Out for a walk with our hosts in Darmstadt, we stopped at a sundial. One looked at the watch and said “It’s not correct.” The other said, “It is summer time. If you allow for that, it is accurate.” Once you have calibrated a sundial it lasts as long as the earth does not tilt on its axis more than it has done in the last few hundred years. I don’t know exactly how long the earth’s axis will remain fixed, but certainly longer than recorded. While I’d been looking at a detail and thinking of the end of civilization, The Family had been admiring human-sized things.
Turning to me, she asked “Can you take a photo of the whole column?” I did. It was a beautiful baroque column in the middle of a garden laid out around it for the enjoyment of a prince who built his baroque palace nearby. Darmstadt is a prettier town than I’d discovered earlier. You see a town so much better with gracious hosts who walk with you around their hometown.
Heavy footsteps came rapidly down the corridor. There was a knock on our door. It was the man we’d talked to in the restaurant a while ago. He said “It’s lighting up, look out. I came to my room to get my camera. It’s easy to photograph from outside the hotel.” There”d been a huge solar flare two nights before, and the mass of plasma ejected from the sun must have just hit the atmosphere. We switched off all the lights in the room and looked out of the window. The sky was absolutely clear. It was a spectacular show.
We’d taken trips out to the lake on the previous two nights, and had got some views on one night. But this was much more than what we’d seen before. The Family said “I can see colours with the naked eye.” Unfortunately I was caught unprepared. I had no tripod, so I had to take long-exposure shots without one. ISO of 1600, exposure of between 8 and 6 seconds, the most that I could keep reasonably steady with my bare hands. The results are what you see here. In the first one I got some of the pink colour that I’d seen before. The curtains of light rippled and shifted. The main show lasted ten minutes, but we could still see a weak glow later. Typically a storm of this strength stays for about 12-14 hours.
Much later, in the middle of the night, The Family woke me up. “It’s started again,” she said. This was even more spectacular, but I was not sure that I was awake enough to take photos again. Pinwheels and bars of light unfolded across the sky. And then again a couple of hours later. It was a satisfactory end to our travel to Abisko National Park in the frozen north of the world. This is the kind of spectacular show I remember unfolding in the clear sky over Helsinki on a winter’s night twenty three years ago. It was a wonderful reprise for me, and a new experience for The Family.
Polar circle! As a child I’d spun my globe, tracing my finger over the dashed line which indicated the latitude of 66°34′ North, imagining stepping into the frigid air of the region north of this line, mind full of muddled thoughts about penguins and igloos. The reality is different. Yes, it is cold. When we landed in Sweden’s northernmost airport, Kiruna, I was taken aback by the fact that the plane was taxiing on ice. However, from the air I’d seen forests surrounding numerous lakes and streams, frozen now in early February, promising wonderful forest walks in the summer.
We’d quickly donned our layers when the seat belt sign was switched off. The lady seated on the third seat in our row told The Family “You are well prepared. You’ll enjoy this.” She lived in Stockholm and was visiting her daughter in Kiruna for a few days. The ladder was attached, the door opened, and we stepped down. Kiruna is about 140 Kms north of the Polar Circle, which means that when the sun sets on 10th December this year it will rise only on the 2nd of January next year. We were a bit late in the season for that.
It didn’t feel as cold as it had one afternoon in Stockholm. The Family and I stopped on the tarmac for a selfie. The flight had been full, about half of the passengers were people who had some business in Kiruna. The rest were like us: tourists. You could tell the difference now. Tourists were busy snapping off photos on their phones.
Satisfied for the moment, we walked on into the small terminal. The lights inside the doors looked welcoming and warm. It was a matter of minutes before we’d found our bags and located our taxi. Taxi services here might collapse without Somali immigrants. It was a pretty short drive to our hotel. We kept looking at the sky hopefully, but it was still too bright to spot auroras.
