Thank you SteelBird!
Why is the Mid-Autumn festival in September? It's still summer. Summer does not end until September 22nd. I guess it's like the Spring festival that takes place in the Winter.
Well, the Mid-Autumn festival is also called moon festival or harvest festival. The Chinese first celebrated harvesting on the full moon of August (the Chinese calendar) about 16th to 10th century BCE. Since people typically connect the season of autumn with harvesting and they did the celebration on a full moon, they started calling it mid-autumn or moon festival. Now, the mid-autumn festival mainly is about celebrating family and loved ones being together.
About the Spring festival, traditionally, it is called the New Year festival or the festival of passing the year. It is literally the celebration of the Chinese New Year. The name "Spring festival" is actually quite new. People did not start using the term "Spring festival" until the 1910's, possibly because the Chinese New Year typically falls in the month of February in the then newly adopted Gregorian Calendar. In China, spring starts in March and farmers begin planting the seeds a little before that in the month of February. So the Chinese New Year typically is pretty close to spring.
BTW, the moon cake is one of my favorites although it is a nutritious disaster. As the moon festival passes, the price of the moon cakes will drop like crazy. So in the next couple days, I will go on-line and snatch some delicious moon cakes, especially those with egg yokes in them...