By Michel Vandeputte
The year 2018 will enter the books as a peculiar weather year. High pressure areas reigned very long over northern Europe with great drought and real heat waves as a result. The corner in the southeast of France was just clamped in the ‘saddle area’ between the high pressure from the Azores and northern Europe. This generated rather a changeable weather type with episodes of unstable heat including a lot of thunderstorms and showers. In between also quieter moments when high pressure had more influence on the Provence region. The big drought and heat, as we were confronted in 2017 (including severe forest fires) in the Provence, was not at all an issue this year. Yet we were once again lured to the Provence thanks to the extremely favorable observation conditions at astronomical level: a new moon on 11 August.
Present at Aubenas les Alpes for a stay between 4 and 17 August 2018: Carl Johannink, Casper ter Kuile, Karin and Jos Nijland, Koen Miskotte, Michel Vandeputte and his family. Our rented house, ‘les Escauffiers’ is located at an altitude of 600m and towers above the valley of the river ‘le Largue’. A very comfortable and spacious gantry, equipped with the necessary cooling (pool!) to get through the warm days comfortably. In the field of nocturnal darkness, Aubenas les Alpes has exceeded our expectations by far. After all, the surrounding hills formed a perfect buffer for the limited light pollution of the neighboring villages of Reillane, Vacheres and St. Michel l’Observatoire (and at a safe distance of the larger towns of Forcalquier and Manosque). Also, Aubenas clearly had less trouble with orographic clouds triggered by the larger mountain ranges (Mont Ventoux and the Montagne de Lure) which form the barrier between the Provence and the inland.
Figure 1 – The beautiful accommodation of the group of observers near Aubenas Les Alps. It was not until 10 August that the sky finally got that distinctive deep blue Provencal color!
Our first confrontation with the Provençal landscape was unusually green in 2018! And it became clear to us quite quickly how that came about. We knew in advance that the first week was going to be quite unstable and that the probability of doing observations might well be disappointing. But we lived on hope: around 10 August we expected a stabilization in the weather with nice opportunities for 11-12 August (the premaximum night). The maximum night itself bothered us a lot with bad weather predictions…
The first 2 evenings we had heavy thunderstorms. Somewhere this was a relief if you came from a Benelux heat wave … Unfortunately, these storms also had an impact on the night sky. For example, 05-06 August was completely lost in the remaining clouds after a heavy thunderstorm. On the night, 06-07 August, after the thunderstorm the sky gradually opened but was saturated with moisture. Nevertheless, we did some observations for a few hours until the moonlight was reflected too much over the humid air layers. The meteor activity was normal. Also, on 7 August the heat dominated the weather. And that again generated heavy thunderstorms above the mountain ranges of France. After the storms another ‘soggy’ sultry night sky followed (07-08 August). A true feast for the mosquitoes and other insects! This night we observed briefly. The observation conditions were very moderate, especially down to the horizon. Observations were therefore stopped fairly quickly after moonrise. August 8 hardly scored better: sultry day with the formation of violent storms in the afternoon/evening. The result…once again a moist night sky after solving the remaining clouds. And during this session even formation of low clouds in the valley which sometimes came up to the height of the cottage (600m). The light domes of the surrounding villages betrayed the bad observation conditions even more. Fortunately, it was still fairly acceptable at a higher altitude in the night sky, with some observations done until the moonrise. Can the weather be worse in Provence? Yes, it can! 9 August was an unusual weather day during which an ‘episode of Mediterranean’ took place. This is a regional ‘heavy weather’ phenomenon which occurs normally in the autumn and winter when warm, unstable air from the Mediterranean Sea collides with cooler continental air from above the southern French relief (mainly the Cévennes, but also the Ardèche and the Provencal Alps). This results in stationary storms that gradually emerge as a curve over the entire southeastern (Mediterranean) part of France. The precipitation amounts can sometimes assume catastrophic proportions with heavy flooding. In this ‘Episode’ especially the Ardèche got it hard to endure with precipitation amounts of up to 200mm in a 24-hour period! In Aubenas it began to rain continuously from the late morning until midnight at varying intensity. From August 10, a temporary improvement in the weather was expected under the favorable influences of a spur of the high pressure area of the Azores. Our weather forecasts were therefore fortunate …
Figure 2 – Our rented house as seen from the observation site about a few hundred meters away of the house. We had an all sky view on the heaven on that place!
