The Evening Star-Venus

Anybody who has looked up into the western sky after sunset in the past month will have noticed a brilliant white object – the planet Venus,  sometimes called the Evening Star. It is brighter than any other planet and ten times brighter than the brightest star Sirius, also known as the Dog Star.


The “Evening Star” Venus next to the Moon just after sunset – image from NASA

There are three reasons why Venus is so bright. Firstly, it comes closer to the Earth than any other planet.  Secondly, it is relatively large compared to other inner planets, roughly twice the diameter of Mars and three times that of Mercury. Although the giant planets – Jupiter, Saturn Uranus and Neptune – are larger than Venus, they are further away and so appear smaller. Thirdly, the thick clouds which completely cover Venus reflect most of the light back into space. In fact Venus reflects 65% of the sunlight hitting it, more than any other planet. Venus is so bright that it even possible to see it during daylight. If you know exactly where to look it appears as a faint white dot against the bright blue sky

Venus over the next two years

Venus is both closer to Sun and moves faster in its orbit than the Earth and, on average, it takes 584 days for Venus to be in the same place in its orbit as seen from the Earth. The reason for this 584 day cycle is given in the notes at the bottom of this post. Because the orbit of Venus is inside the Earth’s orbit, Venus can never appear too far away from the Sun in the sky.  In general it is only clearly visible for at most a few hours before sunrise or a few hours after sunset (see note 2). The two points where Venus appears furthest away from the Sun are called the greatest elongation points and are marked as A and B in the diagram below.



Data from Espinak (2014)

Venus has just passed a greatest elongation point which it reached on 12 January 2017, and it is a brilliant object in the western sky, visible for at least 3 hours after sunset, depending on your latitude.  Over the next few month as it gets closer to the Sun it will be visible for a shorter and shorter time after sunset. On 25 March Venus will pass between the Earth and the Sun. This is known as inferior conjunction, and for a few weeks or so either side of this date Venus will be very difficult to see because it will only be visible in daytime close to the Sun.

Looking the diagram above, you might think that Venus will pass directly in front of the Sun at inferior conjunction. However, this diagram only shows the picture in two dimensions. As shown below, because the orbit of Venus is tilted with respect to the Earth, at inferior conjunction it normally passes above or below the Sun.


Rarely at inferior conjunction Venus will pass directly in front of the Sun. When this occurs it is known as a transit of Venus.

Transit of Venus

A transit of Venus. Venus is the dark dot crossing the Sun’s surface – image from Wikimedia Commons

After inferior conjunction, it will appear to move away from the Sun and will rise and set earlier in the day and will start to become visible in the eastern sky before sunrise. At this point in its orbit Venus is known as the Morning Star. It will reach the other greatest elongation point on 3 June 2017, when it will be visible for least 3 hours before sunrise.

After reaching the greatest elongation, Venus will start to move closer to the Sun again. It will be visible for a shorter and shorter time before sunrise. On 9 January 2018 Venus will be directly behind the Sun. This is called superior conjunction and, for a few weeks or so either side of this date, Venus will be very difficult to see because it will only be visible in daytime and will appear close to the Sun. After superior conjunction Venus will appear in the evening sky after sunset and as it gets further from the Sun it will be visible for longer and longer before the Sun sets

On 17 August 2018 Venus will reach the greatest elongation point it had previously reached on 12 January 2017 and once again it will be visible for at least 3 hours after sunset as a brilliant object in the western sky.

Venus’s phases during the 584 day cycle

As seen from the Earth over the 584 day cycle, Venus goes through a full set of phases in a similar way to the Moon.  However, because Venus appears so small, these are only visible through a telescope.

Venus Phases

At inferior conjunction, point A in the diagram above, when Venus is between the Earth and the Sun, the sunlit part of Venus faces away from us making the planet almost invisible. The amount of the sunlit part of Venus we can see gets larger or waxes through to a crescent phase (B), to a half Venus (C) at the greatest elongation and then to a full Venus at superior conjunction (D), when the whole sunlit side facing the Earth is illuminated.  It then gets smaller or wanes back to a half Venus (E) at greatest elongation, then to a crescent (F) and then finally back to being almost invisible at inferior conjunction

Galileo’s discovery

The first person to discover the phases of Venus was the Italian astronomer Galileo Galilei (1564-1642).


Image from Wikimedia Commons

In 1543, just before his death, Nicolas Copernicus (1473-1543) had published the theory of heliocentrism which was completely revolutionary in its day – that the planets orbit the Sun. However, in Gallileo’s time, the teaching of the Catholic church favoured geocentrism, the widely held view that the Earth was the centre of the Universe and the stars, planets, the Sun and the Moon were in orbit around it. Indeed certain verses of the bible could be interpreted as supporting that viewpoint, such as Psalm 104:5  “the Lord set the earth on its foundations; it can never be moved.”

However, the phases of Venus and the way that it appears smaller when it is a full Venus can only be fully explained by Venus orbiting the Sun, not the Earth.  Therefore, Galileo concluded that the geocentric theory was incorrect.   Unfortunately for Galileo, in 1616 the Catholic church declared heliocentrism to be heresy. Heliocentric books were banned and Galileo was ordered to refrain from holding, teaching or defending heliocentric ideas.

Despite this ruling Galileo continued to defend heliocentrism, and in 1633 the Roman Inquisition found him “vehemently suspect of heresy”, sentencing him to indefinite imprisonment. Galileo was kept under house arrest until his death in 1642.

