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02/02/2019 – Ephemeris Extra – Groundhog Day and other seasonal days

February 2, 2019 Comments off

Note:  I wrote this article as part of the Grand Traverse Astronomical Society’s Stellar Sentinel for February 2019.

Groundhog day coming this month got me to thinking about the seasons and those special seasonal days, like solstices, equinoxes and cross-quarter days. February 2nd is a cross-quarter day, supposedly when winter is half over. Below is a table I created of the seasons for one year starting with last December’s winter solstice.

I took the date and times from Astronomical Tables of the Sun, Moon and Planets, Third edition by Jean Meeus. TD is Dynamical Time, used to calculate the positions of bodies in the solar system, is about 68 seconds fast compared to Universal Time (UT), which is tied to the Earth’s rotation. The difference is slowly changing at less than a second a year and doesn’t enter into the calculations. The Julian Date is a consecutive date starting on January 1, 4713 BC at noon UT. It’s used by astronomers to calculate date differences. like the length column in the table above without worrying how many days months have or how many leap years are in the interval. If you want to convert a calendar date to a Julian date or a Julian date to calendar date go to the Naval Observatory web page here: https://aa.usno.navy.mil/data/docs/JulianDate.php.

Note that the seasons are of different lengths. This is because the Earth’s orbit is slightly elliptical. It reached perihelion, its closest to the Sun, this year on January 3rd, and it will reach aphelion, its farthest, on July 4th. The Earth or any planet moves fastest when near perihelion. And with perihelion 14 days into winter, makes winter the shortest season. Autumn is the second shortest season 90 days compared to winter’s 89 days. Summer at nearly 94 day’s length is 4.7 days longer than winter. However we’re too far north to really notice it. Spring is second with nearly a 93 day length.

The rest of this article is based quite a bit on the web page: Common Holidays in Relation to Equinoxes, Solstices & Cross-Quarter Days – https://www.naic.edu/~gibson/cal/. It’s a cool list. Naic.edu is the website of the Arecibo Observatory in Puerto Rico. Apparently it was someone’s (Gibson’s) personal post.

The equinoxes and solstices are quarter days, for the four seasonal quarters of the year. The table above has Mid-Season and Date for the half way point in the season. The Cross-Quarter Days column are the dates which are more or less celebrated down throughout history.

The first celebrated cross-quarter day is February 2nd, Groundhog Day Which the famous weather prognosticating rodent in Punxsutawney, PA forecasts the length of winter based on if he sees his shadow. Supposedly, if he sees his shadow winter will last for six more weeks, if he doesn’t then spring is just around the corner. Actually from February second to the vernal equinox is six and a half weeks. If we had a winter like last year with a snowy April, winter lasted until the second cross-quarter day. The actual first cross-quarter day this year is February 4th. February 2nd, 40 days after Christmas, is also celebrated as Candlemas Day, when candles are blessed for the year, and the Feasts of the Purification of the Virgin Mary and The Presentation of the Child Jesus by the Catholic and some other Christian Churches.

The first quarter day is the vernal equinox, which occurs in our time zone on March 20th. The Ides of March, the 15th is pretty close to the vernal equinox and was the start of the year for a time with the Romans. It was the date in 44 BC that Julius Caesar was assassinated. March, named after the god Mars was also for a long time the first month of the year. They, for a time had 10 months, and consigned the winter months to ?. Later they added two months in front of March, which is why our 9th through 12th months are named September (7), October (8), November (9) and December (10).

The second cross-quarter day to be celebrated is May 1st, May Day. The actual 2nd cross-quarter day this year is May 6th.

The second quarter day, the summer solstice is on June 21st. It’s near midsummer day, the 24th, the feast of St. John the Baptist. It’s a big deal in Europe. If you had a midsummer’s night dream it would be on the night of June 23-24. Of course if that date was really midsummer, summer would have to start in early May.

The third cross-quarter day is August 1st, Lughnasadh. This is Celtic. It was the wedding day of Lugh, their sun god with the goddess of the Earth. This causes the crops to ripen in time to harvest in the fall. The actual date this year is August 7th.

The third quarter day is the autumnal equinox. This year it’s on September 23rd.

The fourth cross-quarter day is celebrated on October 31st, Halloween. It is the day before All Saints Day, and Day of the Dead in Mexico. The actual cross-quarter day this year is November 7th.

The fourth quarter day is the winter solstice, December 21st. This is in the midst of festivals ancient and modern around the time the Sun starts heading north again. Festivals of light, like Saturnalia, Yule, Christmas, and Hanukkah

There you have the days of our seasons.

Categories: Ephemeris Extra, Seasons