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Skywatching

The universe has a skeleton

We have known about Dark Matter and Dark Energy for at least a decade, but, as yet, still have no idea what they are.

To make the issue worse, these two ingredients of the universe make up about 95% of the matter in it. The matter making up us, our planet, the sun, Milky Way and everything else we can see in the universe adds up to the other 5%.

A discrepancy this big cannot be put down to bad measurements. It must be real.

Dark Matter turned up when astronomers measured the orbits of stars in galaxies. If we know the orbital speeds of stars and how far they are from the centre of their galaxies we can determine the mass of the galaxy and how it is distributed. However, the calculation indicated there is much more material in galaxies than we see.

This unknown stuff needed a name, so it ended up being called Dark Matter. The name is meaningless in that we have no idea what it is, or even if it is what we understand as matter at all.

The issue of Dark Energy is even stranger, and is linked to the expansion of the universe.

When that expansion was first discovered, it was logical to see if the expansion could be calculated backwards to see what happened in the past.

This led to the discovery that at a point in the past, currently estimated to be just under 14 billion years ago, everything in the universe, including space and time, were in one lump, which then started to expand.

The Big Bang Theory was born.

If the Big Bang threw everything outward, the expansion would be working against the gravitational attraction of everything in the universe trying to pull it all back together into one lump. The result would be that the expansion would slow over time, and might even reverse one day.

However, the most distant galaxies tell us a different story; the expansion is speeding up.

Imagine throwing a ball in the air and instead of it slowing and then falling back, it accelerated upwards, out of sight. As both common sense and Newton's First Law say, things only accelerate when a force is acting on them.

This outward force has become known as Dark Energy. As in the case of the Dark Matter, giving it a name does not tell us what it is.

But now a project is coming together that should be a major step towards finding out.

The main priority is to come up with more and better data on how quickly really distant galaxies are being carried away from us by the expansion.

Since the light from a galaxy a billion light years away from us has spent a billion years getting to us, we see it as it was a billion years ago.

By looking at more and more distant galaxies we are looking further and further back in time. By measuring the speed that galaxy is moving away from us, we know how fast the universe was expanding back then.

To help us get a better understanding of what dark energy might be, we need a lot more measurements of really distant galaxies.

To address this need, an international team of researchers have come up with a device called the Dark Energy Spectroscopic Instrument (DESI).

Inside DESI are 5000 optical fibres. Each of these fibres can be used to capture the light from one galaxy. Measuring one selection of 5,000 galaxies will take about 20 minutes, including galaxies as far as 10 billion light years away — that is 10 billion years back in time. 

The observing plan is to measure 35 million galaxies.

Our ignorance is underlined by the diversity of ideas as to what it could be. One idea is that it is "vacuum pressure" — random fluctuations in the fabric of space-time.

Another is that gravity is more complicated than we think. In nature every force has a counter-force, except gravity.

Maybe it does, and we are seeing evidence of it. We need data.

  • Jupiter and Saturn lie low in the southwest after dark.
  • The moon will reach Last Quarter on the 18th.
  • Mars lies very low in the east before dawn.


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Mercury transiting the sun

On Remembrance Day, Mercury, the closest known planet to the sun, will cross the solar disc.

Observers will see a small, round disc move slowly across the sun from one side to the other. If you don't see this one, you will have to wait until 2032 before it happens again.

However, if you are not an experienced solar observer, with the right hardware, trying to observe this event can be extremely dangerous, with a serious risk of permanent eye damage.

Looking at the sun through a telescope or binoculars not fitted with filters made explicitly for this purpose by a reputable telescope manufacturer can be deadly. It is even risky to stare at the sun with naked eyes.

Since Mercury and Venus orbit between us and the sun, they are the only planets we will ever see as small, round silhouettes crossing the solar disc. All the other planets pass behind the sun.

In the past, astronomers tried hard to observe transits of Mercury and especially Venus, because carefully timed observations from precisely located positions on the Earth made it possible to establish the actual scale of the solar system.

Most other measurements give us results like the "this one is seven times further away than that one" measurements we were otherwise stuck with.

Mercury takes about 88 days and Venus 225 days to orbit the sun. Since the Earth takes 365.25 days to complete each circuit around the sun, and all the planets orbit the Sun in the same direction, Mercury and Venus will overtake us on the inside lane every 116 and 584 days respectively.

