The Sky at Night Phần 3 doc

22 6 News from the Planets
This is not at all. Cassini showed that a high mountain ridge runs for a long
distance round Iapetus, making it look rather like a table-tennis ball which has been
broken in half and then unskilfully glued together. The ridge is high, rising to a
maximum of 8 miles above the surrounding terrain, running for 800 miles almost
among the geographical (should it be the Iapetographic?) equator. It is unlike any-
thing else known in the Solar System, so how was it formed? Could it be that it is
due to icy material which welled up from below and then solidified? Could it be
that, as suggested by Paulo Frerie of Arecibo observatory, Iapetus once grazed the
outer edges of the ring system, and later retreated to its present distance? It has even
been suggested that Iapetus itself may have had a ring – a ringed satellite orbiting
a ringed planet. Less plausibly, some UFO enthusiasts have claimed that Iapetus
itself is artificial, put together by the usual nebulous aliens from afar. Certainly, it
may be a popular sight for future interplanetary tourists because its orbit is inclined
to the plane of Saturn’s equator by almost 16°, and travellers will see the rings well
displayed – while the inner satellites, including Titan, orbit almost in the equatorial
plane so that seen from them the ring system will always be edgewise-on.
Perhaps, the greatest surprise of all came from Enceladus, discovered in 1787 by
William Herschel. It is a mere 310 miles across (about the distance between
London and Penzance) and was expected to be icy and inert. This is certainly true
of the even smaller Mimas, discovered by Herschel at the same time; incidentally,
these were the first of the few important results coming from Hershel’s largest
telescope, the 40-foot focus reflector with its 49-in. mirror. Mimas is dark with one
vast crater, which had led to its being compared with Darth Vader’s “Death Star”.
Enceladus has the highest albedo of any Solar System body; there are no large
craters and wide areas where there are no craters at all. This must mean that these
areas are young, and have been resurfaced in comparatively recent times.
When Cassini flew past Enceladus on 17th of February 2005, at a range of
725 miles, it detected a tenuous but appreciable atmosphere – totally unexpected for
a world with so weak a gravitational pull; In fact no atmosphere could be retained
for long, and so there must be continual replenishment from below. Next came the

discovery of ice geysers spouting from the south polar region; the jets rise to hundreds
of miles above the ground. At NASA, they caused great excitement. To quote
Carolyn Porco, head of the Cassini imaging team: “I think this is important enough
to see a redirection in the planetary exploration programme. We’ve just brought
Enceladus to the forefront as a major target of astrobiological interest.” The readings
from Enceladus’ geyser plumes indicate that all of the prerequisites for life as we
know it could exist below Enceladus’ surface. “Living organisms require liquid
water and organic materials, and we know we have both on Enceladus now”.
A few tens below the surface the temperature and pressure may be sufficient to
keep water in a liquid state. Further evidence comes from the so-called “tiger
stripes”, which indicate cracks. The ice here is a more amorphous and virtually
crater-free, so that it must have welled up comparatively recently. The geysers rise
upward for several 100 miles, so that they are violent – and violence was the last
thing to be expected on a world as small as Enceladus. Most of the ice crystals fall
back as snow, but some break and free altogether to become part of the wide, thin
236 News from the Planets
E-ring. It is not yet clear whether the venting and the geyser activities confined to
the South Pole region. If so, this must be the hottest part of the whole globe. Can
there be hydrothermal vents below? At any rate, Enceladus is one of the only two
bodies active enough for its heat to be detected by remote-sensing instruments – the
other is Jupiter’s satellite Io, but Io and Enceladus are very different worlds.
Certainly, the past few months have been of immense interest. So many new
phenomena have been seen. Which is the most intriguing? Make up your own mind –
but I have to say that my personal vote must go to the fountains of Enceladus.

