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13/1/09
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a guide to DEEP SPACE
2009 SPACE ODYSSEY
THE PILLARS OF CREATION
In the constellation of Serpens lies the Eagle Nebula, (right) a giant
cloud of interstellar gas and dust. Here new stars are being born,
condensing out of the nebula. The radiation from these stellar infants
is energizing the gas, causing it to glow. A closer look at the Eagle Nebula
reveals intriguing structures including the famous Pillars of Creation.
These dark structures are columns of cool gas, mainly hydrogen and dust,
that serve as incubators for new stars. Astronomers have detected blobs
of much denser gas inside the Pillars, these appear to be forming solar
systems. Eventually the new star will become visible as their radiation
blows away the surrounding material. Each Pillar is several light years
long. The Pillars and the surrounding nebula are 7000 light years from
Earth, so we see them as they were 7000 years ago. Possibly they no
longer exist, the shockwave from a nearby exploding star may already
have ripped through them and we will see this happening
a few thousand years from now - or maybe tomorrow.
THE HUBBLE SPACE TELESCOPE
Probably the most famous astronomical satellite ever,
the Hubble Space Telescope has given us amazing views
of the wonders of the cosmos. Placed into orbit by a
Space Shuttle mission in 1990, the HST initially suffered
from a focussing problem. This meant that its images
were blurred. A NASA investigation revealed that its
main mirror had been manufactured incorrectly and the
testing that should have disclosed this error had been
cancelled as a money-saving measure.
Happily astronauts were able to install a new component
to correct this problem in 1993. Since then the HST has
provided unparalleled views of deep space objects.
Many of these are stunningly beautiful and have become
familiar through their reproduction on posters, album
covers and in science fiction movies. Visits by Space Shuttle crews
to service the HST and replace worn-out components have extended its life but the
end is in sight. The next servicing mission will be the final one, and all being well
the HST will be replaced by the bigger still James Webb Space Telescope in 2013.
TO THE ENDS OF THE UNIVERSE
Since the invention of the telescope 400 years ago, astronomers have been striving to see
further and further into the heavens. Every time you look up at the night sky, you are looking
back in time. The light we can see left the stars and galaxies hundreds or even thousands of
years ago. In fact, some of the stars we can see may not even be there any more.
We live in a galaxy called the Milky Way, a vast flat spiral of hundreds of billions of stars.
Our Sun and its family of planets, including the Earth, circle the Milky Way’s centre in a
long slow orbit. The Milky Way’s size defies human comprehension: a beam of light
would take 100 thousand years to travel from one side to the other.
Until the 1920s many astronomers believed that our galaxy
was essentially the entire Universe. Other galaxies were
visible but were thought to be ‘spiral nebulae’, relatively
small objects inside the Milky Way. Then Edwin Hubble,
a flamboyant character of an astronomer, recognized a type
of star called a Cepheid in the Andromeda Nebula, the largest
of these spiral nebulae. Cepheids, stars which pulse at a rate
governed by their brightness, are extremely useful ‘standard
candles’ for astronomers, who can easily tell how far away a
Cepheid is just by observing how long it takes to cycle
from minimum to maximum brightness. Hubble did the
calculations and discovered that the Andromeda Nebula
was very distant indeed (2.2 million light years away is the
accepted figure today), so far in fact that it could only be a galaxy in its own right.
The Universe must be far larger than previously thought. At the time this was very
controversial, but Hubble was about to create an even greater stir. However to
understand what he did, we firstly will need to discuss light.
HOW FAR ARE THE STARS?
Light travels as a wave, and hence it has a wavelength. If you
imagine waves in the ocean, their wavelength is the distance
between each crest. Just for a moment think about the
familiar colours of the rainbow (or spectrum). At one side we
start with red which has a long wavelength, next orange with
slightly shorter wavelength, moving through the colours to
blue and violet the wavelengths get smaller and smaller.
Light waves from moving sources are stretched or
compressed by the motion. If an object is coming towards you
its light is blueshifted meaning the light waves are squeezed
together appearing more bluish, similarly if it is receding the
light is redshifted. This is called the Doppler Effect and is very useful in many aspects of astronomy.
