September 18 The Shortest Day

Not many people know this, but next Tuesday 18 September, is the shortest solar day of the year. I’ve decided to re-blog my post from 2015 on this interesting fact.

The Science Geek

Revised 10 September 2018

Most people are probably unaware of this but the length of a solar day, which is the natural day measured by the rising and setting of the Sun isn’t  always 24 hours. It varies slightly throughout the course of the year and that September 18 is in fact the shortest solar day in the year. This post discusses this curiosity, which is not widely known.

Background- the variation in the length of the day.

Although a day for practical timekeeping purposes is always 24 hours, the actual length of a solar day, which is the time difference between two successive occasions when the Sun is at its highest in the sky, varies throughout the year. As shown in the graph below, it is at its longest, 24 hours 30 seconds, around Christmas Day and is at its shortest, 23 hours 59 minutes 38 seconds, in mid-September.

Day length

How the length of a solar…

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June 21 2018 – the solstice

This year, the June solstice will fall on 21 June.  In the northern hemisphere, it is the day when there is the most daylight and when the Sun is at its highest in the midday sky.


Sunrise at the solstice at Stonehenge, England – image from Wikimedia commons

The origin of the word solstice is from two Latin words:  sol, which means Sun, and sistere, to stand still. This is because, at the time of the solstice, the Sun stops getting higher, appears to stand still at the same height for a few days, and then gets lower in the midday sky.


The graph below shows the maximum height, or elevation, of the Sun, measured in degrees above the horizon, during the month of June. The graph is for a location 50 degrees latitude North, which is the same latitude as the southern tip of the British Isles.  

The fact that the Sun’s elevation changes gradually means the amount of daylight also changes very little around the solstice. This is shown in the table below, which gives the sunrise and sunset times and the amount of daylight in hours, minutes and seconds for June in London.

Table of sunrise and sunset times for London (Time and Date 2018).


Precise definition of the solstice

The diagram above shows the Earth’s orbit around the Sun. For clarity the sizes of the Earth and Sun have been greatly exaggerated.




  • During June, marked as Ain the diagram, the Earth’s North Pole is tilted towards the Sun and the days are longer in the northern hemisphere.
  • During December, marked as Cin the diagram, the Earth’s South Pole is tilted towards the Sun and days are longer in the southern hemisphere.
  • At points Band D, known as the equinoxes, neither pole is tilted towards the Sun and the amounts of daylight in the northern and southern hemisphere are equal.

The precise astronomical definition of the June solstice (also called the summer solstice in the northern hemisphere) is the exact point in time when the North Pole is tilted furthest towards the Sun. The times for this event for the years 2016-2020 are given in the table below – in GMT, in Tokyo time (which is 9 hours ahead of GMT) and in Hawaiian time (which is 10 hours behind GMT).

June Solstice Times



As you can see, the time of the solstice varies from year to year. It can fall on 20, 21 or 22 June, depending on your longitude (and thus your time zone).

Importance of the solstice to early man

The solstice was of great importance to early man, and many prehistoric sites appear to have been built to celebrate it. The most famous of these is Stonehenge, which is located in Wiltshire, England. It is a set of concentric stone circles built between 4000 and 5000 years ago. It was an amazing feat of construction for stone age man. The stone circle is over 30 metres in diameter. The largest stones are more than 9 metres tall, weigh over 25 tonnes and were hauled over 30 km to the site. It is reckoned that the smaller stones were moved from western Wales, a distance of 225 km (Jarus 2014).


Image from Wikimedia commons 

At the centre of Stonehenge is a horseshoe arrangement of five sets of arches called triliths, each containing three stones.  The open side of the horseshoe points North East towards a large stone 80 metres away from the main circle. Today this large stone is given the name  ‘The Heel Stone’.



Image from Wikimedia commons

The monument is arranged in such a way that, for a few days either side of the June solstice and only at those dates, someone standing in the centre of the horse shoe and facing North East will see the Sun rise over the Heel stone.

Heel Stone Sunrise

How sunrise at the summer solstice at Stonehenge would have looked after the monument’s construction.

It is amazing that prehistoric man built such a large monument to line up with the June solstice. It clearly must have been a major event for a people living outdoors with only natural daylight, and in fact the solstice is still celebrated at Stonehenge today. Modern groups with ancient origins, such as Druids and Pagans, who revere the natural world more than many modern humans, join approximately 30,000 people who flock to Stonehenge to watch the Sun rise at the solstice each year.

