As mentioned in Chapter 1, to my mind astronomy is the study of everything that is not of Earth. But this poses a problem, and it has all to do with the nature of space. When we are observing the universe on the ground, the thermal currents in the Earth’s atmosphere distort any light rays coming from the night sky, making stars appear to twinkle and dance (see The Planets). As we travel higher and higher above sea level, at greater altitudes the air gets thinner and thinner (so there is less atmospheric distortion), and the stars twinkle less. This is why many of the world’s largest telescopes are located on mountainsides, where the amount of turbulent atmosphere above them is minimal. With the Hubble Space Telescope scientists went even further by launching a telescope into orbit in 1990 about 550km (342 miles) above Earth, at a distance where 90 per cent of the atmosphere is considered to be below us. At this height objects are virtually in the vacuum of space where observations should be much easier, although the vacuum can be challenging in itself. While a vacuum is a poor medium for transmitting most energetic waves, electromagnetic radiation travels well in it.
The electromagnetic spectrum is the entire range of electromagnetic radiation (EM radiation, or EMR), which is made up of different forms of electromagnetic energy waves (see diagram). All these waves travel at the speed of light, but they oscillate (or vibrate) at different frequencies. The building blocks of EM radiation are photons, which are minute particles of light that have no mass. Due to their nature, each of these forms of EM radiation can travel through a vacuum and so can therefore travel through space and propagate over vast distances. When we undertake the act of astronomy, amateur and professional alike, we are interacting with EM radiation that has passed through the vacuum of space to be eventually detected by ourselves. By analysing EM radiation, we can gain a better understanding of what is happening beyond the Earth.
Take a packet of EM radiation energy: a photon that has been generated in the heart of a distant star and has escaped from its surface. This photon, which may have travelled billions of miles through the vacuum of space, if passing in the right direction, will interact with the Earth. One of the other influences of how that photon will fare as it approaches the Earth is very much dependent on the Earth’s atmosphere. This is because only some forms of EM radiation can pass through our atmosphere.
We can tell that visible light can pass through the atmosphere because that is what we can detect with our eyes and we can observe the light of distant stars with no difficulty, so visible light passes through the atmosphere virtually unattenuated. Radio waves are similar to visible light. We bounce these waves across the Earth and use them as our main means of communication over large distances.
Other parts of the EM spectrum do not do so well in our atmosphere. X-rays, gamma rays and a lot of ultraviolet radiation are mostly absorbed by the chemicals that make up the Earth’s atmosphere, so much of this radiation does not reach sea level. This is actually very good news for us, as each of these types of radiation can cause damage to living cells. In humans, for example, they generally disrupt DNA and cause cancer, so we’re very lucky to have an atmosphere that protects us.
However, if we want to observe the universe as widely as possible, access to these other parts of the EM spectrum is very useful. To reach them, scientists have launched telescopes with special EM radiation detectors into space, to sit above the Earth’s atmosphere. Space telescopes also have the benefit of avoiding the visual distortions mentioned earlier, so can achieve much better resolution than their ground-based counterparts.
GROUND-BASED AND SPACE-BASED TELESCOPES
Professional telescopes fall into two distinct categories of telescope: ground-based and space-based systems. I have been very lucky to work on both in my career, and there are amazing aspects to both types. To be part of a team working on a system that will one day be launched into space and help us gain knowledge of our place in the universe is a true honour. At the same time, while working on ground-based systems I have been filled with immense joy as the Sun sets and an observatory structure the size of a cathedral is opened for a night’s observing – truly inspiring.
A few decades ago space-based systems were generally considered superior to ground-based telescopes. This was partly due to their ability to detect radiation that would otherwise be filtered out by the Earth’s atmosphere and partly due to their location above the atmosphere, free from any turbulence.
But in that last few decades much of this has changed and there has been a massive growth in the size of ground-based telescopes. This has been due to a technology called adaptive optics. Thanks to this method we now have ground-based optical systems that can challenge some attributes of the space-based telescopes. Rather than being limited to space-based telescopes with mirrors 3-4m (10-13ft) in diameter, we have the wondrous ground-based leviathans set up today of 8-10m (26-33ft), with bigger telescopes planned for the near future.
What makes these amazing professional telescopes so great and how they are helping us learn more about the universe around us?