Figure 3 – Groupphoto of the Perseid 2018 team. F.l.t.r. Casper ter Kuile, Rientje, Koen Miskotte, Boris, Inneke Vanderkerken, Karin Nijland, Jos Nijland, Michel Vandeputte and Carl Johannink (photo-credit).
Aubenas Les Alps at its best!
Fortunately, it was not all trouble in the Provence … In the night from 09 to 10 August there was a slight Mistral wind. It blew away all the clouds and opened the entire sky in a short period of time, in which we were actually able to observe unexpectedly! An excellent night sky awaited us; finally, the night sky that we wanted to see from Aubenas! The Milky Way and the zodiacal light popped out at SQM values rising to 21.5. Due to the amount of humidity some lower clouds were formed in the valley for a while; but with one small attempt, this mess was hanging down nicely, partly under pressure from the deploying Mistral wind. Many meteors were seen. The Perseids showed also many bright meteors up to the magnitude -4 class. No interference of the moon this night, because moonrise was during the morning twilight. The good intentions regarding the weather were also prolonged during the day on 10 August: sunny, a deep blue Provençal sky with a tight Mistral wind on top. The night of 10 to 11 August then also went completely cloudless and crystal clear with SQM values again rising to 21.5. We were able to observe for a longer time for the first time during our stay, an undisturbed meteor session until the morning twilight arrived. The Perseids activity had increased further; but especially rich in weak meteors and a rather gusty activity. Exactly what you can expect at this time in August. Of course, also a few nice meteors were seen up to magnitude -4.
Figure 4 – This beautiful Capricornid of magnitude -3 was observed on 12 August 2018 around 02:03 UT. Camera: Canon 6D. Lens: Canon 8-15 mm F 4.0 zoom fish eye lens. ISO: 2500, F: 5.0, 8 mm, Exposure time 58 sec.
Also, August 11 was a beautiful summer day at temperatures rising to 30 ° and a moderate Mistral to give the necessary cooling. We also had good weather during the night 11 on 12 August. We started observations early because we knew that the maximum night would more than likely become a fiasco. Unfortunately, the wind started to linger as the night progressed. This slightly reduced the quality of the night sky compared to the two previous nights. The SQM values stayed around 21.3, at the end of the session a bit better. Of course, everyone went for a longer observation session and observed a beautiful, once again gutsy, Perseid activity. In the morning a lot of meteors were visible with on average one Perseid per minute (roughly ZHR ~ 50 a 60). There were also a number of bright meteors up to -4 with a cluster in the period 23:00 – 23:30 UT. The Capricornids also managed to produce a nice, long meteor of magnitude -3. Very satisfied faces after this session!
An eventful maximum night!
The weather of daytime on 12 August did not really suggest that the maximum night would go down in the clouds. This Sunday was absolutely warm and sunny with some classic shallow cloud turrets in the afternoon. This gave us a little hope: but the satellite images told another story. There was an immense cold front approaching from a British depression that reached to the south of Spain. August 12-13 approached. The sultry wind continued further from the southern corner and yet the night seemed to start with a clear sky! We did not hesitate for a minute to start from the twilight in the evening. At 19:58 UT (!), when hardly any stars were visible, a first beautiful Perseid earth-grazer appeared through Pegasus. At 20:02 UT an extremely long and really beautiful magnitude -4 Perseid earth grazer with an extremely long path between Cassiopeia to the northern parts of Sagittarius. Everyone screamed! In that first early hour (20:00 – 21:00 UT) several earth grazers of negative magnitude followed. It quickly became pretty dark: SQM increased to almost 21.5. But we could not escape the cirrus which now resolutely made its advance from the west. This announced the approaching cold front on which a violent storm had formed over the southern French departments of Herault and the Gard. That thunderstorm slowly moved towards the Haute Provence. The stroboscopic storm increased dramatically in intensity. Jos actually observed a ‘sprite’ with the naked eye above the gigantic anvil over the western horizon. The eastern and northern sky remained the longest free so we could even observe until 23UT. An unexpected three-hour session during this maximum night. Actually, this was a very peculiar experience. The Perseids activity increased strongly in force in the clear sky over the north and east while it flashed very bright on all other sides. After 23 UT the last clearings disappeared to the east and we could go to sleep. The whole night long there was intense lightning; but it was not until the morning that the active system passed with rain and thunder. In the morning we were all equally awakened by two huge booms …
Figure 5 – The spectaculair earthgrazing Perseid of 12 August 2018 20:02 UT in an even light sky. Visually, the meteor was already noticed in Cepheus and moving to the northern parts of Siggitarius!
