A rainy measurement at Ponta do Clérigos

In light of the LIFE Natura@Night campaign, SPEA Madeira is performing various measurements of artificial light at night (ALAN) around the island. This blog describes one of the meauserement sites, Ponta do Clérigos.

Ponta do Clérigos is a pointy cliff situated in the north-east of Madeira in the Santana municipality. This points gives an amazing view of the east coast of the island and from here, it is possible to see Rocha do Navio more to the west and looking to the east, you can see the city Faial, the Guindaste viewpoint and the huge rock formation Penha d'Aguia.

There is no public road going towards Ponta do Clerigos, only a gravel road with a lot of twists and turns that gets very muddy after rain. Locals use this road to get to their small agriculture fields in this area. The point is also reachable by foot from Santana.

We arrived in Santana at around 15:00 with the bus and from there we had to walk to the measurement site (see the trail  here ). The weather forecasts were not too positive for the evening and night, but we remained hopeful. This hope quite literally went down the drain when we left the bus, as it started raining right when we got out. But it is normal in Madeira to have bit of rain and wind now and then, it often quickly gets dry, especially near the coast.

Normally, we perform our measurements and just return home afterwards, but this was not possible for this site. Therefore, we had to bring our tents and camp on the site. I personally really enjoy camping and I can't be bothered by a bit of rain and stormy weather but this camping experience was something else.

But first, the measurements. We chose to set up the camera at a spot not too far form the tents. When we decide on the exact measurement point, we always have to keep in mind that we have an open view around to capture the full night sky, if possible. So preferably, there are not too many high trees or structures around. Besides that, we also have to think about replicability as some sites have already been photographed and measured in previous years. The idea is to set up the camera and a photometric device called a TAS on exactly the same location. This is however not always possible as seasons change and with that vegetation grows. Also, weather conditions can make it harder to reach previously (safely) accessible locations. The latter was the case for this site. Last year, the measurements were taken at a point more towards the end of the point of Clérigos but the way there had become slippery because of the rain.

After finding a good measurement spot, we took the daylight pictures with the camera and fisheye lens. We then went back to the basecamp to take shelter form the rain and to wait for the next measurement moment.

We were actually quite lucky this measurement day. Of course, it would have been better if we had a clear sky and no rain but at least we had dry periods during the measurement moments. We took the night pictures at 22:00 and 01:00 and filled in the survey. The questions in the survey are related to the location of the site, the external conditions (e.g. visibility, humidity, moon phase) and the present sources of artificial light.

In between the night measurements, we rested a bit in the tents which was good to prevent them from flying away.

Without even looking at the results of the TAS measurement, it was obvious that most ALAN came from the area east of the measurement point, namely the village Faial, the Guindaste viewpoint and the surrounding area. We could see direct and indirect sources of light coming from here. Indirect means that the artificial light is reflected in clouds or water and in this case it was reflected in both. If you can see light reflected in the sky, it is called sky glow. The effect of this is stronger during rainy and cloudy nights because the water droplets enhance reflection in multiple directions.

There was also some light coming from the area on the west. There were some stronger light sources which should be coming from the hotel that is situated at the cliff towards São Jorge and closer form the area around the teleférico at Rocha do Navio (which is also a measurement site).