Julian day in the context of "1st millennium"

Sir John Frederick William Herschel, 1st Baronet KH FRS (/ˈhɜːrʃəl, ˈhɛər-/; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor and experimental photographer who invented the blueprint and did botanical work.

Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus – the seventh planet, discovered by his father Sir William Herschel. He made many contributions to the science of photography, and investigated colour blindness and the chemical power of ultraviolet rays. His Preliminary Discourse (1831), which advocated an inductive approach to scientific experiment and theory-building, was an important contribution to the philosophy of science.

The 1st millennium BC, also known as the last millennium BC, was the period of time lasting from the years 1000 BC to 1 BC (10th to 1st centuries BC; in astronomy: JD 1356182.5 – 1721425.5). It encompasses the Iron Age in the Old World and sees the transition from the Ancient Near East to classical antiquity.

World population roughly doubled over the course of the millennium, from about 100 million to about 200–250 million after the birth of Jesus Christ and the establishment of the Julio-Claudian dynasty led by its founder Octavian.

A calendrical calculation is a calculation concerning calendar dates. Calendrical calculations can be considered an area of applied mathematics.Some examples of calendrical calculations:

• Converting a Julian or Gregorian calendar date to its Julian day number and vice versa (see § Julian day number calculation within that article for details).
• The number of days between two dates, which is simply the difference in their Julian day numbers.
• The dates of moveable holidays, like Christian Easter (the calculation is known as Computus) followed up by Ascension Thursday and Pentecost or Advent Sundays, or the Jewish Passover, for a given year.
• Converting a date between different calendars. For instance, dates in the Gregorian calendar can be converted to dates in the Islamic calendar with the Kuwaiti algorithm.
• Calculating the day of the week.

Calendrical calculation is one of the five major Savant syndrome characteristics.

Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle (ERA, which serves as the replacement for Greenwich Mean Sidereal Time). UT1 is the same everywhere on Earth. UT1 is required to follow the relationship

where T_u = (Julian UT1 date − 2451545.0).

The third millennium of the Anno Domini or Common Era is the current millennium spanning the years 2001 to 3000. It began on January 1, 2001 (MMI) and will end on December 31, 3000 (MMM), (21st to 30th centuries; in astronomy: JD 2451910.5 – 2817151.5).

Ongoing futures studies seek to understand what will likely continue and what could plausibly change in this period and beyond.

The Holocene calendar, also known as the Holocene Era or Human Era (HE), is a year numbering system that adds exactly 10,000 years to the currently dominant (AD/BC or CE/BCE) numbering scheme, placing its first year near the beginning of the Holocene geological epoch and the Neolithic Revolution, when humans shifted from a hunter-gatherer lifestyle to agriculture and fixed settlements. The current year by the Gregorian calendar, AD 2025, is 12025 HE in the Holocene calendar. The HE scheme was first proposed by Cesare Emiliani in 1993 (11993 HE), though similar proposals to start a new calendar at the same date had been put forward decades earlier. Emiliani thereby dismissed his original proposal to align the era with the 7980-year Julian cycles, i.e. start with the epoch in 4713 BCE (5288 HE).

The second millennium of the Anno Domini or Common Era was a millennium spanning the years 1001 to 2000. It began on January 1, 1001 (MI) and ended on December 31, 2000 (MM), (11th to 20th centuries; in astronomy: JD 2086667.5 – 2451909.5).

It encompassed the High and Late Middle Ages of the Old World, the Islamic Golden Age and the period of Renaissance, followed by the early modern period, characterized by the European wars of religion, the Age of Enlightenment, the Age of Discovery and the colonial period. Its final two centuries coincide with modern history, characterized by industrialization, the rise of nation states, the rapid development of science, widespread education, and universal health care and vaccinations in the developed world. The 20th century saw increasing globalization, most notably the two World Wars and the subsequent formation of the United Nations. 20th-century technology includes powered flight, television and semiconductor technology, including integrated circuits. The term "Great Divergence" was coined to refer the unprecedented cultural and political ascent of the Western world in the second half of the millennium, emerging by the 18th century as the most powerful and wealthy world civilization, having eclipsed Qing China, Edo Japan, the Islamic world and India. This allowed the colonization by European countries of much of the world during this millennium, including the Americas, Africa, Oceania, and South and Southeast Asia.