APOD: Julius Caesar and Leap Days (2024 Feb 29)

[APOD Robot]

Julius Caesar and Leap Days

Explanation: In 46 BC Julius Caesar reformed the calendar system. Based on advice by astronomer Sosigenes of Alexandria, the Julian calendar included one leap day every four years to account for the fact that an Earth year is slightly more than 365 days long. In modern terms, the time it takes for the planet to orbit the Sun once is 365.24219 mean solar days. So if calendar years contained exactly 365 days they would drift from the Earth's year by about 1 day every 4 years and eventually July (named for <a href= "http://www.literaturepage.com/read/shak ... ml">Julius Caesar</a> himself) would occur during the northern hemisphere winter. By adopting a leap year with an extra day every four years, the Julian calendar year would drift much less. In 1582 Pope Gregory XIII provided the further fine-tuning that leap days should not occur in years ending in 00, unless divisible by 400. This Gregorian Calendar system is the one in wide use today. Of course, tidal friction in the Earth-Moon system slows Earth's rotation and gradually lengthens the day by about 1.4 milliseconds per century. That means that leap days like today will not be necessary, about 4 million years from now. This Roman silver coin, a denarius, depicts Julius Caesar (left) and Venus, Roman goddess of love.

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[canopia]

APOD: The Leap Day tradition, this silver coin, I like it.

Tunç Tezel

[Rauf]

APOD: The Leap Day tradition, this silver coin, I like it.

Tunç Tezel

Except in 2012 and 2008 which different pictures were featured!
https://apod.nasa.gov/apod/ap120229.html
https://apod.nasa.gov/apod/ap080229.html

I see that 2008 picture is yours Have you added any more lunar eclipses to that picture since then?

[canopia]

APOD: The Leap Day tradition, this silver coin, I like it.

Tunç Tezel

Except in 2012 and 2008 which different pictures were featured!
https://apod.nasa.gov/apod/ap120229.html
https://apod.nasa.gov/apod/ap080229.html

I see that 2008 picture is yours Have you added any more lunar eclipses to that picture since then?

Yes, I did. But not as many as I collected between 1996-2008.

Tunç Tezel

[JimB]

I was going to add the other astronomical reference for this APOD - that the sliver in this coin was created in supernova explosions billions of years ago, but some sources say that silver is created in the earth's mantle from sulphur by the intense heat and pressure. Can anyone shed light on which is correct?

[dwkurtz]

A small correction: The length of time it takes the Earth to orbit the Sun is the sidereal year. That is 365.2564 solar days, or slightly longer than 365.25. The tropical year - Vernal equinox to Vernal equinox is the number given, 365.2422 solar days. The difference arises from Earth's orbital precession. Interestingly, the Earth's orbit is not closed; i.e., it does not return to the same place in space (with respect to the Sun) after a sidereal year. It is tugged about by the gravity of the many other objects in the solar system, giving a "wiggly" orbit at the incredible precision that can now be determined for its place in space.

[KW033]

Regarding the 4-million years from now comment, the length of the day will then be almost a minute longer.

[richardschumacher]

some sources say that silver is created in the earth's mantle from sulphur by the intense heat and pressure.

That's incorrect. Transmutation of elements requires conditions like those in the core of a star, which are far more severe than those inside any planet. Quoting the Wikipedia article https://en.wikipedia.org/wiki/Silver#Isotopes "Both [stable] isotopes of silver are produced in stars via the s-process (slow neutron capture), as well as in supernovas via the r-process (rapid neutron capture)".

[richardschumacher]

In the nitpicking department, "of Alexandria" was added to the name Sosigenes only in the 18th Century. Known ancient sources refer to him only as Sosigenes.

https://en.wikipedia.org/wiki/Sosigenes_(astronomer)

[johnnydeep]

Regarding the 4-million years from now comment, the length of the day will then be almost a minute longer.

And 1 minute per day longer results in 6 hours per year longer, which is 24 hours longer over 4 years, which cancels out the need for the extra leap day.

[johnnydeep]

The alternate word for a leap day, I didn't know existed, and still don't understand the etymological meaning of AT ALL:

Bissextile

An old name for 'leap day'

A leap year is a year that has an extra day—366 days, with February 29 as the extra day. It has another name in English: bissextile year (and leap day is also known as bissextile day).

