Original Yom Kippur date is the 8th of the 7th lunar month. This is what Torah originally intended. Please see this post for more details.
Once again, this post is to remind everyone that Yom Kippur DOES NOT happen on the 10th, but rather on the 8th of the 7th lunar month.
Yom Kippur falls on the 1st Quarter Shabbat of the 7th lunar month. Half-moon Yom Kippur Shabbat is to remind us about our sins. Perhaps half-moon symbolizes division between sin (dark side) and good deeds (light side). Very symbolic imho.
So, do not forget that Yom Kippur is on the 8th and not 10th of the 7th lunar month.
We celebrate correct Yom Kippur from sunset of the 7th day of the 7th lunar month until sunset of the 8th day of the 7th lunar month.