THE TURNING OF THE EARTH

At one time, not so long ago, all of us would have been tuned in to the way the world around us changes through the year. We had to be; it was essential for our survival. We depended on the wildlife and wild places within walking distance of our homes

- for food, firewood and even clothes to keep us warm.

Just a few generations on - the blink of an evolutionary eye

- and we are so effectively insulated from the natural world that the connection has been all but severed. We no longer take food or fuel from the woods. And our ability to travel huge distances means that an intimate knowledge of our local area and the way it changes through the year is often lacking. Tie changing weather is still a topic of interest; we certainly talk about it a lot. But we are so well shielded from its effects by central heating, supermarkets and synthetic clothing that our interest is now casual rather than deep-rooted. The weather and the turning seasons have become useful subjects with which to start a conversation, rather than elemental forces that impact significantly on our daily lives.

A deep understanding of seasonal changes comes through spending time in the local countryside throughout the year and observing how the wildlife responds. Even the most urban of us are familiar with the basics. The way that certain birds arrive in spring and leave again in the autumn, to be replaced by winter visitors from the north and east. And the way most trees drop their leaves in order to see out the coldest, darkest months of the year. But there are endless subtleties at play, and only by becoming a careful observer of change can we fully appreciate them.

There are, however, a few shortcuts when it comes to grasping the bigger picture of how the seasons work.

First off is a simple idea that helps tune in to the way the Earth works, without needing to stray far from home; it is the ultimate in ‘think global, act local’. There are four landmark days each year that signal the turning of the seasons. We have the winter solstice, the shortest day, on or around 20 December (varying a little from year to year) and its counterpart the summer solstice, the longest day, around 20 June. At equal intervals between them are the spring and autumn equinoxes (around 20 March and 20 September) when daylight and darkness are exactly balanced, everywhere on Earth. I try to make sure that I spend time outside on each of these four days, for no other reason than the significance of the date.

The most important date for me is the shortest day. It falls at an otherwise hectic time of year, just a few days before Christmas, when like many people I’m rushing around, looking for last-minute presents. The winter solstice offers a moment to pause and reflect, as well as a tiny glimmer of hope, just as we are set to face the two coldest months. The sun is now as low in the sky as it will ever get. From here on, it will creep a little higher each day, and feel a little warmer on the skin, slowly at first but, in time, picking up pace as winter begins to ease into spring. It’s a small, small thing, but I return from a walk on the shortest day with a subtly changed mindset and a renewed anticipation for the coming holiday and the months ahead.

The longest day has a similar effect. It offers a moment for reflection, but this time there is a hint of melancholy. Now the sun begins to sink in the sky, a little more each day. Because our seasons lag well behind the Earth’s annual journey, this happens even before the year’s hottest months of July and August are upon us.

Paying attention to these changes helps me feel a greater connection with the wildlife all around me. Plants and animals are keenly attuned to day length as by far the most reliable indicator of seasonal change. The weather is notoriously unpre­dictable, with frequent unseasonably warm or cold spells. But day length is a cast-iron marker of where we are in the year. If you have a nest to build and a family to rear, it provides essential information so that your timing can be spot on. It is modern humans alone who have found other ways to track the turning of the seasons. Everything else continues to rely on this funda­mental celestial measure.

After the shortest day, birds are far more willing to offer up snatches of song, especially when the weather is settled. Even in late December they have started to anticipate the coming spring and I begin to hear hesitant notes from around the garden. It’s all a little half-hearted at first, but come the spring equinox in March most of our resident songbirds will be singing loudly and persistently, and some will already be building their nests. By the time of the longest day, in late June, breeding will be well underway or even finished for another year. From then on, song drains slowly from our landscapes once again, as the nights begin to lengthen.

The night sky offers another link to things that are outside our control and beyond full understanding, as well as a way of tracking the seasons. Many of the stars visible in the sky change predictably through the year; I’m familiar only with a few of the most prominent constellations but for me they have come to stand for the seasons they preside over. In the northern hemisphere, Orion looms large through the coldest months of winter, the brightest of its stars already visible by the end of the afternoon.

I see in these seasonal patterns, parallels with our common, widespread birds. Orion is prominent during the coldest months, when Redwings and Fieldfares are spilling from the hedgerows into the local fields. The summer triangle is overhead on warm nights when the Swallows and House Martins are waiting patiently at their nests or roosts for daylight to return. Or it provides a backdrop to a late-night trip to see Nightjars or to hear the ethereal song of the Nightingale. It becomes more difficult to see in the autumn, much like the Swallows, as it falls lower in the sky. And then, like the Swallows, it disappears completely for the coldest months. As with our summer migrants, we must wait until spring for it to return. In contrast, the Plough and its close associates represent our common residents. Like the Blackbird, Wren, Dunnock, Robin and Chaffinch, they are there with us through all four seasons, through good times and bad.