25
P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_7,
© Springer Science+Business Media, LLC 2010
On 3 October 2005, there was annular eclipse of the Sun. The track of the annularity
began in the Atlantic and crossed Spain, which was convenient enough. I have to admit

that my travelling days are over, but the Sky at Night team led by Chris Lintott was well
represented in Madrid, and was rewarded with a perfect view. I had to stay at home and
make do with my very small partial…
An annular eclipse occurs when the Earth, Sun and Moon line up, with the Moon
in mid position – but with the Moon in the further part of its orbit, so that its disk is
not quite big enough to cover the Sun completely. The Sun’s mean angular diameter is
Chapter 7
Spanish Ring
Spanish ring eclipse team (Credit: Pete Lawrence)
26 7 Spanish Ring
32 min 1 s of arc; the apparent diameter of the Moon ranges between 33 min 21 s and
<30 min, with a mean of 31 min 8 s. The length of the Moon’s shadow varies between
237,000 and 227,000 miles, with a mean of 231,000 miles. The Moon’s mean distance
from the Earth is 238,700 miles, and from this distance the shadow is too short to reach
the Earth’s surface. It follows that annular eclipses are more frequent than totals in the
ratio of 5:4. This is brought out by the dates of totals and annulars in Great Britain
between 1800 and 2100; six annulars (1820, 1836, 1847, 1858, 1921 and 2003) and
only two totals (1927 and 1999), though it is true that the track of totality on 30 June
1954 just grazed the tip of the northernmost of the Shetland Isles (I do not believe that
anyone actually saw it from there). The next British totalities will be on 3 September
2081(Channel Islands) and 23 of September 2090 (Southern Ireland and Cornwall).
I saw my first annular eclipse on 29 April 1976, from the Greek island of
Santorini – the site of the devastating volcanic outburst which probably destroyed
the Minoan civilisation on Crete, than just about the most advanced in the whole
word. (The Santorini volcano, Nea Kameni, is still smouldering, though for a long
time now it has been reassuringly placid.) With a party of friends, I was stationed
in the courtyard of the excellent Atlantis Hotel, under a perfect sky.
Frankly, I did not know quite what to expect. Annularity can last for more than
12 min so that things are less frenetic than with a total eclipse, and strict precautions
must be taken all the time. Of course, there is no chance of seeing the corona, though

naked-eye prominences have been recorded, and so have Baily’s Beads – in fact the
first description of these beads was given by Francis Baily at the annular eclipse of
15 May 1836, though they had been seen much earlier by MacLaurin at the annular
eclipse of 1 March 1737. I did not know whether the sky would darken sufficiently
for planets or bright stars to be seen; at the Santorini eclipse it did not, and the
diminution in light was so slight that many of the locals failed to realise that
anything unusual was happening. Still it was enthralling to see that the jet-black
disk of the Moon circled by a ring of sunlight. I saw another annular from Mexico,
on 10th of May 1994; this time the sky became darker, but I could see no promi-
nences and certainly no sign of corona.
Eclipse-chasing is addictive, and even an annular is well worth seeing, so I was very
sorry not to be able to join the 3 October party, in Madrid. At least the Sky at Night
was well represented; Chris Lintott and Mark Kidger were our commentators, and the
photographers included Damien Peach, Pete Lawrence, Ian Sharp and Dave Tyler, all
armed with equipment much more sophisticated than anything I could have taken to
Santorini almost 30 years earlier. Nowadays, good results can be obtained even with a
simple digital camera, but digitals belong strictly to the twenty-first century.
The track of annularity passed right through Madrid, and the eclipse took place
in the late morning, so that the Sun was pleasingly high in the sky. The annular
phase lasted for 4 min 11 s, and 90% of the solar surface was covered, but the drop
in the light-level was surprisingly pronounced. It so happened that neither of our
main commentators had seen an annular eclipse before, and they were suitably
impressed, notably by the crescent-shaped shadows which were cast as the Moon
crept slowly and gracefully on to the Sun.
277 Spanish Ring
The sky never became dark enough for Jupiter to be seen (Venus was badly
placed), but the landscape became very dim, and at Madrid was probably about the
same as the light-level to the late twilight – according to those who were there;
watching the picture on my television screen could not give me any real idea.
Baily’s Beads were well seen, and a very interesting set of observations were made

