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Skywatching

Telling aliens where we are

An alien spacecraft coming into the Solar System would have no trouble finding us.

All they would need is a radio.

For more than a century, we have been transmitting radio waves in all directions and over most of the radio spectrum. Hardly any of the signal from a radio transmitter actually gets received and used. Most of it goes off into space.

Today, the Earth is surrounded by an expanding sphere of radio waves with a radius of more than 100 light years.

In addition to advertising our presence in the universe, the sheer power and quantity of our radio emissions is making it hard for us to observe radio emissions from the cosmos.

Just as streetlights and sky glow make it hard to see the stars, a problem that today we call light pollution, our radio emissions are making it hard to see the radio sky.

The problem has been mitigated to some extent by allocating some parts of the radio spectrum for radio astronomical use. Radio transmitters cannot be operated at those wavelengths. However, that is not the entire problem.

Almost all electronic devices, including radio transmitters and receivers, computers, controllers and so on, emit what those in the radio business refer to as unwanted transmissions. Producing these is more or less inevitable, which means that the more devices are operating, the more of this unwanted stuff gets into the radio spectrum.

These transmissions do not care whether they fall in the wavelength ranges allocated to radio astronomy or any other use of radio waves.

What makes this issue worse is that more electronic devices are in use now than at any time in human history, and moreover, the number continues to grow rapidly.

The result is that observing radio waves coming from beyond the Earth is increasingly challenging. We pick sites such as secluded valleys where few live, and the surrounding hills block out interference from beyond. However, now these unwanted transmissions are also coming from aircraft and space.

Modern technical developments are reducing the problem, but we cannot get back to where we were.

That is why for many years astronomers have been discussing the prospects of doing radio astronomical observations from the other side of the Moon, where interference from Earth and satellite transmitters won't be a problem.

The Moon's rotation is locked. It takes as long to spin on its axis as it does to orbit the Earth. If we were on the side of the Moon we can see from Earth, the Earth would remain at the same position in the sky all the time.

On the far side, the Earth never rises above the horizon. This would be a great place to put a radio telescope, assuming we had the transportation problem solved and had a nice, comfortable permanent base in which to live and work.

This brings us to a very interesting experiment going on right now.

The Chinese Yutu 2 (Jade Rabbit 2) rover is prowling the other side of the Moon. Because the Earth will never be above its horizon, its radio signals have to come back to us via a relay satellite, Queqiao (Magpie Bridge).

This satellite is carrying a Dutch-Chinese radio astronomy experiment, making observations at wavelengths that are largely obliterated here on Earth by our own interference. 

This is exciting but also cautionary. The first radio telescope was made as a backyard experiment, and there are radio astronomers around now whose interest started with experiments in the back yard. No doubt their successors are out in their backyard today. What if their curiosity is killed by manmade interference?

We are gradually reclaiming our dark skies from light pollution. The radio pollution problem is another thing altogether, and a serious challenge.

  • Mercury and Mars lie low in the southeast before dawn.
  • Saturn and Venus are close together very low in the southwest in the sunset glow.
  • The Moon will be Full on the 12th.




Binoculars for Christmas

The range of things available to backyard astronomers is now,  er, astronomical.

Choosing presents for the family astronomer is more complicated than ever. That means, unless you also share that interest, getting anything for an experienced backyard astronomer should be done in response to hints, notes left around or other useful information about what he or she wants.

If necessary, insist that Santa wants a List. On the other hand, if your family astronomer is a beginner, then things are easier.

If there are no binoculars in the house, then think of getting some for Christmas. These are great for looking at the Moon, star clusters, exploring the Milky Way, and for searching for comets.

A pair of binoculars consists of two telescopes fastened together so they point in the same direction. Binoculars are described by two numbers, for example 8x30. The first number is the magnification — how many times closer it makes something look.

The second is the diameter of the objective lenses in millimetres. Magnification is nice, but the most important number here is the size of the objective lenses.

Most astronomical objects are faint, so catching as much light as possible is important. One can get huge binoculars that are wonderful astronomical instruments, but they are heavy and will need tripods to hold them steady.

If binoculars are not easy to hold still while you look at something for a few minutes, they are too heavy.

