Our Other Moons

Anyone who reads this blog regularly will know that I don’t call that luminary in the sky “the Moon”, but Cynthia. This is because I think it’s important to acknowledge its existence as a body in the Solar System in its own right rather than simply an adjunct to Earth, and because calling it “the Moon” is like calling Earth “the Planet” without having any other name for it. Also, Cynthia is arguably not actually a moon at all. Looked at from the Sun’s (yes I know) perspective, Earth and Cynthia weave in and out of each other’s paths as they orbit and if Pluto is excluded, Cynthia’s mass is a far greater fraction of Earth’s at 1/81 than the moon of any other major planet. The pull of solar gravity on Cynthia is greater than Earth’s.

This leads us into the “nut” situation, where the thing which we think of as the quintessential example of a category turns out not to be, such as peanuts, almonds and so forth, because maybe “the Moon” is not a moon at all. Further, we get to the predicament of claiming that Earth has no moon at all, and that “the Moon” is something else. This sounds absurd. However, the question arises of whether Earth has any moons now, or had any in the past, or perhaps had more moons which collided and became Cynthia, and again whether these “moons” counted as moons.

One thing which comes to my mind is the Chicxulub Impactor, which wiped out the non-avian dinosaurs sixty-six million years ago. Is it conceivable that that orbited Earth for a while before it crashed down onto it? There isn’t any scientific reason to suppose either that it did or didn’t, assuming it to be an asteroid rather than a comet. If it was a comet, it’s unlikely to have done so as most of its substance would’ve vaporised if it had orbited us for long. It may be worth considering the Chicxulub Impactor separately than just in this post, because the situation is complex and research has suggested different things. Also, in a sense there’s nothing special about it, as this planet has been repeatedly hit by massive bodies in the current Phanerozoic Eon (the time since hard-shelled animals evolved). It’s unlikely that the scientific method can be applied to the paths of any of these objects to determine whether or not they were previously in a long-term orbit about our planet. A side issue here, which I’ve mentioned previously, is the possibility that Earth has had rings at some point due to asteroids approaching this planet but not hitting, and breaking up close to the surface but still beyond the atmosphere. Again, all that can be said about this is that it’s plausible. Evidence might involve finding a higher incidence of meteorites around the equator or climatic differences, but those would both depend on the position of the continents at the time.

In fact it looks like rocky inner planets tend not to have moons if our system is anything to go by. Neither Mercury nor Venus have any, though in the past both were thought to have one at different times. Mariner 10 was briefly thought to have discovered a moon of Mercury in March 1974 but it was actually the star 31 Crateris. Venus was also once thought to have one, named Neith, repeatedly observed by astronomers from 1650 onwards but never detected during a transit. It is odd that it was supposèdly seen so many times even though it doesn’t exist. It was considered to be proportionately the same size as Cynthia and to orbit perpendicular to the ecliptic, which is in itself quite peculiar. It’s now thought that most of the apparent observations were merely stars near the line of sight. Inner planets in general have a bit of a problem keeping moons due to the fact that the Sun’s gravity is relatively greater and the radius in which a moon can exist is small. In fact Cynthia is a good example of this because it orbits separately from Earth.

Mars, of course, has two small moons, but its case is a little different. It orbits closest to the asteroid belt, enabling it to capture asteroids, and being further from the Sun gives it more opportunity to do so. However, its moons orbit unusually close to it and one is unstable and will be broken up by tidal forces in a few tens of millions of years, becoming a ring. I suspect Mars has had a series of moons due to its proximity to a large number of asteroids. If Earth were closer to the belt, it seems likely that it too could acquire at least temporary moons. As it stands, asteroids are mercifully sparser at our orbit and the “price” we pay for this is that we have no captured moons.