by Pete Lawrence. The “beads” are produced when shafts of sunlight cast through
the lower-lying parts of the Moon’s uneven limb. Careful timing showed that the
main “bead” was seen as the sunlight streamed past a very large, deep depression
which could be identified as Mare Orientale, the Eastern Sea. This is a major sea,
almost all of which lies on the Moon’s far side; only a tiny section of it can ever be
seen from Earth, and then only under the most favourable liberation. (I first drew it
in 1949, and suggested its name, American observers rediscovered it later.) It is a
huge ring structure apparently, the youngest of the principal Maria and the only one
of its kind on the far side. It is so large that from Madrid it was able to produce an
obvious and persistent “bead”.
It cannot honestly be said that a great deal of valuable work can be done during
an annular eclipse, but what does this matter? Everyone at Madrid enjoyed it –
including the town band, who came into the main city square to join the astronomers,
and played with great gusto without quite matching the standard of the Royal
Philharmonic. At least the Sky at Night team, their appetites whetted, could look
forward to the much grander spectacle of a total eclipse in March 2007.

29
P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_8,
© Springer Science+Business Media, LLC 2010
Look up into the sky, and you will see the stars as tiny, twinkling points. The twinkling
is due entirely to the Earth’s atmosphere; from space (or on the Moon) stars do not
twinkle (scintillate) at all, and if you have the chance of seeing stars while you are
travelling in a high-flying jet you will find that the twinkling is much less then it is at
sea level. But with the naked eye, no star appears as anything but a dot. If you use a
star as an obvious disk, you may be assured that there is something wrong. Almost
certainly the telescope is out of focus. This being so, it takes an effort of the imagina-
tion to appreciate that some of the stars are huge enough to contain the whole orbit of
the Earth round the Sun – while admittedly others are so tiny that they could fit com-
fortably into the ring road of a small city. For the last the programme of 2005 I was

joined by Professors Richard Harrison and Lucy Green to say something about the
Sun, the only star close enough to be examined in a great deal, and then by Drs John
Mason and Barrie Jones, to discuss the sizes of the various types of stars.
Chapter 8
The Sizes of the Stars
The “Plough” in Ursa Major, photographed by Nik Szymanek
30 8 The Sizes of the Stars
If no stars show obvious disks, then how do we measure their diameters? There
are various methods. Of course, there is no problem at all with the Sun, which is a
normal Main Sequence star of Type G; it is 865,000 miles across. We may not have
discovered all its secrets, but we do know a great deal about it, and it gives us a guide
to other stars – though the stars are amazingly diverse. Some are much larger than the
Sun, others much smaller; some are far more luminous, others remarkably feeble.
Let us deal first with exceptionally luminous stars – which are not necessarily
the largest. According to one set of measurements, the record holder is a remote
celestial search light catalogued as LBV 1906-20, said to be the equal of 40 million
Suns, which is about as powerful as a star could be without disrupting itself by the
pressure of radiation. (LBV, by the way, stands for Luminous Blue Variable.) This
does seem rather dubious. Then we have the Pistol Star in Sagittarius, so nicknamed
by the shape of the nebula, which it illuminates. It is approximately 25,000 light
years away, in the direction of the galactic centre, and it is certainly very powerful and
massive. Were it is not so masked by interstellar dust, it would be an easy naked-eye
object; in fact, it remained undetected until the Hubble Space Telescope imaged it
in infra-red. Its mass seems to be about 150 times that of the Sun, and its diameter
has been given as around 300 times that of the Sun, i.e. roughly 250,000,000 miles,
so that it could contain the whole of the Earth’s orbit. However, the data for Eta
Carinae, the erratic variable in the southern hemisphere of the sky, are more reliable.
The luminosity is at least 5,000,000 times that of the Sun, and it is one of the most
massive stars known. It is also wildly unstable; for a while around 1840 it shone as
the most brilliant star in the sky apart from Sirius, though for well over a century

