Greyline & Sun Times: How to Catch the DX Window at Sunrise and Sunset

The Greyline & Sun Times tool gives you sunrise, sunset, solar noon, and day length for any spot on Earth — plus the sun’s current position and a live indicator of whether that spot is on the greyline right now. It is built for ham radio operators who chase HF DX around dawn and dusk, and for shortwave listeners who want to catch far-away stations when twilight propagation peaks. It is free and needs no sign-up.

👉 Try the Greyline & Sun Times tool

Looking for the other utilities? Browse all tools on the Toolbox hub.

Why the Greyline Matters for HF DX

The greyline is the band of twilight around the terminator — the moving line that divides day from night on Earth (more background on Wikipedia). Near sunrise and sunset, the D layer of the ionosphere, which absorbs HF signals during the day, fades away quickly while the higher F layer stays ionized — so HF signals travel much farther than usual for a short window. This tool tells you exactly when that window opens at any location.

Entering a Location

The tool has one text input, a date picker, and a Show button. The input accepts three kinds of location, in this order of checking:

  1. City name — type Nairobi, Oslo, or any city; it is resolved through the live Nominatim geocoding service (OpenStreetMap), which returns the first match. If nothing matches, an error suggests trying a grid square or coordinates instead.
  2. Maidenhead grid square — 4 or 6 characters, such as JO89. The tool uses the center of the square. Longer locators are not accepted.
  3. Latitude and longitude — decimal degrees, separated by a comma, semicolon, or space, e.g. 40.7,-74.0. Southern latitudes and western longitudes are negative. Values outside ±90° latitude / ±180° longitude are rejected.

Below the field are four chips — New York, London, Tokyo, Sydney. Tapping one fills in its coordinates directly and runs the query at once, with no city lookup needed.

The date picker defaults to today; changing it re-runs the calculation for the current location. Pressing Enter in the text field submits, and the Show button is disabled while a city lookup is in progress. The page loads with New York (40.7,-74.0) already filled in and its results already shown.

Walkthrough: Checking the Greyline for London

  1. Tap the London chip.
  2. The input fills with 51.5,-0.1 and the query runs immediately.
  3. The Sun right now — 51.500, -0.100 card appears, showing the sun’s current elevation and azimuth in degrees.
  4. Below it, the Sun times — 51.500, -0.100 table lists Sunrise, Sunset, Solar noon, and Day length, each in UTC and Local columns, for the selected date.
  5. The 24-hour chart below the table draws the sun’s elevation curve for the whole day, with night shading and dashed sunrise/sunset lines.

That is the whole workflow: pick a location and a date, read the table and the chart.

How to Read the Result

  • Sun right now card — shows the sun’s current elevation (degrees above or below the horizon, one decimal) and azimuth (0° = north). If the elevation is between −3° and +3°, the card turns gold and displays GREYLINE NOW — prime DX window, meaning the location is on the greyline at this moment. Note: this card always reflects the actual current time, even if the date picker is set to another day.
  • Sun times table — one row each for Sunrise, Sunset, Solar noon, and Day length (shown as 12h 45m), in HH:MM. The UTC column is in universal time; the Local column follows *your device’s* timezone, not the searched city’s. If you are in New York and look up Tokyo, the Local column still shows New York time — use the UTC column when planning across time zones.
  • 24-hour sun elevation chart — the blue curve is the sun’s elevation over 24 hours (UTC on the x-axis). Hours below 0° are shaded, marking the night. Dashed amber lines mark sunrise and sunset, and a red line marks “now” when the selected date is today.
  • Polar regions — for high-latitude locations in winter or summer, the table switches to polar mode: Polar night — no sunrise or Polar day — no sunset, with day length shown as 0h 00m or 24h 00m. Solar noon is still calculated.

When to Use It: Greyline DX, Contests, and Shortwave Listening

  • Timing HF DX around the greyline. Check when the greyline passes your location — or your target’s — and plan to call during that window, when low-band signals carry much farther with less absorption.
  • Contest preparation. Know sunrise, sunset, and day length for the contest weekend in advance, so your band plan matches the propagation windows on 160, 80, and 40 meters.
  • Shortwave listening. Greyline DX is not just for hams: medium-wave and shortwave broadcast DX also peaks at twilight. Look up the times, then tune in.
  • Planning portable operations. Before a trip or a portable activation, check the destination’s day length and greyline times for your dates — daylight hours change fast with latitude and season.

Limitations

  • Times are computed estimates. They are calculated in your browser from standard NOAA solar equations, and are typically within a minute or two of true times — good for operating plans, not for applications needing astronomical precision.
  • Local means your time zone. The table’s Local column follows the device you are viewing it on, not the searched location. The UTC column is the reliable reference when locations and operators are in different zones.
  • City search takes the first match. Nominatim returns one result per search; an ambiguous city name may resolve to the wrong place. For precision, use coordinates or a grid square.
  • “Sun right now” ignores the date picker. The live position card and the GREYLINE NOW indicator always reflect the current moment; only the table and the chart follow the selected date.
  • The ±3° greyline is a rule of thumb. The tool flags sun elevations between −3° and +3° as greyline, but real HF propagation varies with solar and geomagnetic activity — a greyline window does not guarantee an open band.
  • City search needs the internet; the math does not. Once a location is resolved, all sun calculations run locally in your browser.

