Orders of magnitude (time)

An order of magnitude of time is (usually) a decimal prefix or decimal order-of-magnitude quantity together with a base unit of time, like a microsecond or a million years. In some cases, the order of magnitude may be implied (usually 1), like a 'second' or 'year'. In other cases, the quantity name implies the base unit, like 'century'. In most cases, the base unit is seconds or years. Prefixes are not usually used with a base unit of years, so we say 'a million years', not 'a megayear'. Clock time and calendar time have duodecimal or sexagesimal orders of magnitude rather than decimal, i.e. a year is 12 months, and a minute is 60 seconds.centisecond1.6667 cs period of a frame at a frame rate of 60 Hz. 2 cs: cycle time for European 50 Hz AC electricitydecisecond(1 das = 10 s)7.1 hs(11 m 50 s): time for a human walking at average speed of 1.4 m/s to walk 1 kilometre(1 ks = 16 min 40 s = 1,000 s)1.8 ks: time slot for the typical situation comedy on television with advertisements included 3.6 ks: one hour (h), time for the minute hand of a clock to cycle once around the face, approximately 1/24 of one mean solar day7.2 ks (2 h): typical length of feature films86.399 ks (23 h 59 min 59 s): one day with a removed leap second on UTC time scale. Such has not yet occurred.86.4 ks (24 h): one day of Earth by standard. More exactly, the mean solar day is 86.400 002 ks due to tidal braking, and increasing at the rate of approximately 2 ms/century; to correct for this time standards like UTC use leap seconds with the interval described as 'a day' on them being most often 86.4 ks exactly by definition but occasionally one second more or less so that every day contains a whole number of seconds while preserving alignment with astronomical time. The hour hand of an analogue clock will typically cycle twice around the dial in this period as most analogue clocks are 12 hour, less common are analogue 24-hour clocks in which it cycles around once.86.401 ks (24 h 0 min 1 s): one day with an added leap second on UTC time scale. Note that while this is strictly 24 hours and 1 second in conventional units, a digital clock of suitable capability level will most often display the leap second as 23:59:60 and not 24:00:00 before rolling over to 00:00:00 the next day, as though the last 'minute' of the day were crammed with 61 seconds and not 60, and similarly the last 'hour' 3601 s instead of 3600.88.775 ks (24 h 39 min 35 s): one sol of Mars604.8 ks (7 d): one week of the Gregorian calendar(1 Ms = 11 d 13 h 46 min 40 s = 1,000,000 s)2.36 Ms (27.32 d): length of the true month, the orbital period of the Moon2.419 2 Ms (28 d): length of February, the shortest month of the Gregorian calendar2.592 Ms (30 d): 30 days, a common interval used in legal agreements and contracts as a proxy for a month2.678 4 Ms (31 d): - length of the longest months of the Gregorian calendar23 Ms (270 d): approximate length of typical human gestational period31.557 6 Ms (365.25 d): length of the Julian year, also called the annum, symbol a.31.558 15 Ms (365 d 6 h 9 min 10 s): length of the true year, the orbital period of the Earth126.232 6 Ms (1641 d 0 h 34 min 40 s): the elected term of the President of the United States or one Olympiad(1 Gs = over 31 years and 287 days = 1,000,000,000 s)2.5 Gs: (79 a): typical human life expectancy in the developed world3.16 Gs: (100 a): one century31.6 Gs: (1000 a, 1 ka): one millennium, also called a kilo-annum (ka)63.8 Gs: approximate time since the beginning of the Anno Domini era as of 2019 - 2,019 years, and traditionally the time since the birth of Jesus Christ194.67 Gs: Approximate lifespan of time capsule Crypt of Civilization, 28 May 1940 - 28 May 8113363 Gs: (11.5 ka): time since the beginning of the Holocene epoch814 Gs: (25.8 ka): approximate time for the cycle of precession of the Earth's axis(1 Ts = over 31,600 years = 1,000,000,000,000 s)31.6 Ts (1000 ka, 1 Ma): one mega-annum (Ma), or one million years79 Ts (2.5 Ma): approximate time since earliest hominids of genus Australopithecus130 Ts (4 Ma): the typical lifetime of a biological species on Earth137 Ts (4.32 Ma): the length of the mythic unit of mahayuga, the Great Age, in Hindu mythology.7.9 Ps (250 Ma): approximate time since the Permian-Triassic extinction event, the actually largest known mass extinction in Earth history which wiped out 95% of all extant species and believed to have been caused by the consequences of massive long-term volcanic eruptions in the area of the Siberian Traps. Also, the approximate time to the supercontinent of Pangaea. Also, the length of one galactic year or cosmic year, the time required for the Sun to complete one orbit around the Milky Way Galaxy.16 Ps (510 Ma): approximate time since the Cambrian explosion, a massive evolutionary diversification of life which led to the appearance of most existing multicellular organisms and the replacement of the previous Ediacaran biota. 