A
yeir
(frae
Auld Inglis
g?ar
;
Gothic
j?r
;
Runic
j?ran
) is a
unit
o
time
based on tha
orbital period
o tha
Yird
movin aroond tha
Sun
. Fur an observer at is oan tha Yird, thes corresponds tae tha period it taes tha sun tae complete a bodie coorse throoghit tha
Zodiac
alang tha
ecliptic
. In
astronomy
, tha
Julian year
is a unit o time at is defined as 365.25
days
o
86
400
SI seconds
each (nae
lowp seconds
).
Internaitional Astronomical Union
"
SI units
" accessed Februar 18, 2010. (see table fife an section fife.15.) reprintit frae
George A. Wilkins
& IAU commission fife,
"The IAU Style Manual (1989)"
(PDF file) in
IAU Transactions
vol. xxb Thaur is nae universally acceptit seembol fur the year as a unit o time. The
Internaitional Seestem o Units
disnae propose a bodie. A common abbreviation in internaitional uisage is
a
(fur the
Laitin
wird
annus
), in
Scots
an
Inglis
an aw
y
or
yr
. Due tae the Yird's
axial kelter
, the coorse o a year sees the passin o the
saisons
, merked bi varioos changes in
weaither
, hoors o
daylicht
, an consequently
vegetation
an
fertility
. In
temperate
an
subpolar
regions, generally fower
saisons
ur recognised:
ware
,
simmer
,
hairst
an
winter
, each wi different
temperatur
an
wather
, astronomically merked bi the sun reachin the pynts o
equinox
an
solstice
—althoogh the climatic saisons
lag
behind thair astronomical markers. In some
tropical
an
subtropical
regions it is mair common tae spick o the
rainy
(ur dreich, or
monsuin
) saison versus the
dry saison
. A
calendar year
is an approximation o the Yird's orbital period in a gien
calendar
. A calendar year in the
Gregorian calendar
(as weel as in the
Julian calendar
) haes aither 365 (
common years
), or 366 (
lowp years
) days. The wird "year" is an aw uised o periods loosely associatit but nae strictly identical wi aither the astronomical or the calendar year, sic as the
saisonal year
, the
fiscal year
or the
academic year
, etc. Bi extension, the term
year
can pure techt the orbital period o onie
planit
: fur example, a "Maurtian year" is the time in which
Maurs
completes its ain orbit. The term is an aw applied mair broadly tae onie lang period or cycle, sic as the "
great year
".
oed
, s.v. "year", entry tae.b.: "
transf.
Applied tae a huir uv a lang period or cycle (in
chronology
an
mythology
, an vaguely in
poetic
uise)."
The year is aft dividit intae twal consecutive periods o time cried
months
:
Januar
,
Februar
,
Mairch
,
Apryle
,
Mey
,
Juin
,
Julie
,
Augist
,
September
,
October
,
November
, an
Dizember
.
Further information:
j?ran
West saxon
gear
(
j?ar
),
Anglian
g?r
continues
Proto-Germanic
*j?ram
(
*j
?2ram
).
Cognates
ur
German
jahr
,
auld high german
jar
,
auld norse
ar
an
Gothic
jer
, aw frae a
pie
*y?rom
("year" or "saison"). Cognates ootwith o Germanic or
Avestan
yare
("year"),
ancient Greek
?ρα
("year", "saison", or "period o time"), whence "
hoor
",
auld kirk slavonic
jaru
an
Laitin
hornus
("o thes year"). Laitin
annus
(a
2nt declension
masculine
noon
);
annum
is the
accusatife singular
;
anni
is
genitife
singular
an
nominatife
plural
;
anno
is the datife an ablatife singular) is frae a
pie
noin
*at-no-
, which yielded
Gothic
aþnam
("year") an aw. Baith
*y?-ro-
an
*at-no-
ur based oan verbal ruits fur expressin movement—
*at-
an
*ey-
, respectively—baith meanin "tae go" fur ordinar. The Greek wird fur "year",
?το?
, is cognate wi Laitin
vetus
("old"), frae peh
*wetus-
("year"), preserved in thes meanin in
sanskrit
vat-sa-
("yearlin cauf") an
vat-sa-ras
("year") an aw. Derived frae the Laitin
annus
ur a nummer o Scots wirds, sic as
annual
,
annuity
,
anniversary
, etc.;
per annum
means "each year".