In addition, tiring hands start to shake, and magnification makes the shaking more of a problem. So we have to compromise observing power with convenience and usability. For small hands, maybe 7x40 (seven times magnification with 40mm objective lenses).

For average observers, 7x50 binoculars are good, general-purpose instruments to have around. One alternative. which is expensive but getting cheaper. is a pair of "image stabilized" binoculars. These have sensors and a little computer inside which detects the shaking and wobbles little mirrors or prisms to correct it. 

These devices are amazing things to use. If the astronomer has any problems with holding things still, these binoculars will open doors to a new realm of enjoyment.

Binoculars are getting better and better, and the two potential problems described here are getting rarer and rarer. However, it is best to keep an eye open for them, especially when buying from anywhere other than a science store. The first is chromatic aberration.

This arises because the lenses are not focussing all colours equally. Look at the edge of a dark thing against a bright one, like a roofline against the sky.

The problem will show up as false colours. There shouldn't be any. The second problem is the two telescopes making up the binoculars might not be pointing in exactly the same direction, a problem called poor collimation.

This manifests itself as either a feeling of not-quite-rightness, or you might even see double. Your brain can often correct this, but at the expense of discomfort and headaches. It should be possible to set up the binoculars so they are completely comfortable to use, for long periods.

If you have a science store or a good camera store nearby, go there. Try out the goods before buying.

Another possibility is talk to members of the local astronomy club. Otherwise buy from a good dealer. I suggest buying an astronomy magazine, such as SkyNews (Canadian), Sky and Telescope (American) or Astronomy (American).

The companies advertising in them are reputable and there are usually articles about hardware choices. Have a read before going shopping.

I end with a warning though; you might get hooked yourself.

  • Mercury and Mars lie low in the southeast before dawn.
  • Jupiter and Venus are close together very low in the southwest in the sunset glow.
  • Saturn is a little higher and to the left.
  • The Moon will reach First Quarter on Dec. 4.


Oxygen on Mars

The most powerful tool we have for searching for life on other worlds is to look for its chemical signatures in their atmospheres.

There are chemicals that are associated with the processes of life, and which rapidly disappear unless they are continually topped up by living things.

The Earth's atmosphere is rich in oxygen. It is a by-product of photosynthesis in plants. Moreover, oxygen is so reactive that it will disappear rapidly by combining with surface minerals or anything containing iron or carbon.

These losses, including the oxygen taken up by living things are being dealt with by plant life. This is why the discovery of oxygen in the atmosphere of Mars is generating a lot of cautious excitement.

This oxygen was detected by the Curiosity rover, which is exploring the Gale Crater. The rocks in that area are sedimentary rocks laid down billions of years ago at the bottom of an ocean.

At that time, Mars was a warm, wet world, just like ours, and we know that on Earth, as soon as conditions became suitable, about four billion years ago, life appeared.

Could this apply to Mars too?

The concentration of oxygen rises in the Martian spring, peaks in summer, declines in autumn and sits at a low level in winter. This fits the idea of life burgeoning in the spring, thriving in summer, slowing down in autumn in preparation for lying dormant in the winter.

It all fits the way life works here. It is tempting to jump to the conclusion that Mars, despite now being an arid, cold world with a very thin atmosphere, is still a living world, with living things descended from those warm, wet days, eking out an existence on today's Mars.

It would be an important discovery; our first solid evidence we are not alone in the universe. However, just because something happened in a particular way on Earth, we cannot just conclude things happen in the same way on other worlds.

Although Mars was very like Earth once, there are important differences now. The Red Planet's atmosphere is now very thin, with a surface pressure about 0.4% that of the Earth.

The atmosphere is mostly carbon dioxide and nitrogen. Oxygen is present only in traces, whereas on Earth it constitutes 20% or so of the atmosphere.

The thin atmosphere presents almost no greenhouse effect, so the planet is cold and experiences enormous temperature changes between day and night. Finally, because of the thin atmosphere, solar ultraviolet radiation, which is blocked by our thick atmosphere, gets all the way down to the surface.

If Martian life were like ours, the ultraviolet would be very dangerous to it. It would probably have to live underground.

