Easter Sunday is the first Sunday after the first full moon past the vernal equinox in the Gregorian calendar. This Christian holiday, celebrating the resurrection of Jesus of Nazareth, is based on the Jewish Passover (beginning on the 15th day of Nisan, the first month in the Hebrew calendar), which is a commemoration of the exodus of the Israelites from Egypt (thus freeing them from slavery). This year, Passover started at sundown on Monday, March 25th, nearly coinciding with the Holy Week of Christians, which started on Palm Sunday, March 24th, and ended on Holy Saturday, March 30th, one day before Easter Sunday.

The first days of these holidays fall within the month (30-day period) following the vernal equinox every year. The timing within the annual cycle is provided by the sun, while the phase of the moon brings us near or to the beginning of these periods. In the case of the Christian calendar, a third (weekly) cycle marks the exact days (the Hebrew calendar is lunisolar and is therefore synchronized to the motions of the sun and moon).

In astrological terms, both holidays start while the sun is in the tropical sign of Aries. Since in the temperate zones of the northern hemisphere – where the two cultures originate from – it is always springtime during the “month” of Aries, it is no wonder that the holidays’ symbolism of resurrection and freeing from bondage both point to the renewal of nature in spring. In the English language, the term for this season indicates a “bursting forth” or “springing up” of plants. Starting at the end of the 19th century, the verb form of this word took on the meaning of “release” (from imprisonment), closely paralleling Passover symbolism. Other meanings of the same word include “source of a stream” and “elastic coil”, both painting the imagery of coming to life.

It is this time of year when various media outlets proudly announce the start of spring, equating this day (even the exact time) with the timing of the vernal equinox. From a symbolic perspective, there can be no doubt that the two holidays occur during springtime. Does it follow then that the vernal equinox, as one of four “corners” of the year, marks the start of spring? To answer this question, we first need to find out what “spring” means.

And here we come up against a bit of a challenge: there seems to be no precise and unambiguous definition of seasons. Moreover, the definition of spring depends on which reference one checks. There are three main definitions, and the following is an overview of which camp the major references belong to (results are from the first three pages of a web search for “define spring season”):

• Astronomical definition (from the vernal equinox to the summer solstice, March 20/21 – June 21/22): Cambridge Dictionary, Encyclopedia Britannica, The Old Farmer’s Almanac, Collins Dictionary

• Meteorological definition (the three-month period between the coldest and warmest months, typically March, April and May): American Heritage Dictionary, Oxford Dictionary

• Natural or ecological definition (according to the cycles of nature; timing depends on local conditions and varies from year to year): BBC Nature UK blog http://www.bbc.co.uk/blogs/natureuk/2011/02/how-do-you-define-spring.shtml
  

Wikipedia mentions all three definitions (and some more) with the following introduction: “There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs.”

It is clear from the above that only by adopting the astronomical definition could spring possibly start on the day of the vernal equinox. But does it really? The vernal equinox is the moment when the sun crosses the celestial equator in a northerly direction (in the northern hemisphere). This is equivalent to saying that the sun moves into (ingresses) tropical Aries at that time. So what is the relation of this movement to the season of spring? The clue lies in the meaning of the word “equinox.” There are two equinoxes and two solstices each year, marking the four cardinal points of the zodiac. The word “equinox” means “equal night” in Latin: this time of year, day and night are about the same length (but not exactly due to the size of the sun’s disc and the bending – refraction – of light by the atmosphere). “Solstice” on the other hand means “sun coming to a standstill” because on these days the sun reaches its highest and lowest points (altitude) in the sky, making them the longest and shortest days of the year, respectively.

The significance of these four points is that they are markers for the varying amount of sunlight we are receiving during the year. If we graph how the length of the day (amount of daylight) changes throughout the year, we get a familiar sine wave such as the one above (courtesy of ptaff.ca). The blue line depicts this for Ottawa, Ontario, Canada. The days are the longest around the summer solstice (June 20/21) and the shortest around the winter solstice (December 21/22). The lengths of day and night are about 12 hours each at the vernal and autumnal equinoxes (March 20/21 and September 22/23).

In terms of daylight (or the sun’s altitude, to be precise), it would then make sense to define astronomical summer as the one and a half months preceding and the one and a half months succeeding the summer solstice since this is the quarter of the year when the days are the longest. Similarly, astronomical winter would be defined as the three months surrounding the winter solstice, coinciding with the shortest days of the year; therefore, winter solstice would mark the middle of winter. To say that (astronomical) winter starts at the winter solstice is just as nonsensical as saying that night starts at midnight (when the sun reaches its lowest points during the daily cycle). Similarly, midday doesn't start at noon (which is the marker for the middle of the day) just as (astronomical) summer cannot start at the summer solstice, the highest point of the sun’s annual cycle.

It is easy to see then that the vernal equinox cannot possibly mark the start of spring, even in the astronomical sense of the term (other definitions have no direct relation to the Aries point). The four cardinal points of the year mark the middle of astronomical seasons and so the vernal equinox coincides with the middle of astronomical spring. It would be more appropriate to say that the start of (astronomical) spring is in early February, which is around Candlemas in the Christian calendar. The symbolism of the presentation of child Jesus at and later his first entry into the temple is analogous with the sun’s presentation at and entry into the new season of (astronomical) spring. The simple reason for having eight significant points within the year, meaning the cardinal points of the annual circle and their midpoints, is exactly to demarcate the sun’s annual path into four seasons. The midpoints (Candlemas, Ascension, Transfiguration and All Soul's Day in the Christian calendar), falling approximately in the middle of fixed signs in the zodiac, signify the starts and ends, while the corners (Christmas, Easter, St. John the Baptist and Michaelmas), positioned close to the beginning of cardinal signs, mark the middle of astronomical seasons. In the pagan wheel of the year, these festivals are exactly aligned with the tropical zodiac and are called Imbolc, Beltaine, Lughnasadh (Lammas) and Sanhain for the seasonal boundaries, and Yule (Midwinter), Ostara, Midsummer and Harvest Home (Mabon) for the middle of astronomical seasons.

We are only talking about astronomical seasons of course; nobody in their right mind would actually say that spring arrives in early February in places where the lengths of the four seasons are roughly equal. Heat follows light due to a number of factors, and this is the primary reason why we experience seasons closer to the meteorological and natural definitions. Notional springtime is the three-month period from March to May in the northern hemisphere, but the actual start of spring will vary depending on location and year-to-year variations in nature. While this might be difficult to pin down, one thing is for sure: it will not coincide with the vernal equinox other than by sheer luck.

It is the end of Easter Sunday here but in Greenwich the clock has already turned over to a new day and a new month. But just because it is April 1st there, it doesn’t mean that I’m joking here. And that of course is another topic for another day!