Frequently Asked Questions

How accurate are the sunrise and sunset times?

Times are computed in your browser using standard NOAA solar equations and are typically within a minute or two of actual times. Treat them as estimates for operating and planning purposes.

What exactly counts as “greyline” in this tool?

The tool defines greyline as sun elevation between −3° and +3°. When the sun’s current elevation at your location falls in that range, the “Sun right now” card turns gold and shows the GREYLINE NOW banner.

Why is the Local column in my own time zone?

The Local column is rendered from your device’s clock settings, not from the searched city’s time zone. That is by design: it answers “what time is that for me,” which is what you need when operating. Use the UTC column for absolute times.

Can I look up a past or future date?

Yes. The date picker accepts any date — look back at last year’s contest weekend or ahead to a planned trip. The table, the chart, and the polar day/night handling all follow the selected date.

I’m a shortwave listener, not a licensed ham — is this tool useful for me?

Yes. Greyline enhancement also applies to medium-wave and shortwave broadcast reception, so the same sunrise/sunset and greyline times help you plan listening sessions for distant stations.

Related Tools

  • Band Conditions — check live HF conditions around your greyline window before calling CQ.
  • Callsign Prefix Lookup — identify the country behind a greyline DX catch before logging it.
  • Repeater Lookup — find VHF/UHF repeaters at a destination when planning a portable operating trip.

Disclaimer

Location data comes from public sources (live Nominatim / OpenStreetMap geocoding). Sun times are computed in your browser from standard NOAA solar equations and are estimates for reference and education only; times are typically within a minute or two. They do not confirm licensing, and a greyline window does not guarantee usable propagation. Always verify licensing and operating rules with your national telecommunications authority before transmitting.

👉 Try the Greyline & Sun Times tool · Browse all tools

灰线与日出日落工具使用指南：在日出日落前后抓住 DX 窗口

灰线与日出日落工具可以给出地球上任意地点的日出、日落、太阳正午和白昼时长，还有太阳的当前位置，以及该地点此刻是否正好在灰线上的实时提示。它是为在黎明黄昏追 HF DX 的火腿准备的，也适合想掐着晨昏传播高峰收听远方电台的短波收听爱好者。免费使用，无需注册。

👉 试用灰线与日出日落工具

想看看其他工具？去工具箱总览页浏览全部工具。

为什么灰线对 HF DX 重要

灰线是晨昏线——地球昼夜分界线——周围的那一圈暮光地带（背景可看维基百科）。日出日落前后，吸收 HF 信号的电离层 D 层迅速消散，而更高的 F 层仍然电离——于是 HF 信号在这段短暂窗口里传得比平时远得多。这个工具就是告诉你：任意地点，这个窗口具体在什么时候打开。

输入地点

工具只有一个文本输入框、一个日期选择器和一个查询按钮。输入框接受三种地点写法，按以下顺序识别：

  1. 城市名——输入 Nairobi、Oslo 或任意城市，通过实时 Nominatim 地理编码服务（OpenStreetMap）解析，只取第一个匹配结果。查不到时会报错，建议改用网格坐标或经纬度。
  2. Maidenhead 网格坐标——4 位或 6 位，如 JO89。工具取网格的中心点。更长的网格写法不被接受。
  3. 经纬度——十进制度数，用逗号、分号或空格分隔，如 40.7,-74.0。南纬和西经用负数。纬度超出 ±90°、经度超出 ±180° 会被拒绝。

输入框下方有四个快捷 chips——New York、London、Tokyo、Sydney。点一下就会直接填入该城市的经纬度并立即查询，不走城市名解析。

日期选择器默认是今天；修改日期后，当前地点会重新计算。输入框里按回车也能提交；城市名查询进行中时，查询按钮会暂时禁用。页面打开时已经预填了纽约（40.7,-74.0）并显示它的结果。

实操演示：查伦敦的灰线

  1. 点 London chip。
  2. 输入框填入 51.5,-0.1，查询立即执行。
  3. 出现 Sun right now — 51.500, -0.100（此时太阳位置） 卡片，显示太阳此刻的高度角和方位角（度）。
  4. 下方 Sun times — 51.500, -0.100（日出日落时间） 表格列出日出、日落、太阳正午、白昼时长，所选日期的 UTC 时间和本地时间各一列。
  5. 表格下方的 24 小时曲线图画出全天的太阳高度角变化，夜间区域有阴影，日出日落处有虚线标记。