now it has hovered on the brink of naked-eye visibility. In the foreseeable future –
perhaps tomorrow, perhaps not for a million years – it will explode as a supernova,
ending up as either a neutron star or a black hole.
The largest of all stars are red supergiants. A star begins its career by condensing
out of the material inside nebula; it shrinks, under the influence of gravitation, and
the inside heats up. When the core temperature reaches about ten million degrees,
nuclear reactions are triggered off. The main “fuel” is hydrogen, the most abundant
element in the universe; the hydrogen atoms combine to form helium, and the star
begins to shine. (Yes, I know this is horribly oversimplified, but it will suffice for
the moment!) When the supply of the available hydrogen runs low, different reac-
tions begin, and elements heavier than helium are built up. With a modest star such
as the Sun, the process is halted before it can go too far. The star will briefly
become a red giant (not a supergiant) and will puff off its outer layers and become
a beautiful “planetary nebula”. When the outer layers are finally lost, what is left of
the star collapses into what is known as the white dwarf stage. It will then go on
shining feebly until all its light and heat have gone, leaving it as cold, dead
globe – a black dwarf; – it is quite possible that the universe is not yet old enough
for any black dwarfs to have formed.
But with a much more massive star, equal to (say) over ten Suns, the story is
different. The star evolves much more quickly, and the element-building process is
not halted so soon. The star heats up until its core is at a temperature of millions of
degrees, and the globe is blown out to produce a supergiant. The surface has
318 The Sizes of the Stars
cooled-hence the red colour – but the luminosity is immense, though without
matching Eta Carinae. The best known red supergiant is Betelgeux in Orion (the star
marks the great hunter’s shoulder, the name can be spelt in various ways and some
people pronounce it “Beetle Juice”). Its apparent magnitude varies slowly between
0.2 and 1; sometimes it equals Rigel, the other brilliant star in Orion, while at others
it is comparable with Aldebaran, in Taurus, which looks like the same colour but is
a giant rather than a supergiant. Betelgeux is just over 500 light-years away, it must

have a diameter of around 550 million miles, and shine 15,000 times more powerful
as the Sun. In luminosity it cannot match Rigel, well over 40,000 Sun power, but
Rigel is hot, bluish white star, and it is not nearly as large as a red supergiant. But
Betelgeux, vast though it is, is by no means the record-holder.
Even larger is Mu Cephei, in the far north of the sky not far from the W of
Cassiopeia; over Britain if it never sets. It is variable between magnitudes 3.6 and 6,
but as its seldom drops between the fifth magnitude it is almost always within
naked-eye range. It is so red that William Herschel christened it the “Garnet Star”,
and the nickname has stuck; through binoculars it looks rather like a glowing coal.
It is further away than Betelgeux (perhaps 5,000 light-years) and much larger, more
massive and more luminous, since it could equal 350,000 Suns. For a long time it
was said to be the largest star known but we have now found that it is outmatched
by four others – VV Cephei, V354 Cephei, KW Sagittari and KY Cygni – and possibly
also a fifth, VY Canis Majoris, though the various measurements used here do not
agree really well.
Consider KY Cygni around 5,200 light years away in the constellation of the
Swan. The diameter is thought to be around 1,000,000,000 miles. Imagine that you
could stand upon the surface and go for a walk, how long would it take you to go
right around, walking at a steady 3 mph and never stopping? The answer – 150,000
years. Yet, although KY is 300,000 times as luminous as the Sun, it has only 25
times the solar mass. Large stars are always less dense than smaller ones; it is almost
like balancing a lead pellet against a meringue.
Go and look for KY Cygni by all means; its position is RA 20h 26m 52s2, dec.
+38° 21¢11″, but I warn you that it will not be easy. It lies in a rich area, but its
apparent magnitude is a modest 13.3. Rather surprisingly, the star with the largest
known apparent diameter is none of these supergiants, but R Doradus in the far
southern constellation of the Swordfish. The distance is 200 light-years, the lumi-
nosity 6,500 times that of the Sun and the diameter 150 million miles. It is red, and
a variable star of the pulsating type.
From incredibly large stars to very small ones, we have noticed that a modest star

