undirmánuðu

Undirmánuðu is an Icelandic term that translates to "under-moon" or "waning moon." It refers to the period of the lunar cycle when the moon is decreasing in illumination from full to new. This phase is characterized by a shrinking visible portion of the moon each night. In traditional Icelandic culture, the waning moon was often associated with certain activities and beliefs, though these are largely considered folklore today. For instance, some believed that planting certain crops during the waning moon could lead to better root development, while others associated this phase with endings or divestment. The concept of undirmánuðu is distinct from other lunar phases such as full moon (fullmánuðu), new moon (nýmáni), or waxing moon (yfirmánuðu). It is a natural and observable phenomenon of the moon's orbit around the Earth and its changing illuminated surface as viewed from our planet. The precise timing of the waning moon can be tracked astronomically and is a predictable part of the lunar calendar.