Posts Tagged ‘Passover’

12/20/2022 – Ephemeris – Hunting for the Star of Bethlehem: When did Herod the Great Die – Part 1

December 20, 2022 Comments off

This is Ephemeris for Tuesday, December 20th. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:04, and it will rise tomorrow at 8:16. The Moon, 3 days before new, will rise at 6:20 tomorrow morning.

In looking for the year Jesus was born and the appearance of the Star of Bethlehem, we look to the latter years of Herod the Great’s reign. Jewish historian Josephus recounts that Herod died shortly after an eclipse of the Moon occurred. The date of that eclipse, according to many historians, was March 13th, of 4 BCE and before Passover, a month later. The Greek text of Matthew states that Herod’s visitors, looking for the newborn King of the Jews, were Magi. Magi were priest-astrologers of the Zoroastrian Religion of Persia. That being the case, the Star could have been the triple conjunction of Jupiter and Saturn against the constellation of Pisces, when three times Jupiter passed Saturn between the end of May and early December of 7 BCE.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –5 hours). They may be different for your location.


Triple conjunction

The Jupiter-Saturn triple conjunction of 7 BC. Click on the image to enlarge and animate. This animation is at 5-day intervals. The conjunctions took place against the stars of Pisces the fish, a constellation thought, in those days, to be associated with the Jews. The Moon will be popping in and out of the view. It ends in February of 6 BC, when Mars and the Moon enters the picture. Click on the image to enlarge it. Created using Cartes du Ciel and GIMP.

Above is an animation of the triple conjunction of Jupiter and Saturn of 7 BCE in 5 day steps. The body popping in and frame is the Moon. The first conjunction was on May 29th. Both planets stopped their eastward motion around July 6th. Astrologically, they became stationary and began their westward or retrograde motion. The second conjunction was on October 11th. Both planets stopped their westward or retrograde motion on November 1st. Again they were stationary to resume their normal eastward motion. The third and last conjunction was on December 8th. Two months later, on February 21st, of 6 BCE, Mars joined the group as they all move off to the western sky in the evening. Using this triple conjunction as the Star of Bethlehem, Jesus would have been born in the late autumn of 7 BCE or early winter of 6 BCE.

Lunar Eclipse, March 13, 4 BCE

This lunar eclipse candidate for the eclipse that heralded the death of Herod the Great, and the favorite, since the time of Johannes Kepler, is the lunar eclipse of March 13, 4 BCE. It was a partial eclipse, only visible in the predawn hours. This eclipse occurred one lunar month before Passover.
Too little time for all the events Josephus describes. A better lunar eclipse occurred a bit less than three years later. Those defending the 4 BCE eclipse sometimes suggest that the Passover mentioned by Josephus was the next year’s Passover of 3 BCE. If it was the next year’s Passover, why mention Passover at all?

Tomorrow I’ll take a break to look to the naked eye planets, and to the winter solstice. Winter begins tomorrow! Thursday I’ll look to a better lunar eclipse and begin to explore another Bethlehem Star candidate.

04/07/2020 – Ephemeris – Today is the Paschal full moon

April 7, 2020 Comments off

This is Ephemeris for Tuesday, April 7th. Today the Sun will be up for 13 hours and 6 minutes, setting at 8:18, and it will rise tomorrow at 7:09. The Moon, at full today, will rise at 7:55 this evening.

Tonight’s full moon is the Paschal full moon, the first full moon of spring which is tomorrow in the Holy Land, so Passover begins at sunset tomorrow. Easter for western churches falls on the first Sunday after the first full moon of spring, which is this next Sunday the 12th. Orthodox Easter rule adds that it must fall after Passover,a week long observance, which pushes their Easter celebration to a week later, April 19th. Both Christian churches attempt to mimic the Jewish Lunar Calendar by setting Easter by the first full moon of spring using solar based calendars and assuming that spring started on March 21st. This year actual spring started on the 20th in the Holy Land, and 19th here by 10 minutes, in our Gregorian Calendar and 13 days earlier by the old Julian Calendar. This is all very complicated.

