Seventh month? I thought Yom Kippur occured on the 10th day of the new year (month 1) - we just had Rosh Hashannah (Tishri 1) -- or am I missing something?
The New Year thing slipped in from their time in exile in Babylon (the names of the month slipped in at that time too- they are not Hebrew but Babylonian names) . Rosh Hashannah is not in the first Biblical month.
Jewish holidays often seem confusing to people who are used to the Gregorian calendar. While holidays in Judaism generally occur around the same time each year, celebrations and other traditions rarely appear to fall on the same date. Hanukkah can occur days before Christmas, or it can fall weeks ahead of time. Passover can occur in March, or take place in April.
The reason for this variation has to do with the difference between the rotational cycle that is used in the Hebrew calendar, which uses a combination between a lunar calendar and a solar calendar, and the Gregorian system; most North American and Western European timekeeping is based on the latter system.
The Hebrew calendar takes into account three distinct astronomical happenings: the rotation of the earth on its own axis; the rotation of the moon around the sun (approximately every 29.5 days); and the rotation of the earth around the sun (what comes out to be 12 or 13 months, or an average of 12.4 months per lunar calendar).
In contrast, the Gregorian calendar is an arithmetical calendar that is grouped in allocations of 365-366 days and is adjusted periodically over a span of 400 years.
Therefore, the Hebrew and Gregorian calendars often vary when compared.