UTC in the context of Leap seconds

The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the Solar System as Earth's North Pole.

Due to Earth's axial tilt of 23.439281°, there is a seasonal variation in the lengths of the day and night. There is also a seasonal variation in temperatures, which lags the variation in day and night. Conventionally, winter in the Northern Hemisphere is taken as the period from the December solstice (typically December 21 UTC) to the March equinox (typically March 20 UTC), while summer is taken as the period from the June solstice through to the September equinox (typically on 23 September UTC). The dates vary each year due to the difference between the calendar year and the astronomical year. Within the Northern Hemisphere, oceanic currents can change the weather patterns that affect many factors within the north coast. Such events include El Niño–Southern Oscillation.

The Babylonian calendar was a lunisolar calendar used in Mesopotamia from around the 2nd millennium BC until the Seleucid Era (294 BC), and it was specifically used in Babylon from the Old Babylonian Period (1780s BC) until the Seleucid Era.

In the Seleucid Era it was reformed as "Greek time", Anno Graecorum was introduced and used in the Middle East and Egypt until the middle of the first millennium when the First Council of Nicaea AD 325 defined the Church year based on the Roman early Julian calendar. As Anno Graecorum formed the basis for time references in the Bible and spread westward, it rather increased the Babylonian calendars importance. The Babylonian calendar is also partly reflected in calendars in South and East Asia and the Islamic calendar as well as Iranian calendars. The Julian calendar inherited the definitions of the 12 month system, week, hour etc. from the Babylonian calendar and the current Jewish calendar can be seen as a slightly modified Babylonian calendar that still exists today and is practised, but with Anno Mundi Livryat haOlam year calculation since the creation of the world. Today's global time system UTC (Gregorian calendar) therefore has its main structure inherited from the Babylonian calendar.

Apollo 11 was the first spaceflight to land humans on the Moon, conducted by NASA from July 16 to 24, 1969. Commander Neil Armstrong and Lunar Module Pilot Edwin "Buzz" Aldrin landed the Lunar Module Eagle on July 20 at 20:17 UTC, and Armstrong became the first person to step onto the surface about six hours later, at 02:56 UTC on July 21. Aldrin joined him 19 minutes afterward, and together they spent about two and a half hours exploring the site they had named Tranquility Base upon landing. They collected 47.5 pounds (21.5 kg) of lunar material to bring back to Earth before re-entering the Lunar Module. In total, they were on the Moon’s surface for 21 hours, 36 minutes before returning to the Command Module Columbia, which remained in lunar orbit, piloted by Michael Collins.

Apollo 11 was launched by a Saturn V rocket from Kennedy Space Center in Florida, on July 16 at 13:32 UTC (9:32 am EDT, local time). It was the fifth crewed mission of the Apollo program. The Apollo spacecraft consisted of three parts: the command module (CM), which housed the three astronauts and was the only part to return to Earth; the service module (SM), which provided propulsion, electrical power, oxygen, and water to the command module; and the Lunar Module (LM), which had two stages—a descent stage with a large engine and fuel tanks for landing on the Moon, and a lighter ascent stage containing a cabin for two astronauts and a small engine to return them to lunar orbit.

Moscow Time (MSK; Russian: моско́вское вре́мя, romanized: moskovskoye vremya) is the time zone for the city of Moscow, Russia, and most of western Russia, including Saint Petersburg. It is the second-westernmost of the eleven time zones of Russia, after the non-continguous Kaliningrad enclave. It has been set to UTC+03:00 without DST since 26 October 2014; before that date it had been set to UTC+04:00 year-round on 27 March 2011.

Moscow Time is used to schedule trains (until 1 August 2018), ships, etc. throughout Russia, but air transport in Russia is scheduled using local time. Since 1 August 2018, Russian railways switched to using local time. Time in Russia is often announced throughout the country's other timezones on radio stations as Moscow Time, which is also registered in telegrams, etc. Descriptions of time zones in Russia are often based on Moscow Time rather than UTC; for example, Yakutsk (UTC+09:00) is said to be MSK+6 in Russia.

Yekaterinburg Time (YEKT) is the time zone five hours ahead of UTC (UTC+05:00) and 2 hours ahead of Moscow Time (MSK+2).

In 2011, Russia moved to year-round daylight saving time. Instead of switching between UTC+05:00 in winter and UTC+06:00 in summer, Yekaterinburg time was set to UTC+06:00 until 2014, when it was reset back to UTC+05:00 year-round.

