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Skywatching

Everything about nothing

In the 17th century, Evangelista Torricelli invented the barometer.

In the same century, Blaise Pascal carried one of Torricelli's barometers to the tops of high buildings and mountains, and found that the air pressure falls off with increasing height.

Since those barometers consisted of vertical metre-long tubes filled with mercury, and had to be kept vertical, this was no trivial matter.

Barometers were taken up in balloons, affirming that as the altitude increased, the air pressure continued to drop. Above about five kilometres, the air pressure falls to a point where there is not enough oxygen to sustain anyone not extra healthy and adapted to high altitudes.

Modern airlines fly at heights of around 12 km, but the aircraft have to be pressurized.
 
Air pressure is the force we feel from being hit by a huge number of the molecules and atoms making up the air. The more of them bouncing off us per second, or the faster they are moving, the more pressure we feel.

Above 100 km or so, the number of atoms per cubic centimetre is very low; as we continue to get higher, the atmosphere eventually merges with space, where there are just a few atoms per cubic centimetre.

This is a far better vacuum than any we can achieve in the laboratory. We could consider space as being essentially "nothing," and we would be wrong.

Although there is almost everywhere, even in the denser cosmic clouds, what we would call a very good vacuum, containing almost nothing per cubic metre, there are other things going on, in addition to dark matter and dark energy.
 
Isaac Newton saw space as just a huge empty volume in which objects and radiation moved around and interacted. It is easy to imagine the Big Bang — the beginning of our universe — almost 14 billion years ago, as a massive explosion, with things blasting off in all directions into the empty space Newton imagined.

The expanding universe would be just the cloud of debris getting bigger and bigger as it moves further out into space, forming galaxies, stars and planets as it goes. This is the easy picture, and it does not work.

One interesting aspect of this picture is that the expansion of the universe appears to us exactly the same in every direction we look.

That would mean we live at the centre of the universe. Once we believed we were. Now, we know we are just one very small part of it.

The picture we get from the work of Albert Einstein and others fits better, and is far more intriguing. Imagine a bunch of ants running around on the surface of an expanding balloon.

Each ant would see the same thing: all the other ants getting further and further away, with the more distant ants receding faster than the nearby ones. The ants are not moving with respect to the balloon; they are being carried along by the balloon's expansion.

That balloon represents a two-dimensional universe expanding in a third dimension. Our universe seems to be a three-dimensional universe expanding in a fourth dimension.

However, what plays the role of the rubber surface of that balloon, which is carrying all those ants with it? Einstein showed that space is not a "nothing;"  it is part of a multidimensional "something" called the fabric of space-time.

In our case, the ants are the galaxies we see around us, being carried further and further apart as our space-time "balloon" expands. This leads to another interesting thing. At the moment of the Big Bang, everything, including space-time, came into existence.

So far we have not managed to come up with any firm scientific idea about what existed before that moment.
 
At 6:54 p.m., on the 22nd, the sun will cross the equator, heading south, marking the autumn equinox. On that day the, sun will be above the horizon for as long as it is below.

  • During the evening Mars, the red planet, is conspicuously low in the southeast.
  • Saturn is low the south
  • Jupiter very low in the southwest.
  • The moon will be full on the 24th.


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The expanding universe

The universe is expanding. It started to expand at the Big Bang almost 14 billion years ago.

We know how fast it is expanding and that it is accelerating. We owe our knowledge to three instruments.

The first is the telescope. Distant objects can be extremely faint, and the biggest possible light collector is needed to catch enough light to make an image or to analyze.

For example the 3.6-metre diameter mirror in the Canada France Hawaii Telescope (CFHT), which is now by no means the largest telescope in the world, collects more than 50 million times as much light as our unaided eyes.

In addition to making images, the light collected by the telescope can be fed to two devices.

One is the photometer, a device for measuring precisely the apparent brightness of cosmic objects. The other is the spectrometer, which is used to measure the composition of the light.

In addition, the universe is so big that looking further and further away is looking further and further back in time.

If we look at an object a billion light years away, we see it as it was a billion years ago, when its light started on its way to us.

By looking at more and more distant objects, we can read the history of the universe, providing we know how far away the objects are. Then, to study the expansion of the universe we need to be able to know how fast objects are receding from us.