The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


03/29/2018 – Ephemeris – The Easter date is set by the first full moon of spring and a developing conjunction

March 29, 2018 Comments off

Ephemeris for Thursday, March 29th. The Sun will rise at 7:29. It’ll be up for 12 hours and 37 minutes, setting at 8:06. The Moon, 2 days before full, will set at 7:21 tomorrow morning.

This Sunday, April 1st will be Easter for western churches. Because it falls on the first Sunday after the first full moon since March 21st. The Full Moon is Saturday the 31st. It happens that Passover begins at sundown the 31st. Orthodox churches will celebrate Easter on April 8th, a week later. It’s going to be a somewhat busy weekend in the sky also. Sunday Mercury will pass from the evening sky to the morning sky in an event called an inferior conjunction of the Sun. It is not visible, but folks in the southern hemisphere will easily spot Mercury late in April. In the morning sky Mars will pass below Saturn between the mornings of the 2nd and 3rd. They are close to the same brightness, but Mars is distinctly redder.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Conjunction animation of Mars passing Saturn

Conjunction animation of Mars passing Saturn at daily intervals at 6 a.m. for March 30 to April 4, 2018. This will occur above the Teapot asterism of the constellation of Sagittarius. Created using Stellarium ans GIMP.

02/28/2016 – Ephemeris Extra – The years of our lives

February 28, 2016 1 comment

The continuing story of a small planet revolving around its star

Updated from the originally published in the January 1997 Stellar Sentinel, the monthly newsletter of the Grand Traverse Astronomical Society and republished in the February 2016 edition.

This year, 2016, is a leap year.  In leap years we have the US presidential elections, the Summer Olympic Games, and February has 29 days.  So what exactly is a leap year, and why am I writing about this earthly phenomenon in an astronomical society newsletter?  Well it’s astronomical of course. And if you think a year is a year is a year, well think again.
The calendar we use today is based on the Sun.  In ancient times the calendars of the Babylonians, Jews and many other ancient civilizations were based on the Moon, using the lunation, the period of about 29.5 days between new moons, as the basis for the calendar.  Lunar calendars tended to have months alternating 29 and 30 days, and years of 12 or 13 months to keep the whole scheme roughly in sync with the seasonal year.  There are vestiges of this system today in the various folklore of planting by the Moon.

The ancient Egyptians actually used two calendars.  The first was one based close to the sun and had 365 days.  It had 12 months of 30 days, each containing three 10 day decans.  There were 5 days at the end of the year that were holidays, and belonged to no month.  This civil calendar was used for state and accounting purposes.  The agricultural calendar was based on the Moon.  These two calendars were reconciled every 25 civil years which equaled 209 lunations, divided into 16 ordinary 12 month years, and 9 ‘great’ years of 13 months.  Still, since the Egyptian civil year is nearly a quarter of a day a year short, the civil calendar shifted slowly in relation to the seasons.  The Egyptian agricultural year started with the flooding of the Nile, which in those days was coincident with the heliacal rising of the brightest night time star Sirius, which they called Sothis.  A heliacal rising is when a star or planet is first visible in the morning twilight.  This heliacal rising occurs at a mean interval of 365.2507 days.  Thus the Egyptian civil calendar would be in sync with the agricultural year every 1460 years, a period called the Sothic Cycle.

The ancient Greek calendars were lunar ones.  Early on, each locality had their own calendar.  Starting in the 6th century BC the calendar situation got better when a cycle synchronizing lunar calendars with the sun was discovered.  It is the Metonic Cycle, probably discovered in Babylon.  Here 19 years of 365.25 days equal almost exactly 235 lunations.  That’s 12 ordinary 12 month years and 7 ‘great’ years of 13 months.  We find remnants of the Metonic Cycle with the Golden Number for the year given in almanacs, a number ranging from 1 to 19.  This year’s Golden Number is 3.  The year 1 BC was 1.  Under the old Julian calendar it was use to help determine the date of Easter.