THE GEMINI SOUTH TELESCOPE
My favourite telescope on Earth today is the Gemini South telescope. As the name implies, there are two Gemini telescopes, collectively known as the Gemini Observatory. These twin telescopes are located on two of the best locations on the planet for observing the night sky: Hawaii, in the northern hemisphere and Chile, in the southern hemisphere. Each one has an impressive mirror 8.19m (26ft 10in) in diameter. Although these two telescopes don’t have the largest mirrors in the world, they are definitely world-class, with cutting-edge technologies that allow scientists to see more and further. I had the thrill of working at Gemini South for around 18 months starting in 2003. It was a true joy for me, as I had made a telescope of around 150mm (6in) diameter as a child, so to be working on this amazing piece of engineering was a dream come true. My team and I had spent the previous three years building a new instrument for this telescope in a basement at University College London. The instrument itself did something quite special. It was a spectrograph: an instrument that takes light gathered by the huge telescope and splits it into its rainbow colours (spectrum). By analysing this light it is possible to work out whether a star is moving towards us or away from us and to establish where chemical reactions are taking place in the heart of a star. It was a magical time for me, so I always remember this telescope with absolute fondness.
SOLAR OBSERVATORIES
It may come as a surprise, but there are also dedicated telescopes used to observe the Sun. These solar observatories have been around for many years, with the first one founded in 1901 in Kodaikanal, India. As you can imagine with these daytime telescopes, they are designed with powerful solar filters and cooling systems. The study of space weather – the term used to describe the effect that the Sun has on conditions here on Earth – has become a large area of inquiry, due to the huge impact that solar events can have on some of our technology both on and in orbit about the Earth today. Solar activity of note include sunspots (dark spots that appear on the surface of the Sun), solar flares (violent bursts of radiation) and solar storms.
The solar storm that occurred in 1859, known as the Carrington event, for example, is one of the largest geomagnetic solar storms on record to date. Such storms occur when the sun sends out a giant cloud of magnetized matter (called a coronal mass ejection) that disturbs Earth’s magnetic field. The Carrington event was so powerful that it took out much of the telegraph system in Europe and North America, and gave some telegraph operators electric shocks. It also enabled people to see the Northern Lights (aurora borealis) as far south as Hawaii and Cuba. If a similar storm were to hit with the same conditions today the effect on our satellites, communications and power transformers could be quite devastating.
Analysis of ice core samples have indicated that storms of this magnitude occur around once every 500 years, with smaller events of around a third of the magnitude occurring approximately three times per century.
Currently there are also around 10 active space solar observatories in orbit about the Earth. The Solar Dynamic Observatory (SDO) was launched in 2010 to help us understand how the Sun affects life on Earth. It observes the Sun in a range of wavelengths that are combined to work out what sort of solar activity is happening. The SDO website is very informative and displays a series of images of how the Sun looks at the moment.
SPACE TELESCOPES
As well as the solar space observatories, there are currently around 30 active space telescopes in operation, probably the most famous of which is the Hubble Space Telescope (HST). It is named after American astronomer Edwin Hubble (1889–1953), who was pivotal in giving us some of the first evidence that the universe is expanding. The HST, which is a reflector telescope about the size of an American large school bus, has been in operation for around a quarter of a century, and in that time it has transformed our understanding of the universe.
The HST did have some initial problems when scientists realised that one of its optical components had been manufactured to the wrong shape. After a very expensive fix, however the HST has gone on from strength to strength. Over the years it has beamed down breathtaking images from space that have given us an understanding of the age and size of the universe, the formation and life cycle of the stars and insight into some of the more exotic bodies out there, such as black holes and quasars (short for quasi-stellar radio sources; these are very distant and extremely bright objects that scientists believe are powered by black holes).
But to my mind the greatest thing that the HST has given us is a better view of our place in the universe. A series of pictures known as the Hubble Deep Fields has provided us with a clearer idea of how many galaxies there are in the universe. From data obtained by these images we now believe that there are around 100 billion galaxies in the universe. If each one of these galaxies has on average just 50 billion stars in them, and each of these stars has on average just two planets in orbit, you end up with… a feeling of how truly small we are in the scale of things.
It also gives us an indication of how likely it is that other forms of life may be out there.
Amateur stargazing has gone from strength to strength in the last few years and I think that this trend will definitely continue into the future. As manufacturing processes continue to improve, although I don’t believe that telescopes for amateurs will become cheaper, I think that we may get more for our money. The push for professional instrumentation with better CCDs (light-sensitive imaging devices; CCDs stands for ‘couple-charged device’) will eventually filter down to the commercial market, making larger and more efficient CCDs in telescopes available to the general public at relatively reasonable costs.