A
saisonal yeir
is the time atween successife recurrences o a
saisonal
event, sic as the
fluidin
o a river, the
migration
o a
species
o
spyug
, the
flouerin
o a species o
plaunt
, the first
frost
o the yeir, or the first scheduled gam o a certaint
sport
. Aw thir events can hae wide variations o mair nor a
month
frae yeir tae yeir.
A
calendar yeir
is the time atween tois dates wi the sam nam in a
calendar
. A half-year (ain half o a year) main rin frae Januar tae
Juin
, or
Julie
tae
Dizember
. No astronomical yeir haes an
integer
nummer
o days or lunar months, sae onie calendar at follows an astronomical yeir main hae a system o
intercalation
sic as
lowp years
. Financial an scienteefic calculations aft uise a 365-day calendar tae simplify daily rates. In the
Julian calendar
, the average lenth o a yeir is 365.25 days. In a non-lowp yeir, thaur ur 365 days; in a
lowp yeir
, thaur ur 366 days. A lowp yeir occurs aboot every fower yeirs. The
Gregorian calendar
attempts tae keep the
northward equinox
oan or shortly afair Mairch 21, hence it follows the
northward equinox year
. The pure techt lenth o the yeir is
365.2425
days (as 97 it o 400 yeirs or lowp yeirs); thes is within a bodie
ppm
o the current lenth o the pure techt
tropical yeir
(
365.242
19
days). It is estimatit at bi the yeir 4000, the northward equinox will faa back bi a bodie day in the Gregorian calendar, nae coz o thes difference, but coz o the slowin doon o the Yird's rotation an the associatit lengthenin o the
Sidereal day
. The
Revised Julian calendar
, as uised in some
Eastern Orthodox churches
, an aw tries tae synchronize wi the tropical yeir. The average lenth o thes calendar's yeir is
365.242
222
days (as 218 it o 900 year or lowp yeirs). Gregorian an revised Julian calendars will stairt tae differ in 2800. The
persian calendar
, in uise in
Afghanistan
an
Iran
, haes its yeir begin oan the day o the northward equinox as determined bi astronomical computation (fur the time zain o
tehran
), as opposed tae uisin an algorithmic system o lowp yeirs.
A
calendar era
is uised tae assign a
nummer
tae each individual yeir, uisin a reference pynt in the pest as the beginnin o the era. In mony coontries, the maist common era is frae the tradeetional (thoogh noo believed incorrect) yeir o the birth o
Jesus
. Dates in thes era ur designatit as
anno domini
(Laitin fur "in the yeir o the Lord"), abbreviatit AD (fur
Anno Domini
) or CE (fur "
common era
"). The yeir afair yin AD or CE is designatit yin "
befair Christ
" (BC) or "befair the common era" (BCE); the yeir afair at tae BC; etc. Hence thaur wisnae
year 0
AD/CE. When the computations involvin yeirs ur dain involvin baith yeirs AD an years BC, it is common tae uise
astronomical yeir nummerin
, in which yin BC is designatit "0", tae BC is designatit "?1", an sae oan. Ither eras ur an aw uised tae enumerate the yeirs in different cultural, religioos, an scienteefic contexts.
A
fiscal year
or financial year is a 12-month period uised fur calculatin annual financial statements in businesses an ither organisations. In mony jurisdictions, regulations regardin accoontin require sic reports ance per twal months, but dinnae require at the twal months constitute a calendar year. Fur example, in
Canada
an
Indie
the fiscal year runs frae
Apryle
1; in the
Unitit Kinrick
it runs frae Apryle yin fur purposes o corporation tax an government financial statements, but frae Apryle sex fur purposes o personal taxation an payment o state benefits; in
Australia
it runs frae Julie 1, while in the
Unitit States
, the fiscal year o the
federal government
runs frae
October
yin.
