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Tools / Grey line map and UTC clock

Grey line map and UTC clock

See where it's day, night and twilight right now, when the grey line passes over you today, and which far-off stations share it with you.

UTC––
Your time––
Sun overhead at–Subsolar point
Day of year––

Day and night now

Darker shading is deeper night. The narrow band between day and night is the grey line, where the sun is between 0° and 6° below the horizon. The map redraws every minute.

DaylightGrey line (0° to −6°)Twilight (−6° to −18°)Night

Your station

Maidenhead locator, like IO91wm
From your deviceYour location stays in your browser.
Enter a locator.

DX locations now

When both ends of a path are in the grey line, low-band DX is at its best. Bearings and distances are from your locator.

LocationNowSunriseSunsetBeamDistance

What the grey line is

The grey line, or terminator, is the band of twilight that circles the Earth between the day side and the night side. It moves westwards at about 1,670 km an hour at the equator, and it tilts through the year as the seasons change. At midsummer it tilts so far that everywhere north of the Arctic Circle stays in daylight, and around the equinoxes it runs almost straight from pole to pole.

Radio amateurs care about it because of how the ionosphere behaves at dawn and dusk. During the day the low D layer soaks up signals on 160m, 80m and 40m. At night it disappears, but the higher F layer also weakens. Along the grey line the D layer has faded while the F layer is still strong, so signals on the lower bands can travel remarkably far with little loss.

How to use grey line propagation

  • Find a station on the same line. The best paths run along the terminator, when both you and the other station are near sunrise or sunset. The DX table shows which locations are in the grey line now.
  • Listen around your sunrise and sunset. Openings often last only 20 to 40 minutes, so be on the band before your sunrise or sunset rather than after.
  • Try the long path. From the UK, VK and ZL are often worked on 40m and 80m via the long path around our sunrise or sunset, beaming roughly the opposite way to the short-path heading.
  • Use the lower bands. The effect is strongest on 160m, 80m and 40m, and still useful on 30m and 20m.

Why amateurs use UTC

Coordinated Universal Time is the same everywhere, so logs, schedules and contest rules all use it. In the UK, UTC is the same as GMT in winter and one hour behind BST in summer. The clock above shows UTC and your device's local time together, with the date, which matters when it's already tomorrow in UTC.

How the map is drawn

The map works out the sun's position from the time on your device, then shades every point on Earth by how far the sun is below the horizon there. Sunrise and sunset times use the sun's centre at the horizon and are accurate to within a minute or two, which is plenty for planning. Map data is from OpenStreetMap.

Questions

What time is it in UTC now?

The clock at the top of this page shows the current UTC time, taken from your device's clock and updated every second. In UK winter, UTC is the same as GMT. During British Summer Time, UTC is one hour behind UK time.

Which bands work best on the grey line?

160m, 80m and 40m benefit most, because the absorbing D layer has faded while the F layer is still strong. 30m and 20m also see grey line openings, especially for long-path DX.

How long does a grey line opening last?

Usually 20 to 40 minutes around sunrise or sunset at your end. In winter, at higher latitudes, twilight lasts longer, so openings can stretch to an hour or more.

Can I work Australia from the UK on the grey line?

Yes. Around UK sunrise or sunset, VK and ZL are regularly worked on 40m and 80m via the long path. Use the long-path beam heading, roughly the opposite of the short path.