For example, by studying the light from a star we can tell if it is coming in our direction (blueshift)
or moving away (redshift), or we can use the Doppler Effect to measure its speed. Between 1912 and
1917, astronomer Vesto Slipher was using the Doppler Effect to measure the speed of ‘nebulae’, at
the time still believed to be nearby objects inside our own galaxy. To his surprise, of twenty five
nebulae, four were blueshifted (and therefore coming towards us) and the rest were redshifted
and hence moving away from us. By the late 1920s Hubble was using the 100 inch Mount Wilson
telescope, the largest in the world at the time, to look at distant galaxies. By 1929 he had catalogued
46 galaxies by their distance and speed (measured by the Doppler Effect). The conclusions were
unmistakeable and confirmed Slipher’s results. Firstly most galaxies are receding from our galaxy,
Secondly, the degree of redshift (and therefore the galaxy’s velocity) is directly proportional to its
distance away. In other words, if a galaxy was twice as far away as another, it would appear to be
travelling twice as fast. This is now called Hubble’s Law, and it made his name. Hubble’s Law opened
up a new way of determining intergalactic distances. If we measure the redshift of a galaxy,
we will know its velocity, and by Hubble’s Law, we will automatically know its distance away.
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THE BIG BANG THEORY
Edwin Hubble’s observations showed that the Universe is
expanding. This implies that in the past the Universe was
much smaller than it is now. Then the galaxies would have
been closer together, going further back in time there
would have been a time when they were squeezed closer
together still and ultimately there would have been a time
when everything was at a single point. In the 1930s, Belgian
physicist and priest Georges Lemaître suggested that if the
Edwin Hubble
evident expansion of the universe was reversed until it
could contract no further, all the mass of the Universe would be squeezed into what he
called the ‘primeval atom’ or ‘cosmic egg’. This had exploded, expanding outwards to
create the Universe we see today. In 1948 two physicists Ralph Alpher and George
Gamow calculated that most of the chemical elements could have been created in this
massive explosion. Their work implied that heat from this explosion should be spread
throughout space, appearing as a faint radio (or microwave) emission. Alpher and
Gamow did not believe it would possible to detect this background radiation.
THE SEARCH FOR E.T.
Searching for life elsewhere in the Universe is a fascinating endeavor. Astronomers in the 1800s used telescopes
to search for signs of life and even civilization elsewhere
in the Solar System. Some even believed they saw signs
of intelligent life on Mars in the form of a grid of canals
across the Red Planet’s surface. Illustrations and maps of
Mars published by NASA as late as the early 1960s still
showed these. Disappointingly, visits to Mars by
spaceprobes from the mid-60s onwards revealed it to be more barren and inhospitable
than previously thought. There is still a possibility that life arose on Mars billions of
years ago when conditions on the planet were milder, and perhaps some bacteria-like
organisms cling on to life under the surface. We probably will not know if this is true
or not until people travel to Mars to explore. Elsewhere in the Solar System, there is
evidence for oceans of water under the icy surfaces of Jupiter’s moon Europa and
Saturn’s moons Enceladus and Titan. These may be the best prospects for life-bearing
sites in the Solar System. Could bizarre aquatic life swim in the inky depths of these
alien seas? Given the difficulties of sending a mission to drill through the crusts of
these distant moons, we will probably not know the answer for centuries.
DARK MATTER
96% of the Universe is invisible to us! Astronomers reached this unsettling conclusion
by studying galaxies. Observations showed that the spin rates of galaxies are faster
than they should be, in fact high enough to pull them to pieces, so some unseen force
must be holding the galaxies together. This could not be the gravity of the stars we see
in the galaxies as there are not enough of them. The only reasonable conclusion is that
some mysterious form of undetectable matter dominates each galaxy. This has been
called Dark Matter ( because it does not give out any light). Some of it may be tiny
black holes or brown dwarf stars drifting between the stars but most of it seems to
be composed of sub-nuclear particles which have yet to be studied in the laboratory.
The unexpected discovery of dark matter shows that there is still so much for
us to learn about the Universe.