I sometimes look up at the night sky and try to picture our ancestors doing the same thing. It feels like a connecting thread back to ancient times. And yet the shapes of our familiar constel­lations are constantly changing. On the scale of a human lifetime, the patterns remain true, as does the timing of their appearance in the sky through the seasons. But, in reality, the stars involved are all hurtling through space in every direction, and at wildly different speeds.

It’s not just their relative positions in the sky that are subject to change, but the very existence of the stars themselves. We see stars not as they are but as they once were; their light takes a truly cosmic amount of time to reach us. The vast distances involved lead to some unsettling conclusions. Most of the starlight that enters our eyes began its journey before we were born. Take the three prominent stars that make up Orion’s belt: if they had all ceased to exist in 1000 bce then we would notice nothing until two of them flickered out of sight around 200 years from now. The third would finally vanish from view sometime around the year 3000. We have no way of distinguishing them, but some of the stars are already ghosts.

The planets are more haphazard than the constellations in their appearances. No regular patterns are discernible to the untrained eye. These days, of course, there are apps to tell us exactly what we are looking at. But a little inbuilt knowledge adds to the experience. The brightest planets - Jupiter, Venus, Saturn and Mars - are often more brilliant than any visible star. They don’t make their own light but shine only because their surface reflects the sun, and they have a firm, steady light. The stars are distant balls of blazing gas, like our own sun, but much farther away, and the brightest ones can be seen to flicker (or twinkle) because of the huge distance the light has to travel and the way it is refracted before it reaches us. With a little practice, this knowledge alone can be used to distinguish between a bright star and a planet.

But which planet? That’s trickier, though there are some distin­guishing features. Mars glows an eery red, betraying the nature of its rocks. Saturn has its rings, which can be made out with good binoculars (just), or more clearly through a birdwatching telescope.

Our own moon has a special draw and power, both real and imagined. It pulls the oceans around and it plays with our minds if we let it. My parents remind me that I’d sometimes refuse to go to sleep as a child until I’d tried to see the moon and either succeeded, or satisfied myself that it was hidden by cloud or not present in the sky that night. This pock-marked sphere of rock circles us every month, following its own routine and offering another way in which we can keep track of timelines here on Earth. From a delicate, thin crescent it increases a little in size each night as it waxes, until it shines out as a full moon, roughly once each month. Then it wanes, back to a slim crescent before disappearing completely, only to return a few days later as the cycle begins once more.

As with the planets, we see the moon only because the sun’s light is reflected from its surface. When it is on the far side of the Earth to the sun, the whole surface receives light and is visible to us. But when it moves around so that it is almost between us and the sun, the light catches the edge and we see only the thinnest of slithers.

The darker areas of the moon are known as seas because that’s what they were mistaken for by early astronomers. Actually, they are areas where volcanic activity has produced rocks that are less reflective than the rest of the surface. The moon is a stunning object when viewed with binoculars, or even better through a birding telescope, especially in its crescent form when the texture of the seas and craters stand out most clearly.

The moon always looks bigger when low down in the sky than when riding high overhead. This so-called moon illusion is a trick of perspective, resulting from proximity to the horizon. The illusion is so powerful that many people refuse to believe that the size difference is not real. But it’s easy to confirm by matching the moon’s size to one of your fingernails held out at arm’s length. It will take up the same amount of space wherever it is in the sky.

Dust in the atmosphere gives the moon an ethereal yellow or orange glow when it’s low in the sky. This is exacerbated in the autumn by dust from harvesting crops and in September or October (depending on the year) the harvest moon is well known for this. The full moon always rises in the east just as the sun is setting in the west. In summer this means that it appears late in the evening when most of us are indoors. But by the autumn it has become an earlier event.

The moon is a constant, reassuring presence through our lives. When I think back to ‘Eastfield’, the old family home where I grew up, there is one memory that stands out above all others - the view from my old bedroom on perhaps a handful of evenings each year. I can see it now: stark, leafless winter trees where the woods meet the back lawn, and a huge, butter-coloured moon rising up behind skeletal branches as darkness settles over the garden. I can remember sitting back in bed, head fixed in position, so that I could make out the moon’s slow but relentless movement against the horizontal branch of a Beech tree, watching as it touched the bottom edge, and not allowing myself to move until it had started to emerge into the blackness above the same branch. I still do the same thing occasionally, today, using the edge of a window frame. It takes me straight back to that old, familiar house.

By staggering coincidence, the moon is 400 times smaller than the sun but 400 times closer to Earth. As a result, they both take up exactly the same amount of space in the sky, something that occasionally results in a total solar eclipse, the moon slipping perfectly over the disc of the sun. Another seemingly remarkable coincidence is that the moon spins at precisely the rate required to keep the same face presented towards Earth as it orbits - hence the unseen and (until recently) unknowable dark side. Evidence for divine intervention? Perhaps not, but, once again, it plays with your mind.

