May marks a noticeable shift in the Northern Hemisphere, where the period of daylight extends rapidly as the Earth progresses toward the Summer Solstice. The simple question of “when it gets dark” is complicated because the transition from day to night is a gradual process, not an instant event. True darkness, for practical human activity, does not begin at the moment the sun dips below the horizon. Understanding the precise time requires looking beyond the widely published sunset time and considering the stages of twilight.
Defining Darkness: Sunset Versus Twilight
The moment of sunset is technically defined as when the Sun’s upper edge vanishes below the horizon line. This event signifies the end of direct daylight, but the sky remains illuminated by scattered sunlight for a considerable time afterward. The period following sunset is known as twilight, which is divided into three distinct phases based on the Sun’s angle below the horizon.
The first and brightest phase is Civil Twilight, which lasts until the Sun is 6 degrees below the horizon. During this time, there is generally enough natural light available that most outdoor activities do not require artificial light, and objects are clearly visible. For most people, the end of Civil Twilight, often called civil dusk, is the point when the sky becomes practically “dark.”
Following civil twilight is Nautical Twilight, which continues until the Sun is 12 degrees below the horizon. Then comes Astronomical Twilight, which lasts until the Sun is 18 degrees below the horizon. Once the Sun sinks past 18 degrees, the sky reaches its maximum possible darkness, known as astronomical night, and the faintest celestial objects can be observed.
The Progression of Darkness Throughout May
The time of darkness advances significantly later throughout May as the Northern Hemisphere gains daylight hours. This increase is a result of the Earth’s tilt causing the Sun’s path to spend a longer time above the horizon as the June solstice approaches. For a mid-latitude location, such as one around 40 degrees North, the time of civil dusk may be delayed by approximately one to two minutes each day.
This daily shift accumulates to a substantial change, pushing the time of practical darkness later by roughly 30 to 60 minutes between May 1st and May 31st. For instance, if civil dusk is at 8:30 PM at the start of the month, it could easily be past 9:15 PM by the end of May. The rate of this change is not constant; it gradually slows down as the summer solstice arrives because the curve of daylight hours flattens out near its peak.
How Latitude Influences Darkness Times
The specific time it gets dark is heavily dependent on an observer’s latitude, or their distance north or south of the equator. Near the equator, the Sun’s path is nearly perpendicular to the horizon, causing a quick descent after sunset. This results in civil twilight lasting as little as 24 minutes, meaning the transition from sunset to practical darkness is very swift near the tropics.
Conversely, at higher latitudes, the Sun sets at a much shallower angle, which dramatically increases the duration of twilight. For locations north of about 48 degrees latitude, the twilight period can be significantly longer, extending the time before civil dusk occurs. This effect becomes so pronounced further north that in late May, locations above roughly 60 degrees North latitude may experience “white nights,” where the Sun never sinks far enough below the horizon for true astronomical darkness to occur at all.
The consequence of this latitudinal difference is that May darkness arrives much earlier for someone in the southern United States than for someone in Canada or Northern Europe. The angle of the Sun’s path, which is determined by the observer’s latitude, is the primary factor dictating how quickly the sky darkens after sunset.
Practical Tools for Finding Local Sunset Data
To find the precise time when it will get dark in your location, it is necessary to consult specific astronomical calculation tools. General weather applications often provide sunset times, but specialized resources are needed to determine the end of civil twilight. A search for “Civil Twilight” or “Civil Dusk” for your specific city and date will yield the most useful result for planning purposes.
Reliable sources include governmental websites, such as the US Naval Observatory’s astronomical data services, which provide accurate times for the beginning and end of all three twilight phases. Many dedicated astronomical websites and mobile applications also offer this precise data based on your location’s latitude and longitude.