22 Ps (704 Ma): approximate half-life of the uranium isotope 235U.31.6 Ps (1000 Ma, 1 Ga): one giga-annum (Ga), one billion years, the largest fixed time unit used in the standard geological time scale, approximately the order of magnitude of an eon, the largest division of geological time.+1 Ga: The estimated remaining habitable lifetime of Earth, according to some models. At this point in time the stellar evolution of the Sun will have increased its luminosity to the point that enough energy will be reaching the Earth to cause the evaporation of the oceans and their loss into space (due to the uv flux from the Sun at the top of the atmosphere dissociating the molecules), making it impossible for any life to continue.136 Ps (4.32 Ga): The length of the legendary unit kalpa in Hindu mythology, or one day (but not including the following night) of the life of Brahma.143 Ps (4.5 Ga): The age of the Earth by our best estimates. Also the approximate half-life of the uranium isotope 238U.315 Ps (10 Ga): approximate lifetime of a main-sequence star similar to our Sun.435 Ps (13.8 Ga): The approximate age of the Universe1.08 Es (+34 Ga): time to the Big Rip according to some models, but this is not favored by existing data. This is one possible scenario for the ultimate fate of the Universe. Under this scenario, dark energy increases in strength and power in a feedback loop that eventually results in the tearing apart of all matter down to subatomic scale due to the rapidly increasing negative pressure thereupon300 - 600 Es (10 000 - 20 000 Ga): The estimate lifetime of low-mass stars (red dwarfs)9.85 Zs (311 000 Ga): The entire lifetime of Brahma in Hindu mythology.1.310 019 × 1012 Ys (4.134 105 × 1028 years) – The time period equivalent to the value of 13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.13.0.0.0.0 in the Mesoamerican Long Count, a date discovered on a stela at the Coba Maya site, believed by archaeologist Linda Schele to be the absolute value for the length of one cycle of the universe2.6 × 1017 Ys (8.2 × 1033 years) – the smallest possible value for proton half-life consistent with experiment An order of magnitude of time is (usually) a decimal prefix or decimal order-of-magnitude quantity together with a base unit of time, like a microsecond or a million years. In some cases, the order of magnitude may be implied (usually 1), like a 'second' or 'year'. In other cases, the quantity name implies the base unit, like 'century'. In most cases, the base unit is seconds or years. Prefixes are not usually used with a base unit of years, so we say 'a million years', not 'a megayear'. Clock time and calendar time have duodecimal or sexagesimal orders of magnitude rather than decimal, i.e. a year is 12 months, and a minute is 60 seconds. The smallest meaningful increment of time is the Planck time, the time light takes to traverse the Planck distance, many decimal orders of magnitude smaller than a second. The largest realized amount of time, given known scientific data, is the age of the universe, about 13.8 billion years - the time since the Big Bang as measured in the cosmic microwave background rest frame. Those amounts of time together span 60 decimal orders of magnitude. Metric prefixes are defined spanning 10−24 to 1024, 48 decimal orders of magnitude which may be used in conjunction with the metric base unit of second. Metric units of time larger than the second are most commonly seen only in a few scientific contexts such as observational astronomy and materials science although this depends on author; for everyday usage and most other scientific contexts the common units of minutes (60 s), hours (3600 s or 3.6 ks), days (86 400 s), weeks, months, and years (of which there are a number of variations) are commonly used. Weeks, months and years are significantly variable units whose length crucially depends on the choice of calendar and is often not regular even with a calendar, e.g. leap years versus regular years in the Gregorian calendar. This makes them problematic for use against a linear and regular time scale such as that defined by the SI since it is not clear as to which version of these units we are to be using. Because of this, in the table below we will not use weeks and months and the year we will use is the Julian year of astronomy, or 365.25 days of 86 400 s exactly, also called an annum and denoted with the symbol a, whose definition is based on the average length of a year of the Julian calendar which had one leap year every and always every 4 years against common years of 365 days each. This unit is used, following the convention of geological science, to form larger units of time by the application of SI prefixes to it at least up to giga-annum, or Ga, equal to 1 000 000 000 a (short scale: one billion years, long scale: one milliard years).