(Throughout this appendix we will refer to a large number of transient events reportedly observed in the vicinity of the Moon, and will refer to them as they are listed in the works by Middlehurst et al. 1968, Cameron 1978, and Cameron 2006.)

Most TLP reports are visual and in recent decades originated from amateurs. Before 1900, however, many reports came from reputable, professional astronomers, even famous ones: Wilhelm Herschel in 1783–1790 with six TLPs (he also discovered Uranus, several moons, and infrared light); Edmond Halley in 1715 (Astronomer Royal, of Halley’s comet fame); Edward Barnard with several TLPs in 1889–1892 (showed novae are exploding stars, discovered 17 comets and a moon of Jupiter); Ernst Tempel in 1866–1885 (discoverer of 21 comets); Johann Bode in 1788–1792 (famous celestial cartographer); George Airy in 1877 with a TLP confirmed independently (famous Astronomer Royal); Heinrich Olbers in 1821 (confirmed asteroid belt); Johannes Hevelius in 1650 (pioneering lunar topographer); Jean-Dominique Cassini in 1671–1673 (director of l’Observatoire de Paris); Camille Flammarion in 1867–1906 (founded Société Astronomique de France); William Pickering in 1891–1912 (co-founded Lowell Observatory); Johann Schröter in 1784–1792 (first noticed the phase anomaly of Venus); Friedrich von Struve in 1822 (founded Pulkovo Observatory); Francesco Bianchini in 1685–1725 (measured Earth’s axis precession); and Etienne Trouvelot in 1870–1877 (noted astronomical observer). In the twentieth century noted astronomers reporting TLPs included Dinsmore Alter (in 1937–1959), Zdeněk Kopal (in 1963), and Sir Patrick Moore (in 1948–1967). Franz von Gruithuisen in 1821–1839 reported changing luminous and lunar obscured spots, yet also described the Moon inhabited and dotted by cities. (He also was first to conclude that craters result from meteorite impacts.)

When, if ever

When plans for exploring the Solar System with manned spacecraft are discussed, Venus tends to get short shrift. In the near term, of course it is natural to talk about a return to the Moon and the establishment of a manned base there. The short journey times and low gravity are just two of many reasons this is the easiest and least expensive option for human exploration in the near term. It is also a good place to practise survival techniques and develop procedures for living successfully in space before venturing further afield. Also, of course, there is much about the Moon that is of scientific and practical interest that makes exploration still a valid objective 40 years after the first Apollo landing.

Once humans are permanently established on the Moon, almost everyone thinks of pressing on to Mars. Often the two are programmatically linked, with the lunar landings seen explicitly as a stepping stone on the way to the red planet. This was the case for the NASA initiative started under President George W. Bush, and recently terminated by President Obama. Mars remains a long-term goal in Europe under the Aurora programme. The reasons for favouring Mars over Venus are pretty much taken for granted: men and women can land there and explore in the traditional manner, driving buggies, using hammers and drills, climbing mountains and cliffs or descending into deep valleys. It is fairly easy to see, in outline at least, how they could build permanent bases and live in them, becoming self-supporting by growing food and mining ice deposits for water, possibly even making their own rocket fuel. No one would think of trying any of that on Venus.

As a result of the labyrinthine processes described in Chapter 16, we arrive at a ‘best guess’ for the near-term (next two decades, say) future of Venus exploration in the form of some combination of entry probes, balloons and landers. These will come from NASA and the European Space Agency, possibly in tandem but more likely not; and Venera-D from the Russians. Japan may try again to orbit Venus, and something from the Chinese and Indians cannot be ruled out, although they are more likely to focus on the Moon and Mars.

Such a programme is by no means assured, of course; there could be no new mission to Venus for 20 years, at the end of which time everything will have changed. It would be nice to think that several of the world’s space agencies might get together and pool their resources in the future, to mount a single large mission, perhaps sample return. However, history suggests a more fragmented approach can be expected, at best. Despite all of the uncertainty, we now look, in a spirit of optimism tempered with realism, more closely at the plans as they stand and will likely evolve in this possible multi-pronged attack on the remaining mysteries of Venus.

