The night sky
If, like me, you live in a densely populated urban area, where
light pollution means that even on a clear night you can only see
a handful of the very brightest objects in the sky, then you will
probably be hard pushed to recognize many of the stars or planets.
I can still pick out Mars and Venus, our closest neighbours apart
from the moon, but I am no longer sure about the constellations.
As a child, I use to be much more familiar with the night sky.
I was born in Baghdad and spent the first sixteen years of
my life in Iraq, but left the country for good with my family in
the late 1970s when the political climate changed. Prior to that, we
would visit England every two or three years to spend our summer
holidays withmygrandparents. However, the Iraqi summers held
their own magic. The last of the clouds would have dissolved
away by late April, destined not to blemish the blue skies again till
October, and school holidays would stretch out for three and a half
glorious hot months (we did have a six day school week though).
During July and August, temperatures would reach a maximum
in the mid-forties (degrees Celsius) and would hardly ever drop
below an uncomfortably sticky thirty degrees at night.
The most exciting ritual confirming the arrival of the Middle
Eastern summer was when the bedding was carried up to the roof. Houses had stairs leading up to flat roofs where everyone slept for
roughly a quarter of the year to escape the stifling heat and humidity.
Summer nights thus always meant lying awake gazing up at a
sky teeming with thousands of stars, trying tomakeout shapes and
patterns by joining the ‘dots’. Eventually they would be partially
obscured by the mosquito nets that we would pull over the beds
enclosing each of us in our own transparent tent. There was never
the remotest concern that it might rain. It never did in the summer.
Living now in Southern England I have almost forgotten how
beautiful the night sky can be, and I sometimes miss the thrill of
watching out for shooting stars.
So, yes, I use to be able to recognize a few of the stars. Lying
up on our roof as a young child I learned that some of the brightest
‘stars’ were not stars at all but planets, which only shone because,
like the Moon, they reflected the light of the Sun when it was on
the other side of the Earth. The true stars were millions of times
further away than the planets, and so had to be shining many
times more brightly for us to be able to see them. I also vaguely
remember being both a little disappointed and exhilarated when
I found out that a shooting star was nothing more than a tiny rock
burning up as it entered Earth’s atmosphere, and that it was really
called a meteor.
This chapter is a mix of two related scientific fields: astronomy
and cosmology. Most people have a good idea what astronomy is
about, but not many are familiar with what cosmology means.
As far as ’ologies go, you must agree that cosmology sounds
pretty impressive and awe-inspiring. It is the study of the whole
Universe: its size and shape, its birth and evolution, even its likely
fate. It is also seen to be the most glamorous area of physics. It
addresses, and even professes to answer, questions which many
feel are beyond the realm of science.
Most of what we now know about the Universe has
come about through painstakingly careful experiments and
astronomical observations, which are continually being refined as
more powerful telescopes are built andnewtechniques developed.
But while cosmology is, loosely, a sub-field of astronomy, the
knowledge we have gained about the Universe has also come from other areas of science, such as nuclear and particle physics and
theoretical astrophysics. Theoretical cosmology involves creating
idealized mathematical models of the Universe by solving the
equations of Einstein’s general theory of relativity. These can be
formulated in such a way so as to describe the properties of the
whole Universe and not just a small region of space and time in
the vicinity of a massive object, such as a star.
As in other parts of this book, I will be discussing ideas about
our Universe which, at the time of writing at least, represent our
best current understanding and favoured theories. A few years
from now some of these may well be shown to have been wrong.
On the other hand, there are certain properties of the Universe that
we are pretty confident about and which I am sure will stand the
test of time. At the end of this chapter I will summarize which
features of the Universe are, in my view, correct and which are
still open to debate.
To give you an idea of just how rapidly ideas and theories in
cosmology are changing and advancing due to ever more accurate
astronomical measurements, I had to rewrite substantial chunks
of this chapter during the proof-reading stages of the manuscript.
In fact, we shall see that 1998 was an important year in cosmology.