Interestingly, to prevent damage to such an important ancient monument it is not normally possible to get right up to the stones. However, the charity which manages the site English Heritage open it up every year for the solstice, giving people a rare chance to get up close.

For the BBC report on the 2017 Stonehenge solstice celebrations click on the link below.

The southern hemisphere

To those of you who live in the southern hemisphere the June solstice is the winter solstice, when the midday Sun is at its lowest in the sky. After the solstice the days start getting gradually longer and the nights gradually shorter, although the change doesn’t really become noticeable until July.


Strictly speaking it isn’t true that for the whole northern hemisphere the midday Sun is at its highest in the sky on the solstice. At the Tropic of Cancer, which is 23.5 degrees north, and is shown as the upper red line in diagram below, the Sun is directly overhead at midday on the June solstice. At low latitudes between the equator and the Tropic of Cancer the Sun is directly overhead at midday on two dates either side of the solstice. For example, in San Juan, Puerto Rico, which lies 18.5 degrees North of the equator, the Sun is overhead at midday on May 13 and July 30.


Tropic of cancer


Jarus, O (2014) Stonehenge: Facts & Theories About Mysterious Monument, Available at: 10 June 2016).


Time and Date (2018) London, ENG, United Kingdom — sunrise, sunset, and daylength, June 2018, Available at: 4 June 2018).


Jupiter at opposition 9 May 2018

On May 9 the planet Jupiter will be what is known as ‘at opposition’.  This event, which occurs every 399 days, happens when Jupiter is at its closest to the Earth and at its brightest.  To the naked eye it will be a brilliant white object, three times brighter than the brightest star. Features such as coloured bands and the famous great red spot can easily be seen with a small telescope.


Jupiter through a telescope – image from NASA

What is opposition? 

The series of diagrams below show Jupiter and Earth at different points in their orbits around the Sun. The Earth takes just over 365 days to complete an orbit. Jupiter, which is further away from the Sun and moves more slowly in its orbit, takes nearly 12 years.

In the first diagram, below, Jupiter is at its closest point to the Earth  As seen from Earth, Jupiter is in the opposite direction from the Sun. This is why it is called opposition. All night between sunset and sunrise, Jupiter is above the horizon and it reaches its highest point in the sky in the middle of the night. Jupiter is at its brightest at opposition because it is at its closest to Earth and the entire sunlit side is facing Earth.


In the diagram below, 133 days later, the Earth has completed more than one-third of its journey around the Sun, whereas Jupiter has done less than 3%. Jupiter appears less bright because it is further away from Earth and not all the sunlit side of Jupiter is facing us.  In addition, Jupiter appears fairly close to the Sun and for most of the time is only above the horizon during the daytime, when it is very difficult to see against the brightness of the daytime sky.

199.5 days later the Earth has completed more than half its journey around the Sun, whereas Jupiter has done just over 4.6%. At this point, which is known as a conjunction of Jupiter and the Sun, Jupiter is only above the horizon in the daytime and is impossible for an amateur astronomer to see without specialist equipment, because it is so close to the Sun.

399 days later, the Earth has caught up with Jupiter, so the two are level again in their orbits. Jupiter is once again at opposition.



How bright is Jupiter at opposition?

When discussing the brightness of objects in the sky, astronomers use a scale called magnitude, where the lower the magnitude the brighter the object.

The scale was invented by the ancient Greek astronomers who classified all the stars visible to the naked eye into six magnitudes. The brightest stars were said to be of magnitude 1, whereas the faintest were of magnitude 6, which is the limit of human visual perception (without the aid of a telescope). Today, the magnitude scale is applied to all objects in the sky, not just stars, and the magnitude of the very brightest objects is less than zero. The brightest objects in the sky are (obviously) the Sun, which has a magnitude of -26.7, followed by the Moon, which has a magnitude of -12.7, at a typical full Moon.

The scale is defined so that a decrease in magnitude by 1 means an increase in brightness by a factor of 2.512. Therefore, a decrease in magnitude by 2 would mean an increase in brightness by 6.31, because 2.512 x 2.512 = 6.31. So, for example:

  • a star of magnitude 1 is 15.9 times brighter than a star of magnitude 4. This is because 2.512 x 2.512 x 2.512 = 15.9.
  • a star of magnitude 1 is 100 times brighter than a star of magnitude 6. This is because 2.512 x 2.512 x 2.512 x 2.512 x 2.512 = 100

Jupiter moves in an elliptical orbit around the Sun; this means that its closest distance to Earth is different at each opposition. Therefore, as shown below, the brightness at each opposition will vary as well.