An academic year is the annual period durin which a student attends an
eddicational
institution
. The academic year main be dividit intae
academic terms
, sic as semesters an quarters. Some
schuils
in the UK an USA divide the academic year intae
three
rooghly equal-lenth terms (cried "trimesters" or "quarters" in the US), rooghly coincidin wi hairst, winter, an ware. At some, a shortened
simmer
session, whiles considered a pairt o the regular academic year, is attended bi students oan a voluntary or electife basis. Ither schuils break the year intae
twa
main semesters, a first (teepically
Augist
ben Dizember) an a second semester (Januar ben
Mey
). Each o thir main semesters main be split in half bi mid-term examinaitions, an each o the halves is referred tae as a "
quarter
" (or "term" in some coontries). Thaur main an aw be an electife simmer session and/ur a cuttie Januar session. Some ither schuils, includin some in the Unitit States, hae
foor
eddicational periods o markin. The skale year in mony coontries starts in Augist or
September
an ends in Mey, Juin, or Julie. Some schuils in the Unitit States, notably
Boston Laitin Schuil
, main divide the year intae
fife or mair
markin periods. Some state in defence o thes at thaur is aiblins a
positife correlation
atween report frequency an academic achievement. Thaur ur teepically 180 days o teachin each year in schuils in the usa, excludin weekends an breaks, while 190 days fur pupils in state schuils in the Unititd Kinrick,
New Zealain
an Canada an aw. Tho, in
Indie
, the academic year normally starts frae Juin yin an ends oan Mey 31. Thocht schuils stairt closin in the end o
ware
, the actual academic closure is oan Mey 31, an in
Nepal
it starts frae Julie 15.
[
citation needit
]
schuils an varsities in australia teepically hae academic years at rooghly align wi the calendar year (i.e. startin in
Februar
or
Mairch
an endin in October tae Dizember), as the
soothern hemisphaur
experiences simmer frae Dizember tae Februar. In
Israel
, the academic year begins aroond October or
November
, aligned wi the second month o the
Hebrew calendar
.
The
Julian year
, as uised in
astronomy
an ither sciences, is a unit o time defined as exactly 365.25 days. Thes is the normal meanin o the unit "year" (seembol "a" frae the
Laitin
annus
) uised in varioos scienteefic contexts. The Julian century o
36
525
days an the Julian millennium o
365
250
days ur uised in astronomical calculations. Fundamentally, expressin a time interval in Julian years is a wey tae precisely specify hoo mony days (nae hoo mony "real" years), fur lang time intervals whaur statin the nummer o days woods be unwieldy an unintuitife. Bi convention, the Julian year is uised in the computation o the distance covered bi a
lichtyear
. In the
unified code fur units o measure
, the seembol
a
(withit
subscript
) aye refers tae the Julian year
aj
o exactly
31
557
600
seiconts
. 365.25 days o
86
400
seconds = yin a = yin aj =
31.557
6
ms the SI multiplier prefixes main be applied tae it tae f'rm
ka
(kiloannum),
ma
(megaannum) etc.
Sidereal, tropical, an anomalistic years
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Each o thir three year can be luisely cried an "astronomical year". The
sidereal year
is the time taen fur the Yird tae complete a bodie revolution o its
orbit
, as measured against a fixed fram o reference (sic as the fixed stars, Laitin
sidera
, singular
sidus
). Its average duration is
365.256
363
004
pure techt solar days (365 d sex h 9 min 9.76 s) (at the epoch
j2000.0
= Januar yin, 2000, 12:00:00
tt
). Internaitional Yird rotation and reference system service. (2010).
iers eop pc uiseful constants.
the
tropical year
is the period o time fur the
ecliptic longitude
o the sun tae increase bi 360 degrees. Syne the sun's ecliptic longitude is measured wi respect tae the equinox, the tropical year comprises a complete cycle o the saisons; coz o the biological an socio-economic importance o the saisons, the tropical year is the basis o maist
calendars
. The tropical year is commonly defined
[1]
fur the pure techt motion o the sun alang the ecliptic. Thes differs frae the actual time atween passages o, e.g., the
northward equinox
fur several reasons explained ablo. Coz o the Yird's
axial precession
, thes year is abit 20
meenits
shorter than the Sidereal year. The pure techt tropical year is approximately 365 days, fife hoors, 48 meenits, 45 seconds
[2]
(=
365.242
19
days). The anomalistic year is the time taen fur the Yird tae complete a bodie revolution wi respect tae its
apsides
. The orbit o the Yird is
elliptical
; the extreme pynts, cried "
apsides
", or the
perihelion
?whaur the Yird is closest tae the sun (aboot 3 Januar in 2011)?an the
aphelion
, whaur the Yird is farthest frae the sun (Julie fuir in 2011). The anomalistic year is uisually defined as the time atween perihelion passages. Its average duration is
365.259
636
days (365 d sex h 13 min 52.6 s) (at the epoch j2011.0).