整个流程就是这样：选地点、选日期，看表格和曲线图。

怎么看懂查询结果

  • 此时太阳位置卡片——显示太阳此刻的高度角（地平线上下多少度，保留一位小数）和方位角（0°=正北）。高度角在 −3° 到 +3° 之间时，卡片变金色并显示 GREYLINE NOW — prime DX window（正值灰线时刻——DX 黄金窗口），表示该地点此刻正在灰线上。注意：这张卡片永远反映的是真实的当前时刻，即使日期选择器选了别的日期。
  • 日出日落时间表——Sunrise 日出、Sunset 日落、Solar noon 太阳正午、Day length 白昼时长（如 12h 45m）各一行，时间格式 HH:MM。UTC 世界时列是世界时；Local 本地时间列是你*自己设备*所在的时区，不是你查的那个城市的时区。你在纽约查东京，Local 列仍然显示纽约时间——跨时区计划操作时请看 UTC 列。
  • 24 小时太阳高度角曲线图——蓝色曲线是全天 24 小时（横轴为 UTC）的太阳高度角。低于 0° 的时段有阴影，就是夜晚。琥珀色虚线标出日出日落时刻；选中的是今天时，还会有一条红色”此刻”线。
  • 极地地区——高纬度地区的冬季或夏季，表格会切换为极地模式：Polar night — no sunrise（极夜——无日出） 或 Polar day — no sunset（极昼——无日落），白昼时长显示 0h 00m 或 24h 00m。太阳正午照常计算。

什么时候用得上：灰线 DX、竞赛、短波收听

  • 掐着灰线做 HF DX。 查灰线什么时候经过你这里——或者经过你的目标台那里——在 D 层吸收最低的那个窗口里呼叫，低波段信号传得更远。
  • 竞赛准备。 提前查好竞赛周末的日出、日落和白昼时长，让波段计划对上 160、80、40 米的传播窗口。
  • 短波收听。 灰线增强不只对火腿有用：中波、短波广播的 DX 也在晨昏时分最旺。查好时间再开机。
  • 便携设台规划。 出行或野外设台前，查目的地在你出行日期的白昼时长和灰线时刻——白天长短随纬度和季节变化很快。

局限性

  • 时间是计算估算值。 由浏览器端按 NOAA 标准太阳位置公式算出，误差通常在一两分钟内——够做操作计划用，不够做天文级精密应用。
  • Local 列是你自己的时区。 表格的 Local 列跟的是你看这页的设备时区，不是被查地点的时区。地点和操作人在不同时区时，以 UTC 列为准。
  • 城市名只取第一个匹配。 Nominatim 每次只返回一个结果，重名城市可能解析到错的地方。要精确请用经纬度或网格坐标。
  • “此时太阳位置”不受日期选择器影响。 实时位置卡片和 GREYLINE NOW 提示永远反映真实当前时刻；只有表格和曲线图跟着所选日期走。
  • ±3° 的灰线是经验规则。 工具把太阳高度角 −3° 到 +3° 之间标为灰线，但实际 HF 传播还受太阳和地磁活动影响——灰线窗口不保证波段一定开通。
  • 城市解析要联网，计算不需要。 地点一旦解析出来，所有的太阳计算都在你的浏览器本地完成。

常见问题

日出日落时间有多准？

时间由浏览器按 NOAA 标准太阳位置公式计算，误差通常在一两分钟内。按操作和计划用途的估算值使用即可。

这个工具里，”灰线”具体指什么？

工具把太阳高度角在 −3° 到 +3° 之间定义为灰线。你所在地点太阳此刻的高度角落在这个区间时，”此时太阳位置”卡片会变金色并显示 GREYLINE NOW 提示。

为什么 Local 列是我自己设备的时区？

Local 列是根据你设备的时钟设置渲染的，不是被查城市的时区。这是设计使然：它回答的是”这对我来说是几点”，这正是操作时需要的。绝对时间请看 UTC 列。

能查过去或未来的日期吗？

可以。日期选择器接受任意日期——回看去年竞赛周末，或提前查旅行日期都行。表格、曲线图和极昼极夜处理都会跟着所选日期走。

我是短波收听爱好者，不是持证火腿，这个工具对我有用吗？

有用。灰线增强同样适用于中波、短波广播的接收——同样的日出日落和灰线时间，可以帮你安排收听远方电台的时段。

相关工具

  • 波段传播条件——在灰线窗口里呼叫 CQ 之前，先看 HF 波段传播开没开。
  • 呼号前缀查询——把灰线窗口里抓到的 DX 台记进日志之前，先确认它属于哪个国家。
  • 中继查询——规划便携设台出行时，顺手查目的地的 VHF/UHF 中继。

免责声明

地点数据来自公开来源（Nominatim / OpenStreetMap 实时地理编码）；日出日落时间为浏览器端按 NOAA 标准太阳位置公式计算的估算值（误差通常在一两分钟内），仅供参考与学习。时间不代表执照状态，灰线窗口也不保证传播可用。发射操作前，请务必向本国电信主管部门核实执照状态与操作规定。

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