Omsk Time (OMST) is a time zone in Russia that is six hours ahead of UTC (UTC+06:00), and 3 hours ahead of Moscow Time (MSK). It is used in Omsk Oblast.

Krasnoyarsk Time (KRAT) is the time zone seven hours ahead of UTC (UTC+07:00) and 4 hours ahead of Moscow Time (MSK+4). KRAT is the official time zone for central and east Siberian regions of Krasnoyarsk Krai, Kemerovo Oblast, Khakassia and Tuva.

Novosibirsk Oblast used this time zone until 1993, when it was known as Novosibirsk Time (NOVT/NOVST). The Russian government renamed the time zone shortly after Novosibirsk opted for another time zone instead.

Irkutsk Time (IRKT) is the time zone eight hours ahead of UTC (UTC+08:00) and 5 hours ahead of Moscow Time (MSK+5).

The time zone covers Buryatia and Irkutsk Oblast.

In March 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated for nearly two months until a catastrophic, major explosive eruption took place on May 18, 1980, at 8:32 a.m. The eruption, which had a volcanic explosivity index of 5, was the first to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California. It has often been considered the most disastrous volcanic eruption in U.S. history.

The eruption was preceded by a series of earthquakes and steam-venting episodes caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain's north slope. An earthquake at 8:32:11 am PDT (UTC−7) on May 18, 1980, caused the entire weakened north face to slide away, a sector collapse which was the largest subaerial landslide in recorded history. This allowed the partly molten rock, rich in high-pressure gas and steam, to suddenly explode northward toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the landslide. An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in eleven U.S. states and various Canadian provinces. At the same time, snow, ice, and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly 50 miles (80 km; 260,000 ft) to the southwest. Less severe outbursts continued into the next day, only to be followed by other large, but not as destructive, eruptions later that year. The thermal energy released during the eruption was equal to 26 megatons of TNT.

The 2010 Haiti earthquake was a catastrophic magnitude 7.0 M_w earthquake that struck Haiti at 16:53 local time (21:53 UTC) on Tuesday, 12 January 2010. The epicenter was near the town of Léogâne, Ouest department, approximately 25 kilometres (16 mi) west of Port-au-Prince, Haiti's capital.

By 24 January, at least 52 aftershocks measuring 4.5 or greater had been recorded. An estimated three million people were affected by the quake. Death toll estimates range from 100,000 to about 160,000; the Haitian government estimated the death toll to range from 220,000 to 316,000, although these figures are a matter of some dispute. The earthquake is the deadliest natural disaster of the 21st century for a single country. The government of Haiti estimated that 250,000 residences and 30,000 commercial buildings had collapsed or were severely damaged. Haiti's history of national debt, prejudicial trade policies by other countries, and foreign intervention into national affairs contributed to the existing poverty and poor housing conditions that increased the death toll from the disaster.

The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts and solar flares.

Fermi, named for high-energy physics pioneer Enrico Fermi, was launched on 11 June 2008 at 16:05 UTC aboard a Delta II 7920-H rocket. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden, becoming the most sensitive gamma-ray telescope on orbit, succeeding INTEGRAL. The project is a recognized CERN experiment (RE7).

GRB 030329 was a gamma-ray burst (GRB) that was detected on 29 March 2003 at 11:37 UTC. A gamma-ray burst is a highly luminous flash associated with an explosion in a distant galaxy and producing gamma rays, the most energetic form of electromagnetic radiation, and often followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, and radio). GRB 030329 was the first burst whose afterglow definitively exhibited characteristics of a supernova, confirming the existence of a relationship between the two phenomena.

A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time (UT1), which varies due to irregularities and long-term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972. Since then, 27 leap seconds have been added to UTC, with the most recent occurring on December 31, 2016. All have so far been positive leap seconds, adding a second to a UTC day; while a negative leap second is theoretically possible, it has not yet occurred.

Because the Earth's rotational speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and not precisely predictable. The decision to insert a leap second is made by the International Earth Rotation and Reference Systems Service (IERS), typically about six months in advance, to ensure that the difference between UTC and UT1 does not exceed ±0.9 seconds.

