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Skywatching

Light pollution is the bane of stargazers

Searching for dark skies

The old Royal Greenwich Observatory sits at the top of a hill on the south bank of the Thames, downstream from the centre of London.

Founded in the 17th Century it was set up to improve navigation at sea. The line of zero degrees longitude passes through it. At the time it was built. Greenwich was far out in the country. Then, the telescopes were driven away by the increasing light pollution from a rapidly expanding London to a new location at Herstmonceux, Sussex.

The old building became a museum. The Isaac Newton Telescope, with a 2.4 metre diameter mirror was built at the new site, but the growing light pollution eventually led to the telescope being moved to the Canary Islands, where the skies still dark.

The Dominion Observatory sits close to Carling Avenue in south Ottawa. It was founded in 1902 primarily for time-keeping and navigation. The light pollution from an expanding Ottawa area led to the observatory closing in 1970. In a familiar vein, the David Dunlap Observatory, near Toronto, operated as a front-line research facility from 1935 to 2007, at which point it was closed. Fortunately though it has reopened to provide an opportunity for the public to look at the sky through a large telescope.

Then there is the Plaskett Telescope, with a 1.83 metre mirror, located on a mountain in Saanich, on Vancouver Island, not far from Victoria. It opened just after the First World War. Once again, its value has been degraded by light pollution. Fortunately, it is still doing science and also is used for public observations.

The common thread in all these stories, and many others for which there is not enough space, is that of growing light pollution, which makes it harder to find good sites for telescopes.

The same story applies to radio telescopes. Finding accessible locations remote from our growing cacophony of radio interference is a big issue.

There is another thing—it is usually affordable to locate major astronomical instruments at good sites and these days, to some extent at least, regulate light pollution and radio interference produced around them.

These powers are not available to smaller organizations operating telescopes for research and public use, and even less for the millions of back-yard sky watchers around the world. Light pollution has reached a point where many people have never seen the Milky Way, or anything other than the Moon and the brightest stars and planets.

The cause is most easily seen from space. Images of the night side of Earth taken from the International Space Station show great patches of light marking cities, connected by glowing ribbons of roads.

Western Europe is almost completely lit up and it is easy to see the population distribution in North America. What we are seeing is millions, or billions, of watts of energy being used to pointlessly send light into space.

When we light streets, sending a good fraction of the light in directions other than onto roads, it is wasted energy. How many streetlights are there? Backyard lighting is often needed for security reasons. Lighting up your neighbour's backyard means that in addition to annoying your neighbour, you are wasting money. These days we have the technology to save a colossal amount of energy and avoid dumping into the atmosphere the carbon dioxide we produced generating it.

Getting from my home into town involves driving down a winding hill. The last few hundred metres of road have been equipped with extremely efficient LED streetlights, which send almost all their light down onto the road. All we see from above are illuminated road surfaces.

We have the technology to save money, reduce carbon dioxide production and make it possible to sit in our yards on a summer evening, enjoying the stars.

•••

• After sunset, Venus lies low in the sunset glow, with Jupiter and Saturn low in the south.

• Mercury is low in the predawn sky.

• The Moon will reach its last quarter on Oct. 28.



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Looking for life on the Red Planet

The search for Martians

Jezero crater is the 28-km diameter remnant of an ancient impact on Mars.

Until maybe three billion years ago it contained a large lake that had a major river system flowing into it, forming a large delta.

This crater is now being closely examined using the Perseverance Rover for signs of ancient life. Why would this location be such a good site to search for ancient life on the Red Planet?

It would be very hard to find a three-billion-year-old crater anywhere on Earth.

Plate tectonics is continually recycling the Earth's crust. The only really ancient rocks remaining today occur on the Canadian Shield, in the Canadian Arctic, and in parts of Australia.

If Mars ever had any plate tectonics and recycling of its surface, it ended long ago. That is why there are so many ancient craters and other landforms visible on Mars today.

Three or so billion years ago Mars was a watery, warm world, just like Earth. There were rivers, lakes and possibly seas, lying beneath a thick atmosphere. There may have been ancient living things on Mars, as there were on Earth at the time. The creatures swimming in the Earth's seas were single-celled, and tiny, but there were lots of them. The situation on Mars was probably the same. Life on Earth became much more diverse and complex some 500 million years ago, during the Cambrian Period. Mars never reached this point.

