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| Titel |
Is it possible to receive information about the historical geomagnetic declination from church orientations? |
| VerfasserIn |
Andrea Draxler, Roman Rauch, Karin Gruber, Roman Leohardt |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076493
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| Zusammenfassung |
| It is widely known that the main structure of many churches was planned and built in an
east-ward direction. This procedure, called “easting”, was used for centuries especially in
catholic structures. “Easting” usually refers to the direction of sunrise at the church patron’s
day. Assuming however that this direction is estimated by compasses there could be a
significant correlation between the geographic orientation of the churches and the value of
magnetic declination at the date of building. In Europe compasses are known since the 11th
century. For this study altogether 124 churches located in lower Austria and built between
1100 to 1900 were analysed. Of primary interest is the geographic orientation of the
churches, which was extracted out of georeferenced satellite images in Google Earth and the
NO Atlas. The measured orientation of the church’s nave is then compared to the geographic
east direction as well as to the magnetic east direction, according to the magnetic field
in the church’s construction year which is determined by published geomagnetic
field models. The resulting deviations for the geographic east direction split our
data into two groups: churches that were built before 1500 and churches that were
constructed after 1500. The boundary between these two data sets is marked by
the Ottoman wars in the 16th century, where a lot of churches were destroyed.
After 1500 the differences between the church’s orientation and the geographic east
direction are significantly bigger than before the Ottoman wars, so we shifted our
focus for the following calculations on the time span from 1100 to 1500, where
we found quite small deviations for both the geographic and the magnetic east
direction.
The principle idea of church orientation, usually referred to as “Easting” is to
direct the church to the point of sunrise on the patron saint’s day. Therefore we
also calculated the solar azimuth on the patron saint’s day and compared it to the
orientation of the church. The differences we found were bigger than the deviations we
got from the comparisons to the geographic and magnetic east directions, so this
indicates that practically the solar azimuth was not used for the church’s direction.
Furthermore, our investigations indicate that the orientation of the investigated churches is
more likely to be related to the geographic east direction than to magnetic east. |
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