When Deva sleep Shiva is given 4 month to look after the earth. His Shravan month begins .. Chaturmasya begins in Gemini half or sometimes at the end of Gemini when Deva Shayani Ekadashi falls. , Cancer, Leo, Virgo, Middle of Libra. It forms 4 month of Chaturmasya. Sun will be crossing his point of fall or debilitation in Libra when Devas are awakened when Devotthan ekadashi falls.

These 4 month is dedicated to Vidya because Shiva is lord of Knowledge.

ईशानः सर्वविद्यानामीश्वरः सर्वभूतानां
ब्रह्माधिपतिर्ब्रह्मणोऽधिपतिर्ब्रह्मा शिवो मे अस्तु सदाशिवोम् ॥

Sages don’t move anywhere in Chaturmasyas. It is rainy season. They impart knowledge to their disciples in their Ashramas. You can understand why no auspicious activity is allowed till Sun is in debilitation of in neech avasstha. Devas are awakened only when Sun crosses his point of debilitation. It is because Sun is Atmakaraks. On Vishnu’s flag and temple Sundrashan chakra is Sun itself in his higher form. It is portrayed like Sun.