ phalgunībhyām aham divā
jāto himavataḥ presṣṭha tena mām phalgunaṁ vidhuḥ
“I am known as Phalguna, my dear, because I was born in the snowy season on a day belonging to both Uttara- and Purva-Phalguni.“
The lunar calendar is the primary calendar of Indian culture, because it is designed for religious and spiritual time-keeping and Indian culture is fundamentally religious and spiritual. This method of telling time involves measuring the distance between the Moon and Sun (which basically amounts to the same thing as counting lunar phases). It ties the lunar phase to Earthly days via the Sunrise. The phase of the moon at the time of sunrise becomes the phase of that day, even if the actual phase itself changes before the next sunrise.
There are a few components of the Indian lunar calendar besides the phase-day (tithi). Another is which of 27 star-clusters (nakshatra) the Moon is in. Again, the star-cluster the Moon is in at sunrise becomes the star for the entire day, even if the Moon moves into another star-group before the next sunrise.
It regularly happens that the Moon can pass two phases and/or two star-clusters during the course of one Earthly day (sunrise to sunrise). Or, visa versa, sometimes one phase or star manages to span two sunrises. Say for example that the Sun rises on day 1 when the moon is at the very end of star-group 1. During the course of the day the Moon would move through star-group 2, and by the time of the next sunrise it would be at the very beginning of star-group 3. So day 1 would be a star 1 day, and day 2 would be a star 3 day. There would be no star 2 day in the cycle. Or, visa versa, if day 1’s sunrise occurs with the Moon at the very beginning of star-group 1, day 2s sunrise can occur when the Moon is still at the very end of the same star-group. In that case both day 1 and day 2 would be star-group 1 days.
These “stretched” and “lost” days are special days in the calendar, with special significance.
In the reference quoted above from Mahabharata, it seems that Arjuna is telling his daughter-in-law that he was born on one such special day during the winter (Hima season, the snowy season) where the Moon passed two star groups on a single day. This is somewhat rare and significant, but there is something more rare and significant about Arjuna’s birthday:
Among the 27 star-groups there are a few that are in pairs.
- Purva and Uttara PHALGUNI
- Radha and Anuradha (Radha is also called Vishakha)
- Purva and Uttara ASHADHA
- Purva and Uttara BHADRAPADA
So there are only 8 out of 27 star-groups that are paired up. It is somewhat uncommon to be born on a day where the Moon passes through two star-clusters. It is much more uncommon to be born on a day where those two star-clusters are among these pairs. Arjuna says he was born on a winter day when the Moon did exactly that – passed through two paired star-clusters: Purva and Uttara Phalguni.
This noteworthy birth earned him the name Phālguna.
The Phalgunis are stars of entertainment and friendship. Arjuna (besides being an outright dashing hero) was such a skilled dancer and musician that he could successfully disguise himself for a year as a gender-neutral dance instructor for the royalty (and is thought to probably met Uttara as his student during that time, appreciated her qualities and later introduced her to his son, whom she married!). As for friendship, Arjuna has the Supreme Friend. He is well known as a dear, dear friend of Krishna, for whom the All-Attractive became like a chauffeur of sorts, and was always a close confident and trusted guide. Krishna spoke the very important philosophical and spiritual instructions of Bhagavad-Gita to Arjuna, only because “you are my very dear friend.”
– Vic DiCara