Another aspect of this, already noted in the case of Cynthia, is that orbits look different depending on where you see them from. As far as we’re concerned, Cynthia orbits us once a month and it’s very simple, but from a solar perspective the orbits of the two bodies are braided, somewhat like the coörbitals of Saturn. The same applies to some of the possible moons of Earth. The classic example right now is Cruithne (“kroo-ee-nyer”). This asteroid takes a year, actually 364 days, to orbit the Sun in a roughly similar looking orbit interlocking with Earth’s, but from Earth’s perspective it describes a centuries-long path consisting of various alembic and horseshoe shapes as it moves around us. It’s been described as our second moon, but this isn’t really true, and there are a number of other bodies with similar relationships to both Earth and the Sun. It has a diameter of around five kilometres and its orbit is not entirely stable.

In 1846 an astronomer called Frederic Petit, of Toulouse, reported the discovery of a moon which orbited this planet once every two and three-quarter hours with an apogee of 3 570 kilometres and a perigee of only 11.4! At the time, it wasn’t known how to account for air resistance but even back then scientists were sceptical of a moon which dipped thoroughly into what we’d now call the troposphere. As was fashionable at the time, Petit claimed this accounted for irregularities in Cynthia’s orbit around Earth. His results were never reproduced, but he did end up having his idea mentioned in Jules Verne’s 1865 novel «De la Terre à la Lune». This spurred a lot of people into looking for it, and notably William Henry Pickering, who predicted the position of Pluto and claimed to have detected plants growing on Cynthia, actually looked for a secondary moon of Cynthia itself, which he presumed would have to be a maximum of three metres in diameter.

In 1898, the Hamburger Dr Georg Waltemath claimed not just one moon but a whole string of them. One of them, he claimed, was approximately a million kilometres away, took almost six months to orbit and had a diameter of around seven hundred kilometres. He claimed it had been seen in Greenland during the night period of winter in 1881, and further that it would transit the Sun. He and some companions reported that an object about six arc minutes in diameter did indeed do so, but it so happened that some other astronomers were observing the Sun at the same time and only saw sunspots, so that was the end of that. It may be an illustration of how easily one can be drawn into perceiving something by another’s enthusiasm, conviction or charisma, or maybe just of the power of suggestion. The largest of these moons was named Lilith by an astrologer and an ephemeris was prepared.

Now there are thousands of artificial objects in orbit, to the extent that they threaten future space missions. These are in a sense moons in their own right, though artificial ones. These could also provide evidence for the presence of other moons because of their gravitational influence on their orbits. It has been claimed that this happens, but the data used, at the end of the 1960s CE, were insufficiently accurate to judge. Hence although it seemed that something was detected, it was within the margin of error in the measurements, and it can’t be concluded that there’s anything there.

One thing which definitely does happen is that small asteroids occasionally get temporarily captured by our gravity. Kamoʻoalewa is the name of an object which appears to be a small chunk of Cynthia which is temporarily orbiting Earth. Like many other small planetoids in the system, it’s quite red, but the particular shade of red is dissimilar to those of various asteroids so it’s likely to have come from our main satellite. It appears to be about forty metres across, although it may be very irregular, and actually does describe the kind of orbit attributed to Neith, perpendicular to Earth’s orbital plane. However, although it circles us, it’s also beyond the distance where Earth is the main gravitational influence on it. Like Cruithne, Kamoʻoalewa is what’s known as a quasi-satellite, taking almost exactly the same time to orbit the Sun as Earth does and therefore staying close to this planet, but from Earth’s perspective appearing to travel around us in the opposite direction to our orbit in a kind of bent closed curve. The phenomenon is a little like retrograde Mercury. Mercury occasionally appears to be moving backwards in a loop from our perspective, but it’s because of the relative speed and positions of the two orbits around the Sun, except that it’s exaggerated by the asteroid’s extreme proximity.

There are something like five other asteroids with this kind of relationship with Earth, and incidentally Earth is not unique in this respect. As mentioned previously, there are also the Lagrange points of both the Earth-Sun and terrestrial-lunar systems. Analogous positions associated with other bodies are common, particularly Neptune, as I’ve already been into. There are both clouds of dust occupying the terrestrial-lunar Lagrange points and Earth trojans 60° ahead of or behind Earth in its orbit. No trailing trojans have been detected so far but there are at least two leading ones, one of which has a diameter of three hundred metres. I covered much of this in Antichthon (apparently I called it “Counter-Earth”).