However the facts cannot be disputed. When viewed through a telescope Venus does show changes in size and shape, which can only be satisfactorily explained in a heliocentric model. Eventually, in 1758, the Catholic Church dropped the general prohibition of books advocating heliocentrism.

And finally….

I hope you have you have enjoyed this post. In 2015 and 2016  I published a series of posts on Venus. Some of them are listed below.

Venus a Mysterious world describes Venus in science fiction and compares it these depictions of the planet to reality.


Akatsuki – a second chance describes the mission of the Japanese spacecraft Akatsuki which is currently in orbit around Venus studying its weather. The spacecraft should have gone into orbit in 2010. This didn’t happen but mission control were able to successfully put the spacecraft in hibernation for 5 years before making another successful attempt.

Akatsuki Venus

Terraforming Venus describes how in the future we could alter Venus to make it more Earth-like so that we could live on the planet without needing any special protective equipment.



(1) The diagrams below illustrate why it takes 584 days for Venus to be in the same position in its orbit in relation to the Earth. Venus and the Earth in their orbits around the Sun are like two runners on a track. The Earth takes 365.256 to do one circuit, whereas Venus, whose orbit is inside the Earth and moves faster around the Sun, only takes 224.701 days to do one circuit.

The point in time when Venus is closest to the Earth and lies between the Earth and the Sun is called inferior conjunction. The time interval between one inferior conjunction and the next is the time it takes for Venus to ‘gain a lap’ in its orbit around the Sun. This is shown in the diagrams below.

Venus 584 day 1

Venus 584 day 2

Venus 584 day 3

Venus 584 day 4

After approximately 580 days Venus and the Earth line up again.

In fact, because the Earth’s and Venus’s speed in their individual orbits isn’t constant but varies slightly, the interval between one inferior conjunction also varies. On average it is 584 days but it actually varies between 580 and 588 days.


(2) Strictly speaking, this depends on the latitude of the observer. Venus is visible for much longer at higher latitudes.


Espenak, F (2014) 2017 calendar of astronomical events, Available at: (Accessed: 6 January 2017).


Giving Venus an artificial magnetic field

As discussed in a previous post, in the far future humanity may decide to terraform Venus so that the planet has a similar temperature and atmosphere to that which currently exists on the Earth. However, the lack of a global magnetic field would cause significant obstacles to humans settling on Venus. Without this protective shield inhabitants would be exposed to the risk of serious illness if they ventured outdoor for a significant period of time. This post discusses how we could give Venus a planet wide magnetic field which, like the Earth’s magnetic field, would shield the planet from deadly radiation.

nasa earth mag field

The Earth’s protective shield- image from NASA

As many of you will know from your high school science lessons, when an electric current flows though a loop of wire it induces a magnetic field.

Mag field in Loop

So in principle, it would be possible to generate a magnetic field around Venus if we were to run a wire around the planet then pass an electric current through it.

However it wouldn’t be quite this simple. The strength of the magnetic field depends on the electric current through the wire and the diameter of the loop.

  • The greater the current or the smaller the diameter of the loop, the stronger the magnetic field is.
  • Alternatively, the smaller the current or the larger the diameter of the loop, the weaker the magnetic field is.

This inverse dependence on diameter means that if we were to pass a current of 10 amps (which is roughly the strength of current used by an electric fire)  through a massive metal ring which was the same diameter as Venus (12,100 km) because of the immense size of this loop the magnetic field generated would be around 100 million times weaker than the Earth’s field. To generate a planet-wide magnetic field of a similar strength to the Earth’s field, a current of 1 billion amps would have to be passed through the planet-size loop.

Venus Planet wide ring

This would be a truly enormous current to generate and maintain through such an immense structure. We could reduce the current needed by creating a coil or series of rings and the magnetic field from each individual ring would add up. If we were to construct a planet-sized structure of 10,000 separate rings then we would still need to pass a current of 100,000 amps through each ring. Maintaining such a current through this structure would require an enormous amount of power. If you have studied physics at high school you may recall that the power which is created as heat, when an electric current flows, is given by the equation below:

 power (in watts) = current squared (in amps)  x resistance (in ohms)

Where the resistance is a measure of the extent to which a material resists the flow of electricity. Resistance is measured in units called Ohms, named after the German physicist Georg Ohm (1789-1854).


Wires and cables made out of good conductor such as copper have a low resistance and the thicker the wire the lower resistance.  If you were to make each of the 10,000 planet sized rings out a copper cable 20 cm thick, then the resistance of a metre  of the cable would be very low, only 0.000 000 54 Ohms. (See note 1). Even so, such a large current would mean that 5.4 kilowatts of heat would be generated per metre of cable.

However, this is only the heat generated for a single metre of cable. The total length of the 10,000 rings wrapped around Venus would be 400 billion metres. So the whole structure would generate an incredible 2,000 trillion Watts of heat. In the course of a year maintaining the magnetic field in this way would consume 18 million trillion watt hours of Energy. This is roughly 1,000 times larger than the entire Earth’s electricity consumption in 2014 (Enerdata 2016). If we were to generate this amount of energy by solar power, we have to cover an area of roughly 7 million square kilometers, which is roughly 70% of the area of the US with solar cells. See note 2.

USA Solar

It clearly be would be a significant challenge to generate enough electricity to create an artificial magnetic field in such a way. It would be a huge problem to remove all the heat generated, to prevent the copper coils getting so hot that they would overheat and melt.

