The generally bluish noctilucent clouds (NLCs) are spectacular atmospheric optical phenomena which have great diversity in morphology and appear only around the summer solstice. They are most commonly observed at latitudes between 50° and 70°, but there is evidence that corroborates their gradual increase which may be linked with the slow climate change. They are made of tiny water ice crystals formed in the mesosphere (around 83 km), higher than any other clouds in Earth's atmosphere. Their formation is linked to the summer solstice period because the temperature of the mesosphere is the lowest during that time instead of winter (below 130 K), which is ideal for the formation of these clouds besides the very low humidity.
They become visible from the surface only during the deep twilight when they are illuminated by sunlight from below the horizon. Although, for those researchers who regularly observe NLCs, it is very time consuming to search for or calculate from day to day that exactly when they need to monitor the northern horizon. The NLCWakeUp application can make it easier for observers. As a first step, the application determines the locations of the observers, based on the GPS service of their smart phone, thereafter it calculates the current elevation angles of the Sun. After the evening Sun was setting and the solar elevation reached -6° below the horizon (when the observation window opens), the application plays an arbitrary ring tone, namely it alerts the researcher or the photographer in order to have the opportunity to observe NLCs. The application provides the same alerts even when the solar elevation reached -16° below the horizon (when the possible visibility period ends), thus the application indicates the researcher that it is not worth to continue the monitoring. These alarms repeated in the early hours as well. The application can also use the data of an online weather monitoring service, in which case the observer is alarmed only when the sky conditions are appropriate for observing NLCs.
This app does not guarantee the successful appearance of NLCs, it just indicates the theoretically possible observation period.