An Earthlight Shadow

Originally published in the Informanté newspaper on Thursday, 26 July, 2018.

We’re never actually standing still. At any moment, we’re rotating around the earth at 460 meters per second, the earth is orbiting the sun at 108 000 kilometers per hour, and the sun is orbiting the galactic center at a speed of 828 000 kilometers per hour. Even the moon rushes around the earth in its orbit at 3 660 kilometers per hour. 

During all this movement, sometimes, we get a rare occurrence. When everything lines up to create a spectacular sight. And that, dear reader, will be Friday night, the 27^th of July 2018. At 19h14, the moon will begin its penumbral eclipse. It will start to enter the earth’s penumbral shadow, or partial shadow. When viewed from the moon, it will seem like a partial solar eclipse, with the earth beginning to obscure part of the sun.

By 20h24, a partial eclipse will begin. Parts of the moon will start to enter the earth’s umbral shadow. Should you be on that part of the moon, it will appear like a solar eclipse has started – with the earth completely covering the moon. However, unlike a solar eclipse seen from the earth, the solar eclipse seen from the moon is a bit different. 

The earth, unlike the moon, has an atmosphere, which means that the light from the sun is not sharply cut off at the edges as the moon does when it causes a solar eclipse. The light from the sun is diffracted and scattered by the atmosphere of the earth, yielding a faint glow of the moon. The scattering of light, known as Rayleigh scattering, is also the reason the sky is blue – the atmosphere scatters lower wavelength light much more than higher wavelength light, such as reds.

This is the reason sunsets are always such brilliant hues of reds and oranges, and this means that while the sunlight refracted around the earth to the moon is scattered, the blue/violet part of the spectrum gets scattered into the earth’s atmosphere. The reds and oranges, however, reaches the moon and gives it a reddish colour. The result – a blood moon, as it is called. 

By 21h30, the moon will have moved in its entirety into the earth’s umbral shadow. No matter where you are on the moon, you’d see a total solar eclipse, with the landscape solely lit by earthlight refracting around our planet. The moon is entirely shadowed by the earth. But this is a unique confluence of events, remember? 

At this time of year, the earth is near its apogee, having reached its aphelion (farthest point for the sun in its orbit) on 6 July. As a result, the earth’s shadow is larger than usual. The moon, however, is also reaching its apogee at the same time, meaning that it’s moving comparatively slower around its orbit, and consequently moves slower through the earth shadow. But wait, there’s more! In this specific lunar eclipse, the moon is also in also straight opposition to the sun, meaning it will move through the centre of the earth’s shadow. When taken together, this means this lunar eclipse will be the longest in this century – it will remain in the earth’s shadow for 1 hour and 43 minutes, just short of the 1 hour 47 minute theoretical maximum.

By 22h21 we will have reached the point of maximum eclipse, with the moon directly in the center of the earth’s shadow. Now would be a good time to look for something else – Mars. On 27 July, Mars will be at its closest to earth in 15 years. It, and earth, will be in a straight line with respect to the sun, meaning Mars will be at its brightest. And when the moon is in eclipse, Mars will be the brightest ‘star’ near it, a mere 57.6 million kilometers away. 

By 23h13 on Friday night, the total eclipse will end. Parts of the moon will emerge into earth penumbral shadow, and over the next hour, it will slowly become more visible, as its red sheen fades. By 00h19 the moon will be fully in the penumbral shadow, and by 01h28, the moon will shine at full brightness once again. 

Just a warning, however. The moon has long since been the subject of the greatest optical illusion in history. Photographs and visual inspections make the moon look bigger than it is in actuality – and it has done so for thousands of years. In actuality, the moon in the sky is always about the size of your pinkie finger’s nail when held out at arm’s length, no matter how it looks on the horizon, or its appearance in photographs. It always appears the same size in the sky as the sun, in fact. But that is a subject for another day. So on Friday night, take a walk outside. See the splendor of the sky in its full glory, and revel in the majesty of the universe at its reveals such a special and unique part of itself to you.

A Look At A Warmer Earth

Originally published in the Informanté newspaper on Thursday, 12 July, 2018.