A better way to do this would building the coils out of superconductors. I will discuss superconductors in more details in a future post. In essence superconductors are materials which have zero electrical resistance and thus zero losses to due to heat. An electric current can flow through a superconducting loop indefinitely. See Note 3. They were discovered in the early twentieth century and have many applications including maintaining the high electric currents needed to produce strong magnetic fields in medical devices such as MRI scanners and particle accelerators such as the Large Hadron Collider.


Large Hadron Collider- Image from CERN

Only certain materials can be  superconducting and, up until a discovery last year all superconducting materials only superconduct at very very low temperatures. This means that if we made the planet-sized ring out of superconductor, although there would be no power lost due to electrical resistance, a significant amount of power would need to be supplied to keep the structure very cold. If the cooling failed the material would no longer be superconducting and the magnetic field would disappear. Building such a massive structure of refrigerated planet wide rings would obviously present immense challenges, but these would not be insurmountable for an advanced civilisation able to terraform a planet.

High Temperature Superconductors?

When the first superconductors were discovered,  they only became superconducting close to close to absolute zero, which is the lowest possible temperature at -273.15 degrees Celsius . In the course of time new materials were discovered which superconducted at higher temperatures. However, most of the “high temperature” superconductors don’t support high currents and still need to be cooled to at least -200 degrees Celsius. A real breakthrough was made last year when it was discovered that hydrogen sulphide, the gas responsible for the bad smell in rotten eggs, became superconducting when cooled to -70 degrees, although it must be compressed to a pressure of 1 million atmospheres (Drozdov et al). This amazing discovery raises the possibility that in the future we will have room temperature superconductors, albeit at very high pressures, and perhaps these materials could be used to build a superconducting ring around Venus.

Another more radical option

As I mentioned in a previous post the reason that Venus does not have a magnetic field is because it has a slow rotation rate. In theory it would be possible for a highly advanced civilisation to increase the rotation rate of Venus to a rate similar to that of the Earth. This is such large topic that I will discuss it in a future post.

As a footnote – Artificial magnetic fields on Mars

Although this post is about creating an artificial magnetic field on Venus, the same considerations apply to creating to a magnetic field on Mars. The main difference is that because Mars is roughly half the diameter of Venus only half the current would be needed to create a magnetic field with the same strength as the Earth’s.

Mars Planet wide ring

The Science Geek.



(1) Assuming a resistivity of copper of 17 nano-ohm metres. This would give the resistance of a  1 metre length of the thick cable as 0.54 micro-ohms

(2) The calculation assumes that the average amount of solar radiation hitting a point on Venus’s surface over the course of a year is 700 watts per square metre and that solar panels can be mass-produced with an energy efficiency of 40%, which is much higher efficiency than today’s solar panels, which is typically 10-15%.

(3) All superconductors have a critical current density above which  the material no longer superconducts. This critical current depends upon the type of superconductor and the temperature.


Drozdov A. P., Eremets M. I., Troyan I. A., Ksenofontov V. and Shylin S. I. (2015)Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system, Available at: (Accessed: 24 April 2016).

Enerdata (2016) Global energy statistical yearbook 2015 – Electricity domestic consumption, Available at: (Accessed: 6 May 2016).


The Earth’s magnetic field

The Earth is unique among the inner planets in our Solar System (Mercury, Venus, Earth and Mars) in that it has a strong magnetic field. It is this invisible field which causes the needle of a compass to point North that has been used by navigators for centuries and is used by migrating birds and some land animals to find their way.



Another important function of the Earth’s magnetic field is that it protects us from harmful radiation from space. In this post I will talk about what causes the Earth’s magnetic field and the protection it gives us which we would have to artificially provide if humanity were ever to build colonies on other planets.

The Earth’s magnetic field behaves as though there were a giant bar magnet inside the Earth. The poles of this invisible magnet, marked as Nm and Sm in the diagram below, lie close to the real or geographical poles marked as N and S. See Note 1.

Earth Mag Field

The strength of a magnetic field is measured in tesla, named after the Serbian-American physicist, engineer and inventor Nikola Tesla (1856-1943), shown below. A magnetic field of 1 Tesla is a fairly strong magnetic field. For instance a small bar magnet has a field strength of around 0.01 tesla. The Earth’s magnetic field is much weaker than this. It varies between 30-65 millionths of a tesla – alternatively described as 30-65 microtesla – and is stronger near the magnetic poles and weaker near the equator.


Portrait of Nikola Tesla on the Serbian 100 Dinar Note

What causes the Earth’s magnetic field ?

The generally accepted theory is known as the dynamo theory. The details of the theory are rather complex.  In summary, it states that the Earth’s magnetic field is generated by movements stirred up by the Earth’s rotation known as “convection currents” in the outer core, which is liquid and, because it is made out of iron, is a good conductor of electricity. By this theory, for any planet to have a magnetic field, part of its interior must consist of a liquid which conducts electricity and it must be rotating rapidly enough to generate convection currents.

Earth Interior


What about the other inner planets?

  • Mars has no magnetic field because it is much smaller than the Earth. Its smaller size means that in the time since the planets were formed, roughly 4.5 billion years ago, its inside has cooled down more than the Earth’s, so much so that its entire interior is a rigid solid and there can be no convection currents to create a magnetic field.
  • Venus is the same size as the earth is of similar composition and has a liquid outer core. However Venus does not have a magnetic field because it rotates far too slowly (it takes 243 days to rotate once) to create convection currents in its interior.
  • The innermost planet Mercury has a very weak magnetic field, around 1% of the strength of the Earth’s field.  This is surprising, and still not fully understood. It was assumed that Mercury had no magnetic field for the same reason as Mars – that its small size meant that the inside of the planet had cooled down so much that its entire core was solid. Plus, like Venus, Mercury rotates very slowly, once every 59 Earth days, which meant that even if the outer core were still liquid its rotation would be too slow to create any magnetic field.  However, the visit of the Mariner 10 space probe to the planet in 1974 showed that the assumption was wrong, but astronomers neither then nor now have been able to reach a conclusion as to why the magnetic field exists. Perhaps the core is still liquid, or it may be that there is some sort of solidified permanent magnet within a solid core.  At the moment, it is hard to see how we will ever discover the truth.

