お彼岸（o higan）: The equinoctial week

A week in between the equinox day is called higan (彼岸). But we call o higan (お彼岸). Prefix o (お) is often used to say something politely. There are two o higan in a year, in spring and in autumn. We call them haru no o higan (春のお彼岸) for spring, and aki no o higan (秋のお彼岸) for autumn.
The first day of o higan is called higan no iri (彼岸の入り), the middle day is called higan no chunichi (彼岸の中日), and the last day is called higan ake (彼岸明け).
Higan means the other side of the river, which means the state of enlightment without worldly desires. The Paradise in Buddhism is considered to be in the Far West. At the Vernal and Autumn Equinox Day the length of day and night are equal and the sun will set in the due west. Therefore Japanese people started to do Buddhism services on this occasion. We go to visit ancestor's graveyard and hold a memorial service for them and offer special sweets made of rice and red bean paste. They are called bota mochi (牡丹餅) for spring, and o hagi (御萩) for autumn at the household Buddhist altar.
This side of the world full of worldly desires and wavers are called shigan(此岸).