Our home, Earth, is a rare and peculiarly beautiful planet: a bright sphere effortlessly pirouetting through the black. In reality, it’s constrained within a routine choreographed by gravity and conducted by its home star, the Sun. Moreover, it doesn’t dance through space-time alone but with a partner in the form of the Moon – the relationship between them as unusual as the planet itself. Even the Sun is unusual within its peers. Our home planet is at one and the same time just like all the other countless planets in orbit around trillions of stars and yet, as far as we know, so unusual that we might even be tempted to call it unique. The mere fact of our presence on its surface, beings able to ask the searching questions we do, marks it out as special.
I have written about the Earth before (here), and during lockdown I recorded a talk on the subject (find it here). I’ve no intention of revisiting this material in detail – there would be no point – but I am going to celebrate the Earth in another way by sharing with you some of the images captured during my lifetime that have had a particular impact on me in one way or another. (I note in passing that the entirety of humankind’s rocket-based space exploration endeavours thus far have occurred during my life.) Given the thousands of beautiful, informative and sometimes shocking pictures taken from orbit – through the windows and lenses on the International Space Station for example – one might become a little blasé, or perhaps overwhelmed, by the choice on offer. Fear not, I am side-stepping them all; rather than study these ‘close-ups’ I want to share with you my enjoyment of the long-shots: the images captured from afar which reveal the whole Earth in its role as a rocky, water-rich ‘Goldilocks’ planet within our solar system. I might allow the Moon a look-in as well …
Although not the first picture of our home chronologically speaking, my all-time favourite image is arguably one of the poorest in terms of photographic quality: the so-called ‘Pale Blue Dot’ captured by Voyager 1. It was taken just before its cameras were turned off to conserve power as it headed towards the very farthest reaches of the Sun’s dominance and thence into interstellar space. Voyagers 1 and 2 were launched separately during the summer of 1977 (see here for more information; I was in my mid-twenties at the time!). Both were designed and built to provide the first close-up look at Jupiter and Saturn; Voyager 2 would in addition fly on to Neptune and Uranus, the outermost planets in the Solar System. The mission was to last five years … it’s still in progress four decades later, adding new science to an already astonishing portfolio. That fact alone sets the Voyagers apart in my imagination, but there’s so much more: to have designed a mission of such complexity on what was, relatively speaking, a modest budget and with the very basic electronic computers available at the time remains a triumph of scientific and technological endeavour. I still keep in touch with the mission’s progress via the Voyager Twitter feed.
|‘The Pale Blue Dot’, in spite of its limitations, easily remains at the top of my list of the all-time-great pictures of our home planet. However, an image captured much earlier in the mission (far left) hovers somewhere nearby in terms of its ability to captivate my mind, my imagination. Only a couple of weeks after its launch, Voyager 1 took this picture of the crescent Earth and Moon from a distance of 11.7 million kilometres, and in the process illustrated the mission’s later potential. This was the very first time that the Earth and Moon had been captured in a single image (- the Moon is upper left; it's relatively dull compared to the bright Earth). Many analogous pictures have emerged over the years, each special in their own way. In the centre is a 2017 greyscale picture captured by the ORIRIS-Rex probe on its way to rendezvous with an asteroid. (Because the Earth is so much brighter than the Moon, the image has been processed such that the Moon’s brightness is enhanced by a factor of three.) In 2010 the Messenger probe, sent to study the solar system’s innermost planet, Mercury, looked back out and away from the Sun to capture the view of the Earth⸱⸱⸱Moon duo shown on the right. When viewed from the vicinity of Mercury, both the Earth and the Moon will always appear as bright full discs – no elegant crescents from this perspective. There are so many other broadly similar Earth⸱⸱⸱Moon shots of this type available online; I’ve pruned my selection heavily for this blog and in the process cut superb images such as those shown here and here.|
|If the ‘Pale Blue Dot’ tops my personal list of iconic pictures of home, then a very close-run second place must go to one of the staggeringly beautiful images captured by the Cassini probe during its extended sojourn at Saturn. This one (top) was taken in 2013 with Saturn backlit – in other words we’re looking at its night-time face with sunlight scattering through the ring system and outer atmosphere. A lower right segment of the wide-angle full image, shown lower left, reveals the Earth peeping out from behind the rings (there’s an arrow to help you locate it; Earth is about 1.4 billion kilometres away and at that distance each pixel of Cassini’s camera covers almost 9000 km of the Earth’s surface). Enlarged further in the lower right panel, we can easily discern the Earth⸱⸱⸱Moon duo. For sheer majestic beauty it would be hard to beat such a picture of home. In passing, note the apparent absence of stars in these pictures. The reason for this is simply that they are too faint to show up in an image focused on such a bright target.|