Effect of the lack of magnetic field on Venus

In a previous post I have discussed terraforming Venus. This is a long term engineering project on an unimaginably vast scale which humanity may decide to undertake in the far future, should there be a compelling reason to do so.   Terraforming would make the planet habitable to the extent that people would not need to wear any special equipment such as space suits. After it had been terraformed Venus would have a similar temperature and atmosphere to that which currently exists on the Earth. However, the lack of a global magnetic field would cause significant obstacles to humans settling on Venus.

The Earth’s magnetic field forms a protective shield called the magnetosphere protecting us from a stream of electrically charged particles from the Sun called the solar wind. This is shown in the diagram below.

nasa earth mag field

Image from NASA

Venus, because it has no magnetic field, has no magnetosphere. See note 2. This means that its atmosphere is being slowly blown away into space by the solar wind. However, if humans terraform Venus this atmospheric loss would not be a massive issue. The  amount of atmosphere lost would be very small over the lifetime of a human being. An advanced civilisation capable of terraforming a planet would easily be able to top up the gases blown away into space.

A more serious issue is that the solar wind would prevent an ozone layer being created. On the Earth there is a region of the atmosphere around 30 km above the Earth’s surface where the concentration of ozone gas is at its greatest (NASA 2013).

Ozone Layer

Image from NASA

This ozone layer prevents most of the Sun’s harmful ultraviolet rays hitting the Earth’s surface. On a terraformed Venus, without a magnetosphere, the electrically charged particles in the solar wind would beak up any ozone formed in the upper atmosphere. Without a protective ozone layer, the high levels of ultraviolet radiation hitting the planet’s surface would mean that anyone who ventured outdoors would be exposed to high risk of skin cancer.  Lack of a protective ozone layer would also prevent all forms of agriculture, as the UV radiation would break up all organic molecules.

Another risk to health is that many of the particles from the solar wind and other deadly particles from space known as cosmic rays, which are deflected around the Earth by its magnetosphere, would hit the planet’s surface, exposing its inhabitants to a serious risk of ill health, as cosmic rays are known to affect the process of cell division.  People would therefore be at risk of cancer and growth disorders, but information about this is sketchy, because the only people to have ventured outside the magnetosphere were the Apollo astronauts in the late 1960s and the early 1970s. Most of them reported seeing flashes of light even when their eyes were closed, which were due to cosmic rays which had passed through their spacesuit and their bodies being seen as a flash of light when it hit the back of their eyes.  They have since developed cataracts at a much earlier age than would normally be expected.  Had there been a solar storm during their voyages, they would probably have been killed.

The solution to this extremely serious obstacle would be to give Venus an artificial magnetic field and this will be the topic of my next post.


And finally,

I hope you have enjoyed this post. In the future I will also write about geomagnetic reversals where the Earth’s magnetic field gets gradually weaker and weaker and then switches round so that the North pole becomes the South pole and vice versa and the fact that the magnetic poles aren’t fixed but are gradually moving.

The Science Geek, with a good deal of proofreading and editing from his long-suffering wife, Mrs Geek.



(1) To say the the Earth’s magnetic field is like a bar magnet is only an approximation. The true nature of the Earth’s magnetic field is more complex that this. There are many magnetic anomalies where the Earth’s magnetic field is much stronger or much weaker than it would be with a simple bar magnet model.

(2) Strictly speaking this isn’t quite true. Venus has no global planet wide magnetic field. However, the interaction between the electrically charged particles in the solar wind and Venus’s atmosphere induces a very weak and variable magnetic field which can be as strong as 0.15 microtesla (Lumann and Russell 1997).


Luhmann, J.G. and Russell, C. T (1997) Venus: Magnetic Field and Magnetosphere,Available at: 17 April 2016).

NASA (2013) Ozone hole watch, Available at: (Accessed: 17 April 2016).



Terraforming Venus

Terraforming is the process of changing the global environment of a planet  in such a way as to make it suitable for human habitation. Because it is so far beyond our current technological capabilities, most articles about terraforming have been written by science fiction writers rather than scientists.  For example, there is  an entry for a terraformed Venus in the science fiction work “Encyclopaedia Galactica” which is set thousands of years in the future.

Originally a hot dry greenhouse world, (Cytherian Type) with an atmosphere consisting mostly of carbon dioxide with a surface pressure 94 times greater than that of Earth. The planet was shrouded with clouds of sulphuric and hydrochloric acid and the mean surface temperature was 480 C, making the world extremely hostile to terragen and carbon-based life. Because of this the planet was sparsely populated for many thousands of years; recently it has been successfully terraformed.

(Kazlev et al 2006).

Even though I know of very few references to a terraformed Venus in serious scientific writing, there is no reason why – given sufficient resources and time – an advanced human civilisation wouldn’t be able to terraform Venus. In this post I’ll talk about the challenges to making Venus habitable so that humans can live and work on the planet without any need for protective equipment such as space suits or oxygen supplies.