We’ve all heard the stories about climate change. The Paris Climate Change conference remained in the news over the last two years, first as it aimed to limit global temperature increases to 2 °C, and again when President Trump withdrew from the accords. Yet even by the Paris Conference standards, this temperature increase could result in sea level rises of between 3 and 6 meters by 2100. As it turns out, those climate models may have failed to account for some things…

Two weeks ago, a team of researchers from 17 countries published a paper in Nature Geoscience, entitled “Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond.” Essentially, what these researchers did was study the changes in the paleontological record of the earth (fossils) before and during the last three times the planet experienced climate change due to temperature increases in the same range.

The researchers looked at the Holocene Thermal Maximum (HTM) which occurred between 5 000 and 9 000 years ago, the Last Interglacial period (LIG), occurring about 129 000 and 116 000 years ago, and the mid-Pliocene warm period (MPWP), which occurred about 3.3 to 3 million years ago. The HTM and LIG events occurred due to changes in the earth’s orbit, but the MPWP had occurred due to atmospheric carbon dioxide concentrations of about 350 to 450 parts per million – or about the same as we have today. Of course, it took quite a bit longer for nature to reach those levels. By combining data from ice cores, fossil records, sediment layers, radiometric dating and other paleoclimate methods, they were able to paint a picture of what a warmer earth will look like once global warming has stabilized.

In terms of polar ice sheets, they found a significant retreat of the Greenland and Antarctic ice sheets during those times, giving a global sea level 6 to 9 meters higher than currently. In terms of sea ice, it appears that a reduction of more than 50% was seen, which would indicate much warmer waters. These warmer temperatures caused changes to the marine plankton ecosystem, with a rearrangement of the surface-level habitat. Plankton started to migrate poleward, and experienced blooms in surface waters.

On land there were large changes as well. Most regions experienced a poleward shift of their biomes, as moisture regimes changed. The Sahara desert greened, and eventually vanished. The Great Plains of North America grew arid. The tundra and forest boundaries in the Americas and Asia shifted northward by about 200 kilometres. Even here in Africa, the Nama Karoo and fine-leaved savannah expanded. Across the globe, tropical climates and savannahs expanded as deserts shrunk.

Just these changes could have profound effects for our current nations – farmland becoming unviable as other countries gain them, seafront property in danger – but the fossil record shows the real danger. While humans may be causing an increase in atmospheric carbon dioxide, nature will amplify it. A large amount of carbon is currently preserved in peat – partly decomposed plant matter. Large peatlands are maintain in forests and tropical climates as old plants died and form layers upon layers of them. This makes it the largest carbon sink on the planet.

Peat, however, mostly forms where it’s wet – it’s a wetland phenomenon, after all – and with the increase in temperatures… Well, in the north, peat is usually protected by permafrost in the coldest climates. With widespread permafrost thaw, the peat will release more carbon than it absorbs, accelerating global warming. In tropical regions, climates will move, and savannahs will expand. Fine-leaved savannah that’s quite flammable, especially in warmer weather, and will release massive amounts of carbon into the atmosphere in continent-wide wildfires if it burns over former peatlands. These fires will devastate the edges of tropical forests, slowly turning the entire area into fire-maintained savannah and grassland ecosystems in the wake of natural deforestation. A rapid run-away change towards treeless landscapes will result.

 "Even with just 2°C of warming -- and potentially just 1.5°C -- significant impacts on the Earth system are profound," said co-author Prof Alan Mix of Oregon State University. "We can expect that sea-level rise could become unstoppable for millennia, impacting much of the world's population, infrastructure and economic activity."

"Climate models appear to be trustworthy for small changes, such as for low emission scenarios over short periods, say over the next few decades out to 2100. But as the change gets larger or more persistent, either because of higher emissions, for example a business-as-usual-scenario, or because we are interested in the long term response of a low emission scenario, it appears they underestimate climate change," said co-author Prof Katrin Meissner, Director of the University of New South Wales Climate Change Research Centre.

We here in Namibia have already experienced stranger and stranger weather patterns over the last decade. We’ve often heard of the so-called butterfly effect in weather forecasting – how a butterfly flapping its wings in Tokyo can cause a rainstorm in Johannesburg – and how it shows that long-term weather forecasting is a pipe dream. In more manageable terms, it explains how small changes in initials conditions can result in widely different outcomes in future. This paper shows another side to that – small changes now can have drastic effects on our planet in future. Yet it also gives us a bit of hope. Maybe, by making small changes now to our world, we can flap our wings, and change the outcome for our planet, and ourselves.

The Far Side of the Moon

Originally published in the Informanté newspaper on Thursday, 5 July, 2018.