RADIO ASTRONOMY
In 1930 Karl Jansky was investigating radio interference which was disturbing
transmissions on a trans-Atlantic radio link. Using a giant radio antenna which
could be pointed in any direction he discovered that some of this radio
noise came from the sky and particular the constellation
of Sagittarius. Jansky concluded that the radio noise
originated in the centre of the Milky Way. This was the
start of radio astronomy, radio astronomy has enabled us
to observe a new depth to the Universe. Astronomers use
the natural radio emissions of clouds of hydrogen to map
the galaxy including regions obscured to our sight.
We have been able to explore and chart the core of the
Milky Way in great detail and determine that a vast black
hole must dominate its centre. Pulsars, fast-spinning
remains of exploded stars were discovered through radio
observations by Portadown-born Jocelyn Bell Burnell.
Radio astronomy shows that there is more to the
Universe than meets the eye!
2009 SPACE ODYSSEY
Astronomers accept that, rather than being two
separate entities, space and time are one, sometimes
called spacetime. Rather than simply saying where
something is located, it would be more correct to say how
long it is there for too. This is based mainly on the work
of Albert Einstein, specifically his theory of General
Relativity. Einstein’s theories had other important
implications, one of which is that an object’s gravity
distorts spacetime. Rather than saying a planet exerts a
Albert Einstein
gravitational pull towards it, it is truer to say its gravity
bends the space around it. The path of a beam of light passing a star would be curved
as it passes through the warped space around the star. This has been observed and
astronomers are now well aware of the phenomena of ‘gravitational lensing’ when the
image of a distant galaxy is distorted by the gravity of other galaxies between it and
the Earth. Stranger still as space and time are one, gravity distorts time too. Time runs
slower near a massive object such as a star than it in empty space. This is not just some
obscure prediction about the distant Universe, experiments with very accurate atomic
clocks have verified that time moves faster on the Earth’s surface than it does on high
mountain peaks. This difference is so tiny as to be imperceptible to human senses
but would be obvious near a black hole. If an astronaut could leave her spacecraft
to somehow safely approach a black hole, her crewmates would see her appear
to slow down until she became almost frozen in place.
British scientist Fred Hoyle championed a rival explanation called the Steady State
theory and fiercely disagreed with this explosion theory which he sarcastically called
‘the Big Bang Theory’. This name stuck and has been used ever since.
The Steady State theory is no longer accepted. In the early 1960s, two engineers Arno
Penzias and Robert Wilson, were employed by the Bell corporation to find a source
of radio interference picked up in a satellite communications antenna.
The interference was a faint but steady radio noise coming from every direction the
antenna was pointed. It appeared to come from all over the sky. Penzias and Wilson
consulted other scientists and realised that they had accidentally discovered the
Cosmic Microwave Background predicted by Gamow and Alpher.
Today’s free poster
SPACE AND TIME
DEEP SPACE
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13/1/09
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Jodrell Bank radio telescope
2009 SPACE ODYSSEY
Today’s free poster
DEEP SPACE
Since 1995 astronomers have discovered 300 or so planets orbiting other stars.
The vast majority so far discovered are huge gas giant planets like Jupiter or Saturn but
as technology improves we ought to find worlds more like Earth. To find life out there
all we can do at present is try to listen for radio signals from alien beings. This is the
Search for Extra-terrestrial Intelligence (SETI) and is conducted mainly as a spare-time
project by some astronomers. At present no government funds SETI research, but
private groups such as the Planetary Society have paid to scan the sky for artificial
signals. Grandest of these efforts is the Allen Telescope Array, 42 linked 6 metre radio
telescopes funded by Microsoft billionaire Paul Allen. We humans have sent our own
messages into space. Plaques and discs of data were been bolted to the Voyager and
Pioneer deepspace probes should any space travelling ETs find them.
Many astronomers would say that alien life is a possibility, but one astronomer, Frank
Drake, has tried to work out the number of extraterrestrial civilizations active in the
galaxy. The Drake Equation uses estimates of how common planets are around other
stars, how many are suitable for life, on how many actually develop life and so on to
give ‘N’ the number of alien civilizations. Unfortunately, most of these values are little
more than guesses at the moment, so values of N vary from hundreds of thousands
to just one (ourselves!). Perhaps the Cosmos is full of life or perhaps we are alone.
Either possibility is awe-inspiring.
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Poster design by Jonathan Simms