Julius Caesar created the Julian calendar, which replaced the extra month with an extra day in February. 'Bissextile day' comes from the Latin 'bissextus' and means the "second sixth day" or "double sixth day."

Why the two names?

In the original ten-month Roman calendar, days that marked the position of the moon were named: the calends was the first day of the month, or new moon, and the ides was the middle of the month, or full moon. An extra month was added every few years to ensure that agricultural festivals and holidays remained at the appropriate time of year. Julius Caesar created the Julian calendar, which added days to each month throughout the year and replaced the extra month with an extra day—a leap day. Because the Romans referred to dates according to their relationship with the named days, the sixth day before the first day of March was called diem sextum Kalendas Martias ("the sixth day before the calends of March").

The extra day fell on February 24 (when the former extra month was added) and was therefore called the bissextile day or bissextus, “second sixth day” or “double sixth day.” In Latin bis means “twice” and sextus means “sixth.” The word bissext was also used in English to refer to leap day. Days inserted into the calendar are called intercalary days.

[JimB]

some sources say that silver is created in the earth's mantle from sulphur by the intense heat and pressure.

That's incorrect. Transmutation of elements requires conditions like those in the core of a star, which are far more severe than those inside any planet. Quoting the Wikipedia article https://en.wikipedia.org/wiki/Silver#Isotopes "Both [stable] isotopes of silver are produced in stars via the s-process (slow neutron capture), as well as in supernovas via the r-process (rapid neutron capture)".

Thanks. That clears up my confusion .

[Ann]

The alternate word for a leap day, I didn't know existed, and still don't understand the etymological meaning of AT ALL:

Bissextile

An old name for 'leap day'

A leap year is a year that has an extra day—366 days, with February 29 as the extra day. It has another name in English: bissextile year (and leap day is also known as bissextile day).

Julius Caesar created the Julian calendar, which replaced the extra month with an extra day in February. 'Bissextile day' comes from the Latin 'bissextus' and means the "second sixth day" or "double sixth day."

Why the two names?

In the original ten-month Roman calendar, days that marked the position of the moon were named: the calends was the first day of the month, or new moon, and the ides was the middle of the month, or full moon. An extra month was added every few years to ensure that agricultural festivals and holidays remained at the appropriate time of year. Julius Caesar created the Julian calendar, which added days to each month throughout the year and replaced the extra month with an extra day—a leap day. Because the Romans referred to dates according to their relationship with the named days, the sixth day before the first day of March was called diem sextum Kalendas Martias ("the sixth day before the calends of March").

The extra day fell on February 24 (when the former extra month was added) and was therefore called the bissextile day or bissextus, “second sixth day” or “double sixth day.” In Latin bis means “twice” and sextus means “sixth.” The word bissext was also used in English to refer to leap day. Days inserted into the calendar are called intercalary days.

I don't get it either. But to me, this bissextile day thing is just something for the fan club.

In Swedish, a "leap year" is a "skottår". "År" is "year", and "skott" is "shot". You "shoot" an extra day into the calendar, so the extra day is a "shot".

Makes sense, right?

Ann

[johnnydeep]

The alternate word for a leap day, I didn't know existed, and still don't understand the etymological meaning of AT ALL:

Bissextile

An old name for 'leap day'

A leap year is a year that has an extra day—366 days, with February 29 as the extra day. It has another name in English: bissextile year (and leap day is also known as bissextile day).

Julius Caesar created the Julian calendar, which replaced the extra month with an extra day in February. 'Bissextile day' comes from the Latin 'bissextus' and means the "second sixth day" or "double sixth day."

Why the two names?

In the original ten-month Roman calendar, days that marked the position of the moon were named: the calends was the first day of the month, or new moon, and the ides was the middle of the month, or full moon. An extra month was added every few years to ensure that agricultural festivals and holidays remained at the appropriate time of year. Julius Caesar created the Julian calendar, which added days to each month throughout the year and replaced the extra month with an extra day—a leap day. Because the Romans referred to dates according to their relationship with the named days, the sixth day before the first day of March was called diem sextum Kalendas Martias ("the sixth day before the calends of March").

The extra day fell on February 24 (when the former extra month was added) and was therefore called the bissextile day or bissextus, “second sixth day” or “double sixth day.” In Latin bis means “twice” and sextus means “sixth.” The word bissext was also used in English to refer to leap day. Days inserted into the calendar are called intercalary days.

