Martinsloch

The sun shines through the Martinsloch

The Martinsloch is a breakthrough in the Alpine chain of the Tschingelhörner southeast of Elm in the canton of Glarus ( Switzerland ) in the shape of a triangle about 19 meters wide and 22 meters high. It is located just below the mountain ridge that forms the border between the cantons of Glarus and Graubünden . Its height above sea level is about 2600 meters. In spring and autumn the sun shines down on a few days and for a few minutes in the morning through the hole to the town of Elm (altitude about 980 meters).

The Martinsloch was created by geological faults .

A natural spectacle

Martinsloch from the Graubünden side, watercolor by Hans Conrad Escher , July 22, 1812

On a few days in March and September, the sun shines for about two minutes each through the rock hole on the Elmer church tower. The sun then disappears behind the mountains for almost a quarter of an hour before it finally rises over the mountain flank. In hazy weather, the sunlight forms a clearly recognizable 4.7-kilometer-long cone of light, like a spotlight, which throws a roughly 50-meter-wide, more or less round light spot onto the area around Elm.

Behind the village a light ellipse moves from 105 m by 50 m over the landscape, which is only separated by a shadow band of a good 10–15 m through the 44-meter high saddle above the Martinsloch. The light spot crawls down the western slope from top left to bottom right at around 32 cm per second (depending on the angle of incidence). This phenomenon occurs every year on the 12th or 13th of March at 8:52 CET and autumn on 30 September and 1 October at 9:33 pm EDT. Because the two equinoxes vary by one day as a result of the leap days , the maximum event also falls on a day earlier or later.

Various observations

Various writings have been made about Elmer Martinsloch. The sunrises in the rock window are also impressively portrayed in historical travel reports, and it seems as if this extraordinary natural sundial was better known in earlier centuries than it is today. The chronicles also contain more precise information about the occurrence of the solar event. For example, Johann Gottfried Ebel reports in his description of the mountain peoples of Switzerland that the sun on "3rd, 4th and 5th March and 14th and 15th September old style [note: before the introduction of the Gregorian calendar]" was caused by the Hole rail and illuminate the church tower.

The French naturalist H. Besson, who observed the solar phenomenon on his voyage in 1777, writes: “What is remarkable is a round hole at the height of the Falzaber Mountain, which when viewed from the village appears to be about three feet in diameter. On March 3rd, 4th and 5th and on September 14th, 15th and 16th of ancient times the sun wanders behind this hole; you can see its full circle on the 4th and 5th, and it also illuminates the church tower of Elm. The residents say the hole is very large, it could be about 25 feet in diameter. "

All of these descriptions have one thing in common: They always associate the sunrise in Martinsloch with the lighting of the Elmer Church.

In fact, the sun shines through the rock opening at the foot of the Great Tschingelhorn for more than a month, which can then no longer be observed from Elm, but on the opposite slope to the west and south-west of the village.

Direct observation

Martinsloch

When observing the spectacle in clear visibility conditions, similar caution is required as with a solar eclipse . Seen from the village, the hole is partially covered by a rock fold in front of it. Nevertheless, for a distance of a good four kilometers, the price is 11.7% or about an eighth of the apparent solar disk area. The diminution of the light creates a dull illumination of the illuminated areas and very sharply contoured cast shadows, as in a partial eclipse phase of around two thirds of the sun's diameter.

Origin of the phenomenon

Kepler's laws are often cited as one of the main causes of the Elmer phenomenon . However, these have only a minor influence on the events and only cause the time difference between the March and October events of 19 minutes, which results from the difference between the “true” and the “mean” solar time ( equation of time ).

The decisive factor is the inclination of the earth's axis in relation to the ecliptic . Kepler's laws describe the forms of the orbits and movements of the planets. All planets of the solar system revolve around the sun on elliptical orbits; so also the earth. But even if the earth revolved around the sun in a circular orbit, the Elmer phenomenon would arise. However, the uneven movement of the earth around the sun creates a special rhythm according to which the sun passages repeat in the Martinsloch. Exactly 200 days pass from the spring to the autumn event, which can be calculated from the length of the summer half-year of 186 days plus twice 7 days (difference between the event and the spring or autumn equinox ).

For other sun holes, such as the Mürtschen window ( Mühlehorn GL) or the Ela hole above Bergün, there are corresponding symmetries depending on the date of the event and the equinox. Since the earth travels around the sun for a quarter of a day longer than 365 days, the light spot on a certain day shifts annually by about 25 meters south or north compared to the previous year's position. Only when the leap day is corrected does the path of the light spot run over the site again as it did four years earlier.