The diagram above shows that if an opposition occurs where Jupiter is closest to the Sun (point A,) Jupiter will also be closest to the Earth and thus brighter than an opposition which occurs where Jupiter is furthest from the Sun (point B) . In the diagram the elongation of Jupiter’s orbit has been exaggerated. 

The closest Jupiter can get to Earth is 589 million km; when this happens it shines with a magnitude of -2.9. On the May 9 opposition, it will be 658 million km from Earth and will shine with a magnitude of -2.5, making it three  times more luminous than the brightest star Sirius, which has a magnitude of -1.4.  For comparison, the table below shows the average magnitude at opposition of the planets which lie outside the Earth’s orbit.


Data from

How Does the brightness of Jupiter compare to Venus? 

For the two inner planets Venus and Mercury, the situation is a little different. They can never be at opposition because they lie inside the Earth’s orbit. This is shown in the diagram below for Venus.

Venus Phases

As Venus orbits the Earth it goes through phases, similar to those of the Moon. However, because Venus is so small, they are only visible through a telescope. When Venus is closest to the Earth, the point known as its inferior conjunction – labelled A in the diagram – it is almost impossible to see because it is almost in a direct line of sight with the Sun and its sunlit side is facing away from Earth. Venus is actually at its brightest just before and just after inferior conjunction,  points B and F, when it has a magnitude of around -4.5.

Although Venus appears brighter than Jupiter, unlike Jupiter it is never above the horizon all night. At point B it is only clearly visible for few hours before sunrise where it is known as the Morning Star. At point F it is only visible for a few hours after sunset where it is known as the Evening Star.

Properties of Jupiter

As nearly all my readers will know, Jupiter is the largest planet in the Solar System. Its diameter is on average 140,000 km which is roughly 11 times that of the Earth, making its volume 1320 times larger (Williams 2017). It is its large size which causes Jupiter to appear brighter than Mars despite it being more than three times further from the Sun.

Unlike the smaller inner planets (Mercury, Venus, Earth and Mars) which have large iron cores surrounded by rocky materials, Jupiter is mainly composed of gas. It is not known if it has a solid core, but if one exists it will only make up a small proportion of the planet. Being made up of largely of gas means that its density is only 25% that of the Earth. Even so, its mass is still 320 times greater, making it more massive than all the other planets, moons, asteroids and comets in the Solar System put together.

Exploration of Jupiter

So far nine unmanned spacecraft have visited Jupiter. The first was Pioneer 10 in 1973 shown below.


Image from NASA

This was followed by Pioneer 11 (1974), Voyager 1 and Voyager 2 (both 1979), Ulysses (1992), Galileo – which went into orbit around Jupiter between 1995 and 2003, Cassini (2000) and New Horizons (2007). The latest mission Juno (shown below) arrived in 2016 and is currently orbiting the planet studying its atmosphere, magnetic and gravitational fields. For more details on the Juno mission see my post Mission Juno.

Juno at Jupiter

Image from NASA

Jupiter’s moons

Jupiter has its own mini “solar system” of over 60 moons in orbit around it. The four largest moons were discovered by Galileo in 1610 and one of them, Ganymede, the largest moon in the solar system, is bigger than the planet Mercury. The innermost moon Io is the most volcanically active object known to exist anywhere. Europa, the second innermost, is of particular interest because its surface is composed of ice underneath which are thought to lie oceans of liquid water, warmed by a process called tidal friction. Many scientists think that Europa is one of the most promising places in the Solar System to find extraterrestrial life.

NASA  and the European Space Agency (ESA) are developing missions to Jupiter’s moons, will tell us a lot more about them . The ESA mission is called  (JUICE)  which stands for JUpiter ICy moon Explorer and the NASA mission is called Europa Clipper. Both missions are scheduled for launch in 2022.

Jupiter Moons

The four large moons of Jupiter: Io, Europa, Ganymede and Callisto -Image from NASA

I hope you’ve enjoyed this post and that you will have a clear night on the daysaround 9 May to see this sight.


In the discussion of magnitudes all the values quoted are visual magnitudes. This is how bright the objects are in light of wavelength of 540 nanometres, which is in the green part of the spectrum. The values at other wavelengths will be different for different objects. For details on light and the way the eye sees different wavelength as different colours see


Williams, D. R. (2017) Jupiter Fact Sheet, Available at: (Accessed: 28 April 2018).

