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Venus

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      How to simulate a transit of Venus with an orange and a knitting needle. The Romans thought Venus was hot. Too right! She is the hottest thing in the Solar System. A bit smaller than the Earth, with an atmosphere full of CO 2 , she boasts a ground temperature of 475°C, enough to melt lead. This is what happens when the greenhouse effect goes crazy. Astronomers use the Astronomical Unit (AU, the radius of the Earth orbit) for distances. In the 1600’s, it was already known that Venus’ orbit radius is about 0.7 AU. The trouble was that they only had a vague idea of the actual size of the AU. Then in 1716 Edmund Haley proposed a method to calculate it using the transit of Venus. When Venus is aligned with the Sun, she looks like a black spot that crosses the Sun surface. You can make a simulation at home with an orange and a knitting needle like on the photo. Look at the needle head path on the orange as you gently rotate it. You can also tilt it back and forth to simula
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Mercury

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  An astronomer told me one day that most of his mates have never seen Mercury. Why? Simple. Mercury being the closest planet to the Sun (at most 28 degrees from it), you can only see it during twilight. Most astronomers need full darkness to do their jobs, so by the time they start observing stuff, Mercury is well and truly set. Tonight at around 6:30 - 7 pm you can beat that lot. If you look at the Western sky, you can’t miss Venus, the brightest object after the Moon. Mercury is about half-way between Venus and the horizon just a tad under Alpha Virgo. Done! Mercury is quite interesting. It is hardly bigger than our Moon and looks a lot like it. That makes it the smallest planet. It is also the most eccentric. Most planets have a semi-circular orbit but Mercury’s is very egg-shaped. Its perihelion point (the closest to the Sun) is only 2/3 of its aphelion (the farthest point). Being so close to the sun it is the fastest, with a period of only 88 days. So it goes at
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The Galilean Moons

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  If you go out after sunset at the moment and face East, you can’t miss Jupiter, the second brightest object out there after Venus. He is very bright at the moment because he is close to its nearest position from us. If you have a small telescope with a x12 magnification (or even good 7x50 binoculars propped on something solid), point at Jupiter and you will see some of his biggest moons, known as the Galilean Moons, discovered by Galileo Galilei with his home made telescope around 1610. From Jupiter outwards, they are called Io, Europa, Ganymede and Callisto.   Slightly bigger than our Moon, Io has the most violent geology in the Solar System due to the huge tidal forces Jupiter hammers it with. It has over 400 active volcanoes. Its orbital period is about 42 hours (that the time it takes to go around Jupiter). Europa is a bit smaller and a lot quieter. It is covered by a frozen water ocean that may be liquid under the surface. A good candidate for simple extra-terrestri
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The Broken Phosphorus Cycle

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  The gardeners among us know about NPK. These three elements N (nitrogen), P (phosphorus) and K (potassium) are the main constituents of a complete fertiliser. Nitrogen is considered the most important and luckily it’s not hard to get. After all it makes up 80% of the atmosphere so we have an almost inexhaustible tank around us. Potassium is perhaps less easy but so far I have never heard of a possible potassium shortage. I am not too sure how big farms go about it but at a home compost bin level, banana peels and hardwood ashes seem to do the trick. How about phosphorus? Again not a big deal on a small garden scale. Nothing wrong with a bit of horse poo, for example. But since the mid 19 th century large crop farms have become increasingly dependent on super-phosphates. One of the problems with this stuff is that it is not renewable. It comes from big mines, most of which are located in five countries, and it takes huge amounts of energy to process. Not unli
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Le Plantain (Plantago)

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      This stuff grows everywhere. In parking lots, on walls and even on my garden. Now that says something because I am a very bad gardener! There is some in the grass around my house too and the sheep just ignore it. What a pest! So I looked at ways to get rid of it. Instead, I found that various species of this plant grows on all continents and has been used as a medicinal plant since prehistoric times. You know, if the Dakota Indian tribe used it to cure snake bites, it was not to spread misinformation among white Yank settlers. They did it because it works. Among many other things, it is astringent, anti-toxic and anti-inflammatory. For topical applications, a poultice can be used on wounds and cuts and it promotes a very quick healing. So I decided to give it a go. The variety that grows in our garden is Ribwort plantain (Plantago lanceolata). A few weeks ago, my wife grabbed most of it. The leaves were washed, then cut to small pieces in a food processor and immersed
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Is the Gulf Stream running out of steam?

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      I recently read an article saying that the Gulf Stream was slowing down. This would be bad news for France and the UK, I thought. This part of the world still enjoys mild winters. For example Edinburgh is at the same latitude as Moscow and doesn’t get nearly as cold. What powers the Gulf Stream? In short, it’s three giant pumps. The Gulf Stream is part of a global system called the Thermohaline Circulation. In Greek, this means temperature (thermo) and salinity (haline). Cold water is heavier than warm water so it sinks. Salty water is heavier than fresh water so it sinks. The three giant pumps are the three deep water formation places shown on the map. There, water sinks because it is cold and because when sea ice forms, some salt is left behind so the water gets saltier. All this cold salty water sinks fast. It is replaced by warm(er) surface water and it feeds the deep cold water currents. The trouble is that global warming slows this down in two ways: 1- The p
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The Deadly 2004 Tsunami

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  Many of us remember the 2004 tsunami. It was the deadliest in history, killing 230,000 people. My mate David was in Kuala Lumpur, Malaysia, at the time and he told me KL was not affected. However we both went to Penang soon after and found out that 50 people had died there on a single beach. A tsunami happens when a very large volume of water is suddenly displaced. This can happen at the boundary between two tectonic plates when one plate suddenly slips under, or over the other. In the 2004 tsunami case, the epicentre was somewhere near the Northern tip Sumatra, on the West side. This creates a circular wave in the water, a bit like when you throw a stone in a pond. Only much bigger and faster. The odd thing is that in open water, the wave is hardly noticeable with a height of less than 1 m. But it moves at a frightening speed, like 500 to 1000 km/h, and hardly loses any energy. That’s why the 2004 beast killed people all the way to the East coast of Africa. When it
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