like the Sun will become a white dwarf when its supply of hydrogen fuel is exhausted.
We know a great many white dwarfs, the most famous is the faint companion of Sirius
which was also the first to be identified. All the atoms are crushed and broken, and
the component parts packed together with almost no wasted space; matter of this sort
is termed “degenerate”, and a cupful of it would balance the weight of an ocean liner.
Atoms in a normal state are mostly empty space. The best analogy I can give – not a
good one, I know – is to picture a snooker table upon which the balls are set out ready
for a game. They take up a good deal of room – but pack all the balls together, and
32 8 The Sizes of the Stars
you can cram them into a suitcase. The white dwarf companion of Sirius is slightly
smaller than the Earth, but as massive as the Sun. It is a mere 8.6 light years away,
and would easily be seen with binoculars where it not so drowned by the glare of its
primary; even so, a modest telescope will show it. Smaller white dwarfs are known,
with diameters comparable of that of the Isle of Wight.
Finally – the neutron stars left as the remnants of supernova explosions. Here,
protons and electrons – the main constituents of atoms – have been unable to withstand
the pressure and have been forced to merge, producing neutrons. The density is
unimaginable; our cupful of neutron star material would weigh thousands of millions
of tons. The most celebrated neutron star is the remnant of the supernova of 1054,
now seen as the Crab Nebula, without much doubt the most studied object in the sky.
The diameter of a neutron may be less than a dozen miles. If the centre of one of these
curious bodies lay in the village of Sidlesham, the globe would barely hold the city
of Chichester on one side of my home at the end of Selsey Bill on the other.
Indeed the stars are of many kinds. It is strange to reflect that to the early civili-
sations, even the Greeks, they were no more than tiny lamps attached to an invisible
crystal sphere.
33
P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_9,
© Springer Science+Business Media, LLC 2010
How far does the Solar System extend? The answer to this question is not as

straightforward as it might be expected. Neptune, the outermost planet, moves
around the Sun at a mean distance of 2,793 million miles; beyond come the members
of the Kuiper belt, of which Eris is the largest known and Pluto the brightest, and
Chapter 9
The Edge of the Solar System
Launch of the New Horizons probe to Pluto (Credit: NASA)
34 9 The Edge of the Solar System
there are various trans-Neptunians, such as Sedna, which travels out to immense
distances, almost to the fringe of the Oort Cloud, where the Sun’s gravitational pull
has become relatively weak. Some comets range much further and may leave the
Solar System permanently. Comet Arend-Roland, the subject of my very first Sky at
Night programme, will never return. There is one reasonable definition. The nearest
stars, those of the Alpha Centauri system, are just over four light-years away. It
seems to me, therefore, that the Sun’s dominance may end at a distance of around
2 light-years, 12 million miles. We cannot hope to track a spacecraft out as far as
that, but the Kuiper Belt ought to be within range, and our probe New Horizons is
on its way there. It was launched on 19 January 2006, and this seems to be a good
time to devote a programme to it. I was joined by Professor Mike A’Hearn of the
University of Maryland, who gave us the latest news about the Deep Impact space-
craft which had hit comet Tempel 1, and then by two of our regular visitors, Drs
Mark Kidger and Lucie Green.
Solar System bodies are of many kinds. Planets and comets are certainly very
different, but there may well be a link between comets and small asteroids; it is
widely believed that some small asteroids are the cores of old comets which have
lost all their volatiles, and that one of these, Phaethon, may be the parent of the
Geminid meteor stream. There are a few bodies which have “dual nationality” and
the distinction is not so clear-cut as used to be thought. The Deep Impact probe to
Tempel 1 was immensely informative. One surprise was the abundance of organic
material. As expected, the comet was made up chiefly of ices, with water dominant
and plenty of ices such as methanol and carbon dioxide; assembling it must have

been a gentle process. But what about more massive bodies which in some ways
behave like comets? Chiron, which spends most of its time between the orbits of
Saturn and Uranus, is well over 50 miles in diameter and has been given an asteroid
number (2060), but when it draws into perihelion, it develops what may be called
either an atmosphere or a coma and has also been given a cometary number,
though to me this seems irrational. And then what about Pluto, way out in the
Kuiper Belt?
Pluto has an eccentric orbit. When near perihelion, it has a thin but surprisingly
extensive atmosphere, though its companion, Charon, has not. (Do not confuse
Sharon with Chiron; it is a pity that two names are so alike; in mythology Chiron was
the wiser centaur while Charon was the gloomy boatman who ferried departed souls
across the river Styx into the underworld.) Pluto was last at perihelion in 1989.
Its orbital period is 248 years, and it is generally believed that in near future it will
temporarily lose its atmosphere, which again would be a cometary behaviour.
Recent doubts have been voiced, because as it swings outward Pluto’s temperature
seems to have increased rather than fallen, and this is probably due to slight fluctua-
tions in the output of the Sun, another indication of “global warming”. (P.C fanatics,
please note – there are no factories on Pluto to produce greenhouse gases!) We must
wait and see what happens during the next few decades, but in any case Pluto is an
interesting world and is due to be bypassed by the New Horizons spacecraft in 2015.
Perhaps significantly, New Horizons was planned when Pluto was still regarded as
359 The Edge of the Solar System
a true planet rather than KBO. It has been allotted an asteroid number, 134340,
though together with Eris and Ceres it is still called a “dwarf planet”.
New Horizons has an ambitious programme. After launch, on 19 January 2006
from Cape Canaveral, it was put into its planned orbit. In size and shape NASA
likened it to a grand piano, or better, a grand piano glued on to a cocktail-sized bar
satellite dish. It was launched by a three-stage rocket, of which the bottom section
was an Atlas V 551, and it was sent out towards Jupiter, so that the pull of the Giant
Planet could help New Horizons on its way. It was equipped with a radioscope

