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Skywatching

Living on the far side

The Earth's gravity pulls at the side of the moon closest to us more strongly than it pulls at the other side.

Long ago, when the moon was still hot and soft, it got pulled by this "tidal force" into an egg shape. The distortion was slight, but enough for the Earth's gravity pulling at the bulge to lock the moon's rotation to its motion around the Earth. That is why we only get to see one side of the moon. For an observer on the far side, the Earth never rises above the horizon. However, there is a lot of interest in the moon's other side. Not only is it scientifically and puzzlingly different from the side we get to look at, there are also practical benefits to being located where we never see the Earth in the sky. One is the possibility of having a radio observatory there, and of course a base to support it and the other activities that interest us.

Radio astronomy is the science of studying the radio emissions generated by objects in space. These are of natural origin and tell us a lot about what exactly is going on out there. The power of the signals produced by cosmic objects can be enormous, but they have to come such a great distance, taking up to billions of years to get here, that by the time they reach the Earth they are extremely weak. Our manmade radio signals, and even the radio interference we produce as by-products of our way of life, are all enormously stronger than any signals coming from beyond the Solar System. The signal from a cell phone on the Moon would be stronger than any cosmic radio source and we could detect a cell phone on Mars.

For decades we have dealt with these issues by putting our radio telescopes in remote places or in valleys screened by hills. However, this does not protect observatories from interference coming from nearby space. By working with satellite designers and operators, it has been possible to address some interference issues, but as the number of satellites rises, the interference problem will grow. Although we see an ongoing need for radio telescopes on Earth, really high-sensitivity observations would be best made on the other side of the Moon, where the horizon blocks out the radio noise we are generating.

The Moon is a very hostile environment. The atmosphere is extremely thin, basically a pretty good vacuum. The temperature variations on the surface are huge, from around the boiling point of water during the day, to far below zero at night. The average lunar surface temperature is about minus 50 Celsius. A few metres below the surface the temperature remains close to this value all the time. In addition to escaping the wild temperature variations, a few metres of lunar soil would block out most of the harmful radiation coming from the Sun and elsewhere in space. On Earth our atmosphere protects us. There is no such protection on the Moon. On the plus side, no atmosphere means every day is a sunny one, so solar energy should be able to provide for all the energy needs of the base.
 
There is water available at least at some places on the Moon; in addition to being something to drink, solar-generated electricity can be used to break it down into hydrogen, and more usefully, oxygen. If energy is available many of the raw materials should be obtained from the Moon, and agriculture is a possibility. The downside of being on the far side of the Moon is that in order to have radio communication with Earth, a relay satellite will be needed. That is how the problem is being solved with the Chinese rover on the far side of the Moon. There is one other problem: transportation, which will mean Earth-based radio astronomy will remain important for at least another few decades.

  • Venus lies low in the southwest after sunset and Mars rises in the early hours, Jupiter a bit later, and Saturn low in the dawn glow.
  • The Moon will be reach first quarter on the first day of February.


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Can we believe our eyes?

In some way or other, our eyes have been strongly involved in almost every scientific discovery we have ever made. 

Despite this they are pretty awful measuring instruments. They are not good at judging colour, angles, brightness or sizes. The only way we can measure with them is to compare what we see with calibration standards. Of course, they are not intended to do that. Our eye/brain combination is supposed to give us optical information about our environments under a wide range of light levels and light colour balances.

We can get a good indication of what our eyes can do on these dull, grey winter afternoons. We can work outside, seeing quite well, and it is only when we go into our well-lit houses, and then look out through the windows, we see it is really dark out there. Our eyes can adapt to large differences in light level. 

On those same afternoons, when we are sitting in our warm houses, lit by incandescent lights, our rooms look comfortably lit but the outside world looks bluish. 

Then, after spending some time outside on those afternoons, shovelling snow or doing some other activity, the light outdoors looks perfectly normal and the light coming out of the windows looks yellow. This is because the light outside is more white, and our eyes adapt to that. 

Then, inside, the light from our incandescent light bulbs is mainly yellow, without much red or blue, so our eyes and brains compensate for that. 

