About Kṛṣṇa Janmāṣṭamī
In brief. On the eighth night of the dark fortnight of Bhādrapada — the night when Aṣṭamī tithi meets Rohiṇī nakṣatra, or the night that most closely approximates that meeting — Śrī Kṛṣṇa was born in the prison-cell of Mathurā to Devakī and Vasudeva. The tradition keeps vigil on this night as few others: fasting through the day, temple pūjā through the evening, and the Nishīta pūjā at midnight — the hour of the Lord’s descent.
The story the tradition remembers. The Bhāgavata Purāṇa’s tenth skandha opens with this night, and every reciter of the Bhāgavata returns to it as the story’s still center. Devakī had been imprisoned by her brother Kaṁsa, who had heard the voice from the sky prophesy that her eighth child would be his death. Kaṁsa had already killed six children; the seventh (Balarāma) had been transferred to Rohiṇī’s womb by yoga-māyā. On the eighth conception, the whole cosmos held its breath. The Purāṇa’s language for the birth is not the language of ordinary parturition: the prison lights dimmed, the guards fell into sleep, Devakī and Vasudeva beheld the Lord in His four-armed Viṣṇu form before He assumed the infant body, the shackles fell away, the doors opened, and Vasudeva carried the child through the storming Yamunā — the river itself parting, Śeṣa held above as canopy — to Gokula, where he exchanged the child with the newborn daughter of Yaśodā. What returns to the prison is not the Lord; what is left behind is yoga-māyā herself. The tradition holds that the exact hour of the birth is midnight of Aṣṭamī under Rohiṇī — which is why the observance is nocturnal, and why the Nishīta muhūrta is the pūjā’s living heart.
Why the day matters. Janmāṣṭamī is one of the few nights the tradition asks the household to stay awake with. What is being remembered is not merely a birth; it is the descent — the specific historical-mystical moment when pūrṇāvatāra took human form to lift the burden of adharma from the earth. Kṛṣṇa Himself names the logic in the Gītā: “yadā yadā hi dharmasya glānir bhavati bhārata, abhyutthānam adharmasya tadātmānaṁ sṛjāmy aham” — whenever dharma declines and adharma rises, I take birth. Janmāṣṭamī is the day the tradition celebrates that promise being kept. To fast the day, keep vigil the night, and offer pūjā at the exact hour of the descent is to receive the promise annually — to say the household believes what the Bhāgavata declares and stakes its year on it.
A note on timing that matters. Janmāṣṭamī’s timing is famously contested — the śāstric ideal requires Aṣṭamī tithi AND Rohiṇī nakṣatra to prevail simultaneously at midnight, which happens rarely. When they don’t coincide, the tradition splits: smārta convention prioritizes the Aṣṭamī tithi (household observance); Vaiṣṇava convention (particularly Iskcon and many South Indian temples) prioritizes Rohiṇī nakṣatra with the pāraṇa at its conclusion. Neither is wrong; they follow different śāstric weightings of the same texts. Śubhakāla observes the smārta convention for household observance and states both dates when they diverge.
Observance
Traditionally the observance is: dawn saṅkalpa naming the vrata; fasting through the day (many observe nirjala — without water — as the fast’s strict form); temple or home pūjā through the evening; the Nishīta pūjā at midnight with abhiṣeka of the bāla-Kṛṣṇa vigraha (butter, milk, honey, sugar, ghee — the pañcāmṛta); recitation of the Bhāgavata’s tenth skandha birth chapter or of the Viṣṇu Sahasranāma; and pāraṇa (vrata-breaking) the following morning after Aṣṭamī ends and Rohiṇī departs (or as each paramparā prescribes). Many households prepare nāṇdī (the swing on which the Kṛṣṇa vigraha is rocked at midnight), jhankī (tableau of the Gokula scenes), and bhoga (traditional preparations offered to the Lord and shared as prasādam — 56 items in the classical chappan-bhog, though most households offer a devotionally-scaled version).
Śubhakāla states both the smārta and Vaiṣṇava dates when they diverge; the Nishīta pūjā at midnight — the hour of the descent — is the observance’s living heart. Both conventions are authoritative within their tradition — follow the one your paramparā or family observes.