Juno is a NASA space probe orbiting the planet Jupiter. Built by Lockheed Martin and operated by NASA's Jet Propulsion Laboratory, the spacecraft was launched from Cape Canaveral Air Force Station on August 5, 2011 UTC, as part of the New Frontiers program. Juno entered a polar orbit of Jupiter on July 5, 2016, UTC, to begin a scientific investigation of the planet. After completing its mission, Juno was originally planned to be intentionally deorbited into Jupiter's atmosphere, but has since been approved to continue orbiting until contact is lost with the spacecraft, but it is scheduled to be shut down per the FY2026 budget proposed by the second Donald Trump administration. However, if Juno mission receives a third mission extension, it will continue to explore Jupiter for another three years to study Jovian rings and inner moons area which is not well explored; this phase will also include close flybys of the moons Thebe, Amalthea, Adrastea, and Metis.

Juno's mission is to measure Jupiter's composition, gravitational field, magnetic field, and polar magnetosphere. It also searches for clues about how the planet formed, including whether it has a rocky core, the amount of water present within the deep atmosphere, mass distribution, and its deep winds, which can reach speeds up to 620 km/h (390 mph).

Time in North Korea, called Pyongyang Time (PYT; Korean: 평양시간) or Standard Time of the Democratic People's Republic of Korea (조선민주주의인민공화국 표준시간; 朝鮮民主主義人民共和國標準時間), is since May 2018 equal to Korea Standard Time: 9 hours ahead of UTC (UTC+09:00). Like South Korea, North Korea does not currently observe daylight saving time. Time keeping in North Korea is under the State Commission for Science and Technology.

On 11 March 2011, at 14:46:24 JST (05:46:24 UTC), a M_w 9.0–9.1 undersea megathrust earthquake occurred in the Pacific Ocean, 72 km (45 mi) east of the Oshika Peninsula of the Tōhoku region. It lasted approximately six minutes and caused a tsunami. It is sometimes known in Japan as the "Great East Japan Earthquake" (東日本大震災, Higashi Nihon Daishinsai), among other names. The disaster is often referred to by its numerical date, 3.11 (read San ten Ichi-ichi in Japanese).

It was the most powerful earthquake ever recorded in Japan, and the fourth most powerful earthquake recorded in the world since modern seismography began in 1900. The earthquake triggered powerful tsunami waves that may have reached heights of up to 40.5 meters (133 ft) in Miyako in Tōhoku's Iwate Prefecture, and which, in the Sendai area, traveled at 700 km/h (435 mph) and up to 10 km (6 mi) inland. Residents of Sendai had only eight to ten minutes of warning, and more than a hundred evacuation sites were washed away. The snowfall which accompanied the tsunami and the freezing temperature hindered rescue works greatly; for instance, Ishinomaki, the city with the most deaths, was 0 °C (32 °F) as the tsunami hit. The official figures released in 2021 reported 19,759 deaths, 6,242 injured, and 2,553 people missing, and a report from 2015 indicated 228,863 people were still living away from their home in either temporary housing or due to permanent relocation.

Exploration Flight Test-1 or EFT-1 (previously known as Orion Flight Test 1 or OFT-1) was a technology demonstration mission and the first flight test of the crew module portion of the Orion spacecraft. Without a crew, it was launched on December 5, 2014 at 12:05 UTC (7:05 am EST, local time at the launch site) by a Delta IV Heavy rocket from Space Launch Complex 37B at the Cape Canaveral Air Force Station.

The mission was a four-hour, two-orbit test of the Orion crew module featuring a high apogee on the second orbit and concluding with a high-energy reentry at around 8.9 kilometers per second (20,000 mph). This mission design corresponds to the Apollo 2/3 missions of 1966, which validated the Apollo flight control system and heat shield at re-entry conditions planned for the return from lunar missions.

STS-130 (ISS assembly flight 20A) was a NASA Space Shuttle mission to the International Space Station (ISS). Space Shuttle Endeavour's primary payloads were the Tranquility module and the Cupola, a robotic control station with six windows around its sides and another in the center, providing a 360-degree view around the station. Endeavour launched at 04:14 EST (09:14 UTC) on February 8, 2010, and landed at 22:22 EST on February 21, 2010, on runway 15 at the Kennedy Space Center's Shuttle Landing Facility.

Armenia Time (AMT) is a time zone used in Armenia. It is four hours ahead of UTC at UTC+04:00.

Clock time is about one hour later than solar noon in Armenia. Consequently, population activity hours are similar to those in Paris or Barcelona, which have about the same shift to solar time. They are about one hour later compared to those in Berlin and Vienna, and are two hours later than those in Warsaw and New York.