The circulation and dynamics of Venus’s atmosphere behave in ways that sometimes remind us of terrestrial meteorology, but mostly seem quite bizarre. Yet we routinely compute the dynamical behaviour of Earth’s atmosphere, for weather forecasting and other reasons, and it should be possible to do the same for Earth’s twin. However, even the most basic behaviour on Venus, the four-day ‘super-rotation’, is proving hard to diagnose or to replicate. Despite a great deal of attention by groups using some of the most sophisticated computers and models, Earthlike simulations with Venusian parameters inserted have tended to circulate too slowly.

A lot of meteorological activity – weather – has been observed in Venus’s atmosphere by orbiting spacecraft and measured in situ by descent probes, but understanding and interpreting what is going on is still at an early stage. Researchers continue to argue about whether lightning occurs, and although it probably does, there is no clear picture of how or where it is generated. Some of the small-scale and transitory features, such as the waves seen in the ultraviolet images of the cloud tops, and some of the global and semi-permanent behaviour, for example the Hadley circulation, have some recognisable relationship to similar behaviour on the Earth, although they may have to be scrutinised closely to see it. Other important phenomena seem fairly unique to Venus, not just the fast winds that circle the equator, but the complexity of the giant vortices at each pole, and the behaviour in the upper atmosphere, where the circulation seems to change to a completely different regime.

Tennyson reminds us that despite the scope for humanity of exploration, personal fulfillment rests on immediate accomplishment: on commerce, personal opportunity, and peace versus conflict – measured on a human scale. How can outer space fit into human lives?

From the start, Columbian-era Europeans set out to explore the world for profit. Although investors often lost their stakes and crew-members their lives, both dreamed of riches, and some were rewarded. In intervening centuries ships sailed the globe to exploit and trade in natural resources: spices, whale oil, and more. In the twentieth century, exploration of Earth’s polar regions and outer space was a contest for the prestige of nations and individuals more than profit. Lunar explorers need not fear unreasonably for their lives given precaution (Chapter 11), but what have investors to gain? Can distant space including the Moon be monetized for profit?

Views of Venus, from the beginning to the present day

Observations of Venus with the naked eye as a prominent planet or ‘wandering star’ were recorded by the Babylonians around 3000 bc, and have continued ever since. All the major civilisations have contributed knowledge and myth to a recondite and, until recently, quite abstruse concept of our nearest companion in space beyond the Moon. With the invention of the telescope in about 1610 it became clear to Galileo that Venus shone in reflected light from the Sun and had phases like the Moon, leading eventually to an understanding that Venus is not any kind of star, but an Earthlike object, one that orbits closer to the Sun than we do. The presence of an atmosphere on Venus, filled with cloud that veiled the entire planet at all times and prevented the observation of surface features, was recognised and refined from the 1760s onwards, and the principal composition of the atmosphere was established in the 1930s.

The ‘evil twin’ syndrome

After Magellan, there was a long hiatus in the exploration of Venus by spacecraft that extended from the end of the radar-mapping mission in October 1994 until the arrival of Venus Express in April 2006. The campaign to kick-start that European mission relied in no small part on pointing out that our nearest neighbour had become the ‘Forgotten Planet’, rather as Mars did for a time after the successful landing of the Viking surface stations.

However, at the turn of the millennium, interest in comparative planetology was at an all-time high and it might have been logical to focus our available resources on Earth’s nearest neighbour and closest twin. The Venus Express advocates were also at pains to point out that one of the key comparative aspects was global climate change, with Venus as the ultimate example of a greenhouse-warmed, Earthlike planet.

The Evening Star and the Morning Star

Everyone has seen Venus, as a bright, starlike apparition in the evening sky, following the Sun down towards the horizon and setting a few hours later. At various other times of the year, there comes a brief season where an early bird can see Venus rise brilliantly before the Sun, climbing higher until it seems to dim and vanish as the sky brightens after sunrise. When it rises before the Sun, people have long called Venus the Morning Star; half an orbit later, when on the other side of the Sun so that the Sun sets first, Venus is the Evening Star. Before Copernicus promoted the idea that planets orbit the Sun, it was not obvious that these two phenomena were the same body, and early civilisations had distinct names for them. To the Greeks, they were Phosphoros and Hesperos.