No matter what colour the light, for most of our history, our survival depended on being able to see objects of all colours.

We have trouble judging sizes, too. During a long-ago visit to the Ontario Science Centre, I saw an exhibit where one looked through a window into a room. That room was badly distorted, with one corner maybe 1.5 metres high and the opposite corner maybe three or even four metres high. However, firmly programmed in my brain, and almost certainly yours too, is an idea of what rooms are shaped like, and that is what we see. I saw a normal room, the usual shape. My brain was so keen on rationalizing the shape of the room it was happy to accept that the toy soldier trundling back and forth across the room was changing between maybe one and three metres high! 

One of these illusions that we can see is how large the moon looks when rising or setting, compared with how small it looks when high in the sky. This is not due to refraction or some other atmospheric process. It is something our brain is up to. You can check this by looking at the moon through a drinking straw, where you can only see the moon and nothing much around it. Compare the size of the moon with the disc of sky you can see at moonrise and when the moon is high in the sky. It is not changing size. 

Seeing the horizon with the moon close to it makes our brains change the way they process the image. This could be because through most of our history, threats have come over the horizon much more often than they have come from above, so our brains apply more processing to the areas of potential interest or threat. 

A similar thing seems to happen when things in the sky are very bright. Often people report bright objects in the sky, satellites, planets and so on, and describe them as “big” – although they are not big, they are bright. Once again our brains are up to something.

On a starry night where there are a few clouds, take a long look at the stars. After a while, they seem as though they are moving. It's quite a convincing effect, even though we know that is not happening. This is why in most scientific research we prefer to use our eyes to read a dial, showing a measurement made using a brainless instrument.

  • Venus lies low in the southwest after sunset and Mars rises in the early hours, Jupiter a bit later, and Saturn low in the dawn glow. 
  • Mercury might be visible low in the southeast just before sunrise. 
  • The noon will be new on the 24th.


Whistles from space

In midsummer, quite a few years ago now, an ionospheric physicist friend and I were in a car parked on a remote logging road in Algonquin Park, Ont.

On the ground a few metres away we had laid out about 50 metres of multicore cable in as close to a circle as we could get in the scrub by the road. The wire cores in the cable were cross-connected so that we had a big, multi-turn coil. Another cable brought the end connections of the loop into the car. 

Inside, on the back seat we had a sensitive audio amplifier, just like the ones in record players but more sensitive, and a tape recorder, both battery powered. 

It was night time, and at that remote location, far from city lights, the sky looked grey and speckled with so many stars it was hard to identify the constellations. The trees were silhouetted black against the sky. The poetic atmosphere was, however, wiped out by the need to stay in the car on a hot summer night, with the windows closed because of the hordes of mosquitoes. 

We could not run the car engine and the air conditioning because it interfered with the signals we were trying to detect. We were there to record the waves produced by the sliding of the solar wind over the Earth's magnetic field.

The solar wind, flowing out from the sun at speeds of hundreds to thousands of kilometres a second, rubs over the Earth's magnetic field like a bow on the string of a violin. The waves generated by this follow the lines of the magnetic field down toward the north and south magnetic poles. Some of those magnetic field lines went through our coil, which acted in the same manner as a pickup on an electric guitar. 

The oscillating guitar string generates currents in the pickup coil that can be amplified. The oscillations in the magnetic field lines did exactly the same thing. We had to be tens of kilometres from the nearest power lines because they produce an oscillating magnetic field far stronger than anything from space. We've all heard the effect of power line radiation when it is picked up by audio equipment. We call it "hum."

We listened to the signals while we recorded them. There were tweets, rising and falling whistles, a hiss like sea waves running through shingle, and underneath, some of that manmade hum. This was not surprising. We can even pick up that hum from space, but at least at our location in the park it was reasonably faint. 

The objective of that project, and similar projects done by many others before and since, was to learn a little more about the way the solar wind interacts with our planet's magnetic field. This is an important aspect of what we have come to refer to as space weather.

Space probes flying past Jupiter and Saturn were equipped with similar equipment. Jupiter is particularly interesting because it has a very strong magnetic field. Somehow it didn't sound right that Jupiter's whistles and peeps were higher pitched than those in the Earth's magnetic field. One would expect a giant planet, into which we could cram 100 Earths to speak with a deep voice, not a falsetto. 