[3]
if Yird moved in an ideal
kepler orbit
,
i.e.
a perfect ellipse wi the sun fixed at a bodie focus, each kin o year woods aye hae the sam duration, an the sidereal an anomalistic years woods be equal. Coz o
perturbations
bi the
gravity
o ither planits, Yird's motion varies slichtly, causin the sidereal an tropical years tae vary in lenth bi abit 25 meenits (see the table ablo). Baith ur affectit in the sam wey, sae at the sidereal year is consistently 20 meenits langer than the tropical year, providit at thay ur measured in huir uv a sam wey.
The draconic year, draconitic year, eclipse year, or ecliptic year is the time taen fur the sun (as seen frae the Yird) tae complete a bodie revolution wi respect tae the sam
lunar node
(a pynt whaur the
muin
's orbit intersects the
ecliptic
). Thes period is associatit wi
eclipses
: thir occur anly when baith the sun an the muin ur near thir nodes; sae eclipses occur within abit a month o every half o an eclipse year. Hence, thaur ur tois
eclipse saisons
every eclipse year. The average duration o the eclipse year is:
346.620
075
883
days (346 d 14 h 52 min 54 s) (at the epoch j2000.0). This term is whiles erroneoosly uised fur the draconic or nodal period o
lunar precession
; at is, the period o a complete revolution o the muin's ascendin node aroond the ecliptic:
18.612
815
932
Julian years (
6
798.331
019
days, at the epoch j2000.0).
The
full muin cycle
is the time fur the sun (as seen frae the Yird) tae complete a bodie revolution wi respect tae the
perigee
o the orbit o the muin. Thes period is associatit wi the apparent size o the
full muin
, an wi the varyin duration o the
synodic month
an aw. The duration o a bodie foo muin cycle is: :
411.784
430
29
days (411 d 18 h 49 min 34 s) (at the epoch j2000.0).
The
lunar year
comprises twal foo cycles o the phases o the muin, as seen frae the Yird. It haes a duration o approximately 354.37 days.
Muslims
uise thes fur celebratin thair
eids
an fur markin the stairt o the fastin month o
Ramadan
. A Musleem calender year is based oan the
lunar cycle
.
The "vague year", frae
annus vagus
("wanderin year"), is an integral approximation tae the year equalin 365 days, which wanders in relation tae mair exact years. teepically, the vague year is dividit intae 12
schematic
months o 30 days each plus fife
epagomenal
days. Thes "vague year" wis uised in the calendars o
ancient Egyp
,
Iran
,
Armenie
an in
mesoamerica
amang the
Aztecs
an
Maya
.
calendar description an coordinaition
Maya Warld Studies Center.
A
heliacal year
is the interval atween the
heliacal risins
o a staurn. It differs frae the
sidereal year
fur stars awa frae the
ecliptic
due mainly tae the
precession o the equinoxes
.
The
Sothic year
is the interval atween heliacal risins o the staurn
sirius
. It is presently less nor the
sidereal year
an its duration is huir uv a close tae the pure techt Julian year o 365.25 days.
The
Gaussian year
is the sidereal year fur a
planit
o negligible mass (relatife tae the sun) an unperturbed bi ither planits at is governed bi the
Gaussian gravitational constant
. Sic a planit woods be slichtly closer tae the sun than the Yird's pure techt distance. Its lenth is: :
365.256
898
3
days (365 d sex h 9 min 56 s).
The
Besselian year
is a tropical year at starts when the (fictitioos) pure techt sun reaches an ecliptic longitude o 280°. Thes is currently oan or close tae Januar yin. It wis named efter the
19th century
German astronomer an mathematician
Friedrich Bessel
. The followin
equation
can be uised in irder tae compute the current besselian epoch (in years):
[4]
b = 1900.0 + (Julian datett ?
2
415
020.313
52
) /
365.242
198
781
the "tt"
subscript
indicates at fur thes
formula
, the Julian date shoods uise the
terrestrial time
scale or its predecessur,
ephemeris time
.
Variation in the lengths o the year an the day
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Template:Refimprove section
The exact lenth o an astronomical year changes ower time.
the astronomical almanac online
Archived
2017-08-19 at the
Wayback Machine
[
nae in citation given
]
the main soorces o thes chynge are:
- The poseetions o the equinox an solstice pynts wi respect tae the apsides o Yird's orbit chynge: the first coz o
precession
, an the apsides coz o the long-term effects o gravitational pull bi the ither planits. Syne the speed o the Yird varies accordin tae its poseetion in its orbit as measured frae its
perihelion
, Yird's speed when in a solstice or equinox pynt changes ower time: if sic a pynt moves toward
perihelion
, the interval atween tois passages decreases a bit frae year tae year; if the pynt moves towards
aphelion
, en at period inreases a bit frae year tae year. Sae a "tropical year" measured frae a bodie passage o the northward ("vernal") equinox tae the neist, it differs frae the a bodie measured atween passages o the soothward (hairst) equinox. The average ower the foo orbit disnae chynge coz o thes, sae the lenth o the average tropical year disnae chynge coz o thes second-order effect.
