Look up the date of any Islamic holiday going back to 622 CE

Ramadan will be celebrated twice in 2030 due to the 33-year lunar cycle

Because the Islamic year is 11 days shorter than the Gregorian calendar, Ramadan migrates through every season over a 33-year cycle. In 2030, it will fall twice in the same Gregorian year.

A 101 on why Ramadan is the holiest time of the Muslim year

As a spiritual guide for members of the Brandeis University community, this overview surfaces the highlights to orient readers on Ramadan logistics, practices, and obligations. It's a useful start for those interested in learning the basics around fasting rules, exemptions, the significance of iftar and suhoor, and common greetings.

How to sight the new crescent moon that starts Ramadan

Ramadan doesn't begin on a fixed date. Instead, it begins when a crescent moon is visually confirmed. The Royal Museums Greenwich explains the astronomy behind the sighting, including the conditions that must be met: the sun must be below the horizon, the moon must be above it, and the two must not be within the Danjon Limit (roughly 5 to 7 degrees of separation in the sky, as shown below).

How lunisolar calendars work

Despite being called Lunar New Year, the Chinese calendar that the holiday is based on is actually lunisolar, or based on both the sun and the moon. Many religious holidays—including Easter, Ramadan, Chinese New Year, and Passover—do not have fixed dates according to the now-ubiquitous Gregorian calendar.

Iftar foods from around the world

The global population of Muslims eats and fasts in distinct way around the world. This photo survey spans Morocco's harira soup to Indonesia's kolak (a sweet dessert soup) and Turkey's pide (like pizza but without the tomato sauce). The one universal aspect for most iftar meals is dates and water, following Muhammad's practice. (Some users may experience a paywall.)

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by over 1.5 million Muslims.

Eid ul-Fitr vs. Eid ul-Adha: differentiating the two lesser and greater Eids

Most non-Muslims associated Eid with the end of Ramadan—but that's actually the lesser Eid. The greater one, Eid ul-Adha, comes 70 days later and commemorates Ibrahim's (Abraham) willingness to sacrifice his son. It involves Qurbani, the ritual slaughter of an animal, with meat distributed to those in need.

A readable narrative account of how Muhammad first received the Quran

The story behind Ramadan's origins involves a lesser-known layer of personal drama for Muhammad, who fled the Cave of Hira in fear thinking he had been possessed by the angel communicating with him. Only his wife, Khadijah, was able to reassure him. The first revelation came during Ramadan in 610 CE, but the full Quran took 23 years for the angel Jibril (or Gabriel) to deliver.

Hanukkah is one of 8 major Jewish holidays

This calendar, maintained by the Reform Judaism organization, not only shows when each holiday is to be celebrated in the current year, but also includes short histories and common rituals.

Why Easter's date changes, making it a 'moveable feast'

Unlike Christmas, Easter has no fixed date: It falls on the first Sunday after the first full moon on or after March 21, a formula set by the Council of Nicaea in 325 CE to form a standard across Christianity. The result is a window of 35 possible dates, from March 22 to April 25.

Explore an interactive diary of the International Space Station

The tool enables users to learn about the daily events that occurred on the ISS since continuous human occupancy began on November 2, 2000. Upon selecting a date in the calendar, users can explore activity logs, relevant news, and multimedia content, including videos, photographs, and audiologs, from the onboard crew.

The ancient Roman origins of the leap year

The earth's orbit around the sun takes about 365.2422 days, leaving farmer almanacs the awful job of pretending the calendar year fits into a whole number. This article explores the modern origins of the civil solar calendar and its leap year. The Julian calendar, named after the Roman emperor Julius Caesar, cut the calendar year into 365.25 days, gifting the public an extra day every four years. Learn more of the history here.

A 12-minute crash course on Islam, its beliefs, and history

John Green's Crash Course World History episode overs Islam's core tenets, the Five Pillars, and the religions spread across continents in a jam-packed video under 15 minutes. The video is an efficient on-ramp for newcomers and is an ideal starting point to Islam.

Calibrate to the U.S. government's official clock, synchronized to the atomic standard

The site displays the current time across all American time zones—corrected for network delay—and shows whether your device's clock has drifted. Computer clocks rely on quartz crystals that drift slightly with temperature and age, requiring alignment with atomic clocks (which are so stable that seconds are defined by them).

Check out hurricane history where you live

The NOAA's historical hurricane tracker lets you explore over 150 years of data to see where hurricanes traveled and made landfall. The tool lets you search by location, name, or year; create maps and tables; and read NOAA storm reports.

The term 'algorithm' originated from the Latinized name of al-Khwārizmī, a 9th-century mathematician whose works introduced Arabic numerals and the decimal-based numeral system to Europe and whose treatise 'Al-Jabr' gave algebra its name.