What a terraformed Venus might look like – Image from Wikimedia Commons

High Temperatures and Pressures.

The surface temperature of Venus is around 500 degrees Celsius and the atmospheric pressure is a crushing  92 times that of the Earth. The atmosphere consists of 97%  carbon dioxide (Williams 2015), a powerful greenhouse gas which traps the Sun’s heat. In order to make the planet habitable the surface temperature would need to be around 0 to 35 degrees and the atmospheric pressure similar to that on the Earth.

One way to cool Venus would be to build a giant sunshade to block most of the Sun’s rays from hitting the planet. This was described in detail in a paper written by the late British science writer Paul Birch (1991).

Venus Sunshade

The shade would orbit the Sun at a specific point about 1 million km above the planet’s surface called the L1 Lagrange point, shown as L in the diagram above (see note 1). It would need to be slightly larger than the diameter of Venus, 12,100 km, to fully shade the planet. The cost and technological challenge of building such a shade would enormous. It would need to be 100 billion times larger in surface area than the International Space station, shown below, which is the largest object ever built in space.


It is likely that such a shade would be built up from thousands or even millions of smaller individual shades and would take many decades to complete from start to finish. As the shade neared completion, and most of the Sun’s rays were blocked from hitting the planet, the surface of Venus would begin to cool.  Interestingly, when the shade was complete, because Venus would no longer be lit up by the Sun, to an observer on Earth Venus would go from being the third brightest object in the sky (after the Sun and the Moon) to being invisible.

After about 100 years the temperature of Venus would drop to 31 degrees (see note 2). At this temperature, known as the critical point of carbon dioxide, some of the carbon dioxide in the atmosphere would start to condense from gas to liquid and the low-lying areas of the surface of Venus would begin to be covered in seas and oceans of liquid carbon dioxide, in the same way that much of the Earth’s surface is covered by seas and oceans of water. As it condensed into liquid, the amount of carbon dioxide left in the atmosphere would start to fall and with it the atmospheric pressure.

Eventually the temperature would drop to the freezing point of carbon dioxide (-57 degrees) and the seas, oceans and lakes of liquid carbon dioxide would begin to freeze. Much of the remaining carbon dioxide in the atmosphere would fall as snow.

This entire cooling process would take hundreds of years from start to finish. When it had completed the next step would be to ensure that when the shade was removed, allowing the planet to warm up, the frozen carbon dioxide wasn’t released back into the atmosphere. One way this could be achieved would be to cover up the frozen carbon dioxide oceans with an insulating material and provide some sort of refrigeration system to keep it cool. Once the carbon dioxide was safely locked away the sunshade could then be removed to allow the planet to warm up again. Because nearly all the carbon dioxide would have been removed from the atmosphere it would no longer provide such a powerful greenhouse gas.

No Water

Venus is a very dry planet. Its atmosphere contains only a small trace of water and there is no water on its surface. By comparison, on Earth 71% of the planet’s surface is covered by water and  there are about 1.39 billion cubic kilometers of water on the planet.  The breakdown of how this water is distributed is shown in the tables below (U.S. Department of the Interior 2015)

Earth Water

As water is essential for life, it would be necessary to import water to Venus to make the entire planet habitable for plant and animal life. A lot of water would be needed, but it would not be necessary to have most of the planet covered with deep oceans of water. Probably around 30-50 million cubic kilometres of water would be sufficient. Even so, this is a still a huge amount of water to shift.

How could we get a large amount of water to Venus?

There various ways of doing this. One way would be to transport it from the seas and oceans of Earth. The cost of this would we be prohibitive and even if there are huge advances in technology it would be extremely difficult to transport a huge amount of water by this method.

Another possibility, again prohibitively expensive, would be to import hydrogen by scooping it up on an orbiting ring from one of the giant planets in the outer Solar System. The hydrogen would then be sent onto Venus by a cargo-carrying spacecraft. The hydrogen would produce water by chemical reaction with the remaining carbon dioxide in the planet’s atmosphere.

A fascinating alternative way of getting all the water needed to Venus was suggested in Birch’s paper.  It involves moving one of Saturn’s ice moons into orbit around Venus and then breaking it up, thus releasing all the water needed onto the planet.

Saturn has a number of ice moons such as Hyperion (shown below), an irregularly shaped object 360 by 260 km which consist mainly of ice, covered in a thin layer of rock.


Image from NASA

The proposal is that we could build a huge structure on Hyperion which would use the Sun’s heat, concentrated by mirrors, to put out a jet of steam into space in the same direction as it orbits Saturn. This is shown in the diagram below.

Hyperion Steam Engine


This jet of steam will provide a force which will gradually slow down Hyperion in its orbit causing it to gradually spiral inwards towards Saturn. After about 30 years Hyperion will be in an oval-shaped orbit which will cause it to pass close to the giant moon Titan.

Hyperion Steam Orbit Decay

Titan is much larger than Hyperion and the near collision between the two objects will give Hyperion so much speed that it will be ejected from orbit around Saturn.  If the speed and angle are just right, after it escapes from Saturn it will be on a path which will take it close to the giant planet Jupiter. This technique is known as a slingshot and NASA uses it to send spacecraft to the outer Solar System.

As Hyperion passes Jupiter, the giant planet’s gravity will hurl it into the inner Solar System. If the angle of approach to Jupiter is just right it will be possible to send it on such a path that it will approach Venus slowly enough to be captured by Venus’s gravity and go into orbit around the planet. Once in orbit Hyperion would be gradually broken up and its water transferred to the planet’s surface.

