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Equinoxes, Solstices, and Calendars

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Many of the most important holidays in all religions and cultures are essentially calendar-based, which means that they are set to the rhythms of regular changes that occur throughout the year (like changes in seasons), and that they exist to mark culturally or religiously significant milestones in the passage of time through the year. Thus you usually can't talk about how and why a holiday is important without also talking about how the culture or religion in question conceptualizes time, the passage of time, and calendars.

An essential factor in how people mark the passage of time lies with the orientation of the Earth to the Sun. Because there is a 23.5º tilt in the earth's axis, those living in northern and southern regions have seasons - periods of time in the year when days are shorter or longer, when the weather is warmer or cooler. During one half of the year the northern hemisphere is more exposed to the sun, resulting in longer days and warmer weather; during the other half of the year, the opposite is true.

At one point during the year, whether you live in the north or the south, the sun will reach its highest point of elevation, which results in the maximum amount of daylight all year. In the north this date is usually June 21st. On December 21st, the sun reaches its lowest elevation and we have the least amount of daylight all year. The date with the longest period of daylight is the summer solstice and the first day of summer; the date with the shortest period of daylight is the winter solstice and the first day of winter.

In between these dates are two days when the length of daylight and the length of night are almost exactly balanced at twelve hours each - these are known as the vernal (or spring) and autumnal equinoxes, and they are often treated as holidays just as much as the solstices are. The word "equinox" literally means "equal night" - a reference to the night being equal in length to the day. The spring equinox is generally regarded as a time to mark the passage of the nature from the "death" of winter to the full life of spring, while the autumnal equinox marks the end of harvest and the preparations for cold winter without warmth or crops.

Dating the time of the spring equinox has not always been easy because for most of our history, humanity hasn't had access to precise astronomical data and measurements. We have instead had to rely upon our calendars - calendars which are inevitably inaccurate. Setting the dates for equinoxes (and thus significant holidays) has been a complex problem for calendar makers since calendars were invented.

The ancient Hebrews used a lunar calendar to mark the passage of time and dated their equinox celebrations as the day of the full moon in the month of Nisan, thus a day relatively close to the actual equinox. Early Romans also used a lunar-based calendar which consisted of months of 29 or 30 days, but over time this calendar fell out of step with the actual changing seasons and a new system was necessary.

Thus was developed the Julian calendar, named after its sponsor Julius Caesar. He moved Rome from a lunar calendar to a solar calendar which did a better job of keeping track of the seasons by using a year of 365 days plus one leap-day ever four years. The vernal equinox was set at March 25th, but even this became a problem because the calendar was still not perfectly accurate and errors accumulated. Eventually Pope Gregory XIII was forced to make a new change, shortening the year 1582 by a full ten days. His Gregorian calendar is what we continue to use today.

Our calendar is an important part of how we live our lives, although it might not seem that way at first glance. It may be that most people in the West live as though their lives were divorced from the rhythms of nature, but we're not as separate as we imagine. In place of the immediate effects of the changing seasons we have holidays and rituals to mark the passage of time - both the important events in our lives and the important stages of nature.

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