To find distances we measure the apparent brightnesses of objects. If we know their energy output — their luminosity — we can then calculate how far away they are. If you know that distant point of light is a 100W bulb, you can measure its apparent brightness and then estimate its distance.

For nearby galaxies there are stars such as Cepheids and RR-Lyrae variables, which cycle in brightness in a manner related to their luminosity. For more remote objects, our main yardstick is a type of exploding star.

The explosions are produced by a kind of binary star, where one of the pair is a white dwarf, an Earth-sized relic with no fuel left, still very hot, but very slowly cooling off. It pulls material off its partner, which accumulates on its surface.

When a critical amount has been collected, a runaway fusion reaction takes place, like a supersized hydrogen bomb. Because the explosion happens when a critical amount has been collected, we can estimate the energy output. When one of these explosions occurs in a distant galaxy, we measure how bright it looks, which gives us its distance.

The last tool in our analysis of the universe's expansion is the Doppler effect.

We've all heard it. For example, when a noisy motorcycle passes by, or we watch a train passing us at a level crossing, the sound has a higher pitch when the source is approaching, and a lower tone when it is receding.

The same applies to light. If the source is approaching us, its light is shifted to the blue; if it is moving away, its light is reddened, or redshifted.

All the elements have unique multicolour signatures, or spectra. For example, in the laboratory we can measure the spectrum of hydrogen, a common element in the universe.

Then, we search for the spectral signature of hydrogen in distant, cosmic objects. By comparing the two spectra we can determine how much the cosmic spectrum is red-shifted, which tells us how fast the object is receding.

If we have the distance and the redshift for an object, and noting that distance is linked to time, we know the speed the universe was expanding at that point in the past.

By measuring the redshift of objects at different distances, we can measure how fast the universe is expanding at different points in its history. We would expect the expansion after the initial Big Bang to be slowing down. Instead, surprisingly, it is speeding up. We cannot yet explain this.

  • During the evening Mars, the red planet, is conspicuously low in the southeast.
  • Saturn is low the south
  • Jupiter very low in the southwest.
  • The moon will reach first quarter on Sept.16.


Big sky astronomy

In the past, most radio astronomy consisted of pointing the instrument at the right place in the sky.

Most cosmic objects change little over a human lifetime. Radio emissions from supernova explosions last for months or more and the emissions from the supernova remnant may be observable for millennia.

Even pulsars, producing their regular pulses of radio emission, keep doing so for centuries or longer.

However, over the last few years we have realized that some cosmic events need not only that we look at a particular position, we need also to be doing it at precisely the right time, to the millisecond (thousandth of a second).

This happened on 24 July, 2001.

The radio telescope was the 63-metre diameter radio telescope at Parkes, Australia. It picked up a very short, millisecond pulse of radio emission. The characteristics of the emission showed this pulse originated a very long way away.

The Parkes radio telescope can "see" a patch of sky just a few percent of the size of the Full Moon, so the chance of the telescope being pointed at the right piece of sky at the right moment was minute.

Were these pulses, now called "fast radio bursts" common or was this observation an amazing coincidence?

Even today, most radio telescopes in the world are single-antenna instruments, which see a tiny patch of sky, where to make an image one has to wave the antenna around, scanning the area. There are also radio imagers, which produce pictures of what we would see if we could see radio waves.

Unfortunately, most of these instruments can still only image tiny pieces of sky. The Synthesis Radio Telescope at our observatory is unique in that it can image a bigger piece of sky, maybe a few times the diameter of the full moon.

Making a full image can take two weeks of observations.

However, now we are entering the age of "wide field imagers," such as the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope now being commissioned, also at our observatory.

This radio telescope can image most of the sky above the horizon, and as the Earth's rotation carries the sky past the telescope, it can image all the sky that is ever visible from our part of the world.

Its primary purpose is to map structure in the young universe, but it will also be a front-line instrument for detecting of "fast radio bursts,"  Some time ago, during test observations, CHIME picked one up.

So far a number of fast radio bursts have been detected, by radio telescopes around the world. All we know at the moment is that since the pulses are short, the sources have to be small, and because they lie a long way away, they have to be very powerful.

