iacisrmma
Chazal bring down that having a Yom Tov Sheini is a reasonable compromise between having only one day of yom tov and three days of yom tov, nothwithstanding uncertainty on solar/lunar calendar dates. They also note the upheaval in the heimeshe community if we were to reduce moed by one day from four to three to make up for the additional day of yom tov