Although this somewhat convoluted plan might appear to be something out of an exotic science fiction story, it obeys all the laws of physics and could potentially be achieved by an advanced human civilisation which devoted the resources to do it.

No oxygen

In order to be habitable Venus would need a similar level of oxygen in its atmosphere to that on the Earth. On Earth oxygen makes up about 21% of the atmosphere, whereas Venus’s atmosphere has almost no oxygen.  Compared to the other challenges this would be relatively easy to resolve. The oxygen concentration could be increased by plant life which, as you may remember from your high school biology lessons, uses a process called photosynthesis to convert carbon dioxide and water into carbohydrates and oxygen.


Image from Wikimedia Commons

Long day/night cycle

On Venus the slow rotation of the planet means that a day lasts 116.8 Earth days. Most Earth lifeforms would struggle to adapt to such a long day/night cycle. A shorter day could be created by means of orbiting shades and mirrors.

No magnetic field

On the Earth its magnetic field forms a protective shield around the planet which protects its surface from electrically charged particles from the Sun (the solar wind) and from outer space (cosmic rays). Without a magnetic field  there would be an increased risk of cancer for anyone who ventured outdoors for any significant period of time.  To make Venus completely habitable it would need to be given an artificial magnetic field. This is actually quite difficult to do, even for an advanced civilisation, and will merit its own blog post in due course!


The Science Geek


1) At this point the shade would orbit the Sun in exactly the same time, 224.7 days, that it takes Venus to orbit the Sun. Therefore it would always be shading the planet once it was put in place.

2) Any timescales here should be treated as very approximate. The actual values depend on the properties of the Venusian atmosphere during the cooling scenario.


Birch, P. (1991) Terraforming Venus quickly, Available at: (Accessed: 6 February 2016).

Kazlev, M.A., Sandberg M., Bowers, S., Parisi M (2006) Encyclopaedia Galactica -Venus, Available at: (Accessed: 11th February 2016).

U.S. Department of the Interior (2015) How much water is there on, in, and above the Earth?, Available at: (Accessed: 7 February 2016).

Williams D R (2015) Venus fact sheet, Available at: (Accessed: 6 February 2016).



Living on Venus

In this post I’ll look into the distant future and talk about humans living and building settlements on the planet Venus. Because it is well beyond what we can achieve with our current technology, it is a topic that been more in the realm of science fiction rather than factual scientific writing. However, even though there are many difficult obstacles in the way, I think it is very likely to happen at some point in the distant future.


Venus as seen through a telescope – image from NASA.

Why would we want to live on Venus?

There are a number of reasons why humans would want to colonise Venus.  The first three also apply to the Moon, Mars or Mercury.

  • To ensure the continuation of humanity. While the human species is restricted to life on a single planet it is vulnerable to extinction caused by natural or man made disasters.  If humans could live in a self supporting colony outside the Earth then this would provide a Plan B to allow the continuation of our species. Indeed the British physicist Stephen Hawking recently said:

“I believe that the long term future of the human race must be space and that it represents an important life insurance for our future survival, as it could prevent the disappearance of humanity by colonising other planets.”

Stephen Hawkins NASA

Image from NASA

  • To spread human civilisation to other places.  Since humans first evolved, they have constantly sought to expand to new territories. It seems to be almost a biological imperative to find other places to live.  There are not many uninhabited places on Earth, so humans may one day extend their civilisation beyond our planet.
  • To stimulate the economy.  Despite the enormous cost, building colonies outside the Earth would give a huge stimulus to the Earth’s economy. There may well be spin-offs in the same way that the Apollo programme in the sixties and early seventies led to huge technological developments unconnected to space travel.
  • It is relatively easy to get to. Compared to Mars and Mercury, Venus gets closer to the Earth (Williams 2015 a,b). At its closest approach it is 40 million km away from Earth, whereas Mars at its closest approach is still around 80 million km away. It is therefore easier to reach.
  • Larger surface area. Venus is almost the same size as the Earth (ibid). This means that it has almost 4 times the surface area of Mars and 15 times the surface area of the Moon, giving a greater area to colonise.

Earth Venus Mars

  • Similar gravity to the Earth. When astronauts spend long periods of time in a low gravity environment, such as the International Space Station, their bones and muscles weaken. It is not known if the weak gravity on the Moon (16% of the Earth’s gravity) or Mars (38% of the Earth’s gravity) would be sufficient to prevent this happening. The surface gravity on Venus is 91% of that of the Earth which would be sufficient.
  • More solar energy. Any colony would be likely to use solar energy as its main energy source. Venus is closer to the sun than the Earth and receives roughly twice as much solar energy as the Earth. See Notes at the end of this post.


As readers of my previous post will know, Venus is a very inhospitable world. Its surface temperature is on average nearly 500 degrees Celsius and its air pressure is a crushing 92 times that of the Earth. No spacecraft has been able to survive for longer than about an hour on its surface without being destroyed by the intense heat and pressure. The thick atmosphere forms a thermal blanket around the planet. So even at the poles the temperature is not any cooler and, although the temperature drops with altitude, there is nowhere on the planet’s surface which is less than than 380 degrees Celsius. In addition, there is almost no water or oxygen in the atmosphere – both of which are essential for life and Venus does not have a magnetic field to protect the planet from the harmful effects of the solar wind.

Floating cities?

Because the temperature and pressure both fall with altitude there is a region around 50 km above the planet’s surface where both the atmospheric pressure and temperature are similar to that on the Earth.


