Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 6 · Calendar, Muhurta Elements
कालमानं मुहूर्ताङ्गानि च
याम्यायने गर्हितं च कर्म यत्नात्प्रशस्यते ।माघादि मासौ द्वौ द्वौ च ऋतवः शिशिरादयः ॥ १२७ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 127.
In dakshinayana (the Sun's southward course), these acts are blamed. Only with great care are they approved. The seasons, Shishira and the rest, are two months each, from Magha.
Simple meaning: In the Sun's southward half these acts are blamed, allowed only with great care. Each season lasts two months from Magha.
मृगाच्छिशिरवसंतश्च ग्रीष्माः स्युश्चोत्तरायणे ।
Three seasons fall in the Sun's northward half and three in the southward half.
चांद्रो दर्शावधिः सौरः संक्रांत्या सावनो दिनैः ।
A month can be counted by the Moon, by the Sun, by thirty days, or by the Moon's round of the stars.
मधुश्च माधवः शुक्रः शुचिश्चाथ नभस्ततः ।
These are the first ten names of the twelve lunar months.