Many, perhaps most, NEOs are analogous to extra moons. A group I haven’t mentioned yet is the Amor asteroids, named after the asteroid Amor and also including Eros. These come within 0.3 AU of Earth, or 45 million kilometres, and approach the Sun closest outside our orbit with a period greater than a year. This means they always orbit outside our own path round the Sun and are therefore not Earth-crossers. Four dozen Amor asteroids come within seven and a half million kilometres of Earth’s average distance from the Sun. Of them, Eros has actually been visited by a spacecraft. Most of them cross Mars’s orbit, putting them in the asteroid belt proper at their greatest distance from the Sun.

To finish then, Earth currently has no permanent (other) moons, as might be expected given the status of the other inner planets, and in fact we arguably have no moons at all because of Cynthia’s peculiar nature. If we were closer to the asteroid belt we might acquire some. This raises the question of how many otherwise Earth-like planets have any moons and whether this is significant for the evolution of Homo sapiens, but as I’ve said before, this series is not going to focus on life because everything does that. Interestingly though, although it hasn’t been demonstrated scientifically, it’s quite plausible to suggest that we have had other moons in the past and just as a closing comment, some people believe Cynthia was originally two bodies which collided, partly explaining the difference between the near and far sides.

The Solstice

Photo by John Nail on Pexels.com

Today has been the Summer Solstice in Britain and this time will have been the Winter Solstice in the Southern Hemisphere. It’s a little confusing how the solstices appear to move around. This is mainly because of leap years and the fact that the year is not exactly 365 days long in reality. I think there’s another explanation too, but I have difficulty remembering what it is. It’s also the case that Earth’s axis is precessing, which moves the position in the year of the solstices, and also the eccentricity of our orbit and the position of the points where we’re closest to and furthest from the Sun gradually change, although this may not be directly linked to the equinoctes and solstices.

One of the peculiarities of living in these isles compared to North America is that we’re a lot further north than either people living in North America or we think we are. This is of course because our climate is currently strongly influenced by the Gulf Stream. A dramatic way of illustrating how close to the North Pole we really are is to consider our position relative to the Alaskan Panhandle, which extends from 54°43′ to around 62° North. The southern figure is also the latitude of Hartlepool, and the whole of Scotland is north of that latitude, as is about half of Ulster. The northernmost point of Scotland, Out Stack (and not Muckle Flugga as many claim) is about 60°51′ North, meaning that most of the Panhandle is actually south of the Shetlands. As for the Aleutians, they extend as far south as 51° North, which is even south of most of Kent.

Anyway, one of the consequences of this is that even in England we get a six week period around the Summer Solstice where it doesn’t get properly dark. Today, the Sun will set at 10:42 pm on Muckle Flugga and sunrise tomorrow there will be 3:29 am. Compare that to Le Marais de Samarès in Jersey, which is more or less the southernmost point of any part of the Atlantic which might be considered to be entangled officially with our government, where the sunset will be at 9:17 pm and tomorrow’s sunrise at 5:03 am. The midpoint between those two, or rather the closest point on land to it, is the Northumberland village of Boulmer, where sunrise tomorrow will be 4:24 am and sunset tonight will be 9:52 pm. I feel a bit twitchy about the idea that Boulmer, which is only thirty-seven kilometres from Scotland, is in a sense the midpoint of this political entity. This gives us a maximum apparent length of summer solstice night for these three places, north to south, of four hours and forty-seven minutes, six hours and thirty-two minutes and seven hours forty-six minutes, or so says my brain calculator. However, this isn’t the whole story because the Sun will not just cut out when it sets, and this means, for example, that the stars, or strictly speaking any other stars than the Sun, will not become visible for quite some time sunset and will also disappear considerably before sunrise. And even here in the English Midlands it doesn’t get completely dark.