The graph above shows how the temperature and pressure of Venus’s atmosphere varies with altitude (from Wikimedia Common). 1 Bar is air pressure at sea level on Earth

At this 50 km point, the atmosphere of Venus is the most Earth-like environment, other than Earth itself, in the Solar System. In a paper written in 2008, the NASA scientist Geoffrey Landis suggested building floating cities in the Venusian atmosphere (Atkinson 2008) .  The atmosphere of Venus consists of 97% carbon dioxide, which is denser than the Earth’s atmosphere, which is mainly composed of nitrogen and oxygen. Landis suggested that a large space filled with with breathable air could float high above the Venusian surface in the same way that a helium balloon floats in the Earth’s atmosphere.

Venus Floating City

It would be possible to build large enough spaces for humans to live and work in, although there is the obvious risk that if there were a major leak the entire structure would fall down to the surface to its destruction.

Terraforming Venus

I think that humans will only be able to live on Venus after the entire planet has been transformed to make it more Earth like. This is called terraforming. This process, which is well beyond our current technology, and is at the moment more in the realm of science fiction writers, will involve removing nearly all the carbon dioxide from the atmosphere, adding oxygen, reducing the surface temperature and pressure to similar values to those on Earth, and adding water. It will also be necessary to do something about the long day/night cycles.  A day on Venus lasts 116.8 Earth day which is too long for Earth life to adapt to. (Incidentally, Mrs Geek recently read and enjoyed Karen Thompson Walker’s novel “The Age of Miracles” which describes how humanity struggles to adapt to a world in which the length of a day is much longer than 24 hours.)

In my next post I will discuss how, if humanity doesn’t destroy itself and we become a very advanced civilisation, we could terraform Venus.

The Science Geek



Interestingly, the amount of solar energy reaching the surface of Venus is, on average, far less than that reaching the surface of the Earth. This is because, although Venus gets more sunlight, most of the solar energy which hits Venus is reflected back into space by the thick cloud layer high above the planet’s surface. Most of the remaining sunlight is absorbed by the thick atmosphere before it reaches Venus’s surface.  Howver,If Venus is terraformed its surface will get more sunlight than the Earth, because its clouds and atmosphere will be much thinner.


Atkinson N. (2008) Colonizing Venus with floating cities, Available at: (Accessed: 23 Jan 2016).

Williams D R (2015a) Mars fact sheet, Available at: (Accessed: 23 Jan 2016).

Williams D R (2015b) Venus fact sheet, Available at: (Accessed: 23 Jan 2016).

Transit of Venus

On 6 June 2012, a transit of Venus occurred. This rare astronomical event, when Venus passes directly in front of the Sun, and appears as a large black dot on its surface slowly moving from one side to the other in about 3 hours, has only happened eight times since the invention of the telescope (ref 1). This post talks about the transit of Venus and why it has been so important to the development of astronomy.

Transit of Venus 2012

The 2012 transit of Venus – Image from NASA. Venus is the large dot on the top left of the Sun’s surface.

Why transits of Venus are so rare.

The Earth takes slightly longer than 365 days, 365.256 days to be precise, to complete one orbit of the Sun. Venus, which is both closer to Sun and moves faster in its orbit, takes 224.701 days to complete one orbit. The point in time when Venus is closest to the Earth and lies between the Earth and the Sun is called inferior conjunction. The time interval between one inferior conjunction and the next is on average about 584 days. This is time it takes for Venus to “gain a lap” in its orbit around the Sun. This is shown in the diagrams below.

Venus 584 day 1

Venus 584 day 2

Venus 584 day 3

Venus 584 day 4


As you can see in the diagrams, because the interval between inferior conjunctions is not an exact number of years, the date in the year on which an inferior conjunction falls varies from year to year. The dates of the next five inferior conjunctions are given below (ref 2). See Note 1.

  • March 25 2017
  • October 26 2018
  • June 3  2020
  • January 9 2022
  • August 13  2023

The orbit of Venus around the Sun is tilted by a small angle, 3.4 degrees, with respect to the orbit of the Earth, as you can see below.

Venus Orbital Tilt

What this means is that, for the vast majority of inferior conjunctions, Venus won’t pass directly between the Earth and the Sun, giving rise to a transit.  Instead Venus will appear to be just below or just above the Sun in the sky. There are only two narrow time windows in the year when an inferior conjunction can give rise to a transit of Venus. These are marked as A and B in the diagram. The first is for a few days around June 7 and the second is for a few days around December 9. The next time we will be able to see a transit of Venus will on be 11 December 2117. So I won’t be around to see it!

Why transits occur in pairs 8 years apart

One numerical coincidence is that in the time it takes the Earth to complete 8 orbits of the Sun – 2,922 days – Venus completes almost exactly 13 orbits (13.004 to be precise). Or, to put it another way, 8 Earth years is equal to almost exactly 13 Venus years.

This means that every 8 Earth years, because (almost but not quite) a whole number of Venus years have passed, an inferior conjunction occurs on the same date in the year minus 2/3 days. So when a transit of Venus occurs there is almost always another transit 8 years later.

For example, there was an inferior conjunction on 8 Jun 2004 which was a transit of Venus. Eight years later there was an inferior conjunction on 6 Jun 2012 which was also a transit of Venus. The inferior conjunction on 3 Jun 2020 won’t be a transit, as it will lie just outside the time window when transits can occur.

The importance of the transit of Venus

The most fundamental distance unit in astronomy is the astronomical unit, normally abbreviated to AU. This is the mean distance between the Earth and the Sun. In the early 17th century the German mathematician Johannes Kepler (1571-1630) worked out the relationship between the distance of a planet and the speed it orbited around the Sun, a relationship we now know as Kepler’s law.


