Day/Night Terminator

A layer item maintained by a Live Feed routine that regularly computes the approximate location of the Sun, perpendicular to the planet, using the current UTC date and time. Watch as the Sun, Day/Night Terminator, and Horizon pass over your map, highlighting what areas are in dusk, darkness, and dawn. Terminator Polygons include a GeoEnriched attribute containing the approximate Total Population experiencing twilight or darkness. Originally inspired by Jim Blaney's JSAPI item, the data is maintained by a modified Python routine adapted from John Gravois' GitHub JSAPI "midnight-commander" project. Small corrections and enhancements provide the Sub-Solar Point (Sun's location on the planet), the Horizon line (mid-line of the Sun that meets the horizon), and the Twilight features showing dusk and dawn as the Sun reflects light in the atmosphere. Twilight, also known as Dawn and Dusk, is the visible reflective light in the atmosphere as the Sun dips below (Dusk) or approaches (Dawn) the Horizon. Three stages of Twilight are classified at 6 degree increments, producing various shades of darkness and vibrant colors. Civil Twilight is the first stage as the Sun moves below the Horizon (Dusk) or the last as the Sun approaches the Horizon (Dawn). Enough natural light exists for people to see without needing artificial light. Celestial objects are not yet visible. Nautical Twilight is the second stage. Artificial light is now helpful and Celestial objects can be seen with ease. Ships find it difficult to navigate by the Horizon. Astronomical Twilight is the last stage before darkness sets in. Only distant clouds are a glow on the Horizon with bright stars in full view. What can I do with this layer? A continually updated visual representation of this daily cycle provides an additional source of information for planners and decision makers that operate in an environment that is impacted by the day/night cycle. This may include logistics and fleet management, maritime, law enforcement, as well as other first responders who are engaged in search and rescue operations where daylight is critical to mission execution. Example item using Terminator to blend the Earth at Night tile image. Source: Calculation for the Position of the Sun (declination angle of the Sun) Alternate calculation for Equation of time (used to compute Sun's position) Reference details for Twilight Update Frequency: Every 10 minutes (at 5, 15, 25, ...) using the Aggregated Live Feed Methodology Area Covered: The world Coordinate System: GCS_WGS_1984, wkid: 4326, with Latitude limited to ±87.5 degrees for maximum compatibility. Layers: Celestial Bodies: Point layer containing current location of the Sun as it passes directly overhead, perpendicular to the planet. Horizon: Polyline layer containing the mid-line of the Sun as it sets on the horizon. Terminator: Polygon layer containing the 6 degree transitions from sunlight to civil, nautical, and astronomical Twilight (dawn and dusk) plus areas experiencing the dark of night. Also includes output from ArcGIS Online GeoEnrichment attribute field "KeyGlobalFacts.TOTPOP" containing the approximate Total Population covered by each Polygon. Sample: See animation of data mapped at midnight each day for one year. Revisions February 18, 2026: Update to Layer Popups to enhance presentation of information. July 30, 2025: Reduced Cache Control to 2 minutes down from 5 minutes. More frequent delivery for Map Layer refresh! This layer is provided for informational purposes and is not monitored 24/7 for accuracy and currency. If you would like to be alerted to potential issues or simply see when this Service will update next, please visit our Live Feed Status Page!本图层项由实时馈送（Live Feed）例行程序维护，该程序基于当前UTC日期与时间，定期计算垂直于行星的太阳近似位置。您可观察太阳、昼夜分界（Day/Night Terminator）与地平线在地图上的移动轨迹，清晰标识出处于黄昏、黑夜与黎明时段的区域。 分界多边形（Terminator Polygons）包含一项地理富集（GeoEnriched）属性，用于统计处于暮光或黑夜时段的近似总人口。本数据集最初灵感源自Jim Blaney的JSAPI图层项，现由基于John Gravois在GitHub上的JSAPI "midnight-commander"项目修改而来的Python例行程序进行维护。经小幅修正与功能增强后，本数据集新增了太阳下点（Sub-Solar Point，即太阳在行星表面的直射位置）、地平线弧线（太阳与地平线相切的中点连线），以及展现太阳在大气中反射光线所形成的黄昏与黎明状态的暮光特征图层。 暮光（Twilight）亦称黎明与黄昏，指太阳降至地平线以下（黄昏时段）或升至地平线附近（黎明时段）时，大气中可见的反射光线。暮光共分为三个等级，以太阳高度角每6度为划分增量，可呈现出不同层次的黑夜氛围与绚丽色彩。 民用暮光（Civil Twilight）为第一阶段：黄昏时太阳降至地平线以下，或黎明时太阳升至地平线附近的最后阶段。此时自然光充足，人们无需人工照明即可视物，但仍无法观测到天体。 航海暮光（Nautical Twilight）为第二阶段：此时需要借助人工照明，天体清晰可见，但船舶难以通过地平线进行导航。 天文暮光（Astronomical Twilight）为黑夜降临前的最后一个阶段：仅能看到地平线处远方云层的微光，而明亮的星辰已清晰可见。 本图层可应用于哪些场景？该每日周期的持续更新可视化展示，可为受昼夜周期影响的规划者与决策者提供额外信息支撑，应用场景涵盖物流与车队管理、海事作业、执法工作，以及其他依赖日光完成任务的搜救行动应急人员。 示例：利用分界图层融合夜间地球瓦片影像的效果。数据来源：太阳位置计算（太阳赤纬角）、日面时差替代计算（用于求解太阳位置）、暮光参数详细参考资料。 更新频率：采用聚合实时馈送（Aggregated Live Feed）方法，每10分钟更新一次（即每小时的5分、15分、25分……时刻）。 覆盖范围：全球。 坐标系：GCS_WGS_1984，WKID为4326；为保证最大兼容性，纬度范围限制为±87.5度。 图层组成： 1. 天体图层（Celestial Bodies）：点图层，用于展示太阳垂直直射行星表面的实时位置； 2. 地平线图层（Horizon）：线图层，用于展示太阳与地平线相切时的中点连线； 3. 分界图层（Terminator）：多边形图层，包含从日照区到民用暮光、航海暮光、天文暮光（黎明与黄昏）的6度高度角过渡区域，以及完全黑夜的区域。该图层还包含ArcGIS Online地理富集属性字段"KeyGlobalFacts.TOTPOP"的输出结果，用于统计每个多边形覆盖的近似总人口。 示例：可查看一年内每日午夜时刻的数据制图动画。 更新记录： 2026年2月18日：优化图层弹窗，提升信息展示效果； 2025年7月30日：将缓存控制时长从5分钟缩短至2分钟，实现地图图层更频繁的刷新更新！ 本图层仅用于信息展示，不会全天候监控其准确性与时效性。若您希望接收潜在问题的预警，或查询本服务的下一次更新时间，请访问我们的实时馈送状态页面。