Without moonlight (i.e. if our moon was non-reflective or black, but with exactly the same gravity and motion), would life on Earth be any different?
Hillary Shaw
Newport, Shropshire, UK
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Human culture would be very different without moonlight. Ancient stargazers, with no artificial light to drown out the stars, would see a black void crossing the sky. Perhaps this would lead to legends of an evil sky demon, similar to that described in Isaac Asimov鈥檚 1941 short story Nightfall, about a planet that experiences the darkness of night for the first time.
The biggest differences would be in the Islamic and Jewish calendars, both of which are lunar. And without the light of the moon, the seven-day week might not exist, being about a quarter of a lunar phase cycle. We would also have no months.
Lunar cycles were important to set agricultural dates and religious festivals, so we might have developed elaborate sun-angle observatories, similar to Jantar Mantar in India.
Eric Kvaalen
Les Essarts-le-Roi, France
There are many animals whose behaviour is timed to the phase of the moon. There are zooplankton in the Arctic, for instance, that sink when the sun is up and rise to feed on phytoplankton during the night. But during winter, when it is always night in the Arctic, they time this behaviour by the moon, which rises every 25 hours and sets 12 or 13 hours later.
Mike Follows
Sutton Coldfield, West Midlands, UK
There would undoubtedly be an impact on life if the moon stopped reflecting light. Some animals use moonlight to find food or a mate, or exploit the relative darkness to avoid becoming dinner. Others use the moon for navigation. There would be winners and losers and it wouldn鈥檛 be easy to predict the outcome in advance.
That said, losers might include the Mormon tea plant (Ephedra foeminea) that is pollinated during the full moon. Each of its cones produces droplets of nectar, which help stick pollen to insects that are attracted by the polarised moonlight the droplets reflect.
Some birds, such as the Barau鈥檚 petrel, use day length and the phase of the moon to time their migration. And the period of near total darkness between sunset and moonrise that occurs in the nights after a full moon seems to trigger mass spawning in corals.
However, many nocturnal animals would cope, perhaps with a slight adjustment to their behaviour. After all, there are already examples of animals that have exploited changes in their environment: sky glow allows city birds to remain active when their rural counterparts have already roosted, and pipistrelle bats are drawn to artificial lights for the easy meal of insects they attract.
The 18 species of bat in the UK navigate using echolocation, but switch to their powerful night vision when conditions are favourable. This allows them to conserve energy while reducing the chance that predators will detect them. Without moonlight, they would have to spend more time echolocating.
By and large, animals cope when there is an overcast sky or a thick veil of dust following a volcanic eruption. Even with a black moon, we would still have starlight. Human vision isn鈥檛 outstanding, yet we can often see well enough to find our way using starlight. Many nocturnal animals have enhanced night vision due to a reflective surface called the tapetum lucidum at the back of their retinas 鈥� the cause of eyeshine when such animals are caught in a beam of light.
鈥淭here would undoubtedly be an impact on life if the moon suddenly stopped reflecting light鈥�
[Ed 鈥� look in the forthcoming Christmas issue to learn how the tapetum lucidum helps reindeer to see in the dark]
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