Mars is smaller than the Earth, and its core cooled faster. When it solidified, any tectonic recycling of its surface stopped. From there on the only things changing the surface were erosion and meteoric impacts. More importantly, when the core solidified the flows of molten core material ceased too, which shut down the dynamo processes generating the Red Planet's magnetic field.

As the magnetic field decayed, it stopped shielding the planet from the solar wind. The atmosphere was scrubbed away, the greenhouse effect keeping the planet warm ended, and the planet became a frozen, almost airless desert. There would never be the Martian equivalent of the Cambrian explosion of life. The Earth still has a strong magnetic field, which is keeping the solar wind away from the top of the atmosphere.

If we were looking for life on Mars, where would be a good place to look? There may be things eking out a tough life there now, but as is the case on our world, there should be ancient rocks containing the remains of the creatures living in the rivers lakes and seas that existed around three billion years ago.

On Mars, where should we look?

In seas and lakes, there is a continual rain of particles and other things falling and accumulating on the bottom. Included in this rain are the remains of living things: shells, bones, carapaces and other hard parts, and more rarely, soft parts. These get buried by further sediments, and over millions of years, the sediment layers become layers of rock. So we should look at the rocks formed from these sediments.

Perseverance has sent back images of suitable sedimentary rocks. In addition, creatures leaving their remains in a river would have some of those remains, especially those of tiny life forms, carried downstream by the current.

As a river flows into a lake, the flow slows and the river dumps this material forming a delta. Therefore the deltaic materials could contain a concentration of animal and plant remains. So Perseverance is going to focus a lot of its attention on the rocks derived from deltaic sediments. These sediments will also tell us the history of the river and the lake, including the increasing number of droughts as the Red Plant dried up and froze. Maybe this space mission will tell us about the sad story of Martian life, and maybe detect some tough descendants eking out a life somewhere beneath the surface.

•••

• After sunset, Jupiter and Saturn will be low in the southwest and Mercury will be low in the predawn sky.

• The Moon will be full on Oct. 20.



How unique is our Solar System?

A system of stability

During Earth's 4.5 billion-year history, it has been hit by things and possibly experienced small changes in its orbit.

The earliest evidence for life we have found so far on our world is 3.8 billion years old, and from then to the present day living things have been around in profusion.

Because even a small change in the Earth's orbit could sterilize our planet, things must have remained stable at least as long as there has been life on Earth.

Understandably, our ideas as to what other planetary systems might be like were moulded by what we saw in our own. For years it was the only one we could study and what we saw made sense.

Things start off with the collapse of a big cloud of gas and dust. It forms a gradually shrinking rotating disc, which condenses into a number of lumps. The lump in the middle, the biggest, becomes a star. The lumps forming far from the star are not strongly affected by it, so the resulting planets hang onto lots of the gases present in the birth cloud.

In our Solar System, these are the planets Jupiter, Saturn, Uranus and Neptune, known as the "gas giants".

Further in, the heat, radiation and wind from the young star remove a lot of the gases, but not all, leaving rocky planets with relatively thin atmospheres, like Venus, Earth and Mars.

Planets closer in get all their gases blasted away, as with our planet Mercury. It all fits our theories and is consistent with a system that is stable over the long term, and ideal for life.

This explains the shock we had when we first started getting a good look at other planetary systems. Most of them were nothing like ours at all. Some of them had Jupiter-sized gas giant planets orbiting close to their stars. They could not have formed there because the gas would have been blasted away; they must have moved somehow.

In all, very few of those other planetary systems look like ours. The picture we get is of planets changing their orbits quite drastically over time, going from the outer reaches to their system to close to their stars, and then somehow moving off to somewhere else.

Because even a tiny change in the Earth's orbit would freeze or fry us, we know this shuffling of the planet's tendency could not have happened here, or if it did, it must have been a long time ago. So the picture we get of our Solar System is one of exceptional stability, and if life can only thrive in exceptionally stable planetary systems, it might be rarer than we thought.

This change in our thinking is interesting because years ago, at a conference, a scientist described work he had done on computer simulations of planetary systems, and the results suggested instability.

