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Whether it feels or looks like spring or like winter outside your home today, spring is officially here. It slipped under my pillow while I was still asleep this morning at 6:28 am ET here in the Northern Hemisphere.
Our ancestors my not have understood what was happening to our planet from a celestial viewpoint, but they were more careful observers of the world around them and definitely marked today as something significant. Ancient observers built devices, buildings and places like Stonehenge to measure and mark changes in the Sun’s movements. Of course, that was what they thought was happening – that the Sun was moving closer or further from Earth. They may have been wrong on that part, but they were able to mark that today was midway between the sun’s lowest path across the sky in winter and highest path across the sky in summer.
Though we visualize an equinox as occurring on the imaginary dome of Earth’s sky, it is a very real point on Earth’s orbit that is halfway between the two extremes of the sun’s path in your sky. “Your sky” because though the equinox occurs at the same time for all of us. The seasons are based on whether you are in the Northern or Southern Hemisphere.
One thing you can observe easily at each equinox (no Stonehenge required) is that the sun rises due east and sets due west from where you live. An equinox happens when the ecliptic – or sun’s path – intersects the celestial equator, that imaginary line above Earth’s equator.
Go outside around sunset and sunrise and notice the location of the sun on the horizon with respect to local landmarks. You can then use those landmarks to find those cardinal directions in the months ahead and observe how the sunrise and sunset points move southward or northward. I showed my young sons this many years ago by crudely tracking the sunrise moving from window to window during the year from the vantage point of our East-facing family room. It was a pretty interesting lesson in science.
Today the sun is on the celestial equator. It may be springlike outside or it may still seem like winter, but the new season has arrived.
The 2016 astronomical spring for the Northern Hemisphere begins on Sunday, March 20. It will end on another Sunday in June.
This equal illumination of Earth by the Sun is the equinox,this time vernal and later this year autumnal.
You won’t fall over, but the tilt of the Earth’s axis is now inclined neither away from nor towards the Sun. The Sun is vertically above a point on the Equator.
Those ancients, who were better about paying attention to what was happening in the sky and on the ground, made the word equinox from the Latin aequus (equal) and nox (night), because the night and day are approximately equal in length.
You have probably been noticing the day lengthening already. I keep track of the Sun’s movement around my house. I have a chart and record the angle using a compass from a spot at my window. All winter, the morning Sun would come through the patio doors and shine on my chair in the family room where I sit to read and write. Now, it makes its early morning appearance in the east at another window and sends a beam on the couch where my wife has her morning coffee and reads the news.
In the Abrahamic tradition, the Jewish Passover usually falls on the first full moon after the northern hemisphere vernal equinox, although occasionally (currently three times every 19 years) it will occur on the second full moon. Christian churches calculate Easter as the first Sunday after the first full moon on or after the March equinox. The official church definition for the equinox is March 21. The Eastern Orthodox Churches use the older Julian calendar, while the western churches use the Gregorian calendar, and the western full moons currently fall four, five or 34 days before the eastern ones. The result is that the two Easters generally fall on different days but they sometimes coincide. The earliest possible Easter date in any year is March 22 on each calendar. The latest possible Easter date in any year is April 25.
I like knowing about other calendars, like the traditional East Asian ones, that divide a year into 24 solar terms. There the vernal equinox and the autumnal equinox mark the middle of the spring and autumn seasons, respectively.
In June the season will change again, not with an equinox, but with the summer solstice.
I have been writing about the changing of the seasons for a few years now and there is only so much you can say about the spring equinox, autumn equinox and the solstices of summer and winter. I try to find a new path into them and for this season I am thinking about spring in music and in the sky.
As a quick review, “equinox” is derived from the Latin aequus (equal) and nox (night), because the night and day are approximately equal in length on that day. We experience an equinox in spring and fall when the tilt of the Earth’s axis is inclined neither away from nor towards the Sun which is vertically above a point on the Equator. An equinox actually occurs at a specific moment in time (for 2015, today, March 20 at 6:45 pm EDT), but commonly people refer to the entire day as the equinox or first day of the season.
It is very “northern” of me to say it is the Spring Equinox, because in the Southern Hemisphere this celestial observation means the start of autumn. Being that autumn is my favorite season, I have often thought that I should travel between the two hemispheres to get two autumns each year. Unfortunately, the Sun doesn’t allow me to live in a three-season world and avoid winter.
(Soundtrack to this post)
The Four Seasons (Italian: Le quattro stagioni) is a set of four violin concertos by Antonio Vivaldi (1720) and his best-known work. My knowledge of classical music is shallow, but I was reading about this piece and discovered a few interesting nuggets.
I like that Vivaldi provided some additional instructions with the music, such as “The barking dog” in the second movement of “Spring.”
It seems that there is some debate as to whether or not the concertos were written to accompany four poems (sonnets) or if the sonnets were written to accompany the music. It doesn’t seem to be known who wrote these sonnets,and some say that Vivaldi wrote them himself. Either by plan or coincidence, each sonnet is broken down into three sections, nicely corresponding to a movement in the concerto.
The Four Seasons is sometimes classified as “program music,” instrumental music that intends to evoke something extra-musical. For me, the four pieces, especially “Spring,” does evoke the season.
If you listen to the music tonight, I suggest that you turn your eyes to the sky and look for Arcturus. It is one of the brightest stars. Due to its northerly location on the sky’s dome, it is visible for much of the year in the Northern Hemisphere and its appearance in the evening sky heralds the coming of the spring equinox.
Like other stars, Arcturus rises four minutes earlier every day and now Arcturus will appear at dusk (instead of nightfall or early evening) which is its signal of spring in our hemisphere.
Arcturus is the brightest star in the constellation Boötes the Herdsman. It is not one of the best-known constellations. The name comes from the Greek Βοώτης, meaning herdsman or plowman (literally an ox-driver; from boos, related to the Latin bovis, “cow”). It is one of the 48 constellations described by the 2nd century astronomer Ptolemy, but it was first used by Homer in his Odyssey as a celestial reference point for navigation.
Homer described it as “late-setting” or “slow to set.” It is not clear exactly whom Boötes is supposed to represent in Greek mythology is not clear. The story I will go with is that he was a son of Demeter, twin brother of Plutus, a ploughman who drove the oxen in the constellation Ursa Major. The ancient Greeks saw what we call the “Big Dipper” as a cart with oxen.
It seems a nice match with the spring that one myth associated with Boötes is that he invented the plow which certainly is associated with spring and planting. If you think of him as a “herdsman,” that works too, as those who watch over a herd of cows, sheep or other animals leads a nomadic life very much guided by the seasons. Spring is the time to move to those areas that were snow-covered and the tain and melting turns the land green again.
If staring up at the big sky makes you feel small and timeless – a good feeling, I believe – then also consider this: even the equinoxes are constantly changing. They are not fixed points but move westward along the ecliptic, passing through all the constellations of the zodiac in a period of 26,000 years. This motion is called the precession of the equinoxes. And we think that the 5000 year Mayan calendar was looking at a long period of time…