Historically, cholera has repeatedly disrupted the Hajj for Muslims

Outbreaks of the disease throughout the 19th century and the beginning of the 20th, killed thousands of religious pilgrims as they sought to complete this obligatory pilgrimage.

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

Smaller companies’ IPO information can be hard to track down

This calendar keeps you updated on the current IPO dates and pricing from different companies. You can search for upcoming and future IPO dates and see which companies withdrew from the IPO process.

You can find the value of a dollar dating back to 1635

The value of a dollar hasn’t been consistent throughout history. An inflation calculator lets you compare the value of dollars from any two years over the past four centuries.

See a timeline of the events that shaped the Iranian Revolution

From a defamatory newspaper editorial that sparked protests in January 1978 to Khomeini's return from exile and the Shah's flight from Iran in 1979, this timeline traces the rapidly escalating chain of events—protests, crackdowns, and political collapses—that toppled one of the Middle East's most powerful monarchies.

US holiday retail sales reached $973B in 2024

In 2024, US holiday retail sales reached $973B—nearly one-fifth of annual sales. Many companies depend on this season to bolster revenues.

The term 'algorithm' originated from the Latinized name of al-Khwārizmī, a 9th-century mathematician whose works introduced Arabic numerals and the decimal-based numeral system to Europe and whose treatise 'Al-Jabr' gave algebra its name.

Halloween originated with the Celtic festival of Samhain

Halloween, a holiday primarily popular in the US and Canada, originated 2,000 years ago with the Celtic people. The Celts interpreted this transition as when ghosts returned to the land of the living, leading to rituals like feasts, bonfires, and wearing costumes made of animal body parts on Oct. 31.

The US Commission on International Religious Freedom monitors and reports on religious persecution

USCIRF is an independent, bipartisan federal commission that tracks religious freedom conditions worldwide and provides policy recommendations to the president, secretary of state, and Congress.

This real-time tracking of the hantavirus cruise ship outbreak in May 2026 offers a unique glimpse into the global reach of the outbreak and whether the virus sickened passengers and their communities around the world.

Due date is calculated from the first day of the last menstrual period—not when sex occurred

The standard counting system considers a woman pregnant from the first day of her last menstrual period, which means someone may technically—for the purposes of measurement—have become pregnant even before she had sex. This standard starting point is used because it reliably marks when the body began preparing for pregnancy—even though it's typically two weeks before conception. On average, most women are pregnant for 280 days from the last menstrual period.

A primary source timeline of US history (1600-1968)

Compiled by the Library of Congress, this archive walks through important events in US history through civil rights era, while providing primary sources to explore.

Visualizing Byzantium in the year 1200

This is a computer reconstruction of the Byzantine capital at its apogee, just before the Fourth Crusade. Alongside detailed renderings of the Hippodrome and Hagia Sophia, it includes dozens of the imperial city’s less famous monuments, many of which can still be found in modern Istanbul. The reconstruction is a work in progress, and the Byzantium 1200 X account routinely posts updates.

Stanford built a Google Maps for the Roman Empire, revealing how much it cost to travel in the ancient world

44% of Americans say they pray at least once a day—discover how your state's religiosity stacks up against the rest of the country.

Calculate how much of your tax dollars go to each federal program based on your income, filing status, and number of children

Iran's Revolutionary Guard Corps is independent of Iran's regular army and is one of the most powerful and influential military-political organizations in the Middle East.

Learn more about the history of fireworks, which dates back to an accidental invention during an alchemist's quest for information about immortality.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

A century of Billboard issues documenting the evolution of popular music.

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

The United States has had a tumultuous relationship with Cuba since its 1959 revolution, highlighted by a nuclear crisis and a decades-long trade embargo.

US housing costs have risen by roughly 175% between 1991 and 2026—but a growing number of Gen Zers are becoming homeowners anyway. In 2025, 4% of homebuyers were Gen Z, up from 3% the year before.

One of the most famous portraits ever taken is 'Afghan Girl' (1984) by Steve McCurry, yet the subject Sharbat Gula went much of her life without being identified or benefitting from the image's success.

Meet the 56 signers of the Declaration of Independence—most of whom didn't put pen to paper until August 2, 1776—and see their original signatures.

'Shogun,' a 1980s TV series, helped popularize sushi in the US by stimulating an American interest in Japanese culture.

See a ranking of the best (and worst) Federal Reserve Chairs since 1914 out of the 16 men and women who have held the office since.

Poison ivy can cause rashes year-round since all parts of the plant contain urushiol, the oil that triggers our allergic response.

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

This site reaches millions of visitors who are tired of AI chatbots and seeking human connection. Pretend to be an AI chatbot and ask questions, provide answers, and draw for people in real time.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.