Only the declination of the celestial body that appears through the Martinsloch is essential for the study of the Elmer events and their visibility . This must have the exact value of −2.82 ° (−2 ° 49 ') if the property should be seen from the Elmer church. The declination of the sun is almost exclusively determined by the inclination of the earth's axis.

Otherwise only precession, the advancement of the vernal equinox, has an effect on the appearance of stars in the hole, but only over huge periods of time. All constellations of the zodiac appear in the Martinsloch according to their cycle of 25,800 years (the " Platonic Year ").

2000 years ago the sun rose in Martinsloch on the equinox in the constellation of Pisces ; their rise in the hole is currently right on the border between the constellations Aquarius and Pisces.

In the equinox 2000, the current 50-year span (1975–2025) of the precession, there are only two fixed stars brighter than about 5th magnitude that shine through the Martinsloch and could theoretically be seen with the naked eye. One of them, 58 Eta Serpentis, is even 3.4 magnitudes bright and could be seen from the church in the hole on May 27 at 11:42 p.m. CEST. The other, the 31-tau hydra, is a double star that only shines at 4.9 magnitudes. He will be in the hole on February 22nd at 8:01 p.m. CET.

The star Mira , which changes its brightness between about 3.4 and 9.3 magnitudes in 331 days, can - if its brightness is sufficient - be seen from the intersection at the Elm church on October 15 at 22 : 25 p.m. CEST. On this day or the day after, the sun can also be followed in the morning in Martinsloch, but from the Ämpächli.

"Martinsloch full moon"

The moon and a number of planets also shine sporadically through the Martinsloch onto the church. Some sources state that the full moon shines through the rock window in either spring or autumn every 19 years, hitting the church on the same day as the sun, but twelve hours later. The last comparable event took place on October 2, 1982 at 8:32 p.m. CET, the next, during which the full moon can again be experienced exactly from the church, only on October 1, 2058.

The full moon rise calculated by the physicist and amateur astronomer Hans Weber for October 2, 1982, turned out to be a coincidence, as this event is extremely rare and only visible again 76 years later.

The most recent double event series (sun and full moon on the same day in Martinsloch) can be used as evidence for this. The full moon was again on October 2, 2001, exactly 19 years after the 1982 event. If one believes statements, one should have seen the moon from the church. But because of the high declination of the full moon, you had to look for an elevated observation point on the western mountain slope (Chappelen area) in order to be hit by the moon's light spot.

On September 30th and October 1st, 2001 the moon was still too low and only sections of the route in the Gerstboden and Spicher areas were considered as observation places. The moon could certainly not be seen from the church on any of the days.

The supposed 19-year cycle is essentially derived from three lunar cycles, which also play a role in the Saros for determining eclipses and which lead to almost the same constellation again after a certain time interval. The 19 years correspond to exactly 6939 or 6940 days, depending on whether four or five leap years fall within the respective 19-year period.

Synodic orbits (same phase to same phase): 6939 or 6940 days, divided by the synodic month of 29.53059 = 234.97668 or 235.01054 synodic months. The remainder of −0.68865 or +0.31135 days or −16 h to +7 h by which the moon advances or lags after each 19-year span, however, can lead to slightly waxing or waning phases of the moon over the centuries.

The draconian month (passage through orbital junction with ecliptic ), which also determines the ecliptical latitude and thus also the declination in relation to the celestial equator, ensures that the moon position is almost the same in relation to the lunar node: 6939 or 6940 days divided by 27.21222 days = 254 , 99573 and 255.03248 revolutions. The remnants of −0.1161 or +0.884 or just under 3 hours or a good 21 hours, however, only have a minor effect on the node movement from one to the next double event. Only after several centuries does the junction of the lunar orbit become noticeable in the Elmer event, similar to how the zones of visibility of solar eclipses gradually shift north or south across the terrestrial globe.

Only the anomalistic month (time interval between two successive passages of the moon through its closest point), which plays a subordinate role in the double phenomenon, does not do us the favor of an integer approximation: If we divide 6939 or 6940 by its period of 27.5546 Days, you get 251.827 and 251.864 orbits. The remainders, which correspond to three to five days here, result in considerable deviations in the declination between two March or two October events.