Ancient humans would have followed the moon’s progress with interest as a valued illuminator of the night to aid hunting, to avoid predators and, in more recent times, to help gather in the crops. They would no doubt have been aware that a full moon casts far more than twice as much light as a half-moon: it is around ten times as effective as a light source. This is because the moon is directly opposite the sun when full, and so light hits it straight on from the Earth’s perspective, with more of it reflected to us. In contrast, the landscape of the illuminated part of a crescent or half-moon is partly in shadow, making it more inter­esting to look at with a telescope but far less effective at lighting up the Earth.

Just after the full and new moons, when the Earth, moon and sun are lined up, the gravitational pull from moon and sun work together. At these times, the sea reaches higher up the beach and falls further back, revealing more of the lower shore. Early humans, eyeing the shoreline for a spot of foraging, would surely have considered the state of the moon to plan the timing of their visit.

We have no need to track the moon’s progress so carefully these days. I often notice it and have no idea where it is in its cycle. Luckily, there’s a handy trick. In the northern hemisphere, if it can be made into an imaginary (lowercase) ‘b’ by adding a stem then it is ‘beginning’ and will get bigger each night until full. If the addition of a stem turns it into a ‘d’ then it is in decline and will decrease a little each night.

The Earth shines when it is bathed in sunlight, much like the moon. This is obvious in photos taken from space, but it is also revealed by the moon itself in certain conditions. The familiar sight of a slim, bright crescent with the rest of the moon’s surface faintly visible is sometimes referred to as ‘the old moon in the new moon’s arms’. It happens because sunlight falling on Earth shines back out into space and is caught by the moon, including the areas not lit directly by the sun. Just as light from a full moon illuminates our fields at night, so the sunlight reflected from Earth is enough to shine upon the moon’s seas and craters - and then back again to our earthbound eyes.

One thing about our night sky is changing rapidly. It is no longer a wholly natural refUge if you are seeking solace and distraction from modern life. Ever greater numbers of satellites are being launched, and many of them are visible as they trace across the sky, taking a minute or two to pass over. I’ll never forget seeing my first, about thirty-five years ago on a late-night walk back to my university accommodation. I was dumbfounded that a human-made object, out there in space, beyond the boundaries of our atmosphere, could be seen from the ground. These days it’s all too easy to see four or five within a few minutes, and some, including the International Space Station, are brighter than the brightest stars or planets.

All the distant bodies we see out there in the night seem impossibly remote, unknowable and otherworldly. And yet we have the understanding, and the mathematics, to be able to predict the timing and location of their passage across the sky with astonishing accuracy. Does that lessen the magic just a little? If so, then it might explain why the objects I most delight in seeing are still well beyond the reach of human predictions. The timing of meteor showers is known well enough, and the same ones come around at the same time each year. But the appearance of each individual meteor, its brightness, and the direction it will take across the sky are all down to chance. For once, an app won’t help.

Meteor showers are named after the constellation from which they appear to radiate. We have the Orionids, Perseids, Leonids and Geminids, to name four of the best known. And each produces shooting stars that have subtly different characteristics. As well as the number of meteors per hour, the colour and brightness vary, as do the speed at which they streak across the sky and the likelihood that they will leave a trail behind them. If you’re a fan of slow-moving yellow fireballs then try the Alpha Capricornids in late July, though don’t expect to see very many. Two weeks later come the far more abundant Perseids, which tend to be bright and fast, and sometimes leave a trail.

Every meteor I see is a small, unexpected, but wonderful shock to the system; a flash and a trail across the blackness, gone before there is time to pause and dwell on the spectacle. A scrap of rock that has existed, in some form, somewhere, for countless millennia, enters our atmosphere and, in a last blaze of light and speed, is gone.

There is one final, time-honoured, way of appreciating how the Earth moves in relation to the rest of the universe: its daily spin on its own axis. It’s easy to forget that we are all hurtling through space at upwards of 1,000 kilometres per hour. Watching a sunset (or sunrise) is one way we can get some sense of that speed. Only at these times does the sun’s proximity to the horizon allow the pace of movement to be seen clearly. Any low, reasonably level, horizon will work but the sea is by far the best place. It is completely flat, and the play of light across the water adds to the magic. Once the bottom of the sun touches the horizon, it begins to sink at such a rate that the turning globe becomes a believable reality. Just a few seconds later and it will be gone completely for another day.

If your luck is in, you might even see the fabled ‘green flash’ in the last moment before the tip of the sun finally slips away. This is caused by the way that light is refracted and scattered in the atmosphere, and it is best seen on a day when the air is clear and stable. I’ve seen it just twice in fifty years. The last time was a few years ago on a family holiday near Tintagel in north Cornwall. Seven of us were stood on the high cliffs looking out over the sea and witnessed a climax to the day so stunning that we felt like applauding - a final brief pulse of green light, and then nothing but the gradual dimming of the sky towards nightfall.