Camera: Canon 6D. Lens: Canon 8-15 mm F 4.0 zoom fish eye lens. ISO: 2500, F: 5.0, 8 mm, B = 58 sec.
A Big Surprise during the post maximum night!
August 13. During the day it soon became drier with varying clouds. In the evening the clouds increased again with approaching new storm cells over the southwest of France and cells over the Alps. We did not expect making observations that night. We were rather looking forward to the first clearings by the morning: putting an alarm here was the message. Although the author sleeps very frequently in waking mode, from his window he saw the stars of the Big Bear sparkling in the night sky just before midnight. WOW: it had become completely clear! Not immediately a top sky such as 10-11 and 11-12 August, there was still too much moisture in the lower air layers. But we could be immediately starting the observations! Fifteen minutes after midnight local time, Koen and the author lay under the clear sky with another 5 hours of observing pleasure ahead of them. Jos and Carl started a bit later. The Mistral wind blew weakly at the start of the session. Then it lay down for a while and from 02 UT onwards, literally started to blow violently from scratch and thus creating top conditions in the end of this session.
The Perseids were quite active. The first hour was almost normal; but then the Perseids started to appear more and more! They came in strong gusts with sometimes multiple meteors per minute. In fact, this even went unusually hard for a post maximum night! The majority of the meteors was relatively weak, but a nice -5 Perseid appeared in the Big Dipper. Everyone observed a lot of meteors! For example, the author had a top quarterly count between 02:15 and 02:30 UT with a whopping 39 Perseids and counted 102 Perseids in the last hour before dusk. In total, almost 400 Perseids in 5 hours observation time! This quantity you actually only see in a good regular maximum night! Preliminary ZHR calculations show that the activity peaked at 90 to 100 in this night which is a remarkable amount for a post maximum night. This nice activity was also confirmed internationally by other observers from the European continent. 03:15 UT: the morning twilight came fast now. Very clear sky, the first winter constellations already appeared above the eastern horizon … a fresh Mistral wind … everyone turned into bed very satisfied. We had enjoyed such a beautiful meteor activity so much! Moreover, we were lucky to be present in Aubenas. After all, many low – orographic – clouds had formed over the mountain massifs north of us; a typical local phenomenon when sometimes a hard Mistral wind blows. A stay in Revest had more than likely been a less successful story …
Figure 6 – Composition of images shot between 00:27 and 01:27 UT on 14 August 2018. The brightest meteors are magnitude -4. Camera: Canon 6D. Lens: Canon 8-15 mm F 4.0 zoom fish eye lens. ISO: 2500, F: 5.0, 8 mm, exposure time 58 sec.
Beautiful final nights from Aubenas
August 14. The combination of the Azores high pressure and a small Genoa depression over Italy also created top conditions in the night of 14-15 August. The Mistral, which came out hard during the day, gradually started to linger. Without any headaches regarding the weather we could observe meteors to our heart’s content. And a lot was seen! The Perseids activity was still quite worthwhile with a rather gutsy activity: quiet moments sometimes alternated with nice and firm activity.
We also had beautiful observation conditions in the night of 15-16 August, which was opened grandly to Jos and Koen with a beautiful -6 Perseid fireball. Unfortunately, in the morning, from the north, there was some orographic high clouds, because of which the observations had to be aborted prematurely. Also, in our last night (16-17 August), three hours were observed for the morning twilight under very good observing conditions. The Perseids declined further in strength. And for the last time we went with all our equipment (Koen’s all sky camera, field beds, sleeping bags and other things) from our observation area towards the house, enjoying the morning twilight for the last time. Saying goodbye to Perseus and her Perseids, the rising winter constellations and a weak Mistral wind which whispered in our ear: you will return to Provence anyway?
Figure 7 – The best capture of this Perseid expedition. This Perseid of -6 appeared on August 16, 2018 at 00:02 UT. Camera: Canon 6D. Lens: Canon 8-15 mm F 4.0 zoom fish eye lens. ISO: 2500, F: 5.0, 8 mm, Exposure time 58 sec.
Table 1. Overview of all individual observations made from Aubenas Les Alps, Pr