Greyline · Sunrise & sunset · Beam map
Greyline & beam map
A live day/night map with the greyline band, where low-band DX often opens along the twilight edge. Enter your location to get your sunrise, sunset and greyline windows in UTC, plus a great-circle map centred on your station that shows the beam heading and distance to anywhere you tap.
World day & night
Sun at your location
Path to
Headings are from true north. Distance and short-path heading are on the WGS-84 ellipsoid (same as the grid tool).
Beam heading map
How it works
Sun position uses the NOAA Solar Calculator algorithm (NOAA Global Monitoring Laboratory), which is built on Jean Meeus's Astronomical Algorithms: the Sun's apparent longitude, declination and the equation of time from Meeus's low-accuracy solar theory. NOAA quotes its sunrise and sunset times as accurate to about a minute between 72° N and 72° S and within about ten minutes nearer the poles. Real-world times can differ from the calculation because of terrain and atmospheric refraction. Times are rounded to the nearest minute.
Sunrise and sunset are when the centre of the Sun is 0.833° below a flat horizon, which allows for 34′ of refraction plus the Sun's 16′ semidiameter. Civil twilight begins and ends when the centre of the Sun is 6° below the horizon. We call the civil twilight periods (dawn to sunrise and sunset to dusk) the greyline. The band on the map is the same zone, between −0.833° and −6°. Ham definitions of the greyline vary, and the propagation enhancement is a tendency, not a guarantee.
“Today” and “tomorrow” are the calendar days at your location (by local mean solar time), each centred on that day's solar noon. Polar day and polar night are reported when the Sun stays above or below the threshold all day.
The beam heading map is an azimuthal equidistant projection on a sphere centred on you. Any straight line from the centre is a great circle, its angle is the beam heading, and its length is proportional to the distance. The outer rim is your antipode, about 20,000 km away. The heading and distance shown for a tapped point come from the ellipsoidal calculation, which can differ from the spherical map by a fraction of a percent. Callsign lookups use FCC data from callook.info (mailing address, so the position is approximate).
- NOAA GML Solar Calculator and “Solar Calculation Details”: gml.noaa.gov/grad/solcalc.
- J. Meeus, Astronomical Algorithms, 2nd ed. (Willmann-Bell, 1998): ch. 15 (rising and setting, h₀ = −0°50′), ch. 25 (solar coordinates), ch. 28 (equation of time).
- U.S. Naval Observatory, “Rise, Set, and Twilight Definitions”: civil twilight is when the Sun's centre is 6° below the horizon.
- Coastlines: Natural Earth 1:110m land (public domain), via the world-atlas TopoJSON package. Maps are drawn with d3-geo.