Sun path calculator for a home: hours of sun on each side

A home, a room or a yard faces the direction you look in when you stand at its windows and look out. A south-facing backyard is behind a house whose back looks south. Listings use the same words: "south-facing living room", "southern exposure", "north-facing lot".

In the northern hemisphere, away from the tropics, the sun is due south at solar noon every day of the year. A south-facing side gets direct sun most of the day in winter, when the sun is low and its light reaches deep into the rooms. In summer the sun is high at midday and its light falls steeply, so less of it comes in through the windows.

East-facing rooms get the morning sun and lose it around midday; west-facing rooms get the afternoon and evening sun, which comes in low and long on summer evenings. North-facing rooms get little or no direct sun from fall to spring. In summer the sun rises and sets north of east and west, so a north side gets early morning and late evening sun at a grazing angle.

South of the equator it is the other way round: the sunny side is the north. In Sydney, Buenos Aires or São Paulo buyers look for north-facing homes.

The tool's own figures for New York City, for a wall with an open horizon in front of it. Real homes get less where buildings, trees or a hill block the low sun.

• Measure it at the home: stand at the main windows or the patio door, look out, and read the direction with a compass or this tool. Write the direction you measured, such as "living room and deck face south-west".
• Give hours of sun with their day: "about 8 hours of direct sun on the living room windows on 21 December". Say they are calculated for an open horizon; if the building across the street blocks the winter sun, say what the buyer will see.
• Show it in the tour: in a 360 tour, an information text on the window tells buyers when the sun comes in, in the room where they are looking.
• Shoot the 360 photos when the light shows the home as it is: a room photographed with sun on the floor tells buyers more than any sentence.

• Open this page on your phone at the viewing, use your location, and set each side with the phone's compass at the window.
• Look at what stands in front of the windows: buildings across the street, trees, a hill. In winter the sun is low, so a building that looks far away can block it for hours.
• Check the rooms you use at the times you use them: the kitchen in the morning, the living room and the balcony in the late afternoon, the bedrooms at night.
• If you can, visit again at another time of day, or ask for photos taken in the morning and the afternoon.

The sun's position comes from the equations NOAA's solar calculator uses, after Jean Meeus's Astronomical Algorithms: about one minute for sunrise and sunset and a fraction of a degree for the sun's direction. Times are shown in the place's time zone, with daylight saving time, from your browser's own time zone data.

The hours of sun count the time the sun is above the horizon and in front of the wall. They are for a flat, open horizon: read them as what the side gets without buildings, trees or hills in the way. A phone compass points to magnetic north, and the tool places the sun by true north. In most of Europe the two are a few degrees apart, which barely changes the hours. In parts of the US they are 10° to 15° apart (about 15° in Seattle and in Maine), and more in parts of Canada: there, check the direction on a map, or add your local magnetic declination (NOAA's declination calculator gives it) to the compass reading.