Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 6 · Calendar, Muhurta Elements
कालमानं मुहूर्ताङ्गानि च
गृहप्रवेशवैवाहप्रतिष्ठामौंजिबंधनम् ।मघादौ मंगलं कर्म विधेयं चोत्तरायणे ॥ १२६ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 126.
House entry, marriage, installing a deity and the thread ceremony. These good acts should be done in uttarayana (the Sun's northward course), from Magha onward.
Simple meaning: House entry, marriage, installing a deity and the thread ceremony suit the Sun's northward half-year, from Magha.
याम्यायने गर्हितं च कर्म यत्नात्प्रशस्यते ।
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.