Kepler’s other achievements

As discussed in my previous post, Kepler’s improvement of Copernicus’s heliocentric system led to its more general acceptance, and his three laws describing the way planets move are fundamental laws of astronomy. However, this wasn’t his only contribution to science. He was one of the greatest thinkers of the seventeenth century scientific revolution and in this post I’ll outline some of his other major achievements.

Statue of Kepler in Linz, Austria – image from Wikimedia Commons

The Keplerian telescope

The Italian astronomer Galileo Galilei (1564-1642) was the first person to take observations of celestial objects with a telescope . However, Galileo’s telescope could only magnify objects 30 times before the image became distorted. It also had a narrow field of view

In 1610 Kepler began theoretical and experimental investigations of the way that different combinations of lenses could work together to produce a magnified image. He published his finding in a book called Dioptrice, which laid the foundation of modern optics.  Using the results of his investigations, he invented a new type of telescope with a different combination of lenses than that which Galileo had used. This new design became known as the Keplerian telescope.  It is still in use today and enables a higher magnification to be achieved with less distortion than a Galilean telescope.

Keplerian telescope – image from Wikimedia Commons

For more details on the differences between the two types of telescope see the notes at the bottom of this post.

The supernova of 1604

In October 1604 Kepler took observations of a new object which had appeared in the constellation Ophiuchus. Although Kepler was not the first to see it, he took accurate measurements of its position and brightness over a period of year.

He observed that the new object did not move with respect to background stars, so wasn’t an object revolving around the Sun like a planet or a comet. Also, the fact that it did not show any parallax meant that it must be a great distance away and wasn’t a nearby object in front of the stars. This is shown in the diagram below

It it were closer than the background of fixed stars then, at  different times of year, the new star would appear to be in a different positions with respect to the more distant background of fixed stars. As this shift in position was not seen,  the new star must be the same distance as the fixed stars.

The appearance of a new star which increased in brightness and then gradually faded over time contradicted an important belief, which had been held since ancient times, that all the stars were fixed in position respect to each and were unchanging. In 1606 he published his results in a book called ‘De Stella nova in pede Serpentarii’, which like most scientific literature of the time was written in Latin.

Its title translated into English is ‘On the new star in Ophiuchus’s foot’. For those of my readers able to read Latin, it can be downloaded for free from the following website:

Today this object, rather than being a new star, is known to be a supernova, a massive star which exploded at the end of its life. The explosion completely destroyed the star, blowing the outer layers into space in a massive glowing gas cloud, which is what Kepler observed. The remnant of the supernova is officially known as SN 1604 but is  more commonly called Kepler’s supernova and is 20,000 light years away, which is well within our Milky Way galaxy.  It is the last time that a supernova exploded close enough to be visible to the naked eye.

Remnants of Kepler’s supernova – image from NASA

Kepler’s contribution to mathematics

Kepler’s contributions weren’t restricted to astronomy either. In 1611 he produced  a pamphlet entitled Strena Seu de Nive Sexangula (A New Year’s Gift of Hexagonal Snow). In this he published the first description of the hexagonal symmetry of snowflakes.

All snowflakes when freshly formed have a hexagonal symmetry such that shown above.

Kepler discovered a series of regular solid shapes, which are known as ‘the Kepler solids’.  The term ‘regular’ means that all the faces are the same.

The Kepler solids

In 1611 he posed a mathematical problem, which became known as the Kepler Conjecture. It deals with the most efficient way to pack spheres together in a large container, so there is as little empty space as possible. It can be summarised as follows:

Imagine filling a large container with small equal-sized spheres. The packing density is equal to the total volume of the spheres divided by the volume of the container. So a packing density of 1 would mean that there was no free space at all.

The Kepler conjecture states that the maximum packing possible density is:

∏ /(3√2), (which is roughly  equal to 0.7405).

∏ /(3√2)  is the packing density we get if we pack together spheres in layers, as shown in the picture below.

So what the Kepler conjecture in saying is that there is no other arrangement out of the very large number of possible ways to pack spheres together which gives a higher packing density than that shown in the picture. Although Kepler and other subsequent mathematicians believed this statement to be true, they were unable find a way to prove it. For over 400 years, it remained as one of the greatest unsolved problems in mathematics. It wasn’t until 2017 that a team led by the American mathematician Thomas Hales proved it to be true ( 2017).