The Julian Calendar is named for Julius Caesar who instituted it as a part of calendar reform he instituted in 46 BC.  The old Roman calendar was a lunar one, but in the earlier years of Julius Caesar’s reign the adjustments, called intercalations, such as 13th months in some years to keep the calendar roughly attuned to the sun, were neglected.  To straighten all this our, the year 46 BC was made 445 days long.  Starting in 45 BC the new calendar was instituted using the year of length 365.25 days.  Each 4 years an intercalary day was added.  This was February 29th, giving a 366 day year.  This we call a leap year.  Year 45 BC was a leap year, but due to some misunderstanding about the calendar reform, the one leap year in every four, was not kept.  In fact too many leap years were added, so in Caesar Augustus’ reign leap years from 8 BC to AD 8 were omitted to get back on track.

The western world ended up adopting the Julian calendar, and it was humming along just fine with leap years every 4 years.  However the Catholic Church and Pope Gregory XIII became alarmed that Easter was in danger of no longer being a spring feast.  The early church, adopted the Julian calendar rather than the Jewish lunar calendar.  But the most important feasts, the Crucifixion and Easter were tied to the Jewish feast of Passover, a spring feast starting in the middle of the month at full moon time.  Part of the problem was that the Vernal Equinox for ecclesiastical purposes was assumed to fall on March 21st, whether it actually did or not.  The first Sunday after the first full moon was Easter.

The problem is that the seasonal or tropical year is 11 minutes and 14 seconds shorter than the Julian year of 365.25 days.  In 400 years this amounts to about 3 days error.  So the easy correction is to eliminate 3 leap years out of 400 years.  The formula is simple.  All years divisible by 4 are leap years except century years which are not also divisible by 400.  Thus the year 1900 was not a leap year, but 2000 was, and 2100 will not be.

The other part of the reform was harder to swallow.  It was the elimination of 10 days because the real Vernal Equinox was by the 16th century falling on March 11th.  The Church was able to have this adopted in Catholic countries right away, so in the calendar of 1582 ten days were omitted between October 4th and 15th.  Protestant countries generally followed suit later.  England and the American Colonies converted to this new Gregorian Calendar in 1752 when by then 11 days were omitted between September 2nd and 14th.  The last to convert to the Gregorian Calendar was Greece and Orthodox Christianity who also made further improvements for the future.

I had once investigated how Microsoft Excel spreadsheets store dates.  It’s stored as a consecutive date starting with date 1 on January 1, 1900.  I had to convert dates downloaded from an IBM AS400 computer into a format compatible with Excel.  The dates came one day off.  It turns out that Microsoft or whoever devised the Excel dating scheme forgot that the year 1900 was not a leap year in the Gregorian calendar.  For my astronomical research I use dates both far in the past I use dating algorithms that use the Julian and Gregorian calendars where appropriate and takes into account the Gregorian discontinuity of 1582 into account.  These algorithms convert calendar dates to another type of consecutive day scheme called Julian Day Numbers of Julian dates for short, and back again.  In astronomy we see cycles of planetary orbits, variable star periods, etc.  They don’t fit into our hodgepodge of different month and year lengths.  We just want to know how many days between event A and event B.  Julian dates work for us.  The Julian dates start on January 1, 4713 of the Julian calendar, which predates any known historical date.  Oh by the way:  Julian dates start at noon Universal Time (UT) or Greenwich Mean Time (GMT), and fractional days are decimal.
I didn’t even touch when the year begins.  In Great Britain when the 1752 reforms took place they also changed the start of the year from March 25th to January 1st.


  • The Exact Sciences in Antiquity by O.  Neugbauer. Dover Publications
  • Explanatory Supplement to the Ephemeris H.M. Nautical Almanac Office

03/29/2013 – Ephemeris – How we know this Sunday is Easter

March 29, 2013 Comments off

Ephemeris for Good Friday, Friday, March 29th.  The sun will rise at 7:28.  It’ll be up for 12 hours and 38 minutes, setting at 8:06.   The moon, 2 days past full, will rise at 11:14 this evening.