Many amateur users are even abandoning their eyepieces and instead using a CCD. These devices are the same as we have in our digital cameras. So rather than viewing an object directly you can use a CCD to give a live real-time image. The devices available at the moment are black and white, but they give us the ability to set up a telescope outside and then sit in the comfort of our houses and observe via the video acquired by the CCD. There are also some interesting processing techniques that can be used to, for instance, enhance dim images by increasing the gain (the amount of signal you get per photon of light).
CCDs are now used in professional astronomy rather than the old photographic plates as they produce a digital signal that can be easily stored and post-processed. Space telescopes use CCDs to transmit their observations and a digital signal is carried home on a radio wave.
As computer processing power and storage capacities get bigger and cheaper, I think that, as many amateurs are already doing, more and more of us will be enhancing the images we take to get the most out of the light we capture. So I predict that in the future adaptive optics systems may become available for amateurs, but unless commercial telescopes become a lot larger, around the 6-8m (19½-26ft) level, I think this may be a gimmick rather than a useful asset.
On the professional stargazing front, there are some fundamental questions that are still evading scientists and they are looking to build telescopes/instruments that will move them closer to the answers to deep questions, such as what is dark energy and dark matter; are there other dimensions, and are we alone in the universe? (Dark energy, which scientists think makes up about 68 per cent of the universe, is the mysterious energy that appears to be a key factor in the expansion of the universe; see Mysteries and Wonders of the Universe. Dark matter is an invisible matter that scientists think makes up about 28 per cent of the universe. Current measurements of the known, observed mass-energy content of the universe adds up to only 4 per cent – the rest of the universe, scientists surmise, is made up of dark energy and dark matter, but they just don’t know what they are yet.) Scientists have got closer than ever with their understanding of the universe using current technology, but with the next generation of technology they may be able to find the answers that have eluded them. The quest continues in two core technologies: ground- and space-based telescopes and their instruments.
Since the introduction of adaptive optics to the telescope world, telescopes have been getting bigger and bigger and in the future they will continue to grow – we are truly living in exciting times. Radio astronomy (the study of radio signals from space), which can operate relatively unaffected by the atmosphere, is also thriving here on the ground, and there are some grand plans to transform this area of astronomy too. Radio astronomy allows us to peer into regions of space that are opaque to visible light. As mentioned in the previous chapter, looking at all parts of the electromagnetic spectrum gives us a much more detailed view of the processes occurring in the Universe.
The evolution in ground-based optical astronomy is best described through the ambitions of the scientists behind European Southern Observatory (ESO), a leading astronomy organisation in Europe. They were the master-builders behind the Very Large Telescope (VLT). This consists of four 8.2m (27½ft) telescopes located on the Cerro Paranal mountain in the Atacama Desert of northern Chile. This system and others like it are gathering data on the universe that competes well with some of our space-based telescopes, but the ESO team has not stopped there. They have now started construction on the European Extremely Large Telescope (E-ELT). This will be a multi-segmented mirror with a massive primary mirror of 39m (128ft) in diameter. This amazing beast will sit on the mountain next to its smaller VLT siblings in Chile and is due to start gathering light in 2024.
But the E-ELT is not the only new leviathan on the block. The Thirty Meter Telescope (TMT), a collaboration between universities in Canada and America, is due to come online in 2022 on the summit of Mauna Kea in Hawaii. The Grand Magellan Telescope (GMT) is under construction now, with a number of its seven 8.4m (27ft) mirror segments already constructed. This should see first light around 2021 at the Las Campanas Observatory, again in the Atacama Desert of Chile, so there should be some impressive science coming our way in the next few years.
But the ESO team has not just set its sights at extremely large; they want to go all out for ‘overwhelmingly large’ with the proposal for an Overwhelmingly Large Telescope (OWL). This colossus, if it is ever built, would have a segmented primary mirror of 100m (328ft) diameter – that is a light-gathering aperture roughly the size of a large football pitch. It remains a concept for now, but the things that astronomers would be able to see with such a wonderful telescope boggle the mind – undoubtedly, in the world of ground-based astronomy, people are thinking big!
Just as with amateur telescopes, professional ones are designed with different specialisms. The Larger Synoptic Survey Telescope (LSST) should be getting first light around 2019. As its name implies, this will be a survey telescope that will use the world’s largest camera to photograph the whole of the night sky every few nights. To do this the telescope has been designed with a very large field of view. (The field of view is a huge 3.5° in diameter; to give you an idea of the scale, the Sun and the Moon are each a mere 0.5° in diameter when viewed from Earth). The primary mirror of the LSST will be 8.4m (27½ft), the first time that a mirror this size has been used on a survey telescope. Its main scientific goals make good use of its unique features by mapping our galaxy, the Milky Way, and looking for small, undetected objects in our solar system, especially asteroids that pass close to the Earth. LSST will also be looking for evidence of gravitational lensing (when light is bent by the gravitational field of an object in space) in the hope of detecting the signatures of dark energy and dark matter.