I don't get it either. But to me, this bissextile day thing is just something for the fan club.

In Swedish, a "leap year" is a "skottår". "År" is "year", and "skott" is "shot". You "shoot" an extra day into the calendar, so the extra day is a "shot".

Makes sense, right?

Ann

A lot more than a "bissextile". And to be honest, the etymology of "leap year" doesn't make sense to me either:

leap year (n.)

"year containing 366 days," late 14c., lepe gere (not in Old English), from leap (v.) + year. Probably so called from its causing fixed festival days, which normally advance one weekday per year, to "leap" ahead one day in the week. Compare Medieval Latin saltus lunae (Old English monan hlyp) "omission of one day in the lunar calendar every 19 years."

Dutch schrikkeljaar "leap year" is from Middle Dutch schricken "leap forward," literally "be startled, be in fear." The 29th of February is schrikkeldag. Danish skudaar, Swedish skottår are literally "shoot-year;" German schaltjahr is from schalten "insert, intercalate." The Late Latin phrase was annus bissextilis, source of the Romanic words; compare bissextile.

And note that it also mentions your "shoot year"!

[Rauf]

Where I live, leap days is on a different date. Even leap years are calculated differently.

https://www.timeanddate.com/date/iran-leap-year.html

The Solar Hijri calendar year begins and ends with the vernal equinox. Like in the Gregorian calendar, there are common years with 365 days and leap years with 366 days.

The distribution of leap years, however, is not determined by mathematical rules, but by the actual timing of the equinoxes. This makes the Solar Hijri calendar, which is the official calendar in Iran and Afghanistan, one of the world's most accurate calendar systems.

Several proposals for mathematical leap year rules have been made to approximate the inherent accuracy of the Solar Hijri calendar without relying solely on astronomical observations. With a deviation from the solar year of only 1 day in about 110,000 years, the most widely accepted set of rules are about as accurate as the observational calendar:

*Group years into periods of 2820 years each. The current 2820-year cycle began in 1096 CE.

*Divide the periods into 88 cycles of varying lengths, following this pattern for the first 84 cycles:
29 years, 33 years, 33 years, 33 years,
29 years, 33 years, 33 years, 33 years...

*The final cycle in each 2820-year period is 37 years long; the pattern for the final 4 cycles is:
29 years, 33 years, 33 years, 37 years.

*Number the years in each cycle starting with 0. For instance, the year 1096 CE is year 0, 1097 CE is year 1, 1098 CE is year 2, and so on.
*All years whose ordinal numbers are evenly divisible by 4 are leap years. The first year of each cycle (ordinal number 0) is a common year.

I don't know how this makes it more accurate though. Our leap day is at the end of the year, normaly, our 12th month is 29 days. But in a leap year, one day will be added, making it a 30 day month.

[johnnydeep]

Where I live, leap days is on a different date. Even leap years are calculated differently.

https://www.timeanddate.com/date/iran-leap-year.html

The Solar Hijri calendar year begins and ends with the vernal equinox. Like in the Gregorian calendar, there are common years with 365 days and leap years with 366 days.

The distribution of leap years, however, is not determined by mathematical rules, but by the actual timing of the equinoxes. This makes the Solar Hijri calendar, which is the official calendar in Iran and Afghanistan, one of the world's most accurate calendar systems.

Several proposals for mathematical leap year rules have been made to approximate the inherent accuracy of the Solar Hijri calendar without relying solely on astronomical observations. With a deviation from the solar year of only 1 day in about 110,000 years, the most widely accepted set of rules are about as accurate as the observational calendar:

*Group years into periods of 2820 years each. The current 2820-year cycle began in 1096 CE.

*Divide the periods into 88 cycles of varying lengths, following this pattern for the first 84 cycles:
29 years, 33 years, 33 years, 33 years,
29 years, 33 years, 33 years, 33 years...

*The final cycle in each 2820-year period is 37 years long; the pattern for the final 4 cycles is:
29 years, 33 years, 33 years, 37 years.

*Number the years in each cycle starting with 0. For instance, the year 1096 CE is year 0, 1097 CE is year 1, 1098 CE is year 2, and so on.
*All years whose ordinal numbers are evenly divisible by 4 are leap years. The first year of each cycle (ordinal number 0) is a common year.

