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Posts Tagged ‘Sothis’

02/28/2022 – Ephemeris – Ancient Egypt’s most important star

February 28, 2022 Comments off

This is Ephemeris for Monday, February 28th. Today the Sun will be up for 11 hours and 7 minutes, setting at 6:29, and it will rise tomorrow at 7:20. The Moon, 2 days before new, will rise at 7:17 tomorrow morning.

The Ancient Egyptian agricultural year began with the flooding of the Nile, which was announced by the heliacal rising of the brightest nighttime star, Sirius. A heliacal rising is the first appearance of a star in the morning twilight after disappearing in evening twilight some months before. The Greeks called the star Sothis, while the ancient Egyptians called the star Sopdet. The heliacal rising would occur on July 20th had our calendar been in use back then. The relationship between the summer solstice and the heliacal rising of Sothis, 29 days later, stayed the same for nearly three millennia, from at least 2900 BCE to 12 CE, despite precession* of the Earth’s axis moving the Sun from the middle of the constellation Leo at the summer solstice to the western edge of Cancer one and a half constellations west. Sopdet was personified by a goddess, who was the consort to Sah, who is what they called Orion.

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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.

* Precession of the equinoxes. The slow, 26,000 year wobble of the Earth’s axis which causes the Earth, most of the time, to not have a pole star. We’re lucky to live at a time to have a bright star within a degree of the north celestial pole. That star is, of course, Polaris. Precession also changes the point in the sky, along the ecliptic and zodiac, where the Sun appears on the first day of spring, or any season. These points move westward along the ecliptic (the plane of the earth’s orbit of the Sun) one degree every 72 years.

Addendum

The Egyptian used the heliacal rising of Sirius as a signal that the flooding of the Nile was imminent, starting their agricultural year. The Greeks called the star Sothis, while the Egyptians themselves called it Sopdet, a goddess, and consort of the god Sah, our Orion.
Part of my presentation, December 2021 of Ancient Astronomy of the Egyptians and Babylonians.

02/07/2017 – Ephemeris – Sirius: an important star in history

February 7, 2017 Comments off

Ephemeris for Tuesday, February 7th.  The Sun will rise at 7:53.  It’ll be up for 10 hours and 6 minutes, setting at 6:00.  The Moon, 3 days before full, will set at 5:53 tomorrow morning.

The brightest star-like object in the evening sky is Sirius, also known as the Dog Star.  It also is the brightest night-time star in our skies period.  Tonight at 9 p.m. it’s located in the southeastern sky.  The Dog Star name comes from its position at the heart of the constellation Canis Major, the great dog of Orion the hunter.  The three stars of Orion’s belt tilt to the southeast and point to Sirius.  The name Sirius means ‘Dazzling One’, a reference to its great brilliance and twinkling.  Its Egyptian name was Sothis, and its appearance in the dawn skies in late June signaled the flooding of the Nile, and the beginning of the Egyptian agricultural year.  Sirius owes much of its brightness to the fact that it lies quite close to us, only about 8 light years away.

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

Addendum

Heliacal rising of Sirius

A simulation of the heliacal rising of Sothis (Sirius) with the Egyptian Pyramids circa 2000 BC.  Note that Sirius is just visible to the right of the nearest Pyramid. Created using Stellarium and GIMP.

A heliacal rising is the first appearance of a star or planet in the morning after disappearing weeks or months before in the evening twilight.

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.

Bibliography

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

01/25/2016 – Ephemeris – Sirius the Dog Star

January 25, 2016 Comments off

Ephemeris for Monday, January 25th.  The Sun will rise at 8:09.  It’ll be up for 9 hours and 31 minutes, setting at 5:41.   The Moon, 2 days past full, will rise at 7:43 this evening.

While we’re waiting for the bright Moon to leave the evening sky, let’s look at another bright star.  This one is the brightest of all, Sirius the Dog Star.  The Dog Star name comes from its position at the heart of the constellation Canis Major, the great dog of Orion the hunter.  The three stars of Orion’s belt tilt to the southeast and point to Sirius.  The name Sirius means ‘Dazzling One’, a reference to its great brilliance and twinkling.  The Romans thought Sirius added its heat to that of the Sun in summer to bring on the scorching Dog Days of July and August.  Its ancient Egyptian name was Sothis, and its first appearance in the morning twilight in late June signaled the flooding of the Nile, and the beginning of the Egyptian agricultural year.

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

Addendum

Orion's Belt points to Sirius

Orion’s Belt points to Sirius. Created using Stellarium.

01/22/2013 – Ephemeris – Sirius the Dog Star

January 22, 2013 1 comment

Ephemeris for Tuesday, January 22nd.  The sun will rise at 8:10.  It’ll be up for 9 hours and 27 minutes, setting at 5:37.   The moon, half way from first quarter to full, will set at 5:23 tomorrow morning.

The brightest star-like object in the evening sky is Jupiter high in the sky now.  The second brightest star-like object is Sirius, also known as the Dog Star.  It also is the brightest night-time star in our skies period.  Tonight at 9 p.m. it’s located low in the southeastern sky.  The Dog Star name comes from its position at the heart of the constellation Canis Major, the great dog of Orion the hunter.  The three stars of Orion’s belt tilt to the southeast and point to Sirius.  The name Sirius means ‘Dazzling One’ or ‘Scorcher’, a reference to its great brilliance and twinkling.  Its Egyptian name was Sothis, and its appearance in the dawn skies in late June signaled the flooding of the Nile, and the beginning of the Egyptian agricultural year.

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

Addendum

Winter Circle and Jupiter with Sirius

Winter Circle and Jupiter with Sirius at the bottom. Created using Stellarium.

01/11/2013 – Ephemeris – Sirius the Dog Star

January 11, 2013 Comments off

Ephemeris for Friday, January 11th.  The sun will rise at 8:17.  It’ll be up for 9 hours and 6 minutes, setting at 5:23.  The moon is new today, and won’t be visible.

The brightest star-like object in the evening sky is Jupiter high in the south around 9 p.m.  The second brightest star-like object is Sirius, also known as the Dog Star.  It also is the brightest night-time star in our skies period.  Tonight at 9 p.m. it’s located low in the south southeastern sky.  The Dog Star name comes from its position at the heart of the constellation Canis Major, the great dog of Orion the hunter.  The three stars of Orion’s belt tilt to the southeast and point to Sirius.  The name Sirius means ‘Dazzling One’, a reference to its great brilliance and twinkling.  Its Egyptian name was Sothis, and its appearance in the dawn skies in late June signaled the flooding of the Nile, and the beginning of the Egyptian agricultural year.

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

Addendum

Sirius, Jupiter and the winter stars

Sirius, Jupiter and the winter stars and constellations at 9 p.m. Created using Stellarium.