On Newton’s birthday, today, I find myself thinking of comets. Edmund Halley’s first calculations of the orbit of the comet named after him was the first application of Newton’s theory of gravity to any object other than planets and their moons. His calculation of the comet’s period had been corrected by taking into account the perturbation of its orbit by Jupiter before the comet’s next appearance. In modern times Halley’s comet was visited by five spacecrafts in March 1986: by the Russian spacecrafts Vega 1 and Vega 2, the Japanese Sakigake and Suisei and the Giotto of the European Space Agency (ESA). They established that the comet’s nucleus is a lumpy rock with ices. As the comet warms on its approach to the sun, these ices vaporise and jet out of the rocky core, carrying dust, and gravel with it.
The first observations of Halley’s comet has been traced back to 1500 years before Halley. On the other hand, a comet called 8P/Tuttle was only discovered in the 19th century. This is actually what made me think of comets now. The dust and rocks left over from its previous solar encounters create a meteor shower that is seen every year a few days before Newtonmas. This year the peak was at 10:00 UTC on December 22. The meteors seem to come from the direction of the constellation Little Dipper (Ursa Minor). The reason is simple. The dust follows the same orbit as the comet which generated them, and its direction of motion is always tangent to its orbit. The orbit of 8P/Tuttle is highly inclined with respect to the earth’s orbit. At the point where the orbits intersect, when you project the direction of motion of the dust back into the sky, it seems to come from the Little Dipper. Because of the apparent point of origin, the meteors are said to belong to the Ursid meteor shower.
The last two closest approaches of the comet were in 2008 and 2021. A huge number of observations were made at this time, including by the Hubble and Spitzer telescopes. As a result we know that the nucleus of the comet may be modelled as two roughly equal spheres touching each other. In 2008 this shape might have been mildly surprising. But in 2013 the European Space Agency’s Rosetta spacecraft made a rendezvous with the comet 67P/Churyumov-Gerasimenko and took close up photos of it. One such photo is the featured image. It shows that the comet has a strange shape, and as it approaches the sun volatile materials jet out of it to give the “tail” that we see it by. Two balls touching each other is not a bad description of something like this. But why this shape? Perhaps it is due to the loss of the material. Or perhaps on a previous solar encounter the comet actually broke into two pieces, which gravitated back towards each other and stuck. But it will take more observations to figure out why.
The Ursid meteor shower has become fun to watch because it turns out that the number of meteors can be as low as two or three per hour in some years, and as high as nearly two hundred per hour in others. This means that the dust strewn along the orbit of 8P/Tuttle is not uniformly distributed, but is bunched up. What is this due to? Since the days of Halley it has become clear that the gravitational perturbations of Jupiter (and Saturn, to a lesser extent) play a major role in shaping the orbits of comets. It seems that the same effects could cause this bunching in the beam of dust that circulates in the wake of the comet. But exactly how it happens, and the predictions for the rate of meteors visible in the Ursid shower, is still a matter to be settled.
The wonderful thing about Newton’s stroke of brilliance is that it poses questions which challenge others to solve them. In this way Newton’s genius still reaches out through the centuries and touches us, almost as if he was still alive. That’s something to remember the next time you admire the apples and other ornaments on your favourite Newton’s tree.
You are sophisticated enough to realize that January 1 was just like any other Wednesday in the year. You woke up groggy and didn’t feel like going to work. It was nothing special. That’s because the true new year is today. Why? You ask. What makes one day more worth celebrating as the beginning of the year than any other? Today is the day when the earth comes closest to the sun as it rolls around its elliptical orbit. Yes, today is perihelion day.
A year (in most cultures) was the time taken for the sun to complete a cycle through the distant fixed constellations. 482 years ago, in the year that we count as 77 BME (Before Modern Era), Copernicus published his finding that the earth orbits the sun, and that the apparent motion of the sun through the sky is due to it being closer to us than the distant stars. But in his time the earth was supposed to orbit in a circle around the sun. Since any point on the circle is as close to the sun as any other, there could not be an unique point on the orbit, an unique day, which we could choose to celebrate as the end of a year and the beginning of another.
The Modern Era began with the publication of Kepler’s book, 406 years ago. Through his findings, the world recognized for the first time that the earth’s motion around the sun describes an ellipse, with the sun at a focus. One special point on the orbit was the closest that the earth could come to the sun. This is the perihelion. That dawn of the modern era we count as the year zero ME. And perihelion day, the 4th of January, we celebrate as the beginning of the year. So, a happy true new year.
