Ask the Astrologer: June 13-19 — Born on the cusp; which sign am I?

By Christopher Renstrom

I am curious about the chart Chris uses for the San Francisco chronicle horoscopes. My birthday is September 22 and on every chart I have ever seen, that makes me a Virgo. However, since reading the San Francisco chronicle daily horoscopes, my birthday falls under Libra. How does one chart out the dates of the signs? —Brian

Hey Brian, great question! In Astrology the year is divided into twelve zodiac signs and each zodiac sign symbolizes a month. But a month doesn’t begin on the 1st and end on the 30th (or 31st) like a regular calendar month does. In Astrology a month begins when the Sun “enters” a zodiac sign and that can be any time from the 18th or 23rd of any calendar month. For instance this year, 2010, the month of Virgo begins on August 22nd and ends on September 21st which means that anyone born between these two dates in 2010 would be a Virgo. Anyone born on September 22, 2010 would be a Libra. However, in 2007, for instance, the month of Virgo began on August 23rd and ended on September 23rd, which means that anyone born on September 22, 2007 would have been born under the sign of Virgo. Some years Virgo begins on August 22 and some years Virgo begins on August 23. So why does this happen?

We actually live according to two years. There is the sidereal year and the calendar year. The sidereal year is the time that it takes the earth to complete a single orbit around the Sun and that works out to be 365 days 6 hours and 9 minutes. The calendar year—which is based on the Spring Equinox (and which is also what we use to set our clocks by)—works out to be 365 days 5 hours and 48 minutes. What this means is that there is a difference of 20 minutes between our sidereal and calendar years. That difference adds up over time which is why every four years we will reconcile the two by adding an extra day—February 29th—to the calendar. This is the reason for the leap year.

Yet Astrologers can’t wait four years to make this reconciliation. If we did then the timing for our horoscopes would be horribly off. This is why adjustments for the Sun’s change of signs are made every year and if you check the newspaper horoscope column at the start of each year then you will see that some of the zodiac sign dates have changed by a day, but no more than a day. Newspaper horoscope columnists also have the added complication of determining what time of day the Sun changed signs. Sometimes the Sun changes signs at two minutes before midnight and sometimes the Sun changes signs at 1:35 in the afternoon. This is always a vexing problem which is why we will often round up to the next day. In any case you always want to check the year that you were born to see when the Sun changed signs. If you were born in a year when the Sun moved from Virgo to Libra on September 23rd then you are definitely a Virgo.

This article was originally published on June 12, 2010.