There are ways oxygen might be produced by non-life processes, driven by that fierce ultraviolet radiation. The most likely are probably the breakdown of carbon dioxide or water vapour.

Each carbon dioxide molecule contains one carbon atom and two oxygen atoms. Water molecules consist of two hydrogen atoms and one oxygen atom. Ultraviolet radiation can break up both these molecules, releasing oxygen.

There is certainly a lot of carbon dioxide available, but the production process would still be too slow.  Water vapour is a better candidate.

In the Martian spring the amount of water vapour in the air rises, and of course the longer days and the Sun being higher in the sky means there is more ultraviolet available. However, there does not seem to be enough water vapour to explain the amount of oxygen, so this issue remains open.

It would be really exciting if a future explorer turns over a rock and sees something wriggling away.

  • Mercury and Mars lie low in the southeast before dawn.
  • Jupiter and Venus are very low in the southwest in the sunset glow.
  • Saturn is low in the southwest.
  • The Moon will be New on the 26th and will reach First Quarter Dec. 4.


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Underground astronomy

We put our radio telescopes in valleys that screen them from manmade interference, but where there is a good view of the sky.

Our optical telescopes get put in dark places, often on top of mountains, above the part of the atmosphere that makes the images shimmer, and of course, once again with a good view of the sky.

It therefore sounds counterintuitive to put astronomical instruments under ground, usually as far down as possible, or deep in the Arctic or Antarctic ice.

We have also put instruments in the deep ocean.

As we move around in our daily lives, huge numbers of high-energy particles are sleeting through us, producing no noticeable effect, and doing us no harm.

These particles are called neutrinos, since they have no electrical charge. They also have almost no mass and travel close to the speed of light. Since they pass through matter as though it does not exist, it is very hard to make anything that can detect them.

However, on very rare occasions, a neutrino does interact with an atom. In this case, "rare" means one in 1E36 (one followed by 36 zeroes) neutrinos passing through the Earth may hit something.

When this happens, the result is a tiny flash of light.

Considering their extreme elusiveness, why bother trying to observe neutrinos at all?

The reason we want to do this is also the reason they are hard to detect: they pass through anything, and are almost totally unaffected. For example, they provide the only direct way we can look into the core of the sun and other stars.

The energy produced in a star's core has a long, circuitous trip to the surface of the star (its photosphere) before being radiated into space. It gets passed from one atom to another, so that after bouncing from atom to atom for around 200,000 years, it radiates off into space.

By that time, it carries very little information about the processes that produced it, or even perhaps whether that energy process has changed. 

However, energy production in stars also produces neutrinos. They escape from the star with no problem at all, so that when we observe them, we are seeing things produced mere minutes ago.

There are other high-energy processes taking place in space that produce neutrinos; these include supernova explosions and things taking place close to black holes. If we have a scientific need to detect them, how can we do that?

Typically, we want a huge number of atoms with detectors watching them to pick up those faint flashes produced when a neutrino gets caught. A really huge volume of clear liquid or solid, surrounded by detectors would do the job.

For example, the Sudbury Neutrino Observatory, located 2.1 km underground in a mine near the Northern Ontario city consists of a big, spherical tank containing over 1,000 tonnes of heavy water, with the inside wall covered with around 9,600 light sensors.

Other neutrino detectors consist of arrays of sensors buried in ice, or at the bottom of the sea. We have to put our neutrino telescopes far underground, under ice or under water to block the other particles arriving from space. 

Even then, our preferred observing direction is downward, through the rest of the thickness of the Earth. Anything managing to reach the detector through the diameter of the Earth will almost certainly be a neutrino. Moreover, the light flash can tell us the direction in which the neutrino is moving.

These elusive particles are proving to be a powerful tool for studying places we cannot observe in any other way.

It is intriguing to consider that we make these observations from deep under the ground, ocean, or ice caps, looking downward.

  • Mars lies low in the predawn glow
  • Jupiter and Venus low in the southwest in the post sunset glow.
  • Saturn is low in the southwest after sunset.
  • The moon will reach Last Quarter on the 19th and will be New on the 26th.


More Skywatching articles

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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]



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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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