|Moving a little closer to Earth again, I’ll share with you a picture of home that also captivated me: an image taken from the surface of Mars by the Curiosity rover in 2014 (here). It’s nothing special in terms of photographic quality, but it’s reminiscent of the sort of photo one could take of Venus, say, from here: from the surface of one planet, a bright point of light in the evening sky which turns out to be a neighbouring planet. Almost homely. The central panel shows a reprocessed version of the picture with an enlarged inset of the Earth⸱⸱⸱Moon system. Taken at these sorts of distances we can be sure that the relative sizes of the Earth and its moon are about right; although even here one needs to consider the fact that the Moon and the Earth orbit each other such that their separation in space as viewed through a camera lens may appear to change. (Technically, they both rotate about their Barycentre – their centre-of-mass; see my blog post or YouTube video on the Earth for an explanation.) For pictures captured closer to home, like those shown in the Voyager/Osiris/Messenger images above, one needs to be even more careful since the apparent relative diameters may be heavily influenced by their respective distance from the camera. On the right hand side above I have inserted an image I captured on my smartphone of the crescent Moon and crescent Venus: Venus is, in reality, far larger than the Moon – but it is of course much further away from my phone than is the Moon, even if it does appear in the same part of the night sky above my garden.|
I have followed the development of space exploration from about the age of six – I remember Sputnik and Telstar, the first animals to travel to space (and die there) and the start of crewed missions – and was in my mid-teens when the first astronauts left their footprints on the Moon. Although the video images beamed back to our monochrome and distinctly low-resolution TV screens were epoch-defining, they were nothing to write home about in terms of image quality. However, the images taken by crew members …
|The Apollo 8 mission involved using the Earth’s and the Moon’s gravitational field in order to do a loop around the Moon before coasting back to Earth; the crew practiced most of the manoeuvres necessary for a Moon landing without that final all-important stage. In the process, they captured a series of pictures which have become truly memorable. Later missions, through to Apollo 17, added to this collection and/or improved picture quality. Two of the more iconic pictures of home are shown above: ‘Earthrise’ and ‘The Blue Marble’. The latter is fairly self-explanatory, although it’s worth pointing out that the inclusion of a view of Antarctica was a novelty at this stage of the game. ‘Earthrise’ does need some discussion though. The fact of the matter is that Earth never actually rises: the Moon is tidally locked to the Earth, meaning that the same lunar face is always pointing toward us – how could we talk of the far side of the Moon otherwise. So, if one face is permanently facing Earth then it follows that the Earth is always visible above the horizon from half the lunar surface and always invisible from the other half: there is neither rising nor setting. (Just to amuse yourself, take a look at this gif which shows the Moon ‘photo-bombing’ Earth – what we can see here is the far side of the lunar surface, the side we can never see directly from our planet.) However, as the Apollo crew were orbiting the Moon it would appear from their perspective that the Earth rose and set each time they went around. The image on the far right is the actual orientation as seen from the orbiting command module; only by rotating the picture was it possible to present to us the final evocative picture of home as seen on the left. Unsurprisingly, ‘Earthrise’ became a poster-shot for the growing environmental movement of the day.|
|I might have stopped at this point had the chair of the Ashford Astronomy Association*, Jason, not reminded me of another series of spine-tinglingly good shots of our home world taken by Apollo mission crew. There exists some excellent video footage of the astronauts’ ascent from the lunar surface to re-join the orbiting command module (see here for example), but some of the stills are truly astonishing. The image above is one such: Moon in the foreground and Earth, home, shown in the distance.|
I hope you have enjoyed my little gallery of pictures of home; feel free to share your own.
* I joined this lovely club a few months before ‘lockdown’; we’ve been meeting via Zoom ever since. I’ve had lots of good advice from its more experienced members which has probably saved me countless hours of trial and error when trying my hand at astrophotography, and some pretty decent suggestions for beautiful things to observe.