- Each planit's movement is perturbed bi the gravity o every ither planit. Thes leids tae short-term fluctuations in its speed, an therefair its period frae year tae year. Mairowre, it haes caused long-term changes in its orbit, an therefair long-term changes in thir periods an aw.
- Tidal drag
atween the Yird an the muin (an sun) increases the lenth o the day an o the month (bi transferrin angular momentum frae the rotation o Yird tae the revolution o the muin); syne the apparent pure techt solar day is the unit wi which we measure the lenth o the year in civil life, the lenth o the year appears tae decrease. The rotation rate o the Yird is changed an aw bi factors sic as
post-glacial reboond
an sea level rise.
Numerical value o year variation
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Mean year lenths in thes section ur calculatit fur
2000
, an differences in year lenths compared tae 2000 ur gien fur pest an future years. In the tables a day is 86,400 SI seconds lang.
[5]
[6]
[7]
[8]
Mean year lenths fur 2000
Teep o year
|
days
|
hoors
|
meenits
|
seconds
|
tropical
|
365
|
5
|
48
|
45
|
sidereal
|
365
|
6
|
9
|
10
|
anomalistic
|
365
|
6
|
13
|
53
|
eclipse
|
346
|
14
|
52
|
55
|
Lenth o year: difference frae 2000 in seconds
(anly
positive
when lenth fur tabulatit year is greater than the lenth fur 2000)
Year
|
Tropical
|
Sidereal
|
Anomalistic
|
Eclipse
|
?4000
|
?8
|
?45
|
?15
|
?174
|
?2000
|
4
|
?19
|
?11
|
?116
|
0
|
7
|
?4
|
?5
|
?57
|
2000
|
0
|
0
|
0
|
0
|
4000
|
?14
|
?3
|
5
|
54
|
6000
|
?35
|
?12
|
10
|
104
|
- 346.62 days: a
draconitic year
.
- 353, 354, or 355 days: the lenths o common years in some
lunisolar calendars
.
- 354.37 days (12 lunar months): the average lenth o the years in
lunar calendars
, notably the musleem calendar.
- 365 days: a vague year ane a
common year
in mony
solar calendars
.
- 365.242
19
days: a pure techt tropical year (roonded tae fife decimal places) fur the
epoch
2000
.
- 365.242
4
days: a vernal equinox year (roonded tae fower decimal places) fur the epoch 2000.
- 365.242
5
days: the average lenth o a year in the Gregorian calendar.
- 365.25 days: the average lenth o a year in the Julian calendar.
- 365.256
4
days: a sidereal year.
- 366 days: a
lowp year
in mony solar calendars.
- 383, 384, or 385 days: the lenths o lowp years in some lunisolar calendars.
- 383.9 days (13 lunar months): a lowp year in some lunisolar calendars. An average Gregorian year is
365.242
5
days
=
52.177
5
weeks
=
8
765.82
hoors
=
525
949.2
meenits
=
31
556
952
seiconts
(mean solar, nae si). A common year is 365 days =
8
760
hoors =
525
600
meenits =
31
536
000
seconds. A lowp year is 366 days =
8
784
hoors =
527
040
meenits =
31
622
400
seconds. The 400-year cycle o the Gregorian calendar haes
146
097
days, an hence exactly
20
871
weeks
.
Thaur is nae universally acceptit seembol fur the year as a unit o time. The
Internaitional Seestem o Units
disnae propose a bodie. Nist sp811
[9]
an ISO 80000-3:2006
[10]
suggest the seembol
a
, taen frae the Laitin wird
annus
.
[11]
in Scots, the abbreviations "y" an "yr" ur whiles uised, specifically in
geology
an
paleontology
, whaur "kyr, myr, byr" (thoosands, millions, an even billions o years, respectively) an seemilar abbreviations ur uised tae denote intervals o time remote frae the present.
