The Galactic night swim takes place in near total darkness, your body floating between pinpoints of light shining from the billions of stars in the Milky Way Galaxy above and the thousands of phosphorescent plankton in the water below.
Finding a location like this – without light pollution and known for bioluminescence – is of course part of the process, but the swim itself is a surreal and metaphysical experience; more than a time or place. To be suspended in water between the wonders of astronomy and the marine world is inevitably to contemplate the nature of reality, our place in the universe, eternal questions about consciousness and our relationship to all living things. Years after my own Galactic swims, I remember them as experiences that recharged my soul.
In the northern hemisphere during the summer, the billions of stars in our Galaxy look like a luminescent, patchy cloud stretching upwards from the southern horizon where you will find the constellations Sagittarius and Scorpius. The darker and clearer the skies, the more these billions of stars will “pop” out of the darkness. I’m fortunate to hail from the Greek island of Crete, where the skies of the southern coastline are so dark and clear that many people genuinely think that the light from the Galaxy is a cloud in the sky rather than billions of stars at unimaginable distances away from us.
The centre of our Galaxy is in Sagittarius, a constellation that represents a half-man, half-horse centaur holding a bow and arrow. To most people it simply looks like a tea kettle. A curved line of stars to the right of Sagittarius makes up the tail and stinger of the constellation Scorpius, the scorpion. The brightest star in Scorpius located at the head of the scorpion is named Antares, or “opponent of Ares.” Ares is the Greek word for Mars. Both Antares and Ares have a reddish hue, but for different reasons. Ares (Mars) is a nearby planet in our solar system with a solid surface that is composed of reddish dirt. Antares is a very distant red supergiant star burning its last remaining gas, which will culminate in a spectacular explosion that astronomers call a supernova. In the meantime, it’s amazing to ponder that when you look towards Sagittarius, you are gazing at the centre of our Galaxy which contains a black hole—one of the most incredible phenomena in nature—though we cannot see it directly. The fabric of spacetime surrounding a black hole is so distorted that light can never escape and time itself appears to have no meaning.
It’s amazing to ponder that when you look towards Sagittarius, you are gazing at the centre of our Galaxy which contains a black hole—one of the most incredible phenomena in nature—though we cannot see it directly. The fabric of spacetime surrounding a black hole is so distorted that light can never escape and time itself appears to have no meaning.
Annotated night sky by Paul Kalas
As a night swimmer, thousands of blue-white stars flash in front of your hands and arms. These are bioluminescent plankton that need to be physically disturbed in order to glow. The ancient text De Mundo (Περὶ Κόσμου) that was attributed to Aristotle stated, “there are exhalations of fire from the sea” (γίνεται πυρὸς ἐν τῇ θαλάσσῃ), and this could have been an observation of this very same marine bioluminescence. These plankton are probably dinoflagellates, which marine biologists refer to as “dinos”. While stars create light from the energy of fusing atoms, living organisms do it through biochemistry. How does a dino’s flash of light help it? Given that plankton are food for predators, when the food suddenly flashes, this may disturb the predator, or reveal the location of the predator so that it is quickly eaten by yet another predator.
Though plankton shine in the darkness like stars, they wander the seas like planets. Looking up, the ancient Greeks noticed points of light that seemed to move from night to night relative to the other fixed stars. These were named planets because this word means “wanderer.” It would take many centuries of scientific inquiry to understand that these planets are very close to Earth, orbiting the Sun, whereas the stars are located at great distances, orbiting the galactic center in Sagittarius. This means that the motion of a planet in the sky can be perceived to move over many nights, while the stars appear to have the same position year after year. Looking down instead of up, the German medical doctor and zoologist Victor Hensen rigorously studied small marine organisms. In 1887 he decided to call them “plankton” because they did not have the means to propel themselves in water. This “floating stuff” wanders the Earth’s globe, just like the planets wander the celestial globe.
Bioluminescence off the coast of San Diego. Photo: Patrick Fore.
To get the most out of the Galactic night swim, the main ingredient is to swim under very dark conditions. The experience can still be pleasant if you are swimming near lights and with the moon in the sky. But if you are away from the major cities and the moon is NOT in the sky, everything above and below the water will seem much more vibrant and astonishing. The flashes may be more numerous several hours after sunset because bioluminescence follows a circadian rhythm that has peak activity around the middle of the night.
Look for dates around the “new moon” instead of the “full moon”. The swim should take place at least an hour after sunset for the skies to become very dark. So, if you find that sunset occurs at 8:10 pm, the night swim will begin at around 9:10. An important safety measure is to practice the swim during daylight, paying attention to beach access, water entry, and swimming conditions. As for the best month to see bioluminescent plankton, I have encountered them from June to September (I have not tried other months of the year).
The real treat is to take shallow dives with a breaststroke or a sculling motion of your hands and witness the bioluminescence in front of your very eyes. Then come to the surface and float on your back, gazing south toward the Galaxy. Next, dip your head back in the water and look back at your feet as you kick underwater to produce fleeting marine constellations of light.