If we imagine that all of the objects that we see in the night sky sit on the imaginary celestial sphere, then it is possible to work out what sort of angle each object makes when we are observing it. Let’s start locally, if you hold your thumb at arm’s length and then your thumb subtends an angle of about 1° across. A fist subtends an angle of around 10°. In the same way when we look at objects in the sky they subtend an angle in the same way. The Sun and Moon happen to extend the same angle of 0.5° whereas the angle between the Asterism of the Plough and the Pole Star is around 30°.
There are already some huge radio telescopes in operation, such as the Arecibo Observatory in Puerto Rico, which has a diameter of 300m (984ft), and the Lovell Telescope at the Jodrell Bank Centre for Astrophysics in the UK with a diameter of 76.2m (250ft) – which is even more impressive when you consider it was completed in 1957. China’s Five Hundred Meter Aperture Spherical Telescope (FAST) with a diameter of 500m (1,640ft) is under construction in Guizhou Province, southwest China, and should be active by late 2016.
As well as these large single-aperture radio telescopes, there is also a trend for large groupings of smaller radio telescopes. The biggest collection in existence at the moment is the Square Kilometre Array (SKA) project, which, when completed, will have thousands of radio dishes and over 1 million antenna located in Australia and South Africa. The combined collecting area of all of these dishes will be 1 square kilometre (1 million square metres/1,076,391 square feet). An array of this size will be the largest ever built and will be sensitive enough to detect an airport radar on a planet 10 light years away. One of the key science drivers behind the SKA is the search for and understanding of dark energy and dark matter.
Although it is easier and much more cost-effective to build larger and larger ground-based telescopes, the space-based telescopes are not to be outdone.
Space-based telescopes have the advantage of being able to gather data in parts of the electromagnetic spectrum (see The Electromagnetic Spectrum) that ground based telescopes cannot access due to atmospheric absorption. Space-based telescope have been feeding our collective imaginations for a number of years now, with the Hubble Space Telescope leading the field (see Space Telescopes). Having been in space for over a quarter of a century, Hubble has transformed our understanding of the universe and given us images that brighten our hearts just by knowing such objects are out there. However, since the demise of the space-shuttle programme (NASA closed it in 2011), Hubble is on its own with no possibility of further extending its life now that shuttle astronauts will no longer be servicing it, so what will be launched in the next decade that will continue to feed our thirst for knowledge?
The most exciting development to date is the James Webb Space Telescope (JWST), which was originally called the Next Generation Space telescope (a name that has a nice Star Trek ring to it) and is due to launch in 2018. The telescope was renamed after NASA’s second administrator, James E. Webb, which seems a strange thing to do until you realise that he was in this position from 1961 to 1968 and is the administrator who was responsible for getting the Apollo program literally off the ground (the first lunar landing took place the year after his retirement, in 1969).
Although JWST is thought to be the replacement for the Hubble Space Telescope, it will actually be working in a different wavelength. Hubble works from the visible to the ultraviolet and near-infrared ranges, while JWST has been designed to optimise observations in the infrared spectrum. This will allow scientists to see through the cloudy regions of space that only infrared light can penetrate, giving us new vistas into the universe. Due to the universe’s expansion, many of the objects we observe have their light ‘redshifted’, i.e. the objects are so far away that the light they emit has been ‘stretched’ to the red end of the spectrum by the time it reaches our part of the universe. The light emitted from objects even further away that were formed early on in the universe fall into the infrared spectrum, so a telescope that can detect infrared will allow scientists to study some of the objects, such as galaxies, formed in the universe’s infancy – a thrilling prospect.
The amazing telescopes mentioned above are just a small fraction of the exciting astronomical developments that are currently underway or that are being conceived. Professional astronomy is thriving, and this is great for all of us as scientists delve deeper and further out into the universe than ever before.
TOP 10 ASTRONOMERS OF THE ANCIENT WORLD
Astronomy is the science of the ancients and due to a plethora of amazing records we know of astronomers from over 4,000 years ago. Here is a list of notable astronomers who lived before 1000 AD in chronological order.
