In Chinese mythology, there is a love story of Qi Xi (七夕) in which Niu Lang (牛郎, Altair) and his two children (β and γ Aquilae) are separated from their mother Zhi Nü (織女, lit. "Weaving Girl", Vega) who is on the far side of the river, the Milky Way. However, one day per year on the seventh day of the seventh month of the Chinese lunisolar calendar, magpies make a bridge so that Niu Lang and Zhi Nü can be together again for a brief encounter. The Japanese Tanabata festival, in which Vega is known as orihime (織姫), is also based on this legend. (from Wiki)
In 2017, this date falls on Tuesday, 29 August 2017.