For much of the year, Venus sets and rises so near the Sun that we tend not to notice it. During the day, like the true stars at vastly greater distances, Venus is still overhead and just as bright, of course, but it is hard to see because the contrast with the dark sky is lost when the Sun is up. It can be studied during the day if a telescope is used to shut out most of the sunlight, and even with ordinary binoculars if you know where to look. In any observations made over a period of a few months, Venus can be seen to exhibit lunarlike phases (Figure 1.1).

1. You too may be a big hero,

2. once you learn to count backwards to zero.

3. “In German or der English, I know how to count down . . .

4. Und I’m learning Chinese,” says Wernher von Braun.

Lehrer’s song criticizes von Braun’s heroic status in 1960s America despite his fickle national allegiances two decades before; the song aired when his luster in American public opinion was tarnishing (Chapter 3). The Chinese reference is biting, because, several months before, China had exploded her first atomic bomb, the fifth nation to do so, after the United States, Soviet Union, Britain, and France. (Von Braun had little problem counting but admitted before the U.S. House of Representatives having once failed physics and mathematics.) Outer space was the call drawing him down his brilliant if morally ambiguous path, not patriotic inspiration. By age 17 his interest in space flight set the course that determined his career.

Lehrer did not know how ironic his reference to Chinese would become, for two years later, on June 17, 1967, China exploded her first hydrogen bomb, 150 times more powerful than the one Lehrer knew. China took 3 years to transition from fission to fusion weapons, compared to 6 years for the United States, 4 for the Soviet Union, 5 for Britain, 9 for France, and 24 years for India. In October 1966, China launched a nuclear warhead on an intermediate-range missile, detonating it at their Lop Nor test site in Xinjiang (after lofting it over populated Chinese territory).

1. With a holy host of others standing around me

2. Still I’m on the dark side of the moon

3. And it seems like it goes on like this forever

4. You must forgive me

5. If I’m up and gone to Carolina in my mind

People seem forever confused about the Far Side versus dark side of the Moon. Let us be clear – here is an easy mnemonic: the dark side is darker, and the Far Side is farther! They are not the same except once per month, at full Moon. The Moon, like Earth (and other planets), has at any time a side pointed away from the Sun. That is the dark side.

The Moon has another effect in play; the same lunar Near Side always turns to face Earth, with the opposite side – the Far Side – turned away. This matter of physics is common to many worlds. A consequence is that almost half of the Moon’s surface remained hidden to humans until 1959, two years to the day after Sputnik 1’s launch, when the third Soviet lunar probe attempt, Luna 3, photographed the Far Side for the first time (Figure 2.1). Beforehand, that side had been an abyss to human knowledge, more unknown to us than distant reaches of the Universe, and a place where one might peer into space and never see Earth. This sense of isolation James Taylor invokes with the “dark side.”

Choosing the way forward

When Venus Express arrived in April 2006 it became the 25th mission to target Venus successfully. With Japan’s Akatsuki, four spacefaring nations are now engaged in exploring Venus, and the data garnered have painted a vivid and comprehensive picture of what hitherto had been a mysterious, cloud-shrouded world. No seas, swamps or rainforests and no dinosaurs or Treens, but a hot volcanic wasteland with permanent hurricanes and searing acid clouds.

There were, and still are, plenty of puzzles to solve concerning the nature of the surface and interior, and the behaviour of the thick atmosphere. More missions must follow. But what, how and when? The scientists, engineers, managers and politicians who will answer these questions and write the next chapter in Venus exploration cannot consider Venus as a solitary objective. The agencies face huge internal and external competition for resources, and must target the highest priorities if they are to satisfy their own scientific communities, not to mention their government paymasters. Often this means leaving lower priority destinations unprobed for long periods, as has already happened with Venus during the years from 1994, when Magellan shut down, to 2006, when Venus Express commenced operations. So what happens next at Venus depends not only on goals and priorities for that planet, but on where the excitement lies elsewhere in the Solar System and beyond, and where Venus fits in with the rest of the international planetary programme.