En-Hedu-Ana (c. 2285–2250 BC Akkad, now Iran)
En-Hedu-Ana was one of the first astronomers on record. She was the daughter of King Sargon I of Akkad, she was High Priestess of the Moon God. Amazingly we can understand the scope of her work through her poetry:
“The true woman who possesses exceeding wisdom
She consults a tablet of lapis lazuli
She gives advice to all lands
She measures the heavens
She places the measuring-cords on the Earth.”
Aristarchus of Samos (c. 310–230 BC Greece)
Aristarchus of Samos was a Greek astronomer who is the first person on record to talk about the heliocentric or sun-centred universe. In his book The Sand Reckoner he discusses that the universe was greater in size to what had been perceived and talks about the similarity between the stars in the night sky and the Sun. He also posits that the Sun (rather than the Earth) is the centre of the universe, that the Earth is in a circular orbit and that the stars are on a fixed sphere around the Sun. His ideas were rejected in favour of the geocentric universe proposed by Aristotle and Ptolemy.
Eratosthenes of Cyrene (c. 276–194 BC Libya/Greece)
Eratosthenes was a classic academic with interests in mathematics, astronomy, music and poetry. He is also thought to have invented the discipline of geography and made many calculations, including the distance between the Earth and the Sun. He invented the concept of the leap day, and calculated the circumference of the Earth and the Earth’s tilt, all with amazing accuracy.
Hipparchus of Nicaea (Now Iznik, Turkey) (c. 190–120 BC Greece)
Hipparchus was one of the great early observationalists. He was able to work out the motions of the Moon and Sun using his own observations – and probably hundreds of years of data obtained by the Babylonians. He made some of the first star catalogues and also assigned stars magnitude according to their brightness.
Ptolemy (c. 90–168 AD Egypt/Greece)
Ptolemy wrote a number of influential treatises, including the Almagest which described the motions of the heavens using mathematics. In a later volume entitled Planetary Hypothesise, he proposed the model of the universe, later to be called the ‘Ptolemaic System’. This was held to be the correct view of the universe across the world for around 1,200 years, until Copernicus reproposed the heliocentric model.
Aryabhata (c. 476–550 AD, India)
Aryabhata described a geocentric view of the solar system, ordering the objects out from the Earth and Moon: Mercury, Venus, the Sun, Mars Jupiter, Saturn and the constellations. He was able to come up with a scientific explanation for eclipses and calculate the length of a sidereal day and the sidereal year (a day and a year measured with reference to a fixed star) with outstanding accuracy. His year measurement was off by a mere three minutes and 20 seconds – less than 1000th of 1%.
Abū ‘Abdallāh Mu
ammad ibn Mūsā al-Khwārizmī (c. 780–850 AD Persia)
Abū ‘Abdallāh Mu
ammad ibn Mūsā al-Khwārizmī was born in the Islamic Golden Age. Another true all-rounder, he worked as a scholar in the House of Wisdom in Baghdad. He is probably most famous for his introduction of the decimal number system and algebra to Europe. As well as this he composed the Zij, astronomical books used to calculate the Sun’s movement, the Moon and the five known planets of the time.
Al-battani (c. 850–929 AD Mesopotamia, now Turkey)
Son of a scientific instrument-maker Al-battani made improvements to some of the instruments available and was able to accurately calculate the length of a year. He also deduced that the Earth to Sun distance varied by observations of annular solar eclipses where the Sun’s extent in the sky is much bigger than the Moon’s. He was also able to calculate that the Earth tilted on its axis by around 23 degrees (remarkably close to the actual value).
Amad ibn Muammad ibn Kathīr al-Farghānī (c. 880 AD Persia)
Another member of the house of wisdom, Abū al-’Abbās Amad ibn Muhammed ibn Kathīr al-Farghīnī or Alfraganus as he was known in the West – wrote astronomical books entitled Sky Movements and the Science of Star Codes and The Theoretical Computations of Spheres. These books were widely used by both Islamic and European scholars.
Abd al-Rahman al-Sufi (c. 903–986 AD Persia)
Abd al-Rahman al-Sufi was one of the most outstanding practical astronomers of the Middle Ages. He enhanced Ptolemy’s original star charts by making corrections and including more details on their positions, magnitude and colour. His is also the first on record to have identified the Andromeda Galaxy and mention the Large Magellanic Cloud which he had either seen or knew of from reports. He also wrote about the astronomical instrument known as the Astrolabe which was generally used to measure the position of stars, but he included 1,000 additional uses for the instrument.
