The Gregorian calendar was a very minor modification of the Julian calendar (named after Julio Caesar), which is was created and enforced by Pagans, decades before Jesus was born (Dimitrijevic, Theodossiou & Mantarakis, 2008). The addition to the Gregorian calendar was the precision that the average solar year is 365.2425 days long, instead of the 365.25 days claimed by the Julian calendar. The Julian calendar assumed incorrectly that the average solar year is exactly 365.25 days long, which was an overestimate of a little under one day per century.

The only “Christian” aspect of the calendar is its reference to the purported birth of Jesus Christ. That is, the calendar claims Jesus was born 2,022 years ago. However, according to the Ethiopians, Christ was born 2,015 years ago, instead of 2,022 that the Romans claim. Similarly, the Thai solar calendar references Buddhist Era instead of Jesus' birth. The common thing about these calendars is their reference to the revolution of the Earth around the Sun.

The Julian calendar was enforced by Julius Caesar (a Pagan) 45 years before the Roman Catholic claim of the birth of Jesus (Michels, 2015), and the Calender was designed Greek and Romans mathematicians and astronomers such as Sosigenes of Alexandria (Gajic, 2019).

On the other hand, the Islamic Calendar (Hijri Calendar) is based on the moon, not the sun like solar calendars. Further, the Hijri calendar is about eleven days shorter than than solar calendars, because each month begins with the first sighting of a lunar crescent (Raharto et al., 2019). This implies that the months of the Hijri calendar depends on the cloud cover or the brightness of the Sun, which is not scientific.

The biggest problem of the Islamic Calendar is that it cannot be used to predict the climate, which implies that it cannot be used for agriculture (Mughal, 2014). In the Arabia world, this is not a huge problem, because temperatures and the length days do not vary much from month to month. However, in the tropical monsoon climate of Southern Nigeria, it matters a lot. It for this reason that the climatic condition around Ileya (Eid-el-Kabir) varies each year, while that of Christmas and New Year is constant.


References
Dimitrijevic, M. S., Theodossiou, E. T., & Mantarakis, P. Z. (2008). Milutin Milankovic and the reform of the Julian Calendar in 1923. Journal of Astronomical History and Heritage, 11, 50-54. Available at: http://adsabs.harvard.edu/pdf/2008JAHH...11...50D.

Gajic, N. (2019). The curious case of the Milankovitch calendar. History of Geo-and Space Sciences, 10(2), 235-243. Available at: https://hgss.copernicus.org/articles/10/235/2019/.

Michels, A. K. (2015). Calendar of the Roman Republic. Princeton University Press. Available at: https://www.degruyter.com/document/doi/10.1515/9781400849789/pdf.

Mughal, M. A. Z. (2014). Calendars tell history: Social rhythm and social change in rural Pakistan. History and Anthropology, 25(5), 592-613. Available at: https://dro.dur.ac.uk/13842/1/13842.pdf.

Raharto, M., Sopwan, N., Hakim, M. I., & Sugianto, Y. (2019, March). New approach on study of new young crescent (Hilal) visibility and new month of Hijri calendar. In Journal of Physics: Conference Series (Vol. 1170, No. 1, p. 012080). IOP Publishing. Available at: https://iopscience.iop.org/article/10.1088/1742-6596/1170/1/012080/pdf.

SadiqBabaSani:
Go tell d Mischievous slavish Mumurish

Truthisunique:
Must be painful for you but reality is reality

Gregorian calendar start it's counting from B.C to A.D (christbirth) (year of our Lord Jesus Christ)

That you speak English as global language for example doesnt change the fact that the British own the language

tollyboy5:

Let me officiate your ignorance.

tollyboy5:

Let me officiate your ignorance.

Before the Common Era (BCE).
Jesus birth and buddha birth are very similar.

Truthisunique:
The Julian calendar and Gregorian calendar are two different calendar till today

The Catholic church since pope Gregory ascent had to define the line away from the Julian calendar of all Rome.

Julian calendar is not the same as Gregorian and the joke is on you when Julian doesn't agree with Gregorian till date

realstars:
Jesus the light of the world. And with the said calender, Christmas has been celebrated all over the world, to let the world knows that christ is real.

only the antiChrist will not like this comment about Christ.

tollyboy5:

How does some hours modification makes it a christian calendar? Is it because it was pope?

tollyboy5:

Jesus was not born during winter . Stay clear of ignorance and know the origin of christmas

Truthisunique:
let me educate your ignorance that BCE was only adopted in the 17 century "in an attempt to be all inclusive"
to a global audience that had now fallen in love with it.

It doesn't change the (B.C, A,D) which history records it was created for by origin.

It is an aberration to even call it common era because the world has never had a common era at 17th century

tollyboy5:

Religious bigotry is your problem here. First it was a pagan calendar based on astronomical calculations and christian made some scientific modifications to it.
Your bone of contention now is the insertion of 'before christ' which is now optional in today society.

Free your mind bro

tollyboy5:

Jesus was not born during winter . Stay clear of ignorance and know the origin of christmas

Truthisunique:
I know Christianity as the biggest religion in the world really turns your stomach

So turning facts on the head which collaborates how it got to this point is the alternate world you have chosen to live in

Jesus born in winter or summer doesn't change the fact that he existed and has his birth as a marking point calendar wise

tollyboy5:

So if we decide to use mohammad as marking point makes it an islamic calendar ?
Religious people are just comedians

realstars:
I know that, but the concept was to bring the people of the dark to the light.

tollyboy5:

It has no correlation on the origin of calendar which is what is been discussed here.
It was just used to separate events

Truthisunique:
you are the one grasping at straws here, trying to call me a bigot to run from the fact you have been bursted even by facts and history

The Julian calendar is different from Gregorian calendar till today (A fact I have just bursted)

The Gregorian calendar didn't start counting from the 17th century (A fact well established as it starts counting from A.D, BC which is its origin root)

The origin of a calendar is the definition of a calendar (there was dates before Gregorian but Gregorian starts counts from the Christ era and you can't dispute this origin)

Pagan or not should not be your headache If those pagans that continued using Julian calendar till date saw Gregorian as Pagan they would have continued using it

They only stopped because this calendar was dedicated to a new diety i.e Jesus

tollyboy5:

According to wikipedia is was modified and not changed so why the stress?
Modifications are mostly scientic to make things better. If it was actually changed that would have been another story

The julian calendar start counting from the reign of an empire which was later change to a more generally accepted time yardstick.

The supposed birth of christ which stand as a yard stick to separate events is not a thing to bother scientist and historians much.

The date before then were not one. The chinese had theirs, the julian date counts from the reign of an empire which causes more confusion
https://www.quora.com/Before-AD-what-did-people-of-the-BC-era-call-their-years-How-did-they-count-the-years-in-the-BC-era

I can tell you for sure your making things up.
Its more like saying the international system units scientist use to day was dedicated to france.
Because the decision was made there lol.
Stop making allegations where there is none

Truthisunique:
lf you weren't dull you would see that this is the point of all calendar, they don't operate on vacumm they take origin from a significant point because you can't really count time in vacumm

Yes Islamic calendar origin takes beginning from Mohammed flight from Medina which is what makes it an Islamic calendar

All calendar including Gregorian calendar have this

No such thing as common era in 17th century

tollyboy5:

It has two names. Christian calendar like you will like to call it and western calendar like i use to refer it has.

Now why force your notion on me?
They even reference it as modification of julian calendar so what you chose to call it is just a matter of choice.

Islam calendar has was no modification of any previous calendar and has more islamic origin compare to the normal western calendar.