The real life issue is this:

A friend is moving to a new apartment. What is bad here, is if the apartment is getting full sun in the morning or afternoon. So the Sun goes from east to west, right? If the broad side of the house is facing towards the Sun, it is bad.

Just have a look at the image:

enter image description here

and everything in between can be ok, or bad.

Now the problem he has, what direction a house is facing, is not in the descriptions of the houses. But: often in the pictures you can see how the sun light falls into a room. See here:

enter image description here

How to estimate in what direction the house is facing using this picture?

I am not sure to what type of physics this question belongs.

  • $\begingroup$ Look at Google Maps. That will tell you the orientation of the house, without trying to analyze a picture! $\endgroup$ – alephzero Sep 19 '18 at 17:36
  • $\begingroup$ @alephzero yes, right. But I don't know the address of the house $\endgroup$ – Toskan Sep 19 '18 at 19:39

In order to deduce the orientation of the room, one would need the time and date that the picture was taken as well as the latitude of the location in question. The Sun moves from East to West everyday, that's true, but how North or South it will be of the location depends on the season. Half of the year, the Sun will be tracing paths North of the equator and the other half of the year the Sun will be tracing paths South of the equator. The Sun moves to a maximum of ~23 degrees North (Tropic of Cancer) and South (Tropic of Capricorn) of the Equator during the year.

So, for example, if the picture was taken during December at 12 Noon, then the Sun would be shining from roughly directly south of the location, so whichever wall the Sun is shining on then is the Southern wall of that room. If, on the other hand, the picture was taken at 8AM in June, then the Sun would be shining from NorthEast of the location and so the wall that the Sun shines on would the facing NorthEast. One could do some trigonometry to get the exact orientation of the house if one is given the exact time and the exact location (longitude and latitude), but for rough estimations of orientation, one probably just needs to know the latitude of the location, the month in which the picture was taken, and whether the picture was taken in the morning, noon, or afternoon.

  • $\begingroup$ very interesting! colombia, medellin. It was taken in the morning or late afternoon, as the sun seems to be low. If it was taken in the morning or late afternoon, does it have any influence to the amount of sun the house takes? probably not $\endgroup$ – Toskan Sep 19 '18 at 19:43

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