We would expect to see them against the solar disc as they do so. Unfortunately, their orbits and also the orbit of the Earth are slightly inclined, so usually, when they are overtaking us, they will lie above or below the solar disc in the sky, and invisible in the glare.

For us to see them crossing the solar disc the sun, planet and Earth need to be precisely in line. Since Mercury lies closer to the sun than Venus, we see it transit the disc more often.

On average, we see transits of Mercury every few years; because Mercury orbits close to the sun, the transit is visible from a large part of the Earth's surface.

Transits of Venus are much rarer; they occur in pairs a few years apart with more than a century separating each pair. Astronomers have been sent all over the world to observe transits of Venus.

In the 18th Century, one was sent to an island in the Pacific to record a transit of Venus, and was clouded out on the big day, so his bosses told him to stay there for almost a decade to see the next one.

The locals told him that the chosen island was known for its bad weather, and that a nearby island would be a much better bet. He made the mistake of writing to his bosses about his move, and was ordered to return to where they had told him to go, and he was clouded out; the recommended island had clear weather.

At least part of this transit will be visible from most locations across Canada.

Here are the start and end times for a selection of cities across Canada, in Local Standard Time, as obtained from the Observer's Handbook of the Royal Astronomical Society of Canada:

  • Nov. 11: St. John's (09:05-14:34)
  • Charlottetown (08:36-14:04)
  • Halifax  (08:36-14:04)
  • Saint John (08:36-14:04)
  • Quebec, PQ (07:36-13:04),
  • Ottawa (07:36-13:04),
  • Winnipeg (sunrise to 12:04)
  • Regina (sunrise to 12:04)
  • Edmonton (sunrise to 11:04)
  • Vancouver (sunrise to 10:04).

The safest way to observe the event is with astronomers from your local astronomy club or Centre of the Royal Astronomical Society of Canada.

You can find contact information for your local RASC centre at https://www.rasc.ca/centres.

  • Jupiter and Saturn lie low in the southwest after dark.
  • The moon will be full on the 12th.
  • Mars lies very low in the east before dawn.


Double star on Luke's world

There is a scene in the first Star Wars movie where, on the desert planet Tatooine, Luke Skywalker watches the setting of twin suns.

Was this scene realistic?

Are there double stars? Can they have planets, and would those planets be inhabitable? How do double stars form?

There is no question that double stars exist. A good number of stars in our galaxy, and presumably other galaxies, are orbiting one or more stars. 

For example, look at the second star in from the end of the handle of the Big Dipper.

You will see this star, named Mizar, has a companion, called Alcor. Binoculars will show it well.

My favourite double star is Albireo, in the constellation of Cygnus, The Swan. A small telescope shows an orange star with a brilliant, blue partner.

There are countless man-made satellites orbiting the Earth, and at least one natural one, the moon. If we try orbiting satellites in higher and higher orbits, the Earth's gravitational attraction gets weaker and weaker, until it is not strong enough to hang onto a body, and it wanders off to orbit the sun.

We can call this the Earth's "sphere of influence.” Even giant planets like Jupiter have spheres of influence, although with the large mass of the planet and the weaker solar gravity at that distance, that sphere is bigger.

The solar system formed from the collapse of a cloud of gas and dust. The cloud formed a rotating disc and the central part formed the biggest lump, which became the sun.

Other lumps formed the planets, but the sun's grip on the matter in the disc kept their spheres of influence comparatively small, which slowed their growth and made sure the sun had no strong competition when it came to pulling in cloud material.

The result was the solar system we have today, with one star surrounded by a retinue of planets. However, if a bigger cloud collapses, forming a bigger disc, things can be different.

In the outer parts of the disc, any growing lump of material forming would have a much poorer gravitational control over distant parts of the disc, so other lumps forming there would have larger spheres of influence and greater ability to grow to larger masses.

Since whether a lump becomes a planet or a star depends simply on the amount of material in the lump, the lumps of material in larger discs have a bigger chance of becoming stars, so the system might contain two, three or more stars.

Although more material has been grabbed to make stars, there is a chance that some was left over to make planets.  However, their orbits will be rather complicated, and involve enormous changes in temperature, probably not the best places for life to form or for us to colonize.