This might sound wonderful to someone living closer to the Equator, and I admit that I’d like to see the midnight Sun one day, but in fact I find it a complete pain, as do many other people. It makes it difficult for people to sleep and the long days also seem to stir people up and agitate them into “midsummer madness”. Last night I went to bed before sunset, which is always disconcerting. Patients I’ve had with mental health issues, particularly those who are bipolar, often find themselves entering a manic phase at this time of year. It’s sometimes felt like a race against time when a client has started to report problems or behave in a manner which is cause for concern several days before the solstice and knowing that there’s nothing anyone can do to prevent the main precipitating factor from getting worse for a week or more, and double that time coming out of the other side, by which time the person may have done something to themselves which may have a long-term impact on their well-being. It isn’t just bipolar either, because poor sleep is involved in other mental health issues. It’s now thought that the correlation of poor sleep with mental health problems is not causative, but I find myself K-skeptical of that because sleep deprivation clearly does have an adverse influence on it. The worrying and rumination which occur for many when they’re lying awake is not going to get better if it’s too light for them to sleep well, and paranoia and schizophrenia do seem to be triggered by it. This feels sometimes like a train bearing down on one at full speed because obviously we live on a massive great rock with a huge amount of momentum and it isn’t feasible or even desirable just to flip it into an upright position with respect to its orbit, which would in any case probably trigger a mass extinction and cause the ice caps to melt. We can’t live without seasons either.

There’s also the spiritual aspect. Judaism, Christianity and others do have a midwinter festival and this makes sense psychologically because it counteracts the misery of the cold and dark, and also the fact that many sources of food have shut down for the winter so we have to rely on all that is safely gathered in, but a midsummer festival isn’t as celebrated in the Abrahamic tradition today, although of course it is a big thing for Neo-Pagans. Like Xmas, Midsummer is for some reason considered to be several days after the solstice. I don’t know why this is, although if one regards today as the beginning of summer, which it is astronomically (i.e. declared to be so by the astronomical community), summer ought to be over by the start of July. Clearly it isn’t, although it does seem to be rather short here.

The summer solstice is one of those astronomical events which is almost the opposite of an astronomical event, along with the Full “Moon”. It makes it harder to observe the night sky, and in the latter case harder to see details on Cynthia herself as well as fainter objects in the sky at the same time. This issue makes the observation of the Jewish Sabbath more complicated far from the Equator. According to Halakha, which does not speak for all Jewish traditions, the Sabbath ends when three stars are visible in the night sky on Saturday evening. Within the polar circles this may not happen for weeks at a time, and even in England there can be a problem, not least because it tends to be cloudy as well. The alternative is to look at a white and a blue string until it’s no longer possible to distinguish their colours. This too can be a tall order in these parts of the world at certain times of year. As with some other cultures, this links to a timekeeping system where hours vary in length according to the length of daylight and night because of the interval between sunset and when this is no longer possible. In physiological terms it means the point from which the blue wavelength cone cell no longer functions, and in my mind it raises the questions of visual impairment, complete colour blindness and the extent to which the blue string is dyed. In a way, this is not my problem but in another way it is because I want to observe the Sabbath “properly”, even though I’m not Jewish, because mindfulness on the rituals is spiritually significant. In the Church of England, there are a number of sacraments, including the Eucharist and Baptism, and as an ex-deputy church warden it has been my rôle to prepare for both. Pouring water into a font and wine into a chalice are similar experiences, to be done mindfully, almost as a form of meditation, taking care not to spill any and although it’s vital to avoid idolatry, these liquids become charged with spiritual cathexis. The same applies to beginning and ending the Sabbath, and although I also feel that I’m engaging in cultural appropriation here, am I doing so to a greater extent than when I practice Yoga? If it makes it easier for me to behave compassionately towards others by practicing this, I don’t understand why I shouldn’t do it. It’s all rather complicated.

Islam, a proselytising universalist faith to which I ironically feel much less drawn, also has issues when practiced far from the Equator, mainly because of Ramadan. Because in terms of the solar calendar Ramadan cycles through the year, the requirement neither to eat nor drink during daylight hours is difficult to fulfil near the poles because of twenty-four hour daylight for some of the year, although there are rulings regarding this, and also ad hoc practices. Some people, for example, decide to use the time of sunset and sunrise in Mecca to time their fast. A similar problem exists with the qibla for Muslims in low Earth orbit, because this constantly shifts. I was once curious about the antipodes of Mecca and found that it was, as expected, at the bottom of the Pacific Ocean but nonetheless close to Mururoa, since at that location the qibla is in all directions, bringing to mind the possibly apocryphal story about the Sikh guru who fell asleep in a mosque with his feet pointing at the qibla, and on being awakened and made aware of this fact saying “point my feet in a direction where Shabad is not”. I’m afraid my memory of this is rather sketchy and I apologise for that, and for my terminology.