Books often describe planetary systems as a bunch of planets orbiting a star, held in their orbits by that star's gravity. If that were entirely the case the systems would probably be extremely stable over the long term. However, there is another factor. Each planet, as it moves in its orbit, is tugging at all the other planets.

These tugs are tiny, but they are constantly changing as the planets move, and can gradually pump up strange instabilities, just as properly timed pushes on a swing can build up really dramatic movements.

That scientist said the results of his simulations indicated these interactions can make planetary systems inherently unstable.

This raises interesting questions. First, will our Solar System remain stable? Second, what percentage of planetary systems is inherently stable? In this case, how many life-bearing planets can there be?

It is intriguing that, as we puzzle about dark matter, dark energy, black holes and wormholes, we still have basic questions about our Solar System. It is also intriguing that the answers to these questions lie not in today's cutting edge physics, but in the ideas developed by Isaac Newton, written down at early in the 18th Century.

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• After sunset, Venus is very low in the southwest and Jupiter and Saturn low in the south.

• The Moon will be reach First Quarter on 12th October.



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How big can solar flares get?

Size of solar flares

On Nov. 10, 1989 there was a large solar flare.

This produced a coronal mass ejection or solar storm that arrived at Earth on Nov. 13, causing power outages and other damage totalling some $2 billion. The damage was mainly done to infrastructure—power, communications and transportation. In 1859, there was a far bigger solar flare.

Today we are far are more dependent on infrastructure than we were in 1989, with long supply routes and a critical dependence on the Internet, which touches almost all aspects of our lives, so an event like the 1989 flare would probably hurt us a lot more. A repetition of the 1859 flare would be extremely serious. The damage would total something like $2 trillion and take months to fix.

Losing the Internet for even a day would be very serious. We therefore need to have some sort of plan for the future to minimize the impact of solar activity and accelerate the recovery. The first step is to estimate what is the biggest solar flare we are likely to have. Events like this are called "Black Swans”. They might be very rare, but the consequences are so serious we cannot discount the chance of one happening.

Solar flares and coronal mass ejections are produced by stresses and instabilities in the Sun's magnetic fields. Stars are balls of plasma: matter so hot the atoms lose some or even all of their electrons. When we add plasma to magnetic fields we get something rather like rubber or elastic.

This stuff, often referred to as a "magnetoplasma", can be compressed, stretched, sheared or twisted. Just as we store energy in a rubber band by twisting or stretching it, deforming magnetoplasma stores energy in it.

On the Sun, the constant churning of material stores enormous amounts of energy in loops, bubbles, ropes and sheets of magnetoplasma - millions of hydrogen bombs' worth of energy, or more. Most of the time some sort of non-catastrophic stress relief happens, but sometimes this is not possible. Then, just as a snapping elastic band releases all of its stored energy in an instant, all the stored energy in a distorted lump of magnetoplasma can be released in seconds.

Somewhere in the distorted structure the stress becomes too much, instabilities are triggered and the magnetic fields snap. The instability rapidly spreads until there is a huge explosion, producing high-energy radiation, beams of accelerated particles and often ejecting a great chunk of solar material into space at thousands of kilometres a second. This chunk of material, known as a coronal mass ejection, or solar storm, together with the radiation and particles are what cause potentially large infrastructure failures on Earth.

How big can these events get? Looking at past records of solar activity doesn't help, because until the mid-19th Century we were not vulnerable to bad solar behaviour. Fortunately there is another possibility. We can observe flares taking place on other stars, and collect a lot of data.

Examination of stars of all types suggests our star may occasionally produce a flare much larger than the 1859 event. However, we can take some solace in knowing that humans and our ancestors have been wandering around on the Earth for maybe a million years or two, and living creatures for far longer. During that period there must have been periods of very bad solar behaviour, and we are still here.

Solar activity poses little if any direct threat to us. The danger comes from our increasing dependence on vulnerable technology.

It is unlikely we could ever totally avoid the effects of high level solar activity, but we know enough to predict what most of them would be, to prepare for them, and try to minimize the recovery time.

Maybe a key need is to reduce our dependence on vulnerable technologies. Maybe we'd actually enjoy a few days without the Internet. .

•••

• After sunset, Venus is very low in the southwest and Jupiter and Saturn low in the south.

• The Moon will be new on Oct. 6.



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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