I don't know how this makes it more accurate though. Our leap day is at the end of the year, normaly, our 12th month is 29 days. But in a leap year, one day will be added, making it a 30 day month.

Rauf - I take it you live in Iran then? What city if I might ask? Just curious is all.

[Rauf]

Where I live, leap days is on a different date. Even leap years are calculated differently.

https://www.timeanddate.com/date/iran-leap-year.html

The Solar Hijri calendar year begins and ends with the vernal equinox. Like in the Gregorian calendar, there are common years with 365 days and leap years with 366 days.

The distribution of leap years, however, is not determined by mathematical rules, but by the actual timing of the equinoxes. This makes the Solar Hijri calendar, which is the official calendar in Iran and Afghanistan, one of the world's most accurate calendar systems.

Several proposals for mathematical leap year rules have been made to approximate the inherent accuracy of the Solar Hijri calendar without relying solely on astronomical observations. With a deviation from the solar year of only 1 day in about 110,000 years, the most widely accepted set of rules are about as accurate as the observational calendar:

*Group years into periods of 2820 years each. The current 2820-year cycle began in 1096 CE.

*Divide the periods into 88 cycles of varying lengths, following this pattern for the first 84 cycles:
29 years, 33 years, 33 years, 33 years,
29 years, 33 years, 33 years, 33 years...

*The final cycle in each 2820-year period is 37 years long; the pattern for the final 4 cycles is:
29 years, 33 years, 33 years, 37 years.

*Number the years in each cycle starting with 0. For instance, the year 1096 CE is year 0, 1097 CE is year 1, 1098 CE is year 2, and so on.
*All years whose ordinal numbers are evenly divisible by 4 are leap years. The first year of each cycle (ordinal number 0) is a common year.

I don't know how this makes it more accurate though. Our leap day is at the end of the year, normaly, our 12th month is 29 days. But in a leap year, one day will be added, making it a 30 day month.

Rauf - I take it you live in Iran then? What city if I might ask? Just curious is all.

Yeah, I live there. I live in a small town called Borazjan in southern Iran.

https://www.iraniantours.com/city/borazjan/

Scorching hot summers though! Ain't the best place to live.

[Ann]

Yeah, I live there. I live in a small town called Borazjan in southern Iran.

https://www.iraniantours.com/city/borazjan/

Scorching hot summers though! Ain't the best place to live.

Fascinating, Rauf. If you don't mind my asking, are you Iranian? You speak (or write) excellent English. But then, I do my best to write good English, and I'm Swedish.

I used to belong to an astronomy club that I for different reasons lost interest in, but once, perhaps twenty years ago, we were visited by two young Iranian amateur astronomers who told us that many Iranians love astronomy.

Ann

[Rauf]

Yeah, I live there. I live in a small town called Borazjan in southern Iran.

https://www.iraniantours.com/city/borazjan/

Scorching hot summers though! Ain't the best place to live.

Fascinating, Rauf. If you don't mind my asking, are you Iranian? You speak (or write) excellent English. But then, I do my best to write good English, and I'm Swedish.

I used to belong to an astronomy club that I for different reasons lost interest in, but once, perhaps twenty years ago, we were visited by two young Iranian amateur astronomers who told us that many Iranians love astronomy.

Ann

Not at all! I've been born and raised here in Iran, but ethnically my parents are from Afghanistan. But I pretty much feel Iranian. (btw, my sister lives in Sweden, and I've been trying to learn the basics of Swedish in the past 2 months! )
Thanks for your kind words about my English Ann! But I doubt my English is perfect, whatever English I know I learned from Hollywood And your English is definitely better than me, You've been writing in Asterisk for many years now and all of them are perfect in my eyes.

Here, professional astronomy almost doesn't exist! Most people who are interested in astronomy tend to become amateur astronomers. As for myself, I run our small town's only astronomy club and I try to spread enthusiasm among younger people, so yeah! lots of people love astronomy but we usually can't pursue it professionally, at least in our own country.

[johnnydeep]

Yeah, I live there. I live in a small town called Borazjan in southern Iran.

https://www.iraniantours.com/city/borazjan/

Scorching hot summers though! Ain't the best place to live.

Fascinating, Rauf. If you don't mind my asking, are you Iranian? You speak (or write) excellent English. But then, I do my best to write good English, and I'm Swedish.