I don’t want to problematise the solstice though. I’m aware that as I’ve been writing I’ve mainly used this post to complain about the negative side of this day. It’s also a day of high energy, with exuberant plant growth, animals foraging over a longer period of time and feeding their young and so forth. It’s also a breeding season for many species, which makes me wonder if it was in the distant prehistoric past. Would this also have been the time of year that non-avian dinosaurs were displaying, performing courtship rituals and tending their young, for example? Is there a way of knowing? Or were there fewer reasons to do so because the seasons were different and the climate was warm throughout the year? Does it depend on that or is the signal simply the longer days, used to coördinate breeding behaviour?

I have occasionally decided to stay up all night near the solstice, notably in ’86 although that year I actually did it on 26th June. Until very recently, I had never seen a sunrise and in my attempt to do so then I also failed because after a while I realised I was looking at a street lamp from a great distance. There is a problem with deciding when sunrise and sunset really happen if you don’t live in a relatively flat and featureless environment, because the Sun will only appear over the skyline and not the horizon, which is an abstract concept in most places I’ve been. However, there are a few places in Great Britain where one can genuinely see the horizon at sea level, without it being interrupted by land, and where this is in the West, a rarer circumstance than the East, it’s possible to witness the “green flash” and the “green ray”. These are optical phenomena taking place at sunrise or sunset, but the chances of being around to see the sunrise are lower. For a second or two as the Sun becomes invisible or visible behind Earth’s limb, and the air is clear, refraction separates the colours of sunlight and Rayleigh scattering – the cause for the sky being blue – is removed from what’s visible to the eye. Because the shorter wavelengths of light are bent differently than longer ones, the visible portion of the Sun is then green-looking. Sometimes this takes the form of a ray projecting from the horizon. It’s also enhanced by shimmering air, which I think probably makes it more likely at sunset when the air is warmer, and also quite rare in Britain. Hence one likely place for it to be seen is in West Cornwall, which is warmer and faces the Celtic Sea rather than the Irish.

To finish, I want to mention in passing an idea used in the excellent ‘Handbook For Space Pioneers‘ concerning what would happen on a planet orbiting one of the companions of α Centauri. Although there are close binaries around which habitable planets might have stable orbits, one would expect most of them to have a second companion at a distance from the first, i.e. the closest, and therefore there would be a period during which there were two suns in the daylight sky and another when the other sun lit the night sky. This would effectively provide conditions close to daylight around the clock when the planet was on the same side of the star as its companion, and since the stars are also orbiting each other this constant daylight condition would shift around the calendar, sometimes occurring in winter, sometimes in summer. In the book, this is almost as important to the ecosystem as the seasons, with some plants only growing when the night sky is also lit and animals emerging from eggs during this period alone, along with more complex animals using the period to feed their offspring to maturity more quickly. This raises the question of what would happen on a planet with two close binary companions within its orbit, such as the Trojan used for a series of stories including one by Asimov called ‘Sucker Bait’. A Trojan body is one orbiting in an equilateral triangle with two others, the most notable examples in this Solar System being the Greek and Trojan “camps” of asteroids sixty degrees behind and ahead of Jupiter in the same orbit. Two similar Trojan stars would provide 240° of daylight to a planet of this kind, meaning that if it had a twenty-four hour day it would average only eight hours of night. If the stars were of different luminosities and/or spectral types, the colour of sunlight would also vary throughout the day, and if there were a significant axial tilt, things would be even more complicated.

But we live on Earth, and sadly will probably never leave, so at least we won’t have to consider how to observe the Sabbath or Ramadan on other planets.

Happy Solstice!