The secular variation of a
time series is its long-term, non-periodic variation (see
decomposition of time series). Whether a variation is perceived as secular or not depends on the available timescale: a variation that is secular over a timescale of
centuries may be a segment of what is, over a timescale of millions of years, a
periodic variation
In time series data, seasonality is the presence of variations that occur at specific regular intervals less than a year, such as weekly, monthly, or quarterly. Seasonality may be caused by various factors, such as weather, vacation, and holidays a ...
. Natural quantities often have both periodic and secular variations. Secular variation is sometimes called secular trend or secular drift when the emphasis is on a
linear long-term trend.
The term is used wherever time series are applicable in
history,
economics,
operations research,
biological anthropology, and
astronomy (particularly
celestial mechanics) such as
VSOP (planets).
Etymology
The word ''secular'', from the Latin root ''saecularis'' ("of an age, occurring once in an age"), has two basic meanings: I. Of or pertaining to the world (from which
secularity
Secularity, also the secular or secularness (from Latin ''saeculum'', "worldly" or "of a generation"), is the state of being unrelated or neutral in regards to religion. Anything that does not have an explicit reference to religion, either negativ ...
is derived), and II. Of or belonging to an age or long period. The latter use appeared in the 18th century in the sense of "living or lasting for an age or ages". In the 19th century terms like ''secular acceleration'' and ''secular variation'' appeared in astronomy, and similar language was used in economics by 1895.
Astronomy
In
astronomy, secular variations are contrasted with periodic phenomena. In particular, astronomical
ephemerides use ''secular'' to label the longest-lasting or non-oscillatory
perturbation
Perturbation or perturb may refer to:
* Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly
* Perturbation (geology), changes in the nature of alluvial deposits over time
* Perturbatio ...
s in the motion of planets, as opposed to ''periodic'' perturbations which exhibit repetition over the course of a time frame of interest. In this context it is referred to as secular motion.
Solar System ephemerides are essential for the navigation of
spacecraft and for all kinds of space observations of the
planets
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young ...
, their
natural satellites,
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s and
galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...
.
Most of the known perturbations to motion in stable, regular, and well-determined
dynamical systems tend to be periodic at some level, but in
many-body systems,
chaotic dynamics
Chaotic was originally a Danish trading card game. It expanded to an online game in America which then became a television program based on the game. The program was able to be seen on 4Kids TV (Fox affiliates, nationwide), Jetix, The CW4Kids, ...
result in some effects which are one-way (for example,
planetary migration).
In the Solar System
Secular phenomena create variations in the orbits of the Moon and the planets. The
solar
Solar may refer to:
Astronomy
* Of or relating to the Sun
** Solar telescope, a special purpose telescope used to observe the Sun
** A device that utilizes solar energy (e.g. "solar panels")
** Solar calendar, a calendar whose dates indicate t ...
emission spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an electron making a atomic electron transition, transition from a high energy state to a lower energy st ...
and the
solar wind are undergoing
secular trends due to
migration through the
galactic plane. Current consensus has found these to have been
among the smallest of factors as to
climate and
extinction during human evolution, dwarfed by complex
solar cycles
Solar may refer to:
Astronomy
* Of or relating to the Sun
** Solar telescope, a special purpose telescope used to observe the Sun
** A device that utilizes solar energy (e.g. "solar panels")
** Solar calendar, a calendar whose dates indicate t ...
and magnetic cycles.
Moon
The
secular acceleration of the Moon depends on
tidal forces. It was discovered early but it was some time before it was correctly explained.
Earth
Depending on what time frames are considered, perturbations can appear secular even if they are actually periodic. An example of this is the
precession of the Earth's axis
In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particu ...
considered over the time frame of a few hundred or thousand years. When viewed in this timeframe the so-called "precession of the equinoxes" can appear to mimic a secular phenomenon since the axial precession takes 25,771.5 years. Thus monitoring it over a much smaller timeframe appears to simply result in a "drift" of the position of the
equinox in the
plane of the ecliptic of approximately one degree per 71.6 years, influencing the
Milankovitch cycles.
The planets
Secular variation also refers to long-term trends in the orbits of all of the
planets
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young ...
. Several attempts have from time to time been undertaken to analyze and predict such
gravitation
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...
al deviations for planets, observing ordinary satellite orbits. Others are often referred to as post-
keplerian
Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, German mathematician, mathematician, astrologer, Natural philosophy, natural philosopher and writer on music. He is a key figure in the 17th-century Scienti ...
effects.
''
Variations Séculaires des Orbites Planétaires'' (VSOP) is a modern
numerical model
Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be dete ...
that tries to address the problem.
Market trends
Market trends
A market trend is a perceived tendency of financial markets to move in a particular direction over time. Analysts classify these trends as ''secular'' for long time-frames, ''primary'' for medium time-frames, and ''secondary'' for short time-fram ...
are classified as ''secular'', ''primary'' and ''secondary'' for long, medium and short time frames. Some traders identify market trends using
technical analysis.
Geomagnetic secular variation
Geomagnetic secular variation refers to some changes in the
Earth's magnetic field. The field has variations on timescales from milliseconds to millions of years – its rapid ones mostly come from currents in the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
and
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
. The secular variations are those over periods of a year or more, reflecting changes in the
Earth's core. Phenomena associated with these include
geomagnetic jerk,
westward drift
Westward may refer to:
* The cardinal direction West
* Westward, Cumbria, a settlement in north-west England
* ''Westward'' (series), a series of games video created by Sandlot Games
* Westward Islet of Ducie Island
* Westward Television, a former ...
and
geomagnetic reversals.
Biological anthropology
A secular trend, widely tapered off and in some places ended, in which case a discrete developmental shift, has been found to apply across the continents in the average age of onset of
puberty (
menarche
Menarche ( ; ) is the first menstrual cycle, or first menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of fertility.
Gir ...
/first menstruation and beginning of
breast development) of girls from the 1940s to 2010s: beginning roughly 4 months earlier per decade. This is largely believed to be caused by nutritional changes in children over time.
References
{{DEFAULTSORT:Secular Variation
Geomagnetism
Time series