Mithuna Sankranti, one of the twelve Sankrantis, marks the transition of the Sun from Vrishabha Rashi (Taurus) to Mithuna Rashi (Gemini). This four-day-long festival celebrates the arrival of rain.
Jupiter is the Devaguru who will bring in auspiciousness in which ever house it stands in. When it enters Mithun Rashi in retrograde, you can see a huge improvement in the knowledge sector.