Thomas Hales – image from Wikimedia Commons


Interestingly, Kepler also has the distinction of writing what the astronomer and science educator Carl Sagan called the first ever work of science fiction. It was written in 1608 in Latin and is called Somnium (The Dream) and is about a man who travels to the Moon. In this book he describes how the Sun, Planets and the Earth would appear to an observer on from the viewpoint of the Moon. In Kepler’s time is was not known how harsh and barren the Moon was as an environment and some writers had speculated that there might be creatures on the Moon similar to those found on the Earth and even lunar civilisation.

To Kepler it was clear that the dual effects of the lunar climate and the irregular, hostile terrain would produce plants and animals far different from those that inhabit the Earth. in Kepler’s Lavania  (which was the name he gave the Moon in Somnium) there are no men and women, no civilizations.

And finally…

I hope you have enjoyed reading this post. I have tried to outline some of Kepler’s achievements, but in a 35 years scientific career he made many additional contributions, which I’ve not had time to mention, including discovering how the human eye works. What is clear to me is that he is one of most important thinkers of the scientific revolution which took place in Europe during the seventeenth century.

The Science Geek


These additional notes give a brief overview of the differences between the Galilean and Keplerian telescopes. I will discuss them in more detail in a subsequent post on how telescope work.

To understand how these telescopes are constructed it is necessary to understand a little about lenses.

There are two types of lens:

  • A converging lens, shown in the top of the diagram above, causes parallel light rays from a distant object, shown in red, to converge at point known as the focus. The focal length of the lens is the distance between its centre and the focus.
  • A diverging lens, shown in the bottom of the diagram, causes parallel light rays from a distant object to spread out so they appear to come from the focus. Like a converging lens the focal length of the lens is the distance between its centre and the focus. By convention the focal length of a a diverging lens is negative.

A Galilean telescope consists of a converging lens of long focal length (known as the objective) and an eyepiece which is a diverging lens of a shorter focal length.

If FO is the focal length of the objective and FE the focal length of the eyepiece, then  the magnification is given by FO/FE. So a Gallilean telescope with an objective with focal length of 50 cm and and eyepiece of focal length of -10 cm, would have an magnification of -5.  The minus sign just means the objective is the right way up.

A Keplerian telescope consists of a converging lens of long focal length (known as the objective) and an eyepiece which is a converging lens of a shorter focal length. It can achieve higher magnifications than the Galilean telescope and has a larger field of view.

As with the Galilean telescope, if FO is the focal length of the objective and FE the focal length of the eyepiece, then the magnification is given by FO/FE. So a Keplerian telescope with an objective with focal of length 300 cm and and eyepiece of focal length of 5 cm would have an magnification of 60.

References (2017) Mathematicians deliver formal proof of Kepler Conjecture, Available at: 25 January 2018).

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).

Virgin Galactic: what next ?

Like many people, I was was saddened to hear about the crash of Virgin Galactic’s Space Ship Two on a test flight yesterday, which resulted in the death of one of the pilots and the serious injury of the other.

Virgin Galactic Crash


It is far too soon to say what caused the crash. That will have to wait until the official investigation. Richard Branson has vowed to carry on with the Virgin Galactic programme but I think it is likely to delay their first commercial flight by several years.

Looking at the wider picture it is too early to say what effect this will have on the space tourism industry as a whole, which is still very much in its infancy.

If you want to know more about Virgin Galactic then please click here to view my earlier post from 5 August 2014.


45th Anniversary of first Men on the Moon


On Sunday (20th July) it is the 45th anniversary of the first manned Moon landing. To commemorate this. I thought that I’d re-post my article from 4th June which discussed the first Moon landings. I hope you enjoy reading or re-reading it.

My next article, which I will post next week, will be on the subject of space tourism.


On 21 May 1961 President John F Kennedy made the following address to the United States Congress:

“I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth. No single space project in this period will be more impressive to mankind, or more important in the long-range exploration of space; and none will be so difficult or expensive to accomplish.”


President J F Kennedy giving his address on May 25 1961- Image from NASA

At the time, which was in the middle of the cold war between the West and the Soviet bloc, the Soviet Union had a clear lead in space exploration and had achieved three notable firsts:

  • The first satellite in orbit, Sputnik 1, in October 1957
  • The first spacecraft to photograph the far side of the Moon, Lunik 3, in October 1959
  • The first man in space, Yuri Gagarin, in April 1961.

By achieving this goal of landing a man on the moon, which was incredibly ambitious given that in May 1961 America has not yet place a man in orbit, the United States would show to the whole world that it had gained supremacy over the Soviet Union in space exploration.