Wednesday was the day of the Paschal full moon, the full moon after the first day of spring, which is defined by Christian churches as March 21st.  For the date of Easter the actual full moon isn’t used, but a rather complicated formula is used to find the new moon.  There’s a complicated correction to then find the date of the full moon, which 2 days ago.  This year that formula works out correctly.  It can be a day off either way.  The next Sunday then is Easter.  Orthodox churches use the Julian calendar and a different formula but they’ll celebrate Easter on May 5th.  The formula was set up to approximate the Jewish lunar calendar.  It works out close this year because Passover started at sunset last Sunday night.

Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.

02/12/2013 – Ephemeris – Astronomical basis for Lent and Easter

February 12, 2013 Comments off

Ephemeris for Fat Tuesday, Tuesday, February 12th.  The sun will rise at 7:46.  It’ll be up for 10 hours and 20 minutes, setting at 6:07.   The moon, 2 days past new, will set at 9:17 this evening.

The western ecclesiastical season of Lent starts tomorrow.  It lasts 40 days excluding Sundays ending with the celebration of Easter on March 31st this year.  It is a movable feast in that it’s on a different date each year following the first full moon of spring.  It’s an attempt to follow the Jewish Passover, which starts on the 15th of the month of Nisan.  Being a lunar calendar the 15th the generally the night of the full moon.  And since the Last Supper was a Seder, the Christian church wanted to follow Passover as closely as possible using the Roman Solar based calendar.  The western churches eventually adopted the Gregorian calendar to keep in sync with the seasons.  The Eastern churches did not.  Their Easter this year is on May 5th.

Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.


The first day of spring is set by the churches as March 21st.  In Michigan’s time zone spring now it always starts on March 20th, and will occasionally start on the 19th until 2103 after the Gregorian correction takes place in 2100.  The Julian Calendar, instituted by Julius Caesar, was the official calendar for all the Christian world until 1582.  The problem with the Julian Calendar is that the leap year every 4 years overcompensated for the seasonal or tropical year.  The average year of 365 1/4 days turned out to be 11 minutes 14 seconds too long.  By 1582 the actual vernal equinox or first day of spring had slipped back to March 10th.

Astronomers under Pope Gregory XIII proposed a change that was adopted by the Roman Catholic world.  First remove 10 days from the calendar between October 4 and 15 1582.  Then modify the leap year formula to keep the leap year on years divided by 4,  except century years.  Century years were ordinary 365 day years unless divisible by 400.  This 1900 was an ordinary year, but 2000 was a leap year.   The western protestant countries came around eventually.  However the eastern churches still use the Julian calendar to set their feasts, thus Eastern Orthodox rarely coincides with western churches.

Note that the dating for Excel spreadsheets, starts the day count on January 1, 1900, except they thought that 1900 was a leap year.

03/30/2012 – Ephemeris – April Preview

March 30, 2012 Comments off

Ephemeris for Friday, March 30th.  The sun will rise at 7:26.  It’ll be up for 12 hours and 41 minutes, setting at 8:08.   The moon, at first quarter today, will set at 3:36 tomorrow morning.

The 4th month of the year begins Sunday with Palm Sunday.  Daylight hours in the Interlochen/Traverse City area and will increase from 12 hours and 48 minutes Sunday to 14 hours 13 minutes on April 30th.  The altitude, or angle, of the sun above the southern horizon at local noon will be 50 degrees Sunday and will ascend to 60 degrees on April 30th.  The altitude of the sun in the Straits area will be a degree lower.  The actual time of local apparent noon this month for the Interlochen/Traverse City area, when the sun passes due south, will be about 1:43 p.m.  The full moon next Friday is the Pascal full moon meaning the western churches will celebrate Easter the following Sunday.  Passover starts that Friday night, while Orthodox Easter is the 15th.

* Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.