When the Moon blocks the Sun

Anjani Ganase discusses the phenomenon of a total solar eclipse

 

On April 8, parts of the USA, Canada and Mexico will experience a total solar eclipse. A total solar eclipse happens when the moon lines up with the sun and blocks most of the sun’s light to the area of Earth directly in its path. While the full process of the eclipse takes hours for the line-up of the moon and the sun, the time for the total black out of the sun lasts only a few minutes, during which time the sky turns to twilight and in some cases the temperature drops. The last time I experienced a total solar eclipse, I was on a boat on the northern Great Barrier Reef off Lizard Island. The light dipped so much that we were able to see the stars around the sun. The atmosphere was eerie, and it felt as if nature was also silent in observation.  We wondered about the impacts on the ocean life and the behaviours in nature around us. 

 

Solar eclipse of 2017 August 21 in Oregon. Photo by Guiseppe Donatiello CC0 1.0 Universal Public Domain.

 

The movements of the sun and the moon govern most processes on our planet Earth. The sun determines seasons, weather, and is the main source of energy provided to us directly or through the process of photosynthesis. The moon serves as a big clock in the sky by which seasonal and reproductive cycles are timed. The phases of the moon are felt through changes in tides and currents of the ocean.

 

On occasion, however, the earth, sun and moon line up to create an eclipse event. Eclipses are not that rare, typically two to five solar eclipses a year, but the chance of another eclipse in the same location is extremely low. Since the time of the Babylonians, eclipse events have been tracked and today through science and precise tools, eclipses can be predicted down to the second for the next hundred years. Eclipses follow a Saros Series, which is a predictable pattern between lunar and solar eclipses. In a Saros Series, 9 years, 5.5 days after a lunar eclipse a solar eclipse will occur. Then, 18 years, 11 days, and 8 hours after a solar eclipse, the sun, moon and earth will realign in a similar way, but shift 120 degrees westward. There is a narrow band on earth – only 50 miles wide- that would experience any total eclipse.  Beyond that band, partial eclipses are observed.

 

Lunar eclipses occur during a full moon when the earth lines up between the sun and the moon. This results in the earth casting its shadow on the moon. During a total lunar eclipse, the moon turns red because of the refracted long red wavelengths that pass through the earth’s atmosphere and reflect off the moon. As a result, lunar eclipses are called blood moons. During such a lunar eclipse the light from the moon is much lower than a typical full moon night. As lunar cycles are important for many ecological processes, changes in the moon’s brightness can disrupt the typical nocturnal behaviours and predator-prey interactions in fish and other animals.

 

Studying eclipses

In 1919, a total solar eclipse brought the opportunity to test the four-year theory of relativity put forward by Albert Einstein. In 1919, Sir Arthur Edington and Charles Davidson set out to test one of Einstein’s predictions in the theory of relatively that the sun’s mass was capable of bending rays of light on the way to the earth’s atmosphere. In the general theory of relativity, large masses can essentially bend space and time around them and alter light trajectories. Large planets and stars, such as our sun, can alter space, time, and light trajectories. To test Einstein’s formulae which calculated how much the sun would bend light rays from a distant planet, Einstein needed to compare the distance between faraway stars (occurring beyond the sun) that occurred in the presence of the sun (during daylight) and without the sun (during the night). If the theory was correct, the distances should change according to the formula between the two scenarios. However, given how bright the sun was, it was near impossible to make the measurements during regular daylight, so instead they used the opportunity of a solar eclipse to make such observations and measurements. Sir Eddington and Davidson collected photographs during the total solar eclipse in May 1919 from two locations that occurred along the eclipse trajectory – one on Phillip Island off the west coast of Africa and the second in Sobral city in Brazil. The results proved Einstein’s theory that light was being curved around the sun because of its mass with the precise rate that matched Einstein’s Theory of Relativity.

 

Animal behaviour during an eclipse

The sudden darkening of the sky for the short period – from a couple seconds up to 7.5 minutes - can be alarming for someone that is not aware of the phenomenon. Wildlife biologists have been observing the behaviours of many animals, insects, fish, birds, during these brief and rare periods. Many organisms run on a circadian rhythm, a 24-hour cycle influenced by day and night cues. For some organisms, daylight has a strong influence on behaviour but for others, temperature, food and other factors contribute to the daily patterns of foraging, sleeping and they may be less sensitive to the darkening periods. Previous studies have recorded an array of patterns of behaviours during a solar eclipse. Insects, such as bees, retreat to their hive, while butterflies become still in the dark, crickets have been observed to chirp, a nocturnal behaviour. Some bird species make their way back to roost, while others appeared less bothered by the changing light. Some flowers even begin closing in the dark.

 

In the ocean, most of the natural responses have been observed in the shallow photic (light) part of the ocean. Fish species, particularly those dependent on external signals to trigger sleep/ wake schedules, tend to exhibit twilight or night-time behaviours, such as seeking shelter in the reef or gathering into tight schools as a defensive mechanism against predators that hunt in the low light conditions. Other examples of marine responses are the alteration of the vertical migration of plankton in response to the sudden dip in light. During the day, the plankton typically retreat to deeper parts of the ocean to avoid predation in the light. Previous studies have observed changes in plankton behaviour during eclipses where zooplankton migrate to the surface and even glow in the eclipse darkness only to be exposed in the light that follows.

Eclipses may not trigger significant behaviour changes in other animals, such as mammals, that are less dependent on the dark/ light cycle.  However, confusion and uncertainty have been observed, such as the huddling of a family of monkeys. In some scenarios, dogs and foxes were observed to bark during the eclipse and in the aftermath.

 

Eclipses are good reminders that we are, in fact, living on a massive piece of rock in the middle of space influenced by matter – stars, planets – and more that we know little about.

In Trinidad and Tobago, a partial solar eclipse was last viewed in Trinidad in October 2023, and the next one is expected on March 29, 2025. While the next total lunar eclipse for Trinidad and Tobago will be on 14 March 2025, we have a long wait for the next total solar eclipse which will occur over 21 years away on 12 August 2045.

 

References

Gutfreund H (2022) The Solar Eclipse That Validated Einstein’s Theory of Relativity. Front. Young Minds. 10:747040. doi: 10.3389/frym.2022.747040

 

Jennings, Simon, et al. "Reef fish behaviour during a total solar eclipse at Pinta Island, Galápagos." Journal of fish biology 53.3 (1998): 683-686.

 

Wheeler, William Morton, et al. (1935) "Observations on the behavior of animals during the total solar eclipse of August 31, 1932." Proceedings of the American Academy of Arts and Sciences. Vol. 70. No. 2. American Academy of Arts & Sciences.