If a really big cloud collapses, it will form multiple discs, each of which will form one or more stars. The result is a star cluster, which may contain thousands of members.

The Pleiades is a star cluster. In our studies of stars, clusters are very useful since they contain stars of various masses all born at about the same time and at more or less the same distance from us.

The Atacama Large Millimetre Array radio telescope (ALMA), in Chile, is designed to observe and image radio waves with wavelengths of millimetres.

These very short wavelengths enable us to look at what is going on inside clouds in the process of forming stars. Astronomers have very recently used the ALMA to produce an image of a collapsing cloud in the process of forming a double star.

 Rather than just a disc with a new star in the middle, the main features are great streamers spiralling out from the pair of newborn stars.

Any planets forming with them are going to have extreme conditions far worse than Tatooine.

  • Jupiter and Saturn lie low in the southwest after dark.
  • The Moon will reach First Quarter on the 4th.
  • Mars lies very low in the east before dawn.


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When is the moon full?

If you have never watched the full moon rising above the hills on the other side of a lake, you really need to do something about that.

It is beautiful and special. An added mystique comes from knowing we are doing something even our remotest ancestors must have done.

This may be one of the reasons the phases of the moon are listed in most of our diaries and calendars. However, if so why are the dates of the lunar phases sometimes wrong, usually out by a day?

Our ancestors must have taken note of the phases of the moon, although they did not know what was going on. They reckoned the passage of time using the moon. That is where the word "month" came from.

Today, we do understand what causes the lunar phases. They arise from the direction we are looking at the moon compared with the direction of the sunlight illuminating it. We can only see the moon because of the sun lighting it up.

In fact, unless sunlight is being reflected from the Earth onto the unlit part of the moon, a phenomenon known as the "Old Moon in the New Moon's arms,” we only see the sunlit portion.

Imagine you are sitting way out in space, way above the Earth's North Pole. You will see the moon circling the Earth like a ball on a string. The half facing the sun is lit up and the other half dark and invisible.

When the moon lies between the sun and us, the unlit side is facing us. In addition, when the moon is in that position, it is close to the sun in the sky and it is totally lost in the glare.

We refer to the moon at this time as being new.

The path of the moon around the Earth is in the eastward direction. So it moves leftward from the sun until a short time after being new, when it appears as a thin crescent in the western sky after sunset.

What we are seeing is a small sliver of the sunlit half. Many amateur astronomers take on the challenge of seeing the youngest moon possible, as a thin thread of crescent in the sky just after the sun has gone.

From that point, every day the moon will be about 12 degrees further east and rise about 50 minutes later. During this part of the cycle, the waxing moon is lit from the right, so it looks like a "D".

Around a week after the New Moon, the disc will appear exactly half lit, exactly like a "D". The moon is now at First Quarter.

After about another week, the moon will be at the opposite side of its orbit from when it was New. We will be between it and the sun and it will be lit from over our shoulders. We are then facing the fully lit side: the Full Moon.

It will continue on its orbit, over following days we will se an increasing fraction of the unlit part of the moon appearing on the right hand side. The moon is now waning and looks rather like a letter "C".

A week or so later, we will see the disc half lit, except this time lit from the right hand side. We are now at Last Quarter. From then on narrower, until the moon is again New. A simple guide is DOC: D-waxing, O-Full and C-waning.

The times and dates of the phases of the moon can be calculated accurately. We usually get this information in Universal Time (which used to be called Greenwich Mean Time). For example, on Jan. 21 2019, the moon was full at 05:16 UT.

Unfortunately, this is 12:16 a.m. EST on the 21st in Ottawa, but 09:16 p.m. on the 20th in Vancouver.

In general, most of the calendars we buy are printed in Europe or in eastern North America, with the dates of the phases of the moon given for those locations. Those of us living elsewhere have to live with the discrepancy.

This is not really a problem. We can get the exact times from the Web, or from the Observer's Handbook of the Royal Astronomical Society of Canada.

  • Jupiter and Saturn lie low in the southwest after dark.
  • The moon will be new on the 28th (in Eastern Canada) and the 27th (in the West).
  • Mars lies very low in the east before dawn.


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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