Solar calendar in the context of Panguni

The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts of Oriental Orthodoxy as well as by the Amazigh people (also known as the Berbers). For a quick calculation, between 1901 and 2099 the much more common Gregorian date equals the Julian date plus 13 days.

The Julian calendar was proposed in 46 BC by (and takes its name from) Julius Caesar, as a reform of the earlier Roman calendar, which was largely a lunisolar one. It took effect on 1 January 45 BC, by his edict. Caesar's calendar became the predominant calendar in the Roman Empire and subsequently most of the Western world for more than 1,600 years, until 1582 when Pope Gregory XIII promulgated a revised calendar. Ancient Romans typically designated years by the names of ruling consuls; the Anno Domini system of numbering years was not devised until 525, and became widespread in Europe in the eighth century.

A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky – as viewed from the Earth or another celestial body of the Solar System – thus completing a full cycle of astronomical seasons. For example, it is the time from vernal equinox to the next vernal equinox, or from summer solstice to the next summer solstice. It is the type of year used by tropical solar calendars.

The tropical year is one type of astronomical year and particular orbital period. Another type is the sidereal year (or sidereal orbital period), which is the time it takes Earth to complete one full orbit around the Sun as measured with respect to the fixed stars, resulting in a duration of 20 minutes longer than the tropical year, because of the precession of the equinoxes.

A lunar calendar is a calendar based on the monthly cycles of the Moon's phases (synodic months, lunations), in contrast to solar calendars, whose annual cycles are based on the solar year, and lunisolar calendars, whose lunar months are brought into alignment with the solar year through some process of intercalation – such as by insertion of a leap month. The most widely observed lunar calendar is the Islamic calendar. The details of when months begin vary from calendar to calendar, with some using new, full, or crescent moons and others employing detailed calculations.

Since each lunation is approximately 29+1⁄2 days, it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of 12 such lunations, a lunar year, is 354 days, 8 hours, 48 minutes, 34 seconds (354.36707 days), lunar calendars are 11 to 12 days shorter than the solar year. In lunar calendars, which do not make use of lunisolar calendars' intercalation, the lunar months cycle through all the seasons of a solar year over the course of a 33–34 lunar-year cycle (see, e.g., list of Islamic years).

A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, and night. This daily cycle drives circadian rhythms in many organisms, which are vital to many life processes.

A collection of sequential days is organized into calendars as dates, almost always into weeks, months and years. A solar calendar organizes dates based on the Sun's annual cycle, giving consistent start dates for the four seasons from year to year. A lunar calendar organizes dates based on the Moon's lunar phase.

The ancient Egyptian calendar – a civil calendar – was a solar calendar with a 365-day year. The year consisted of three seasons of 120 days each, plus an intercalary month of five epagomenal days treated as outside of the year proper. Each season was divided into four months of 30 days. These twelve months were initially numbered within each season but came to also be known by the names of their principal festivals. Each month was divided into three 10-day periods known as decans or decades. It has been suggested that during the Nineteenth Dynasty and the Twentieth Dynasty the last two days of each decan were usually treated as a kind of weekend for the royal craftsmen, with royal artisans free from work.

Because this calendrical year was nearly a quarter of a day shorter than the solar year, the Egyptian calendar lost about one day every four years relative to the Julian calendar. It is therefore sometimes referred to as the wandering year (Latin: annus vagus), as its months rotated about one day through the solar year every four years. Ptolemy III's Canopus Decree attempted to correct this through the introduction of a sixth epagomenal day every four years but the proposal was resisted by the Egyptian priests and people and abandoned until the decree by Augustus in 25 BC that established the Alexandrian or Coptic calendar. The introduction of a leap day to the Egyptian calendar made it equivalent to the Julian calendar, although (like the latter) it continues to diverge from the Gregorian calendar at the turn of most centuries.

The Assyrian calendar (Syriac: ܣܘܼܪܓܵܕ݂ܵܐ ܐܵܬ݂ܘܿܪܵܝܵܐ sūrgāḏā ʾĀṯōrāyā) is a solar calendar used by modern Assyrian people.

The Rumi calendar (Ottoman Turkish: رومی تقویم, Rumi takvim, lit. "Roman calendar"), a specific calendar based on the Julian calendar, was officially used by the Ottoman Empire after Tanzimat (1839) and by its successor, the Republic of Turkey until 1926. It was adopted for civic matters and is a solar based calendar, assigning a date to each solar day.

Chaitra (Sanskrit: चैत्र, romanized: Caitra) is the first month of the Hindu lunar calendar and the Indian national calendar. The name of the month is derived from the position of the Moon near the Chitra nakshatra (star) on the full moon day. The month corresponds to spring (Vasanta) season and falls in March–April in the Gregorian calendar.

In the Hindu solar calendar, it corresponds to the last month of Mina and begins with the Sun's entry into Pisces. It corresponds to Choitro, the last month in the Bengali calendar, and Chait, the last month in the Nepali calendar (Vikram Samvat). In the Tamil calendar, it corresponds to the third month of Chittirai, falling in the Gregorian months of April–May.

