►What's azimuth?
Azimuth is the compass bearing of the sun measured in degrees clockwise from true north.
Think of it like a clock: north is 12 (0°), due east is 3 (90°), due south is 6 (180°), and due west is 9 (270°).
When we say the sun is at azimuth 90°, it means the sun is positioned exactly to the east of the viewer. Where and when the
sun reaches certain azimuths is highly dependent on one's latitude and the season.
The Street Axis slider in the sidebar lets you set a target azimuth to match your street, since some
streets are slightly off from a true-north orientation (nobody's perfect, not even L'Enfant).
►What's elevation / the horizon?
Elevation (also called "altitude") is basically how high the sun is above the horizon, measured in degrees.
0° means the sun is right at the horizon; 90° would mean it's directly overhead (the "zenith").
Henge moments are most spectacular when elevation is very low, when the sun appears to be just above street level.
This tool flags rays below 10° elevation as henge candidates, shown as orange dots on the end of certain rays.
Note: This tool calculates astronomical elevation. It doesn't account for buildings, hills, or atmospheric refraction, which can shift the apparent horizon by 0.5–1°.
That part's on you!
►Why do the rays fan out like a half-circle?
Over a full year, the sun traces an arc across the sky each day: rising somewhere in the east, reaching its peak to the south, and setting in the west.
Each colored ray on the map represents one minute of sunlight for a given day.
Together, they paint the full range of directions the sun travels throughout the year.
In summer, the sun rises and sets farther north (thus the rays spread wider); in winter, it stays closer to due east/west. The gap between the sunsets/sunrises are what scientists refer to as "night", when the sun goes to sleep.
►What do the ray colors mean?
Rays are colored by the sun's elevation at that moment.
Red = sun very low, just above the horizon (0–5°). The most dramatic crimson light, and the most likely to be framed by the buildings.
Orange = sun low but climbing (5–20°). Think golden hour!
Amber = sun getting higher (20–35°). Good morning!
Yellow = sun high in the sky (35°+). Man, it's a hot one; like seven inches from the midday sun.
►What causes those pretty colors anyway?
Sunlight particles have to travel through the atmosphere to get to us, and in doing so, get "scattered" around.
Ones with shorter wavelengths (blues, violets) get scattered more easily than the ones with longer ones (reds, oranges). The color of the sky
represents whatever shortest wavelength showed up but is still too long to be scattered in the amount of atmosphere present. So during the day, the atmosphere
effectively "filters out" all the purples and violets, leaving that familiar blue color as the first in line. But as the sun rises or sets, it shines through more atmosphere
than it would if overhead, meaning more light gets filtered. By the time it reaches us, only the longer wavelengths remain: yellows, reds,
and oranges.
►How precise are the henge times?
Times are calculated at 1-minute intervals for every day of 2026, using standard solar position equations accurate to roughly +-0.5° in azimuth.
Henge candidates are flagged when the sun's azimuth is within +-0.25° of your chosen street bearing AND elevation is below 10°.
All times are shown in Eastern Time (ET), automatically accounting for EDT (UTC−4) from March 8 and EST (UTC−5) from November 1.
This tool does not account for atmospheric refraction, terrain, or building height; those factors can shift the observable moment by a minute or two.
►How often does a "henge" moment happen?
Because the sun travels across the sky every day, it crosses any given azimuth twice: once while rising in the morning (AM) and once while setting in the evening (PM).
For an east-west street, that means one sunrise henge and one sunset henge on both sides of the summer soltice. Typically this happens in the spring and again in fall when the sun rises/sets close to due east/west.
But, this is highly dependent on the orientation of your city. Manhattan's angle is more offset from true north than DC, so Manhattanhenge occurs in May and July,
when the sunset azimuth is more extreme. DC, however, is gifted because of the uniqueness of our street grid. We've got usual east-west streets, that are more aligned with a straight grid,
but we also have grand avenues that happen to align with azimuths at other times of the year. This tool helps you identify all the potential times and locations!
The AM / PM labels on the map indicate which side of the origin the morning vs. evening rays fall.
►What is DC's L'Enfant grid?
Pierre Charles L'Enfant and Benjamin Banneker designed Washington DC's street plan in 1791. It layers two systems:
a cardinal grid of numbered and lettered streets running true north-south and east-west, overlaid with
diagonal avenues (usually named after states) radiating from traffic circles.
This means DC has multiple street axes at different angles, each with its own pair of henge moments.
Pennsylvania Ave, for example, runs at roughly 128°/308°, giving it a different pair of henge dates than the E–W grid.
Fun fact: people often quote that DC is based after Paris' street plan, but the design of Paris as we know it now did not exist until the 1885 Hausmann plan, almost a century after L'Enfant drew up the District.
So in a way, Paris is based after us!
►Can I use this for other cities?
Yep! Just click anywhere on the map to move the origin point.
The tool recomputes all solar positions for the new location.
The underlying solar math works for any location on Earth. Shouts out science!
Basically, pick any city with a strong city grid and not a lot of natural barriers! Try out Toronto, Chicago, or Melbourne!
(Maybe don't try out Mexico City, Boston, or Marrakesh.)
Potomhenge