Presentation Information
[O12-P40]Researching the mystery of the moon's brightness during a lunar eclipse
*Haruto Kawahara1, Takuma Arimura1, Hinako Takamatsu1, Hiromu Ootakeno1, Shota Kawasaki1, Ryosei Yokoyama1, Haruka Yamaguchi1, Saki Inadome1, Rei Sakamoto1 (1. Kokubu High School)
Keywords:
Total lunar eclipse,Dungeon scale,Stratospheric aerosols,Lewotobi volcano
We continued the research of our predecessors and observed the total lunar eclipses that occurred on September 8, 2025 and March 3, 2026. We began our research because we wanted to investigate the cause of the difference in the brightness of the moon during total eclipses. We observed the total lunar eclipses on September 8, 2025 and March 3, 2026, and discuss the results. The equipment used for the observations was a Takahashi 16cm reflecting telescope with an equatorial mount and motorized tracking. The camera used for photography was a Canon EOS 60D (unmodified, direct focus), and the number of images taken was 546 on September 8 and 582 on March 3. The observation site for both times was Shiroyama Park in Kirishima City, and there was no influence from ashfall from Sakurajima or Kirishima Shinmoedake on either day. The weather on September 8 was mostly sunny, and March 3 was clear throughout. The brightness of the moon during a lunar eclipse was determined by visually observing it using the National Astronomical Observatory of Japan's "Dungeon Scale" at the time of maximum totality. For the two lunar eclipses observed, a campaign was conducted using Instagram beforehand to measure the brightness of the moon during total lunar eclipses with the naked eye. On September 8th, 26 reports were received from all over Japan, including overseas. Many of these reported L=2, indicating that this lunar eclipse was somewhat dimmer. Similarly, on March 3rd, we requested observation cooperation using Instagram, and received 52 reports from within Japan alone. The observation results showed that many reported a somewhat bright lunar eclipse with L=3. To investigate the reason for the difference in lunar brightness between the two lunar eclipses, we examined past dark lunar eclipses where L=0-2 was observed. We summarized the large volcanic eruptions that are considered to be the cause of past dark lunar eclipses. It was found that all of the large volcanic eruptions that influenced clearly dark lunar eclipses with L=0-1 had a VEI of 5 or higher. Upon re-examining volcanic eruptions with a VEI of 5 or higher, including those other than those mentioned above, a total of nine volcanic eruptions were found to have a VEI of 5 or higher. Among these, the eruptions of Mount Agung, Mount El Chichón, and Mount Pinatubo resulted in darker lunar eclipses occurring within 1-2 years after the eruptions. While researching the literature, it was found that for volcanic eruptions that affect lunar eclipses, the abundance of sulfate aerosols released in the stratosphere by the eruption influences the brightness of the moon during the eclipse. The stratosphere has a large atmospheric circulation called the Brewer-Beson circulation, and it was thought that this circulation caused a bias in the distribution of aerosols. Therefore, using SPRINTARS, which publishes air pollution data on the web by the Institute of Applied Mechanics, Kyushu University, the data on sulfate aerosols on September 8, 2025, was examined. When observing a lunar eclipse in the southern Kyushu region, sunlight passes through atmospheric layers at points approximately 90 degrees apart in longitude to the west and east, respectively. In one of those locations, a region in the Pacific Ocean east of Japan, the concentration of sulfate aerosols was moderate. On the other hand, the concentration was high in a region in Europe west of Japan. Therefore, we believe that the reason the lunar eclipse on September 8 was observed to be dimmer was due to the high concentration of sulfate aerosols near Europe. Meanwhile, SPRINTARS data from March 3 showed no high levels of sulfate aerosols in the two regions located approximately 90 degrees away from Japan, which would have affected the brightness of the lunar eclipse. Therefore, we believe that the difference in the brightness of the moon during the total lunar eclipses on September 8 and March 3 was due to the concentration of sulfate aerosols distributed in the stratosphere, and since these originate from large volcanic eruptions, we believe the cause lies in the large eruption of the Lewotobi volcano in Indonesia, which occurred about a month before the September 8 lunar eclipse.