Inex
Encyclopedia
The inex is an eclipse cycle
of 10,571.95 days (about 29 years minus 20 days). The cycle was first described by Crommelin in 1901, but was named by George van den Bergh
who studied it half a century later. A new saros series often begins one inex after the last series started.
It corresponds to:
The 30.5 eclipse years means that if there is a solar eclipse
(or lunar eclipse
), then after one inex a New Moon (resp. Full Moon) will take place at the opposite node
of the orbit of the Moon, and under these circumstances another eclipse can occur.
Unlike the saros cycle
, the inex is not close to an integer number of anomalistic months so successive eclipses are not very similar in their appearance and characteristics. From the remainder of 0.67351, being near 2/3, every third eclipse will have a similar position in the moon's elliptical orbit and apparent diameter, so the quality of the solar eclipse (total versus annular) will repeat in these groupings of 3 cycles (87 years minus 2 months), called triads.
Although the inex series lasts much longer than the saros, it is not unbroken: at the beginning and end of a series, eclipses may fail to occur. However once settled down, inex series are very stable and run for many thousands of years.
An inex also is close to an integer number of days (10,571.95) so solar eclipses on average take place at about the same geographical longitude at successive events, although variations of the moons revolutionary speed at different points of the eclipse mask this relation. In addition sequential events occur at opposite geographical latitudes because the eclipses occur at opposite nodes. This is in contrast to the better known saros cycle
, which has a period of about 6585 1/3 days, so successive solar eclipses tend to take place about 120° in longitude apart on the globe (although at the same node and hence at about the same geographical latitude).
The significance of the inex cycle is not in the prediction, but in the organization of eclipses: any eclipse cycle, and indeed the interval between any two eclipses, can be expressed as a combination of saros and inex intervals. Also when a saros series has terminated, then often one inex after the last eclipse of that saros series, the first eclipse of a new saros series occurs. This in-coming and ex-iting of saros series separated by an interval of 29 years suggested the name for this cycle.
s from -11000 to +15000.
Within each column of the graph is a complete Saros series
which progresses smoothly from partial eclipses into total eclipses and back into partials. Each Inex series extends as a graph row.
The lifetime and form of each Inex series is not simple due to long term period variations: the synodic, draconic and anomalistic months.
Eclipse cycle
Eclipses may occur repeatedly, separated by certain intervals of time: these intervals are called eclipse cycles. The series of eclipses separated by a repeat of one of these intervals is called an eclipse series.- Eclipse conditions :...
of 10,571.95 days (about 29 years minus 20 days). The cycle was first described by Crommelin in 1901, but was named by George van den Bergh
George van den Bergh
George van den Bergh was a Dutch law professor and amateur astronomer.Van den Bergh was the son of Samuel van den Bergh, one of the founders of Unilever. His brother Sidney James and his nephew Maarten would follow his father in business life, while George pursued an academic career. He was a...
who studied it half a century later. A new saros series often begins one inex after the last series started.
It corresponds to:
- 358 lunations (synodic months)
- 388.50011 draconitic months
- 30.50011 eclipse years
- 383.67351 anomalistic months.
The 30.5 eclipse years means that if there is a solar eclipse
Solar eclipse
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...
(or lunar eclipse
Lunar eclipse
A lunar eclipse occurs when the Moon passes behind the Earth so that the Earth blocks the Sun's rays from striking the Moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a...
), then after one inex a New Moon (resp. Full Moon) will take place at the opposite node
Lunar node
The lunar nodes are the orbital nodes of the Moon, that is, the points where the orbit of the Moon crosses the ecliptic . The ascending node is where the moon crosses to the north of the ecliptic...
of the orbit of the Moon, and under these circumstances another eclipse can occur.
Unlike the saros cycle
Saros cycle
The saros is a period of 223 synodic months , that can be used to predict eclipses of the Sun and Moon. One saros after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle...
, the inex is not close to an integer number of anomalistic months so successive eclipses are not very similar in their appearance and characteristics. From the remainder of 0.67351, being near 2/3, every third eclipse will have a similar position in the moon's elliptical orbit and apparent diameter, so the quality of the solar eclipse (total versus annular) will repeat in these groupings of 3 cycles (87 years minus 2 months), called triads.
Although the inex series lasts much longer than the saros, it is not unbroken: at the beginning and end of a series, eclipses may fail to occur. However once settled down, inex series are very stable and run for many thousands of years.
An inex also is close to an integer number of days (10,571.95) so solar eclipses on average take place at about the same geographical longitude at successive events, although variations of the moons revolutionary speed at different points of the eclipse mask this relation. In addition sequential events occur at opposite geographical latitudes because the eclipses occur at opposite nodes. This is in contrast to the better known saros cycle
Saros cycle
The saros is a period of 223 synodic months , that can be used to predict eclipses of the Sun and Moon. One saros after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle...
, which has a period of about 6585 1/3 days, so successive solar eclipses tend to take place about 120° in longitude apart on the globe (although at the same node and hence at about the same geographical latitude).
The significance of the inex cycle is not in the prediction, but in the organization of eclipses: any eclipse cycle, and indeed the interval between any two eclipses, can be expressed as a combination of saros and inex intervals. Also when a saros series has terminated, then often one inex after the last eclipse of that saros series, the first eclipse of a new saros series occurs. This in-coming and ex-iting of saros series separated by an interval of 29 years suggested the name for this cycle.
Solar Saros-Inex panorama
A saros-inex panorama has been produced by Luca Quaglia and John Tilley. It shows 61775 solar eclipseSolar eclipse
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...
s from -11000 to +15000.
Within each column of the graph is a complete Saros series
Saros cycle
The saros is a period of 223 synodic months , that can be used to predict eclipses of the Sun and Moon. One saros after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle...
which progresses smoothly from partial eclipses into total eclipses and back into partials. Each Inex series extends as a graph row.
The lifetime and form of each Inex series is not simple due to long term period variations: the synodic, draconic and anomalistic months.