Solar eclipse in Valle de Mena

The terrain

The horizon at Valle de Mena in the Sun's direction

1. In the direction the Sun will be in at maximum, the ground rises 13.9° above the horizontal at Valle de Mena: a rise of 424 m, 300 metres away, with the reference point of the municipality 348 m above sea level.
2. At that same moment the Sun will be 8.4° above the horizon at Valle de Mena. That is the APPARENT altitude: it already includes atmospheric refraction, which close to the horizon lifts the disc by a couple of tenths of a degree, which is why it does not match the geometric altitude in the card above to the decimal.
3. The subtraction comes out negative: −5.5°. From the reference point of Valle de Mena the ground rises 5.5° above where the Sun will be, so at that exact spot the relief gets in the way. It is a number for the point, not for the municipality: it shifts by several degrees within a few hundred metres, and out of the valley, down on the flat or up on a rise with an open view to the west-northwest the sum is a different one. With these two numbers in hand, the spot is chosen by whoever is standing there.

That obstacle is close, and at that range a 28-metre cell swallows the crest: 14 municipalities with the obstacle that close were checked against the IGN, and in 13 of them this calculation came out below the real terrain, by between half a degree and four. The sum above is optimistic here, so leave yourself room.

This calculation looks ONLY at bare ground: it does not see buildings, sheds or trees. In a village or a city, the building across the street blocks more than the ridge in the distance. It sweeps 60 km all around with cells of about 28 metres and starts looking 300 metres out from the point, which is the distance at which you are no longer looking at your own roof. And the point is the reference point of the municipality: 500 metres away the number shifts by several degrees.

Elevation model served by AWS Terrain Tiles (terrarium format) at zoom 12: about 28 metres per cell at the latitude of Spain. Checked against the IGN's MDT25 (PNOA-LiDAR), the official Spanish model, in 21 municipalities spread along the path (coast, islands, plateau, closed valley and city): the median difference is 0.0° and 20 of the 21 fall within half a degree. Produced using Copernicus data and information funded by the European Union — EU-DEM layers.