Born in Kentucky
in 1889, Hubble joined the staff of the Mount
Wilson Observatory in Pasadena, California, in
the summer of 1919. Another astronomer observed
of him: "He wants to find out about the universe;
that shows how young he is."
Ten years later, Hubble announced his discovery
that every other galaxy appeared to be moving
away from us. It was the result of observation
and calculation, which he was able to express
as a simple mathematical expression: Ho = v/d,
where vis the galaxy's radial outward velocity
(in other words, motion along our line-of-sight),
d is its distance from earth, and Ho is the "Hubble
Constant". From this, it is possible to deduce
that everything must once have been closer together;
rewinding the film of the universe would take
us back to the Big Bang, the moment of creation.
For this reason, it is of prime importance that
Ho is correct, and that the distances to stars
being measured is also correct. Astronomers have
argued bitterly for years about the exact value
of the Hubble Constant; estimates vary by a factor
of two. If the higher estimate is correct, then
the universe might be younger than its oldest
observed stars - a logical contradiction that
would require substantial revision of many astronomical
theories. The Hubble should be able to help calculations
of both velocities and distances.
The HST has helped two teams to converge on the
value of the constant: using it, one puts the
age of the universe at between nine and 12 billion
years; the other puts it at 11 to 14 billion years.
Designed and built through the 70's and 80's
the Hubble Space Telescope (HST) is today open
to the public as an observatory where people can
take pictures of other planets. Located just above
the Earth's atmosphere in low Earth orbit it is
based at John Hopkin's University in Baltimore,
Maryland. [1]
The Hubble Space Telescope is an important astronomical
telescope in space, studying the stars, planets,
and interstellar space. It has in a way been the
most productive astronomical instrument ever made.
It's a general-purpose telescope that one can
point at anything in the sky, planets, stars,
galaxies, gas clouds and so on. And so it's actually
made contributions to all of those fields, the
planets inside our solar system, our galaxy of
stars and the large-scale structure in history
of the entire universe. And in each of those fields,
it's provided considerable surprises. [2]
The orbiting Hubble Space Telescope (HST), a $1.6
billion piece of the most sophisticated viewing
equipment in the world was launched. In theory,
itwould be able to spot a 5p piece from 20 kilometres
away, and see the light of a firefly 16,000 kilometres
distant. Yet, the first pictures relayed from
the system floating 600 kilometres above were
badly blurred. A few problems in the systems of
the telescope- a cylinder the size of a single-decker
bus - were sorted out, but technicians realised
something more serious was wrong. Finally, they
deduced a flaw in the three-metre main mirror:
the curves of the edges had been ground two-millionths
of a metre too flat. This elevation from useless
lump to inspiring example of modern technology
was achieved in December 1993 by an equally inspiring
piece of repair work, consisting of some of the
longest spacewalks ever by the crew of the Space
Shuttle. The process was described by one astronaut
as "like fixing your car with oven-mittens
while hanging upside-down". Essentially,
they added specially designed components to correct
for the aberration inthe mirror. The ground-based
scientists gathered again to see whether the work
had succeeded. It had.
Hubble's transformation was named among the wonders
of the modern world, along with the scanning electron
microscope, the Human Genome Project (which aims
to map all of the100,000 human genes) and the
pyramids of Giza.
It reveals images of spectacular beauty within
the galaxies surrounding us, that are invisible
from our positions on the ground because of the
atmosphere and pollution. Astronomers today face
increasing problems with ground-based observation.
Hubble cannot observe objects that also bring
them in the field of view, and a regionof high-energy
particles over the South Atlantic - caused by
a warp in the earth's magnetic field - make observations
there unreliable. Apart from these limitations,
the sky's the limit.
Distinguished from ground-based observatories
by its capability to observe light in the ultraviolet
and near infrared wavelengths (some stellar processes
emit light at these frequencies) a resolution
and order of magnitude better than is possible
from earth. Light entering its axis and focused
by the internal mirrors falls on to "charge-coupled
devices" (CCDs) that turn light into electrical
signals; these are passed to a computer and combined
to generate an electronic image. It is the digital
equivalent of photographic emulsion, but sensitive
to a far wider range of light than the human eye.
It also takes much longer exposure times to gather
enough light for the pictures so the HST has extremely
sensitive gyroscopes to keep it pointed towards
the same part of the sky during such work.