thermoelectric generator; solar power cannot be used at these vast distances, in the
wastes of the Solar System.
The first encounter was with the mile-wide asteroid 132524 APL, on 13 June
2006 at a range of 64,000 miles. (NB: of course, this and subsequent events took
place after the broadcast of our programme in January 2006. I have suitably updated
this account.) On 4 September 2006, this spacecraft took its first images of Jupiter,
and then, on the following 28 November had its first glimpse of Pluto. All was
going well.
The Jupiter encounter was extremely successful. Details on the disc were well
seen – notably the Little Red Spot, a newcomer to the Jovian scene, which has taken
planetary observers by surprise. Io, the wildly active satellite, was surveyed, and its
huge volcano Tvashtar obligingly produced a plume rising to a height of 200 miles
above the caldera. “Galileo orbited Jupiter for 6 years and never saw a plume like
that,” commented John Spencer, of the imaging team. “We just happened to breeze
by, and there it was”. The distance from New Horizons was 1,400,000 miles.
Clumps of debris in the ring system were seen, trailing the small inner satellite
Adrastea “like ducklings following their mother”. A spectacular picture was
obtained of Europa, perhaps the most intriguing of the Galileans inasmuch as it
may well have a vast ocean of ordinary water beneath its icy crust.

37
P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_10,
© Springer Science+Business Media, LLC 2010
Our first programme of 2006 took us back to Mauna Kea. Alas, I am no longer
able to travel as far as that, but Chris Lintott can, and to Hawaii he went. Atop the
volcano he was joined by a number of eminent astronomers, including the director
Andy Adamson. Mauna Kea is an amazing place; there is nowhere quite like it.
Think of Hawaii, and you will conjure up a picture of palm trees, guitars, bikinis
and an azure blue sea. Many parts of it really are like this, but go to Big Island and you
will find a different scene. There are two towering volcanoes, one dormant and the

other violently active. You will also find one of the world’s greatest observatories. Why
Mauna Kea? Because it is so lofty, and pokes above the thickest and unsteadies layers
Chapter 10
The Telescopes of Mauna Kea
UKIRT Mauna Kea (Credit: ROE)
38 10 The Telescopes of Mauna Kea
of an atmosphere. Not much life can survive – but astronomers love it, and the summit
positively bristles with domes.
Mauna Kea has not erupted for about 4,000 years, and (we hope!) it is not likely to
do so again in the foreseeable future, if ever, but the view is nothing if not pictur-
esque, with cider-stones and lava flows everywhere. From the top you can see the twin
volcano Mauna Loa, which is erupting all the time. On one occasion a flow reached
the outskirts of Hilo, the largest town on Big Island, and according to local lore was
stopped only by the timely intervention of Hawaii’s most powerful witch-doctor.
Mauna Kea is just over 14,000 ft high, and there is a good road for most of the
way to the summit; all of it is drivable, but there is one thing to be borne in mind.
The air at 14,000 ft is thin, and one’s lungs take in only 39% of the usual amount
of oxygen. Some people cannot tolerate this, and I will remember that one young,
fit, rugby-playing BBC assistant had to be brought hastily down to sea level. Most
people have headaches for a while, but I was unaffected because I was an old
(wartime) flyer who used to fly high altitudes. Nobody actually sleeps at the summit,
and most visitors on the way up stay for a day or so in the “half-way house”. Hale
Pohaku is at the height of about 10,000 ft. To drive from Hale Pohaku from the
summit takes a mere 20 minutes, but that extra 4,000 ft makes all the difference.
The air at the volcano top is not only very thin, but also very dry because you
are above 97% of the atmospheric water vapour, and this is a boon to astronomers
working at short wavelengths; water vapour is extremely effective at absorbing such
radiations. Several telescopes suited to these conditions have been sited here,
notably UKIRT, the UK Infra-Red telescope, and JCMT, the James Clerk Maxwell
telescope. (Maxwell, a Scot, was one of the greatest scientists of the nineteenth