While listening to song recently, the lyrics claimed that, to be a man, one had to be ‘mysterious as the dark side of the moon.’ Yet, strangely enough, the dark side of the moon, or as it’s correctly called, the far side of the moon, is not mysterious anymore. It, in fact, hasn’t been since 7 October 1959, when the Soviet Luna 3 spacecraft took the first images of that hard-to-see surface.

The reason we call it the ‘far’ side of the moon, and not the ‘dark’ side is because it is, in fact, not dark all the time. The reason we cannot see the far side of the moon from earth, is because it is tidally locked. As the moon normally creates tides on earth, so too does the earth create ‘tides’ on the moon. Without liquid water to show that force, however, it is not easily observed. If there were, we’d note that due to the massive size difference between the earth and the moon, tides would be MUCH stronger there. 

The gravitational tides therefore serves to induce torque on the moon’s rotation, and eventually caused its rotation to match exactly its orbital period. Once this happens, it’s ‘tidally locked’ and rotates so that once side faces the larger gravitational body constantly even as it orbits it. In other words, it rotates around its axis in such a way that we on Earth only ever see one side of the moon – the near side of the moon.

The moon, however, orbits the earth, not the sun, and as such, its whole surface at one time or another DOES in fact receive sunlight. Whenever a portion of the moon is not lit up on the near side of the moon, a corresponding fraction of the far side receives light. When we have a new moon, the far side of the moon is lit up, and the new moon on 7 October 1959 gave the Luna 3 orbiter the chance to photograph the far side for the first time in history. 

In 1968, the Apollo 8 mission orbited the moon, and humans for the first time saw that side directly. In this case, however, the dark side took on a different meaning, as it meant Apollo 8 went radio silent – the moon blocking all radio transmissions from Earth. This property of the far side of the moon means that it would be an ideal place to set up a radio telescope, as it would be shielded from all of Earth’s radio transmissions… at least, until we start colonising the rest of the solar system, and inter-planetary radio traffic becomes more pronounced. 

So what is the far side of the moon really like? For one, it’s actually quite a different place from the near side which we can easily see with our own eyes. The near side has widespread basaltic plains called ‘maria,’ created by volcanic activity long ago. They enable us to imagine we see a ‘man in the moon,’ or a tree, or hands. Yet on the far side of the moon, volcanic activity was much more limited, and there are only a few maria. As astronauts Williams Anders described it, “The backside looks like a sand pile my kids have played in for some time. It's all beat up, no definition, just a lot of bumps and holes.”

Since the maria covers only 1% of the far side of the moon, compared to the 31% of the near side, it’s much more riddled with craters. One might think that this could be due to the Earth shielding the moon from asteroid impacts on the near side, but this is not so – the Earth only obscures 4 square degrees out of 41 thousand square degrees of sky as seen from the moon. 

Newer research has shown that the real reason is that during the formation of the Earth-Moon system, the moon started to cool down first. Since it was already tidally locked at that time, the far side of the moon condensed first, forming thicker plagioclases out of aluminium and calcium combining with the silicate in the moon’s mantle. As a result, the far side of the moon has a much thicker crust than the near side, which remain liquid for longer. When meteors impacted on the young moon, those on the far side merely caused craters, while those on the near side penetrated the crust, and caused the release of basaltic lava, which formed the maria.

As a result, the far side of the moon boasts the largest crater in the solar system, the South-Pole-Aitken basin, that’s roughly 2500 kilometers in diameter, and the moon’s largest mountain ranges. It is also the region known to have water, or ice, hidden away on permanently shadowed crater walls, and in regions just below the surface. The next expedition to explore the far side of the moon will be launched in December of this year – the Chinese Chang’e 4 mission. It will land a robotic lander and rover, controlled via a relay satellite. The Chang’e missions are named after the Chinese moon goddess, and apt name for what it will be accomplishing. 

So the next time you hear lyrics, poems, or even prose referring to the dark side of the moon, and how ‘mysterious’ it is, you too can now be annoyed by the presumption of artists to assume that humanity has not set its sights on our closest neighbour. Perhaps they feel that the mystique they’ll create outweighs the cost of marginalizing humanity’s history of space exploration? In any case, they should perhaps set their sights on the mystique of space as yet unexplored, for if we are to take our place amongst the stars, we should set our sights higher than the moon.