Tables of double events

The following table of such double events illustrates the rapid change in the height of the moon and shows that we cannot really speak of a 19-year cycle, unless the area of observation sites for the passage of the moon is extended to the area around Elm. Because in many cases it is not possible to experience both the passage of the sun and the moon through the Martinsloch from the Elm church. Especially the passage of the moon often requires a location on the eastern slope of the Schabell or even the Blistock.

Tab. 1 and 2: The two overviews show all the full moon rises in Martinsloch of the current spring and autumn series. If the person observing is standing by the Elmer Church, the azimuth of the Martinsloch is 118 ° 48 'and the height is 20 ° 46' above the mathematical horizon. All full moon rises that can be seen from the church are marked in red, those that are visible in the wider area of the village and black, moon rises that can be seen from the hiking and skiing area.

One reason for these considerable "terrain jumps" are the large daily shifts in length of 12–15 ° (or approx. 50 minutes in right ascension), which can often result in declination shifts of several arc minutes per hour. Since the exact time of the full moon does not occur at exactly the same time after 19 years, its passage through the Martinsloch can usually not be seen from Elm.

It is also noticeable that the event dates in the calendar gradually shift back over several centuries. For example, the double event in 2343 occurs on October 4th and the light cone of the full moon is caught on the slopes of the Mittetaghorn. The current fall event series, which includes the 1982 phenomenon and the most recent double phenomenon in 2001, ends with the event on October 1, 2096. All subsequent events can no longer be regarded as actual double phenomena, because the full moon occurs massively too high as a result of the node shift in declination and rises above the peaks of the Tschingelhoren for the entire area around Elm.

Using an empirical approach, the authors came across secondary cycles comparable to the various Saros families. Our program calculates a full moon rise on October 5th, 1998 around 11:12 p.m. CEST.

However, this event could only be seen far in the hinterland in the “Chnellis” area, while the morning sun shone through Martinsloch at the northern exit of the village. The day before, on October 4, 1998, the almost full moon was visible from the Suworow house, the sun only a good 75 meters north of it, at the level of the Sonne restaurant, through the rock window.

In summary, the following can be said about the apparently cyclically recurring double events: If the sun-full moon phenomenon is restricted to the area of the village of Elm, very few events can be experienced as "double events". The pure “church full moons” are even rarer. The autumn events of 1982 and 2058 will be and remain unique in this sense, and in the current spring series, which has been postponed by eight years from the autumn events, the double phenomenon for the Elmer Church also occurs only twice, namely on March 11th 2085 and March 11, 2104.

Visibility area of the Lunisolar events

When observing solar and lunar events in Elmer Martinsloch, the question of location arises. Where can I watch a particular event from? Does the moon rise for the village of Elm through the rock window or do I have to choose an observation site on the slope of the Ämpächli or Schabell?

For this purpose it is important to know from which areas the Martinsloch can be seen at all. At the bottom of the Elm valley, on the one hand the flank of the Herberig am Mörder in the northeast and, on the other hand, the steep slopes of the Plattenberg in the southeast limit the view of the Tschingelhorn Group and the Loch.

If you walk in the valley floor to the border from which exactly half of the hole is covered by a ridge, a wedge-shaped area emerges in the terrain, which tapers sharply towards the Unterbach area.

To the southwest of the Elmer mineral spring, the visibility limit slides down the Empächli and crosses the main building. Now the line turns to the east and intersects the main street at the level of the house J. Zentner. The border moves further south past the Sandgasse school building over the Sernf, only to turn abruptly north-west just north of the radio antenna. Maintaining this course, the line runs over the sawmill and the power station up to the Volg store, where it crosses the main road for the second time.

The visibility area, seen from the main road, extends over a length of almost 500 meters (House J. Zentner to the north of the Volg-Laden). The Elm Church is pretty much exactly in the middle of this area. Whether the first Glarus people used the Martinsloch as a lunisolar observatory remains pure speculation as long as no finds from pre-Christian times are made.

The declination curves projected into the terrain run practically parallel from west to east in the valley floor. In Elm itself only solar and lunar events can be observed that take place in a declination range of Dec = −1.8 ° and Dec = −4.7 °. In these cases, the light ellipse according to FIG. 4 hits certain groups of houses. With positive declination values, the visibility area shifts further south-west into the hinterland (“Tristel”), while from the “Steinibach” area the Plattenberg and the Gandstock block the view again. On the other hand, sun and moon phenomena with declination values smaller than Dec = −5.0 ° can still be experienced far up into the Ämpächli / Schabell area.