Why Thursday specifically
Thursday (Guruvar or Brihaspativar) is named for Guru, the planet Jupiter, associated with wisdom, teachers and good fortune. In Vedic tradition, Vishnu is worshipped on this day as the preserver of dharma, and Brihaspati himself, the guru of the gods, is honoured alongside him — making Thursday a day associated with both divine wisdom and stability.
How the day is typically observed
Many devotees fast on Thursdays, wear yellow (Vishnu and Jupiter's associated colour), and recite the Vishnu Gayatri Mantra or sing Om Jai Jagdish Hare. It's also considered an auspicious day to begin educational pursuits or seek a teacher's guidance, given Guru's association with learning.
Guruvar Vrat
A specific Thursday fast, Guruvar Vrat, is kept by some devotees seeking marital harmony or a good spouse, involving worship of a banana tree (associated with Brihaspati) in addition to Vishnu.
A day for steady growth
Where Tuesday's energy is protective and urgent, Thursday's is patient and cultivating — a fitting midpoint in the week to focus on long-term wisdom and stability rather than immediate crisis, echoing Vishnu's own role as sustainer rather than destroyer.