century.) Among others are Kecks 1 and 2, which were for some time the largest
telescopes in the whole world. There is a great deal to see, and there have been
major developments ever since I was last able to go there, around 10 years ago.
Chris Lintott’s first report was from UKIRT, which was brought into action in
1978. It has a 50-in. mirror and was designed to work in the infra-red. The mirror
need no to be so accurate as with an optical telescope, which means that it can be
thin and therefore cheap – but in the event it turned out to be so good that it can also
be used visually, which was sheer bonus. It is continuously upgraded, and not long
before our programme a new instrument has been added, the Wide Field and
Planetary Camera, WFPC (annoyingly, people will insist on referring to it as
“wiffpick”). It has the largest field of view of any astronomical infra-red telescope
ever made, and in a single exposure it can cover an area equal to that of the full
Moon, which is 1,200 times larger than that covered by the infra-red camera of the
Hubble Space Telescope. Spectacular pictures have been taken with it, particularly
the so called Chicken Nebula, IC 2044/48, whose shape really does resemble that
of a running hen! There is also a dramatic view of the Orion Nebula, M42, with
numbers of brown dwarfs i.e. – low mass stars whose interiors never became hot
enough to trigger nuclear reactions. A brown dwarf will glow freely for an immense
period and will end up as cold, dead globe – a black dwarf, though it is quite likely
that the universe is not yet old enough for any black dwarfs to have evolved.
M42 is a stellar nursery. Very young stars are associated with dust clouds which
block out visual light, but infra-red radiations can slice through them, and give us
3910 The Telescopes of Mauna Kea
views of star forming regions. Calm though it may look, the Orion Nebula is really
in a state of turmoil because star-birth is an energetic process. Around 5,000 million
years ago our own Sun was born inside a nebula, but by now it has overcome the
instabilities of youth, and has settled down to sober, middle-aged existence. It will
not change dramatically for over a thousand million years yet, whereas UKIRT can
show us definite, short-term changes in part of M42. Deep inside the nebulosity,
there are immensely powerful stars which we can never see, but which betray their

presence by pouring out infra-red radiation. You will never see them because they
will not live long enough for the light to “burn its way” through the gas and dust
which envelopes them, but we know that they are there.
The next call during the programme was to the JCMT, which functions at submil-
limetre wavelengths. This does not resemble an ordinary telescope, and one cannot
look through it because it operates in the region of infra-red and the radio range, so
that it has the look of a radio telescope dish. Clouds do not bother it, and neither
does daylight. It was completed in 1987, and like UKIRT, it has been a tremendous
success. One of its many observational programmes concerns stars which may be
attended by planets, and here its latest camera, Scuba – installed just before the Sky
at Night team arrived – has been particularly informative.
An early target was Fomalhaut in Piscis Australis (the Southern Fish), the south-
ernmost of the first-magnitude stars visible from Britain. Look for it during autumn
evening below the Square of Pegasus, but even from southern England it is always
low down, and from northern Scotland you will be lucky to see it at all. It is a white
star, 25 light-years away and 16 times as luminous as the Sun; its mass is 2.3 times
that of the Sun, and its diameter size is 1,600,000 miles. It is thought to be no more
than 300 million years old, and to be surrounded by a torodial-shaped dust ring with
a very sharp edge. The dust is distributed in a belt between two and 3,000,000 miles
wide, which is significant; can this belt contain a planer or even a swarm of smaller
objects of asteroid size? Scuba has found that the band is “warped”, possibly – even
probably – due to the gravitational pull of a planet. If so, there may well be other
planets, some of them similar to the Earth in size and mass. Of course, this is a
speculation, but it is reasonable speculation. Less than a light-year from Fomalhaut
there is a faint star, TW Piscis Australis, which moves at the same speed and in the
same direction through space, so that it may be a true companion. Any inhabitants
of a planet in the Formalhaut system will have a spectacular view of the sky.
Two of our closest stellar neighbours, both 10–11 light years away, have been
surveyed by Scuba and found to be unlike each other, though both are considerably
smaller, cooler and redder than the Sun. These two, Epsilon Eridani and Tau Ceti,

