How Sun Direction Changes by Season
Understand why sunrise, sunset, solar altitude, and facade exposure change during the year, and how to compare dates without relying on compass myths.
Last reviewed September 18, 2026A direction such as south-facing or west-facing is only the beginning of a sunlight estimate. Latitude, season, time of day, and nearby obstructions determine whether direct sun reaches a real surface.
Open a worked example
Each link restores the stated place, moment and modeled assumptions in the studio.
Inputs for a useful comparison
Start with a receiving point or vertical surface, its latitude and longitude, a local date, a local clock time and the surface bearing when the question concerns a window or facade. Keep the same point, time zone, obstacle dimensions and facing direction while comparing dates. SunCarta reports bearings from true north, not a phone’s uncorrected magnetic compass reading.
Start with true north and latitude
SunCarta reports azimuth clockwise from true north: east is 90°, south is 180°, and west is 270°. A phone may instead show magnetic north, so confirm its compass setting before comparing a field measurement with the map.
Latitude changes the height and side of the sky through which the sun travels. Near the tropics, the noon sun can appear north or south of a location during different parts of the year. At higher latitudes, seasonal differences in day length and solar altitude become much larger.
Compare representative dates
One date cannot describe a home or garden for the whole year. Compare a date near each solstice and at least one equinox, then add dates that matter for the real decision, such as a crop season, lease start, or event day.
- Use the same receiving point and obstacle dimensions for every date.
- Compare the time a shadow edge crosses the point, not only the daily total.
- Treat sunrise and sunset as local civil times for the selected time zone.
Orientation does not replace obstruction geometry
Two windows with the same compass bearing can receive different direct sun because one is above a nearby roofline and the other faces a taller building. Add the closest material blockers and use measured or documented dimensions where possible.
For an outdoor horizontal point, direct sun is not limited by a window-facing direction. For a vertical window or facade, the sun must also be in front of that plane. SunCarta keeps those two cases separate.
Read the result without mixing time policies
Compare offers local-clock and UTC synchronization. For a daily routine such as lunch, hold 12:00 local time. For simultaneous sunlight at two places, hold the UTC instant. These are different questions, and a one-hour DST change can visibly move the solar marker.
The polar chart’s rim is the horizon and its centre is the zenith. June is not summer everywhere: Sydney’s June solstice is winter. Season shortcuts identify astronomical events; they are not fixed June 21/December 21 dates for every year.
Method and a worked example
The worked comparison fixes London at 51.5080° N, 0.1281° W and uses 12:00 local time on 21 June and 21 December 2026. June uses Europe/London BST (11:00 UTC); December uses GMT (12:00 UTC). Astronomy Engine calculates airless topocentric solar-center altitude and true-north azimuth. These are calculated examples with no obstacles, not observations of the actual square.
At local noon on 21 June the solar elevation is 59.47° and azimuth 150.98°. On 21 December they are 15.05° and 180.34°. Standard open-horizon daylight is about 16 h 38 min versus 7 h 50 min. Local noon is not solar noon: the June bearing still points southeast, partly because daylight-saving time moves the clock.
How to interpret the comparison
Read seasonal direction as a time-and-surface relationship, not as a permanent label such as ‘south always means sunny’. Sunrise and sunset are local clock outputs for the coordinate’s time zone, and a lower altitude generally means longer shadows. A zero direct-sun result can mean night, a back-facing vertical surface, or a modeled obstruction; it does not prove that a room is dark because diffuse sky light is not modeled.
Limits of the estimate
This is an educational geometry estimate. It does not verify terrain, rooflines, foliage, glazing, overhangs, weather or a property boundary unless you model the relevant input. It is not a site survey, legal solar-access opinion, daylight study or engineering analysis; use measured geometry and qualified professional advice when the decision is safety- or investment-critical.
What to do next
Open either worked scene, choose Sky to read its polar diagram, then use Compare with the same local-time policy. Try the same-UTC policy and note that the local clock changes in summer. Export CSV or the selected-day SVG to keep the assumptions with the chart.
Questions about this method
Does a south-facing window always receive the most sun?
No. That rule is hemisphere-specific and can be defeated by season, latitude, overhangs, trees, and nearby buildings. Model the exact location and dates instead.
Why can winter shadows be longer?
The sun often stays lower above the horizon in winter. For level ground, lower solar altitude produces a longer geometric shadow for the same obstacle height.