How do we know that the ancient Slavs knew gnomons?

URN:NBN:SI:doc-WHRSZEAL2022Pleterski, Andrejdocuments/doc/W/URN_NBN_SI_doc-WHRSZEAL_001.pdfdocuments/doc/W/URN_NBN_SI_doc-WHRSZEAL_001.txt25articlestr. 283-286, 286-28910.3986/SMS202225141253685791408-6271URN:NBN:SI:doc-WHRSZEALengslvUniversita degli Studi di Pisa, Dipartimento di Linguistica, gia Istituto di Lingua e LetteraturaZnanstvenoraziskovalni center Slovenske akademije znanosti in umetnosti, Inštitut za slovensko narodopisjeStudia mythologica SlavicaBY-NC-NDastronomijaSlovanislovanska religijasončne urestari SlovaniHow do we know that the ancient Slavs knew gnomons?Kako vemo, da so stari Slovani poznali gnomone?