[12]
Nist sp811
[13]
an ISO 80000-3:2006
[14]
suggest the seembol
a
(in the
Internaitional Seestem o Units
, althoogh
a
is the seembol an aw fur the
are
, the unit o aurie uised tae measure lain aurie, but context is uisually enaw tae disambiguate). The abbreviations
y
an
yr
ur uised an aw. The
unified code fur units o measure
[15]
disambiguates the varyin symbologies of ISO 1000, ISO 2955 an ansi x3.50
[16]
bi usin :
ar
fur
are
and: :
at
= a_t =
365.242
19
days fur the pure techt
tropical year
:
aj
= a_j = 365.25 days fur the pure techt Julian year :
ag
= a_g =
365.242
5
days fur the pure techt
Gregorian year
:
a
= yin aj year (withit further qualifier) a definition jointly adoptit bi the
Internaitional Union o Pure an Applee'd Chemistry
(IUPAC) an the
Internaitional Union o Geological Sciences
(IUGS) is tae uise
annus
, wi seembol
a
, fur year, defined as the lenth o the tropical year in the year 2000:
[17]
[18]
:
a
=
365.242
192
65
days =
31
556
925.445
seconds the notation haes proved controversial; it conflicts wi an earlier convention amang geoscientists tae uise
a
specifically fur "years ago", an
y
or
yr
fur a period o ane year.
Fur the followin, thaur ur alternatife forms which elide the consecutife vowels, sic as
kilannum
,
megannum
, etc.
- ka
(fur kiloannum), is a
unit o time equal tae
a bodie
thoosand
(103) years. Thes is teepically uised in
geology
,
paleontology
, an
archaeology
fur
holocene
an
pleistocene
periods whaur a non-
radiocarbon datin
technique (i.e.,
ice core
datin,
dendrochronology
,
uranium-thorium datin
, or
varve
analysis) is uised as the primary datin method fur age determinaition. If age is primarily determined bi
radiocarbon datin
, en the age shoods be expressed in aither radiocarbon or calendar (calibratit) years
befair present
.
- ma
(fur megaannum), is a unit o
time
equal tae a bodie
million
(106) years. It is commonly uised in scienteefic disciplines sic as
geology
,
paleontology
, an
celestial mechanics
tae signify huir uv a lang time periods intae the pest or future. Fur example, the
dinosaur
species
tyrannosaurus rex
wis abundant approximately
65 ma
(65 million years) ago (
ago
mauna aye be mentioned; if the quantity is specified while nae explicitly discussin a duration, a bodie can assume at "ago" is implied; the alternatife "
mya
" unit includes "ago" explicitly). In astronomical applications, the year uised is the
Julian year
o precisely 365.25 days. In
geology
an
paleontology
, the year isnae sae precise an varies?dependin oan the authur.
- ga
(fur gigaannum), is a unit o time equal tae 109 year (ain
billion
oan the
short scale
, a bodie
milliard
oan the
lang scale
). It is commonly uised in scienteefic disciplines sic as
cosmology
an
geology
tae signify extremely lang time periods in the pest. Fur example, the formation o the
Yird
occurred approximately
4.57 ga
(4.57 billion years) ago.
- ta
(fur teraannum), is a unit o time equal tae 1012 year (ain
trillion
oan the cuttie scale, a bodie billion oan the lang scale). It is an extremely lang unit o time, abit 70 times as lang as the
age o the universe
. It's the sam order o magnitude as the expectit life span o a wee
red dwarf star
.
- pa
(fur petaannum), is a unit o time equal tae 1015 year (ain
quadrillion
oan the cuttie scale, a bodie billiard oan the lang scale). The
half-life
o the
nuclide
o
cadmium
-113 is abit eeecht pa.
[19]
thes seembol coincides wi at fur the
pascal
withit a multiplier prefix, thocht baith ur infrequently uised an context will normally be sufficient tae distinguish time frae pressure values.
- ea
(fur exaannum), is a unit o time equal tae 1018 year (ain
quintillion
oan the cuttie scale, a bodie trillion oan the lang scale). The half-life o
tungsten
-180 is yin.8 ea.
[20]
In
astronomy
,
geology
, an
paleontology
, the abbreviations
yr
fur "year" an
ya
fur "year ago" ur whiles uised, combined wi prefixes fur "thoosand", "million", or "billion".