Jewish holidays, also known as Jewish festivals or Yamim Tovim (Hebrew: יָמִים טוֹבִים, romanized: yāmīm ṭōvīm, lit. 'Good Days', or singular Hebrew: יוֹם טוֹב‎ Yom Tov, in transliterated Hebrew [English: /ˈjɔːm ˈtɔːv, joʊm ˈtoʊv/]), are holidays observed by Jews throughout the Hebrew calendar. They include religious, cultural and national elements, derived from four sources: mitzvot ("biblical commandments"), rabbinic mandates, the history of Judaism, and the State of Israel.

Jewish holidays occur on the same dates every year in the Hebrew calendar, but the dates vary in the Gregorian. This is because the Hebrew calendar is a lunisolar calendar (based on the cycles of both the sun and moon), whereas the Gregorian is a solar calendar. Each holiday can only occur on certain days of the week, four for most, but five for holidays in Tevet and Shevat and six for Hanukkah (see Days of week on Hebrew calendar).

In the Gregorian calendar, New Year's Day is the first day of the calendar year, 1 January. Most solar calendars, such as the Gregorian and Julian calendars, begin the year regularly at or near the northern winter solstice. In contrast, cultures and religions that observe a lunisolar or lunar calendar celebrate their Lunar New Year at varying points relative to the solar year.

In pre-Christian Rome, under the Julian calendar, the day was dedicated to Janus, god of gateways and beginnings, for whom January is also named. From Roman times until the mid-18th century, the new year was celebrated at various stages and in various parts of Christian Europe on 25 December, on 1 March, on 25 March and on the movable feast of Easter.

This is a list of calendars. Included are historical calendars as well as proposed ones. Historical calendars are often grouped into larger categories by cultural sphere or historical period; thus O'Neil (1976) distinguishes the groupings Egyptian calendars (Ancient Egypt), Babylonian calendars (Ancient Mesopotamia), Indian calendars (Hindu and Buddhist traditions of the Indian subcontinent), Chinese calendars and Mesoamerican calendars. These are not specific calendars but series of historical calendars undergoing reforms or regional diversification.

In Classical Antiquity, the Hellenic calendars inspired the Roman calendar, including the solar Julian calendar introduced in 45 BC. Many modern calendar proposals, including the Gregorian calendar introduced in 1582 AD, contains modifications from that of the Julian calendar.

Phalguna or Phagun is the twelfth and last month of the Hindu lunar calendar and the Indian national calendar. The name of the month is derived from the position of the Moon near the Pushya nakshatra (star) on the full moon day. The month corresponds to the end of the winter (Shishira) season and falls in January–February of the Gregorian calendar.

In the Hindu solar calendar, it corresponds to the month of Kumbha and begins with the Sun's entry into Aquarius. It corresponds to Falgun, the eleventh month in the Bengali calendar and Vikram Samvat. In the Tamil calendar, it corresponds to the twelfth and last month of Panguni, falling in the Gregorian months of March–April. In the Vaishnav calendar, it corresponds to the twelfth month of Govinda.

The Solar Hijri calendar is the official calendar of Iran. It is a solar calendar, based on the Earth's orbit around the Sun. Each year begins on the day of the March equinox and has years of 365 or 366 days. It is sometimes also called the Shamsi calendar, Khorshidi calendar or Persian calendar and the most recent of the Iranian calendars. It is abbreviated as SH, HS, AP, or, sometimes as AHSh, while the lunar Hijri calendar (commonly known in the West as the 'Islamic calendar') is usually abbreviated as AH.

The epoch (very first day) of the Solar Hijri calendar was the day of the spring equinox, March 19, 622 CE. The calendar is a "Hijri calendar" because that was the year that Mohammed is believed to have left from Mecca to Medina, which event is referred to as the Hijrah.

The Bengali calendar or Bangla calendar (Bengali: বঙ্গাব্দ, romanized: Bôṅgābdô, colloquially বাংলা সন, Bāṅlā Sôn or বাংলা সাল, Bāṅlā Sāl, "Bangla Year") is a solar calendar used in the Bengal region of the Indian subcontinent. In contrast to the traditional Indian Hindu calendar, which begins with the month Chaitra, The Bengali calendar starts with Baishakh. A revised version of the Bangladeshi calendar is officially used in Bangladesh, while an earlier, traditional version continues to be followed in the Indian states of West Bengal, Tripura, and Assam. The Bengali calendar began in 590–600 CE to commemorate the ascension of Shashanka, the first independent king in Bengal's unified polity. Some modifications were done to the original calendar during Mughal emperor Akbar's era, to facilitate the collection of land revenue at the start of the Bengali harvesting season. The first day of the Bengali year is known as Pohela Boishakh (1st of Boishakh) which is a public holiday in Bangladesh.

The Bengali era is called Bengali Sambat (BS) and has a zero year that starts in 593/594 CE. It is 594 less than the AD or CE year in the Gregorian calendar if it is before Pohela Boishakh, or 593 less if after Pohela Boishakh.