I used to belong to an astronomy club that I for different reasons lost interest in, but once, perhaps twenty years ago, we were visited by two young Iranian amateur astronomers who told us that many Iranians love astronomy.

Ann

Not at all! I've been born and raised here in Iran, but ethnically my parents are from Afghanistan. But I pretty much feel Iranian. (btw, my sister lives in Sweden, and I've been trying to learn the basics of Swedish in the past 2 months! )
Thanks for your kind words about my English Ann! But I doubt my English is perfect, whatever English I know I learned from Hollywood And your English is definitely better than me, You've been writing in Asterisk for many years now and all of them are perfect in my eyes.

Here, professional astronomy almost doesn't exist! Most people who are interested in astronomy tend to become amateur astronomers. As for myself, I run our small town's only astronomy club and I try to spread enthusiasm among younger people, so yeah! lots of people love astronomy but we usually can't pursue it professionally, at least in our own country.

Cool. What kind of telescope do you have access to, if any?

( And PS, that should be "better than mine" - )

[Rauf]

Fascinating, Rauf. If you don't mind my asking, are you Iranian? You speak (or write) excellent English. But then, I do my best to write good English, and I'm Swedish.

I used to belong to an astronomy club that I for different reasons lost interest in, but once, perhaps twenty years ago, we were visited by two young Iranian amateur astronomers who told us that many Iranians love astronomy.

Ann

Not at all! I've been born and raised here in Iran, but ethnically my parents are from Afghanistan. But I pretty much feel Iranian. (btw, my sister lives in Sweden, and I've been trying to learn the basics of Swedish in the past 2 months! )
Thanks for your kind words about my English Ann! But I doubt my English is perfect, whatever English I know I learned from Hollywood And your English is definitely better than me, You've been writing in Asterisk for many years now and all of them are perfect in my eyes.

Here, professional astronomy almost doesn't exist! Most people who are interested in astronomy tend to become amateur astronomers. As for myself, I run our small town's only astronomy club and I try to spread enthusiasm among younger people, so yeah! lots of people love astronomy but we usually can't pursue it professionally, at least in our own country.

Cool. What kind of telescope do you have access to, if any?

( And PS, that should be "better than mine" - )

Yeah, my bad. Thanks for the correction! We got a Celestron CPC 1100, and a Sky-Watcher Dobsonian 8".

[johnnydeep]

Not at all! I've been born and raised here in Iran, but ethnically my parents are from Afghanistan. But I pretty much feel Iranian. (btw, my sister lives in Sweden, and I've been trying to learn the basics of Swedish in the past 2 months! )
Thanks for your kind words about my English Ann! But I doubt my English is perfect, whatever English I know I learned from Hollywood And your English is definitely better than me, You've been writing in Asterisk for many years now and all of them are perfect in my eyes.

Here, professional astronomy almost doesn't exist! Most people who are interested in astronomy tend to become amateur astronomers. As for myself, I run our small town's only astronomy club and I try to spread enthusiasm among younger people, so yeah! lots of people love astronomy but we usually can't pursue it professionally, at least in our own country.

Cool. What kind of telescope do you have access to, if any?

( And PS, that should be "better than mine" - )

Yeah, my bad. Thanks for the correction! We got a Celestron CPC 1100, and a Sky-Watcher Dobsonian 8".

Nice scopes both!

[Rauf]

Cool. What kind of telescope do you have access to, if any?

( And PS, that should be "better than mine" - )

Yeah, my bad. Thanks for the correction! We got a Celestron CPC 1100, and a Sky-Watcher Dobsonian 8".

Nice scopes both!

Yeah, I love the Celestron. But unfortunately due to light pollution, we can't get much of the sky with it. And we have no imaging equipment

[johnnydeep]

Yeah, my bad. Thanks for the correction! We got a Celestron CPC 1100, and a Sky-Watcher Dobsonian 8".

Nice scopes both!

Yeah, I love the Celestron. But unfortunately due to light pollution, we can't get much of the sky with it. And we have no imaging equipment

Sounds like it's time to start a Go Fund Me campaign! I'd even contribute.

[Rauf]

Nice scopes both!

Yeah, I love the Celestron. But unfortunately due to light pollution, we can't get much of the sky with it. And we have no imaging equipment

Sounds like it's time to start a Go Fund Me campaign! I'd even contribute.

Thanks!