When astronomers applied Kepler’s law they could work out the distances of the planets from the Sun relative to the distance between the Earth and the Sun. So for example, Venus is a distance of 0.72 AU from the Sun, Mars 1.52 AU, Jupiter 5.2 AU and the Earth is 1 AU. What was not known is how large an AU was. Was it 50 million miles? 100 million miles? or 200 million miles? If we could find out how big an AU was we could work out the real size of the Solar System and the distances between all the objects within it. Determining  the size of the AU became one of the key problems in 17th and 18th century astronomy.

Astronomers realised that observations of a transit of Venus can be used to calculate the size of the AU. The calculations are a little detailed but in essence rely on the fact that transits occur at slightly different times when they are observed at different places on the Earth. If the start and end times of the transit are accurately timed in two different places and the distance between the two places is known, then the distance between the Earth and the Sun can be calculated. More detail is given in the following link:

The first person to measure the size of the AU, based upon observations of a transit of Venus, was the British astronomer Jeremiah Horrocks (1618-1641), pictured below.  Horrocks,  who later died at the tragically young age of 22, observed the 1639 transit and estimated a value of 96 million km by combining his observations made near Preston, in the North West of England, with those made at the same time by a colleague 60 km away.


Horrocks’s value, which is lower than the correct value, was later refined by observations of the 1761 and 1769 transits to 151.7 million km, which is within 1.5% of the accepted value today.

Once the size of the AU was known, it was possible to determine the real size of the solar system and, using a technique called stellar parallax, which I will talk about in a later post, the distances to the stars.

Weighing the Sun

You may remember from your high school science lessons that there is a relationship between the three quantities: the speed a smaller object (such as the Earth) orbits a larger object (such as the Sun), its distance from the larger object and the mass of the larger object . Once the distance from the Earth to Sun and the speed of the Earth in its orbit around the Sun were known, it was then possible to work out the mass of the Sun. This turned out to be around 330,000 times the mass of the Earth.

Venus has an atmosphere

The Russian astronomer Mikhail Lomonosov observed the 1761 transit and reported a bump or bulge of light off the solar disc as Venus began to exit the Sun. He correctly attributed this bulge to the bending of sunlight by an atmosphere around Venus. This was the first time that an atmosphere had been found around any planet other than the Earth.

The 2012 transit of Venus

The 2012 transit of Venus was observed by millions of people throughout the world, although not everyone in the world could see it.


2012 Transit of Venus

Image from NASA

Even though the distance from the Earth to the Sun is now well known, so the transit was of lesser scientific important than earlier transits, it would still have been an interesting sight to observe. The large slowly moving black dot on the Sun’s surface caused by Venus could be safely seen by projecting the image of the Sun onto a piece of paper or observing the Sun directly though a telescope with a filter designed to cut out most of the Sun’s light. It was also possible to view the Sun through the special glasses which are sold to view solar eclipses.

Children Observing Transit in East Timor

Children Observing the 2012 transit in East Timor – image from Wikimedia commons.

The Science Geek


  1. These diagrams are a slight oversimplifications. The Earth’s orbit around the Sun is actually elliptical (oval-shaped) rather than circular. The Earth travels in an uneven speed in its orbit, travelling faster when it is closer to the Sun. This means that the interval between successive inferior conjunctions varies around the 584 day average. This is shown in the table below.

Venus IC dates

Interestingly the orbit of Venus around is much less oval-shaped than that of the Earth (ref 3)


  2. Espenak, F (2014) 2016 calendar of astronomical events, Available at:




Happy new year 2016 from The Science Geek

Happy new year to all my readers and followers. I hope you have had a good festive break. Mrs Geek and I went on a cruise to the Canary Islands, Lisbon and Madeira over Christmas to get away from the cold and damp North West of England. During our holiday I was hoping to do some star gazing from the upper decks, but sadly the lights on the ship and the full Moon were just too bright to enable me to make out the fainter stars 😦 and I was unable to see the Milky Way.  You may remember we were also unable to see a single star from the Kielder Observatory, but that was because of complete cloud cover.  At least we saw some sunshine during the day on this trip!

Images of the month January 2016

For the next few months, in addition to my normal posts, I will be posting a shorter  “image of the month” post.  My image of the month for January 2016 is actually one quite ordinary image from NASA plus two very much more exciting images from the Japanese Akatsuki spacecraft, which were produced shortly after it went into orbit around Venus last month. For the full story on this spacecraft click here. In what is known as ‘visible light’ (see below), Venus is a fairly featureless object:


Venus as seen from Earth in visible light – Image from NASA

The wavelength of the different colours of light is measured in units called nanometres, normally abbreviated to nm. 1 nm is equal to one billionth of a metre. The human eye is sensitive to light with wavelengths in the range of 380 nm to 750 nm and we call this range of wavelengths ‘visible light’.  However, at different wavelengths it possible to see structure in the clouds on Venus. The following images were taken by Akatsuki at different wavelengths.

This one was taken in ultraviolet light at a wavelength of around 300nm, which is a shorter wavelength than the human eye can see:

20151209 Akatsui

Venus in UV light- Image from JAXA

This one was taken in infrared light at a wavelength of around 2,000 nm, which is this time a longer wavelength than the human eye can see:

Venus in IR light

Venus in IR light -Image  from JAXA

I hope you like these images, and that we can look forward to many more images of Venus from Akatsuki over the forthcoming months.