While the HST is a testament to our ability to
engineer to enormous precision, part of its mission
during its 15-year operational life is to give
us a better ruler with which to measure the universe.
This follows on from the pioneering work first
carried out by its namesake, Edwin Hubble.
Before Hubble, for example, it was thought that
there were a very tiny number of exotic objects
known as black holes in the universe. This is
the result of the ultimate collapse of a star
that can't support itself, and it has very exotic
properties due to Einstein's theory of general
relatively, light can't escape and so on. What
Hubble has shown is that not only do black holes
exist-- and that was pretty much known before
launch--but in fact, they are not rare and exotic
things, but rather commonplace. And in fact, it
turns out that probably every galaxy of stars
in our universe, with the exception of just a
few, hosts a gigantic central black hole. [3]
Hubble has been able to probe right into the very,
very center of galaxies to see the swirling motions
of stars around these central black holes. If
you tried to do this from the ground, the center
of galaxies looks just like a huge, fuzzy blob
that can' t be resolved into a fine point. So
it requires Hubble's precise acuity to be able
to make these measurements and infer the presence
of these black holes.
Another example that's really quite astounding
is that for 75 years, we have understood that
the universe is expanding. It started in a giant
explosion, which we call the big bang, and the
result is that we now see galaxies all hurdling
away from each other. Scientists all assumed that
there were only two possibilities for the future
of this expansion. Either it would just sort of
keep coasting along forever, or it would gradually
slow down and the expansion would come to a halt
due to the mutual gravitational attraction of
all the atoms in the universe, and that seemed
to be the only two possible end points.
In fact, Hubble has shown us that that's not what's
happening, but rather the expansion of the universe
is getting faster. The universe is accelerating
since the big bang, and that is a totally unexpected
result which even five or six years ago no one
would have believed.
About ten years ago, Halley's Comet came on the
brief visit to the inner Solar System that it
makes every 75 years. Astronomers knew that Halley,
passing far from the earth this time, would be
a damp squib (and said so). But the media, and
those out to make a fast buck, hyped things up.
Most people felt cheated that they hadn't seen
the celestial sight of the century, and, naturally,
blamed the astronomers.
Then it was discovered that the supposedly perfect
mirror on the $1.4 billion Hubble Space Telescope
was warped - returning images that looked like
"squashed spiders".
In 1995: the well-televised docking of the US
shuttle and the Russian Mir space station, and
the descent of NASA's Galileo atmosphere probe
into the churning clouds of Jupiter. And the Hubble
managed to capture one of the most aesthetically
beautiful pictures of all time: eerie stalactites
of gas surrounding a star being born. Yet, the
most recent spectacular pictures taken by the
Hubble Space Telescope may be missing nine-tenths
of the "stuff" of which the universe
is made.
Although, according to Einstein's theory of relativity,
light is the fastest moving thing in the universe,
it would take a beam of light at least 100,000
years to cross the Milky Way from one side to
the other - longer than the whole history on this
earth of anatomically modern humans. But the Milky
Way is far from being everything there is, and
in its turn is a rather insignificant galaxy among
many others. The broadening of astronomers' horizons
came in 1924 when, after five years of observations
and measurements, the American astronomer Edwin
Hubble proved that the faint smudges - nebulae
- seen by the largest telescopes were actually
other galaxies far beyond the confines of our
own. Five years later, he claimed that the universe
itself was expanding and the galaxies receding
from us at a speed proportional to their distance.
Appropriately, the Hubble Space Telescope in
its turn hugely expanded astronomers' ideas of
the number of galaxies in the universe. The "deep
field" pictures taken by the telescope revealed
far more galaxies
than astronomers had expected. As a result, they
quadrupled their estimate of the total number
in the universe - from 50 billion to 200 billion
galaxies.
The Hubble Space Telescope has pictured galaxies
or pre-galactic fragments from times when the
universe was less than a billion years old, so
there was not enough time - according to current
theories of galactic formation - for ordinary
matter to produce the structures that astronomers
can see. And now as they say the future is still
out there waiting to be captured. As Maran states,
"Now, the Hubble Space Telescope enhances
our vision of the heavens to an unprecedented
degree. But even as the secrets of celestial bodies
are gradually revealed, every answer raises new
questions. Among the remarkable discoveries being
made with Hubble, several tantalizing paradoxes
have emerged." [4]
|