Continuous nautical twilight: a great part of Russia and Canada, northern Denmark in the Northern Hemisphere or Ushuaia in Argentina in the Southern Hemisphere.Continuous astronomical twilight: many European countries, such as northern UK, Ireland, the Netherlands, Germany and many other in the Northern Hemisphere or the Falkland Islands in the Southern Hemisphere.This actually occurs in very popular and accessible places around the world, such as: In function of the latitude, there can be a continuous astronomical twilight, a continuous nautical twilight, or a continuous civil twilight between sunset and sunrise. Continuous twilight between sunset and sunriseĪs written in the previous paragraph, above latitudes of approximately 50°N/S, around the date of the summer solstice, the Sun does not descend lower than 18° under the horizon, which means that, even if the Sun is under the horizon, its rays can still be seen, indirectly, during the whole night, which translates itself into a continuous twilight during the whole “night” hours. This is also valid for higher latitudes, but not around the summer solstice, when the Sun does not descend more than 18° under the horizon during the “night”, and thus there’s no real astronomical night between dusk and dawn.

This scenario is true for people living on Earth between approximately 50° North or South of the Equator at any time of the year. Twilight occurs thus during both periods of the day when the Sun is between 0° and 18° under the horizon. As time passes more, the Sun will ascend more, until it reaches again 0° and it rises the next day. At this moment, dawn occurs, and twilight starts again – this time we’re talking about the morning twilight. When the Sun reaches 18°, dusk occurs, and the observer will not distinguish any indirect sunlight anymore and the astronomical night starts.īecause of Earth’s rotation, the Sun continues its trip and, very early in the morning, before it rises, it will reach again 18° under the horizon.

But before our star reaches 18° under the horizon, there will still be distinguishable light from the Sun for the observer.

Due to earth’s rotation, the Sun will continue to descend more and more under the horizon.

In the evening, at sunset, the Sun will again reach 0° on the left side (West) and it will slowly disappear under the horizon. Now, we’re going to look at how twilight occurs on Earth, when it occurs and… how it doesn’t occur at all in certain places! Standard twilight occurrenceĪ standard twilight occurrence was described in our previous article:ĭuring the course of a day, at sunrise, the Sun appears in the sky from the right (East) and, during the whole daytime, it shines its light directly onto the place on Earth where the observer is located. As a reminder, twilight is the period of the day when a certain point on Earth is illuminated indirectly, by sunlight scattering, when the Sun is below the horizon, but not more than 18°, thus its rays are still visible, indirectly, for an observer located at that certain point. In a previous article we saw what is twilight and what are the main types of twilight.

Twilight dawn dusk