[21]
The age o a stratigraphic unit or the time o a geologic event, as commonly determined bi numerical datin or bi reference tae a calibratit time-scale, main be expressed in years afair the present. The unit o time is the modren year as presently recognised warldwide. Recommended but nae mandatory abbreviations fur sic ages ur SI (Internaitional Seestem o Units) multipliers coopled wi "a" fur annum: ka, ma, an ga fur kilo-annum (103 year), mega-annum (106 year), an giga-annum (109 year), respectively. The uisin o thir terms efter the age value follows the convention established in the field o
carbon-14 datin
. The "present" refers tae 1950 ad, an sic qualifiers as "ago" or "befair the present" ur omittit efter the value coz measurement o the duration frae the present tae the pest is implicit in the designaition. In contraest, the duration o ane remote interval o geologic time, as a nummer o years, shoods nae be expressed bi the sam seembols. Abbreviations fur nummers o years, withit reference tae the present, ur cried informal (e.g.,
y
or
yr
fur "years";
mah
,
m.y.
, or
m.yr.
fur millions o years; an sae forth, as preference dictates). Fur example, boondaries o the late cretaceoos epoch currently ur calibratit at 63 ma an 96 ma, but the interval o time representit bi thes epoch is 33 m.y. thay arenae SI units, uisin
y
tae abbreviate Scots
year
, but followin ambiguoos internaitional recommendations, uise aither the standard Scots first letters as prefixes ("t", "m", an "b") or
metric prefixes
("k", "m", an "g"). Thir abbreviations include:
Non-SI abbreviation
|
SI-prefixed equivalent
|
Order o magnitude
|
kyr
|
ka
|
|
myr
|
Ma
|
|
byr
|
Ga
|
|
tya
or
kya
|
"ka ago"
|
|
mya
|
"Ma ago"
|
|
bya
or
gya
|
"Ga ago"
|
|
Uisage o "mya" an "bya" is deprecatit in modren geophysics, the recommended usage til "ma" an "ga" fur dates
befair present
, but "m.y." fur the duration o epochs. Thes
ad hoc
distinction atween "absolute" time an time intervals is somewhat controversial amongst members o the
Geological Society o America
.
[23]
note at oan graphs uisin "ya" units oan the horizontal axis time flows frae reit tae left, which main seem coonter-intuitife. If the "ya" units ur oan the vertical axis, time flows frae tap tae bottom which is probably easier tae kin than conventional notation.
The "
great year
", or
equinoctial cycle
, corresponds tae a complete revolution o the equinoxes aroond the ecliptic. Its lenth is abit 25,700 year, an cannae be determined precisely as the
precession
speed is variable.
The
galactic year
is the time it taes the Yird's
solar system
tae revolve ance aroond the
galactic center
. It comprises rooghly 230 million Yird years.
[24]
- ↑
P.K.Seidelman (ed.) (1992).
explanatory supplement to the astronomical almanac
. p. 80.
ISBN
978-1-891389-45-0
.
CS1 maint: extra text: authors leet (
link
)
[
deid airtin
]
- ↑
astronomical almanac fur the year 2011
. Washington an Taunton: U.S. Government Printin Office an the U.K. Hydrographic Office. 2009. p. m18 (glossary). Archived frae
the original
on 19 August 2017
. Retrieved
14 Mey
2013
.
- ↑
astronomical almanac fur the year 2011
. Washington an Taunton:
U.S. Government Printin Office
an the
U.K. Hydrographic Office
. 2009. pp. a1, c2.
- ↑
astronomical almanac
fur the year 2010
. Washington an Taunton: U.S. Government Printing Office and the U.K. Hydrographic Office. 2008. p. b3.
- ↑
U.S. Naval Observatory Nautical Almanac Office and Her Majesty's Nautical Almanac Office (2010).
Astronomical Almanac for the year 2011
. Washington: U.S. Government Printing Office. pp. C2, L8.
- ↑
Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touze, M.; Francou, G.; Laskar, J. (Februar 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets".
Astronomy and Astrophysics
.
282
(2): 663?683.
Bibcode
:
1994A&A...282..663S
.
- ↑
Taff, Lawrence G. (1985).
Celestial Mechanics: A Computational Guide for the Practitioner
. New York: John Wiley & Sons. p. 103.
ISBN
0-471-89316-1
.
Values in tables agree closely fur 2000, an depairt bi as much as 44 seconds fur the years furthest in the pest or future; the expressions ur simpler than those recommended in the
Astronomical Almanac fur the year 2011
.
- ↑
Seidelmann, P. Kenneth (2013).
Explanatory Supplement to the Astronomical Almanac
. Sean E. Urban (ed.) (3 ed.). Univ Science Books. p. 587.