If, like me, you live in a densely populated urban area, where
light pollution means that even on a clear night you can only see
a handful of the very brightest objects in the sky, then you will
probably be hard pushed to recognize many of the stars or planets.
I can still pick out Mars and Venus, our closest neighbours apart
from the moon, but I am no longer sure about the constellations.
As a child, I use to be much more familiar with the night sky.
I was born in Baghdad and spent the first sixteen years of
my life in Iraq, but left the country for good with my family in
the late 1970s when the political climate changed. Prior to that, we
would visit England every two or three years to spend our summer
holidays withmygrandparents. However, the Iraqi summers held
their own magic. The last of the clouds would have dissolved
away by late April, destined not to blemish the blue skies again till
October, and school holidays would stretch out for three and a half
glorious hot months (we did have a six day school week though).
During July and August, temperatures would reach a maximum
in the mid-forties (degrees Celsius) and would hardly ever drop
below an uncomfortably sticky thirty degrees at night.
The most exciting ritual confirming the arrival of the Middle
Eastern summer was when the bedding was carried up to the roof. Houses had stairs leading up to flat roofs where everyone slept for
roughly a quarter of the year to escape the stifling heat and humidity.
Summer nights thus always meant lying awake gazing up at a
sky teeming with thousands of stars, trying tomakeout shapes and
patterns by joining the ‘dots’. Eventually they would be partially
obscured by the mosquito nets that we would pull over the beds
enclosing each of us in our own transparent tent. There was never
the remotest concern that it might rain. It never did in the summer.
Living now in Southern England I have almost forgotten how
beautiful the night sky can be, and I sometimes miss the thrill of
watching out for shooting stars.
So, yes, I use to be able to recognize a few of the stars. Lying
up on our roof as a young child I learned that some of the brightest
‘stars’ were not stars at all but planets, which only shone because,
like the Moon, they reflected the light of the Sun when it was on
the other side of the Earth. The true stars were millions of times
further away than the planets, and so had to be shining many
times more brightly for us to be able to see them. I also vaguely
remember being both a little disappointed and exhilarated when
I found out that a shooting star was nothing more than a tiny rock
burning up as it entered Earth’s atmosphere, and that it was really
called a meteor.
This chapter is a mix of two related scientific fields: astronomy
and cosmology. Most people have a good idea what astronomy is
about, but not many are familiar with what cosmology means.
As far as ’ologies go, you must agree that cosmology sounds
pretty impressive and awe-inspiring. It is the study of the whole
Universe: its size and shape, its birth and evolution, even its likely
fate. It is also seen to be the most glamorous area of physics. It
addresses, and even professes to answer, questions which many
feel are beyond the realm of science.
Most of what we now know about the Universe has
come about through painstakingly careful experiments and
astronomical observations, which are continually being refined as
more powerful telescopes are built andnewtechniques developed.
But while cosmology is, loosely, a sub-field of astronomy, the
knowledge we have gained about the Universe has also come from other areas of science, such as nuclear and particle physics and
theoretical astrophysics. Theoretical cosmology involves creating
idealized mathematical models of the Universe by solving the
equations of Einstein’s general theory of relativity. These can be
formulated in such a way so as to describe the properties of the
whole Universe and not just a small region of space and time in
the vicinity of a massive object, such as a star.
As in other parts of this book, I will be discussing ideas about
our Universe which, at the time of writing at least, represent our
best current understanding and favoured theories. A few years
from now some of these may well be shown to have been wrong.
On the other hand, there are certain properties of the Universe that
we are pretty confident about and which I am sure will stand the
test of time. At the end of this chapter I will summarize which
features of the Universe are, in my view, correct and which are
still open to debate.
To give you an idea of just how rapidly ideas and theories in
cosmology are changing and advancing due to ever more accurate
astronomical measurements, I had to rewrite substantial chunks
of this chapter during the proof-reading stages of the manuscript.
In fact, we shall see that 1998 was an important year in cosmology.
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