Monuments are bigger than men. The unfinished tomb of Yasawi in Turkestan, a town in Kazakhstan, dwarfs spectators. It was the first monument planned by Timur, whose architects later went on to build the monuments in Samarkand.
Mountains are bigger than monuments. At sunrise Kanchanjunga floats serenely above the town of Darjeeling. The town does not contain stupendous structures, but is far larger than a Timurid monument.
Continents are larger than mountains. A view of Greenland from eleven kilometers above the earth does not yet encompass a full continent, but it does show a large part of a mountain range. Enormous icebergs are merely dots of white in this photo.
Planets are bigger than geology. Entire continent-sized lowlands are just dark blotches in this photo of half the moon.
The solar system dwarfs planets. I captured a conjunction of the gas giants Saturn and Jupiter in a hand held camera. If you look carefully you’ll notice that the Image of Saturn looks a little elongated. That’s the rings seen obliquely.
This is the limit of what a hand held camera can capture. And the universe is larger still.
You are sophisticated enough to realize that January 1 was just like any other Monday in the year. You woke up groggy and didn’t feel like going to work. It was nothing special. That’s because the true new year is today. Why? You ask. What makes one day more worth celebrating as the beginning of the year than any other? Today is the day when the earth comes closest to the sun as it rolls around its elliptical orbit. Yes, today is perihelion day.
A year (in most cultures) was the time taken for the sun to complete a cycle through the distant fixed constellations. 481 years ago, in the year that we count as 77 BME (Before Modern Era), Copernicus published his finding that the earth orbits the sun, and that the apparent motion of the sun through the sky is due to it being closer to us than the distant stars. But in his time the earth was supposed to orbit in a circle around the sun. Since any point on the circle is as close to the sun as any other, there could not be an unique point on the orbit, an unique day, which we could choose to celebrate as the end of a year and the beginning of another.
The Modern Era began with the publication of Kepler’s book, 405 years ago, which recognized for the first time that the earth’s motion around the sun describes an ellipse, with the sun at a focus. One special point on the orbit was the closest that the earth could come to the sun. This is the perihelion. That dawn of the modern era we count as the year zero ME. And perihelion day, the 4th of January, we celebrate as the beginning of the year. So, a happy true new year.
A clear view of the western horizon might have shown me Jupiter and Mercury before they set. Venus and Mars would be higher in the sky, on either side of the moon. It would be a spectacular sight.Since I was not in a city I could walk out to a place where the horizon was uncluttered. Unfortunately, the glorious view that I had of the sky was nothing to do with distant planets; it was our atmosphere that set up the fantastic light show that you see here.
March had been unseasonally hot this year, and in the last week of the month it got worse. A constant cloud cover allowed the humidity to build up to levels where the air felt about five degrees warmer than it actually was. On this evening, my last away from Mumbai, a storm set in as I went out for my walk. I didn’t dare to take my camera with me just in case the thunderstorm brought a huge downpour.
But the camera was not needed, since the sky remained overcast.spectacular light show My phone was enough to catch the spectacular light show in the sky that day. I missed the line up of four planets (the fifth, Uranus, was not going to be visible to the naked eye) but I got some photos. Was it a fair trade? Who knows?
As the common era carried across the world by European colonialism contracts to its core, everyone is again aware of multiple celebrations of new years. In India different regions have slightly different ways of counting the year, so there are many Indian new years, but there are two major groups: one in the middle of April, another about a month earlier. These traditions are actually wider, being celebrated across much of south and south-east Asia. The Chinese new year falls between the last weeks of January and February. Korea, Vietnam and Tibet have customs similar to this. Parsis and Iranians celebrate the new year on the day of the spring equinox. Several African cultures have a new year during the summer of the northern hemisphere. And there are a whole set of cultures who celebrate new year in autumn. So is the year just a human social construct?
