When does the sun stand due south — is that midday?
No. Solar noon falls around 12:00 on standard time and around 13:00 once the clocks go forward for summer time — plus a correction for how far your longitude sits from your time zone's meridian, and up to a quarter of an hour for the time of year.
Short answer: the sun stands due south — solar noon — around 12:00 on standard time and around 13:00 once the clocks go forward for summer time. On top of that come two corrections: one for longitude, because the clock follows your time zone's meridian (0° at Greenwich for the UK) and the sun arrives 4 minutes later for every degree of longitude you sit west of it — roughly nothing in London, and getting on for half an hour in Belfast — and one for the time of year, up to a quarter of an hour either way, because Earth's orbit isn't a perfect circle. Shadows point due north at solar noon — it's the simplest way there is to find north.
What "solar noon" means
Solar noon is the moment the sun stands exactly due south and, at the same time, at its highest point in the sky that day. It's the anchor for all daylight planning: the day is symmetrical around solar noon, the midday sun angle is measured from that moment, and shadows are shortest at exactly that point.
Solar noon almost never falls at 12:00 on the clock. Three things shift it, and they stack.
Correction 1: summer time — a full hour
Through the summer half of the year, clocks in the UK and most of Europe are put forward an hour. During that period, solar noon falls around 13:00 instead of 12:00.
It's the biggest single shift, and it's also the one people forget most often. A summer evening where the sun sits low at 21:00 would, on standard time, have been 20:00.
Correction 2: longitude — up to half an hour
UK clocks run on Greenwich Mean Time, which follows the 0° meridian through Greenwich in London. Only places sitting exactly on that line have solar noon around 12:00 on standard time. Anywhere west of it gets a later solar noon. If you live in a different time zone, the same maths applies — just use your own zone's meridian, which typically sits on a round multiple of 15 degrees.
Earth turns 360° in 24 hours, which is 15° an hour, or 4 minutes per degree of longitude. The correction is therefore (your longitude west of the meridian) × 4 minutes:
- Lowestoft, about 1.75° east: sits east of the meridian, so solar noon arrives about 7 minutes earlier, not later.
- London, about 0.1° west: essentially on the meridian — about 0 minutes of correction.
- Bristol, about 2.6° west: 2.6 × 4 = about 10 minutes later
- Cardiff, about 3.2° west: 3.2 × 4 = about 13 minutes later
- Belfast, about 5.9° west: 5.9 × 4 = about 24 minutes later
So there's over 30 minutes' difference in solar noon between Lowestoft and Belfast, even though the clock reads the same in both places. It's also why the sun sets later in the evening in Belfast than in Lowestoft — not because the day is longer, but because the whole day is shifted.
Correction 3: time of year — up to a quarter of an hour
The last correction is called the equation of time. Earth travels round the sun on a slightly elliptical path and on a tilted axis, and together those two things mean the solar day isn't quite the same length all year round. The clock ticks evenly; the sun doesn't.
The gap swings across the year by up to a quarter of an hour in either direction. Around the start of November the sun runs ahead of the clock, and solar noon falls at its earliest point in the year. Around the middle of February the sun runs behind, and solar noon falls at its latest. Four times a year the two line up exactly.
For everyday use around a home, the equation of time rarely matters — but it explains why the earliest sunsets in December don't coincide with the shortest day, and why a sundial and a wristwatch can disagree by a quarter of an hour.
Put the three together: a worked example
When does the sun stand due south in Bristol on 21 June?
- Starting point: 12:00 on standard time.
- Summer time: + 1 hour → 13:00.
- Longitude (2.6° west): + 10 minutes → 13:10.
- Equation of time around the summer solstice: a few minutes either way — within the quarter-hour margin.
So the sun stands due south in Bristol around 13:10 at midsummer, not at noon. If you want to photograph a house's shadows at the moment they're shortest and pointing due north, that's the time to set your watch by — and the same three steps apply wherever you live, once you swap in your own time zone and longitude.
Why this is worth knowing
- You can find north without a compass. Push a straight stick vertically into the ground at solar noon and mark the shadow: it points due north. The method isn't thrown off by reinforced concrete, radiators or a magnetic phone case.
- The day is symmetrical around solar noon. Once you know the day's length, you know sunrise and sunset too. At the winter solstice the day in London lasts just under 8 hours, so the sun is up from around 08:00 to around 15:50 on standard time.
- Daylight studies need reading correctly. Look at a simulation set to "12:00" in July and you're not looking at the middle of the day — you're looking an hour early. The sun is still in the south-east, and the shadows point north-west.
- Places further west get evening sun for longer. A west-facing terrace in Belfast gets roughly 24 minutes more evening sun than the same terrace in Lowestoft, at the same time on the clock.
Solar noon and the house's north
Every daylight study of a home rests on two numbers: the address's position and how the house is rotated relative to north. Solar noon is the bridge between them, and it doubles as a free check on whether north has been set correctly.
The test is simple: step outside at solar noon and see which way the shadows point. If that direction matches the north you've set on the floor plan or in the map placement, you're good. If it's off by 20 degrees, something's wrong, and it needs sorting out before you trust any daylight calculation built on top of it.
In HouseSense, a home's position and north direction are set by placing its footprint on the map, and the sun in the 3D model is then calculated for exactly that position, on whatever date and time you choose. To check it's right, set the time to solar noon and see whether the shadows fall the same way they do in real life.