Why the Moon?

The Moon is our nearest neighbour in space, and Kennedy was advised that, given sufficient investment by the richest country in the world, a manned landing could be be achieved before 1970. There was also a good chance that, given the amount of resources needed to develop and test the new technologies needed, the Soviets would not be able to do it by this date.  The Soviet Union simply could not afford to spend so much money in such a short time.

The American Manned Space Program (1961 to 1969)

To achieve Kennedy’s goal, the American government funded the largest commitment every undertaken by a nation in peacetime. At its peak the programme employed nearly half a million people and its total cost (in 2014 dollars) was around $130 billion.

Apollo 11 Mission July 1969

All this effort came to successful fruition on July 20 1969, when Neil Armstrong and Buzz Aldrin became the first men to land on the moon. When Armstrong stepped out of the spacecraft he said the immortal words:

That’s one small step for man, one giant leap for mankind.

The event was shown on live TV to a worldwide audience of over 1 billion, almost a third of the population of the Earth at that time.  As a young child I was one of those billion people but not Mrs Geek, as it was past her bedtime (she was five years old).



Apollo 11 Astronaut Buzz Aldrin on the Moon -Image from NASA

The astronauts planted the United States flag on the lunar surface in view of the TV camera. Some time later, President Richard Nixon spoke to them through a telephone-radio transmission which Nixon called “the most historic phone call ever made from the White House.”

In total the astronauts spent 2.5 hours on the lunar surface, during which time they gathered around 25 kg of moon rock. These samples would be studied by scientists over the forthcoming years and would provide new insights into the origin of the Moon.

They left behind on the Moon’s surface scientific instruments that included an array of mirrors  used to calculate the distance between the Moon and the Earth, and a seismometer used to measure moon quakes.

On their return to Earth, the astronauts were treated as heroes – but they also had to spend three weeks in quarantine, just in case they had picked up any strange and potentially dangerous diseases on in the Moon.  After that they went on a world tour in September and October, and met many prominent leaders, such as Queen Elizabeth II.

Subsequent  Missions

After Apollo 11 there were five further successful missions to the Moon (Apollos 12,14, 15, 16 and 17) plus one unsuccessful mission Apollo 13, which you may well know about from the Hollywood movie of the same name. The diagram below shows all the Apollo landing sites.

Apollo Landing Sites


The Apollo landing sites (Image from Soerfm)

All the landings were on the near side, as it would have been far too risky to land on the far side of the Moon, where they would have been out of direct contact from the Earth.

The later missions involved the astronauts having progressively longer and  longer stays on the Moon.  For the final mission, Apollo 17, the astronauts stayed on the surface for three days and performed three separate moonwalks.

During the final three missions the astronauts used an electric-powered moon buggy to allow them to travel longer distances on the Moon – about twenty miles away from the lunar module – and thus gather rock samples from more varied sites.

Lunar Rover

The Lunar Rover or “Moon Buggy” -Image from NASA

The End of the Apollo Program

After the successful landing of Apollo 11, watched by such a huge proportion of Earth’s inhabitants, public interest in the Moon program started to wane and the US government  quickly came under pressure to reduce the spending on manned space exploration. The last three Apollo missions which should have taken place in 1973 and 1974 were cancelled.

Another victim of the spending cuts was the Moon base, which NASA had been hoping to build on the Moon in around 1980. This Moon base would gradually be extended, over the following years and decades, until it became a fully fledged lunar colony. The intention was that one day people would actually live on the Moon, but these plans were brought to a halt in the early 1970s, purely because of the cost.  Not only that, but for the last 42 years no astronaut has ventured more than a few hundred miles above the surface of the Earth.



Artist’s impression of a moon base -Image from NASA

When will humans next go to the moon ?

I think it is unlikely that the next astronauts to set foot on the Moon will be from America. NASA has no plans to go to the Moon within the next decade, because there is little political will or drive to do it.  It is unlikely that Congress would provide the funding, especially as NASA is already committed to supporting the International Space Station until at least 2020, which will reduce the money available for other manned space missions.

I think the next humans to set foot on the Moon will be from China, in around the year 2025. China has its own ambitious manned space programme, and has recently landed an unmanned probe on the Moon, which is exploring the Moon as I am writing this post.

In fact, there is so much to say about Chinese plans to explore space that I dealt with this in a separate post “Chinese Manned Spaceflight” which was posted on 16 June 2014.