have long been regarded as promising planetary centres. Epsilon Eridani undoubt-
edly does have planets, but Tau Ceti has been a disappointment. It can only be ten
million years old, but there is no well-defined dust disk, and instead the star appears
to be associated with a cloud of debris – comets if you like. Jane Greaves, one of
the Scuba team, has suggested that there may be thousands or even millions of
comets, so that if a planet exists it will be a most uncomfortable place, subjected to
constant bombardment – any inhabitants will be used for seeing comets streaking
across the sky. When efforts were first made to pick up radio messages from extra-solar
planets, way back in 1960, these two stars were the prime candidates. Messages in
40 10 The Telescopes of Mauna Kea
the form of mathematical codes were transmitted, but so far the Tau Cetians and the
Epsilon Eridanians have remained obstinately silent.
During the programme, Chris also went to another of the great observatories,
the Keck, where there are two of the largest telescopes in the world. There he
talked to Geoffrey Marcy, widely (and justifiably) regarded as our leading planet-
hunter. One way to detect them is to measure their gravitational pulls on their
parent stars; the star will move to and fro very slowly and very slightly, provided
that the planet is massive enough. Lightweight bodies comparable with the Earth
are obviously much more elusive, but surely they must exist. Geoff Marcy discussed
a particular star, IL Aquarii, otherwise known as Gliese 876, which is 15 light
years away, with a diameter of 300,000 miles and luminosity little more than 1/100
that of the Sun. Three planets are definitely known. Two are gas giants comparable
in mass to Jupiter; both are very hot because they are so close to the star, and have
what is termed 2:1 resonance – that is to say, the inner planet makes two orbits in
the same time that the inner planet takes to complete one. There is also a third
planet, even closer-in, which may be no more than seven times as massive as
Earth, much less substantial than Uranus or Neptune. Since the star is a feeble red
dwarf, its planet must be bathed in an eerie glow and heated to a temperature of
around 800°C. IL Aquarii itself is thought to be ten million years old and, like
many red dwarfs, is slightly variable.

There is an interesting aside. In 1998, Kevin Apps, an undergraduate student at
Sussex University, paid a visit to Mauna Kea and went to the Keck Observatory. He
drew up his own list of possible planetary centres, and in particular noted a faint star
in Cygnus, over 150 light-years away. Diffidently, he sent his list to Geoff Marcy and
his colleague Paul Butler, who used the Keck telescope, observed the star and found
the planet. Its official designation is HD 187123b, but it is always known as Planet
Kevin. Marcy was impressed; “It is great to have him as a colleague”. After all, not
many people have made a major discovery before completing a degree.
The first Scuba has been replaced by its successor, Scuba 2 (In case you are won-
dering what the name means, it stands for Submillimetre Common-User Bolometer
Array.) Far beyond the Milky Way, we come to the outer galaxies, and in this field of
research, Scuba is unrivalled. It is being used to study very remote systems which
are now called Scuba galaxies; they are hard to detect at optical or infra-red wave-
lengths, but submillimetre radiation is more effective at passing through the dust, We
see them now as they used to be when the universe was young, and apparently the
larger galaxies are cannibals, swallowing up the smaller systems. Scuba galaxies are
frenetically active, with intense star formation in progress all the time.
To give anything like an adequate account of the observatories on Mauna Kea
would take a very long time – and our programme was only an hour long. There was
barely time even to mention the new, huge Gemini South telescope, with its segmented
mirror, or the HARP spectrometer; we had to gloss over technical advantages such as
adaptive optics – there was so much we had to leave out, but I hope we did enough
to show that Mauna Kea is one of the world’s greatest scientific adventures.
Go there if you have a chance, but do not forget that at 14,000 ft it is definitely
wiser to walk rather than to run.