You could treat it as such, but it is also true that the earth has cycles which are independent of humans. The succession of day and night, the slower waxing and the waning of the moon, the even more stately tilting of the axis of rotation which produces seasons, they are all cyclic astronomical phenomena. We base the day on the first, the month on the second, and the year on the third. What we see as the tilting of the earth’s axis is actually due to its pointing in a (more or less) constant direction in space as it takes us on its grand circuit around the sun. So the year is a measure of the time the earth takes to go around the sun. You may think of different cultures of new year as different ways of marking a special point on the earth’s orbit around the sun.
But 404 years ago Kepler opened a way to showing us that one point is really special. He found that the earth’s orbit around the sun is an ellipse, and not a circle as many cultures had concluded. He also discovered that on the day when the earth passes closest to the sun, it is travelling fastest on its orbit. This is the point which the earth reaches today, every January 4. I guess that makes it the true astronomical new year. Today we enter the new year 404 Modern Era.
For two nights before holi we were away from any city. Holi is always on the first full moon day after the spring solstice, so, being away from cities, we had very clear views of the moon at any time between sunset and sunrise. I took a few photos of the last days of its waxing phase. Later when I looked at them, I remembered that I’d heard about how much more is known about the moon today than when I was in school. But I hadn’t ever found out what. So I looked. Apart from a Wikipedia article, there aren’t any books or popsci articles, but there’s a lot of scientific literature. Most of it was beyond me, but I did find a few that referred me to more and more recent papers until I landed on one that gave a nice and brief account of the current state of our knowledge.
Two days before full moon
Why don’t people photograph the moon more often? It is the only other planet whose landscape we can see with the naked eye. Most good zoom lenses allow us to take good photos of sunrise over lunar mountains, and the changing soil across its landscape. I find it fascinating to live on the only double planet in our solar system, constantly gazing up at a companion whose diameter is a bit more than a fourth of the Earth. There’s a mystery about it. Since the Earth’s diameter is (more accurately) three and two thirds as large as the moon’s, its volume should be about fifty times larger. If the mass of a planet is in proportion to its volume, then why does every source say that the earth’s mass is 85 times that of the moon’s? Does this mean that the moon is not made of the same material as the earth?
The day before full moon
The moon rocks that the Luna and Apollo missions brought back fifty years ago showed us that lunar minerals are very similar to that of the earth. But that’s just a comparison of the crust. Almost 15 percent of the earth’s volume is in its iron core. The moon’s core is much smaller, perhaps less than a percent of its volume. This clue, along with detailed chemical analysis of moon rocks, and the ability to simulate numerically many alternative hypotheses about the early solar system, have led to tremendous advance in the understanding of the origin of our double planet. This dates the assembly of the earth-moon system at four and a half billion years, a scant 50 to 60 million years after the explosion of a nearby supernova compressed a cloud of gas and dust into the star we call the sun. When you look back this far, the story of the earth is the story of the sun and the moon.
The day before full moon
The part of the story that is no longer in dispute is that two planets, the proto-Earth, a little smaller than today’s Earth, and the other, now named Theia, about the size of Mars, had a glancing collision at a relative speed of more than twice the speed of sound in rock. The collision threw off some debris. But the larger planet swallowed much of the mass of the smaller, especially most of the core, and became the earth, leaving a little iron, and a lot of rock, to become the moon. A large fraction of the energy of the collision went into melting rock, leaving too little energy for the two planets to escape each others’ gravity. As a result they became a double planet perpetually circling their common center. The explanation bears up against the test of detailed simulations.
The day after full moon
Controversy has not yet completely settled on the immediately preceding history of our planetary system. Did this era contain a few dozen planetary “oligarchs” which had swept up all the material of the nebula from which the sun condensed? Numerical simulations show that multiple collisions between them could create a system where four or five rocky planets circle the sun inward of Jupiter, but none of them look very much like our solar system. This scenario also involves different mechanisms for the formation of the outer giant planets and the rocky inner planets. Nowadays the preferred scenario is that the solar system condensed into pebble-sized rocks which formed both the nuclei of the outer planets and five inner proto-planets, and only one major collision happened later to form our double planet. But this keeps open the question of why there was a collision. Perhaps the Mars Sample Return mission will tilt the balance of opinion in this remaining controversy. Perhaps we will find a simpler explanation of this older epoch in the assembly of the planets.
Don't hold your breath 