ISBN
1-891389-85-8
.
Tabulates length o tropical year frae ?500 tae 2000 at 500-year intervals usin a
formula
bi laskar (1986); agrees closely wi values in thes section near 2000, depairts bi sex seconds in ?500.
- ↑
Ambler Thompson, Barry N. Taylor (2008).
"special publication 811: Guide for the use of the International System of Units (SI)"
(PDF)
.
Naitional Institute o Standards an Technology
(nist). paragraph 8.1. Archived frae
the original
(pdf)
on 11 Mey 2008
. Retrieved
14 Mey
2013
.
- ↑
"ISO 80000-3:2006, quantities and units ? part 3: space and time"
. geneva, switzerland:
internaitional organization fur standardization
. 2006.
- ↑
Russ Rowlett.
"units: a"
.
haw mony? a dictionary o units o measurement
. university o north carolina. Archived frae
the original
on 20 December 2008
. Retrieved
9 Januar
2009
.
- ↑
"agu editorial style guide fur authors"
. american geophysical union. 21 September 2007. Archived frae
the original
on 14 Julie 2008
. Retrieved
9 Januar
2009
.
North American Commission on Stratigraphic Nomenclature (November 2005).
"north american stratigraphic code"
.
The American Association o Petroleum Geologists Bulletin
(article 13 (c) ed.).
89
(11): 1547?1591. Archived frae
the original
on 2 Februar 2014
. Retrieved
14 Mey
2013
.
- ↑
Ambler Thompson, Barry N. Taylur (2008).
"special publication 811 ? Guide for the Use of the International System of Units (SI)"
(PDF)
. National Institute of Standards and Technology (NIST). para eeecht.1. Archived frae
the original
(PDF)
on 11 Mey 2008
. Retrieved
14 Mey
2013
.
- ↑
"ISO 80000-3:2006, quantities an units"
.
Geneva
:
Internaitional Organization fur Standardization
(ISO). 2006. part 3: space and time.
- ↑
Gunther Schadaw, Clement J. Mcdonald.
"unified code fur units o measure"
. Archived frae
the original
on 20 Mey 2008
. Retrieved
14 Mey
2013
.
- ↑
http://aurora.regenstrief.org/~ucum/ucum.html#para-31
Archived
2010-03-04 at the
Wayback Machine
- ↑
Norman E. Holden, Mauro L. Bonardi, Paul de Bievre, Paul R. Renne, an Igur M Villa (2011). "IUPAC-IUGS Common Definition and Convention on the Use of the Year as a Derived Unit of Time (IUPAC Recommendations 2011)".
Pure and Applied Chemistry
.
83
(5): 1159?1162.
doi
:
10.1351/pac-rec-09-01-22
.
CS1 maint: multiple names: authors leet (
link
)
- ↑
Celeste Biever (27 Apryle 2011).
"Push to Define Year Sparks Time War"
.
New Scientist
. Retrieved
28 Apryle
2011
.
- ↑
p. belli
it al.
(2007). "Investigation of β decay of 113cd".
Phys. Rev. C
.
76
(sex): 064603.
Bibcode
:
2007phrvc..76f4603b
.
doi
:
10.1103/physrevc.76.064603
.
- ↑
f. a. danevich
it al.
(2003). "α activity of natural tungsten isotopes".
phys. rev. c
.
67
: 014310.
arXiv
:
nucl-ex/0211013
.
Bibcode
:
2003phrvc..67a4310d
.
doi
:
10.1103/physrevc.67.014310
.
- ↑
North American Commission on Stratigraphic Nomenclature.
"North American Stratigraphic Code"
. Archived frae
the original
on 2 Februar 2014
. Retrieved
14 Mey
2013
.
(c) convention an abbreviations.
- ↑
Bradford M. Clement (8 Apryle 2004).
"Dependence of the duration of geomagnetic polarity reversals on site latitude"
.
Nature
.
428
(6983): 637?40.
Bibcode
:
2004Natur.428..637C
.
doi
:
10.1038/nature02459
.
PMID
15071591
.
- ↑
"time units"
. geological society o america. Archived frae
the original
on 2016-06-16
. Retrieved 2010-2-17
.
- ↑
"science bowl questions, astronomy, sit tae"
(PDF)
.
science bowl practice questions
. Oak Ridge Associated Universities. 2009. Archived frae
the original
(PDF)
on 2010-03-07
. Retrieved 2009-12-9
.
Template:Time topics