With so little information, there are currently more theories to explain the fast radio bursts than the number of observations.

The discovery of fast radio bursts underlines how much we might be missing by using instruments that can only see a tiny bit of sky at a time, like being forced to observe through a keyhole rather than being able to open the door.

Fortunately, advances in image processing techniques and the almost explosive improvement in video processing electronics are changing the game completely.

We are now entering the age where modern radio telescopes will keep an eye on large patches of sky as a routine part of their observations.

In addition to finding out how many fast radio bursts occur each day, we will be keeping an eye open for anything odd occurring anywhere in the sky the radio telescope can see.

We have always been able to go out on a clear night and explore the whole sky, just using our eyes.

Now, for the first time in the history of radio astronomy, we will be able to get the same view of the radio universe.

Mars is now receding from us, but still justifies getting out the telescope. 

  • The red planet lies low in the Southeast after dark.
  • Saturn is in the South and Jupiter very low in the Southwest.
  • The moon will be new on Sept 9.


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Life needs a sun like ours

Current thinking is that here on Earth, chemical-based life, like ours, started in bodies of water, muddy waterside places or on slimy rocks.

Organic molecules inherited from the solar system's birth cloud reacted together to form increasingly complex molecules, until they crossed the boundary between non-living and living material. Laboratory experiments support the idea that this happened.

Until we know of other kinds of life, our search for living things on other worlds is directed at finding chemical-based life.
 
Since the chain of chemical reactions from simple molecules to the complex chemicals driving the processes of life is a long one, we assumed the best planetary candidates for life would be orbiting red dwarf stars.

These stars are stable for billions or tens of billions of years, allowing lots of time for the chemistry to proceed, and do not give off harmful levels of ultraviolet radiation, which can break down complicated molecules.
 
However, we need also to consider the changes that happen on a planet when life gets going.

The planet's original atmosphere, made up of chemicals inherited from the birth cloud, is rich in greenhouse gases. When life got going here on Earth, about 3.5 billion years ago, early plants assimilated those greenhouse gases, and replaced them with oxygen, which is not a greenhouse gas.

This would have caused the Earth to gradually cool. However, we know that the Earth was warm enough for liquid water back then and obviously still is today. The reduction in the greenhouse effect has been balanced by the sun becoming brighter. It is now about 30 per cent brighter than it was when life first appeared.

The result is that over 3.5 billion years the Earth's temperature has not changed enough to endanger the creatures and plants living on it. Consequently, red dwarf stars, with their more or less constant energy output, are probably not the best candidates for having life-bearing planets.

If the temperature on a planet was right for life to start, the reduction in the greenhouse effect would lead eventually to the planet freezing solid. This is one reason to look elsewhere for planets bearing life. Now, we have another reason to think this is the case.

Laboratory experiments have shown that if there is an appropriate and consistent source of energy, those original chemicals can react, producing more complex ones. We can get as far as amino acids, the building blocks of proteins, but no further.

The rest of the path to life probably needs a lot more time and reactions taking place on a planetary scale rather than in a laboratory. Lightning and electrical discharges have been investigated as possible energy sources for driving the chemical reactions, but an appropriate steady level of ultraviolet light might be better.

This would have to come from the new planet's star. The ultraviolet light would excite the molecules without destroying them, allowing them to form more complex arrangements, moving them along the path to the chemicals that are fundamental to living things.
 
Red dwarf stars do not produce much ultraviolet, and are not well suited for driving these chemical processes. On the other hand, stars like the sun produce a good supply of ultraviolet. Hotter, bluer stars produce so much that complex molecules would be destroyed.

Since life as we know it is based upon complex molecules, we would not expect to see chemical-based life on planets orbiting hot, blue stars. That is not to say that all chemical-based life has to be like ours, or even that life has to involve chemistry at all.

However, for the time being we are concentrating on our familiar chemical forms of life. In this case at least we have some idea of what we should be looking for.

Other options can come along later.

After dark look for:

  • Mars in the Southeast
  • Saturn low in the South
  • Jupiter low in the Southwest.
  • The moon will reach Last Quarter on the 2nd.


More Skywatching articles

About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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