There are two reasons for this. Jupiter's magnetic field is stronger than Earth's, and as we know, the more tension we put in a violin or guitar string, the higher the note. However, in this case, the string is also longer, which might make the note lower. It depends on how much tighter the string is compared with how much longer it is. Secondly, on Earth, the ionized atmospheric gases clinging to the magnetic field lines are oxygen and nitrogen. On Jupiter it is hydrogen, which has much lighter molecules. 

Similar waves have been detected by space probes visiting Saturn. When listening to these recordings, it is hard not to think they are biological, like the sounds produced by whales and other sea life, rather than produced by very interesting and challenging physics.

  • Venus lies low in the southwest after sunset and Mars rises in the early hours. 
  • The Moon will reach Last Quarter on the 17th


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Beetle Juice will die soon

Orion, The Hunter is one of the most spectacular constellations in the winter sky.

The easiest way to find it is to start at the brightest, fiercely sparkling white star in the sky, Sirius and then scan up and to the right.

This will lead you to three equally spaced stars lying in a straight line pointing roughly in the direction of Sirius. These stars form Orion's belt. There is a sort of straggling of faint stars hanging down from the belt where a sword would hang.

From there it is easy to see the belt is about halfway down a rectangle of stars, which form Orion's body. The lower right star is Rigel, a bright, white star, and the top left star is red or orange.

Binoculars bring out star colours really well. It is usually referred to as Betelgeuse, but many years ago astronomer Patrick Moore consulted some experts on ancient tongues about this name.

He was told that the name has become highly corrupted and the nearest one can get to something reasonable now is Betelgeux, pronounced Bayteljurze, which does sound more ancient and astronomical than Beetle Juice.

At some point in the not too distant future, that discussion is going to become moot, because Betelgeux is very close to the end of its stellar life, and destined to end it in a spectacular explosion, a supernova.

For a few weeks, it will outshine all the other stars in our galaxy combined, and be easily visible in daylight. It will end up collapsing to form a neutron star, or perhaps even a black hole.

A star's life consists of three parts, rather like ours:

  • Youth
  • Maturity
  • Old age.

The youth part consists of formation and settling down. Then, there is a period — the longest of the three — of stability and maturity. Astronomers refer to this period as the main sequence life of the star.

Finally, there is old age, which arises when the star starts to run out of fuel. For small stars, this consists of sneezing off the outer layers until all that is left is the core of the star, gradually cooling off. Big stars have more options.

When they run out of fuel, they shrink, driving up their core temperatures until they become hot enough for the waste products of previous energy production to provide more energy, enabling them to swell up again.

However, inevitably, the final result is the end of the fuel supply, collapse and a huge explosion where the star blows itself to bits, while compressing its core into a neutron star or black hole.

As stars approach the end of the line, they swell into red giant stars and become immensely brighter, squandering what's left of their fuel and bringing on the inevitable all the sooner.

Betelgeux is now at that point. It is currently shining about 100,000 times brighter than the Sun, and its end cannot be that far off, certainly in the next few thousand years.

In most cases, all the fuel a star will get to power its lifetime of shining it gets when it forms. However, paradoxically, the more fuel it starts with, the shorter its life will be.

For example, Betelgeux has about 12 times the mass of the Sun. During its main sequence life,it would have been about 1,500 times brighter than the Sun. Our Sun will have a lifetime of around 10 billion years.

Even if Betelgeux has more fuel than the Sun, during the main sequence part of its life, it was shining so much brighter than the Sun that its lifetime has to be much shorter, tens of millions of years.

There is another star in the same sort of situation. It is Antares, the brightest star in the constellation Scorpius, The Scorpion. It is visible during summer, low in the south. Like Betelgeux, it is red or orange, depending on your colour vision.

This means there is a supernova candidate star available for us to watch for in the summer and the winter. Just cast an occasional eye in their direction. When it happens you will notice it.

  • Venus lies low in the southwest after sunset
  • Mars rises in the early hours.
  • The Moon will be full Jan. 10.


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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