2 full moons in October

It was a dark and stormy night. The full moon stared through the scudding clouds and the bare tree branches.

It seems  in almost all the spooky movies on TV around Halloween, the moon is always full. Interestingly ,the moon is full on that night only once every 19 or so years, and when it does happen, it is always the second full moon that month.

Two full moons in the same month comes up every two or three years. This second full moon of the month is often referred to as a Blue Moon.

This is where the expression "Once in a Blue Moon" came from, referring to something that does not happen very often. However, this definition of a Blue Moon might not be correct. Apparently the 13th full moon in any given year is referred to as a Blue Moon.

The phases of the moon are caused by the changing arrangement of Sun, Earth and moon as the moon orbits the Earth.

A full moon happens when the Earth lies between the moon and Sun, and we see the moon lit with the light coming from behind us.

The complications in the timing of these events arise because Mother Nature does not seem to like whole numbers.

The interval between two consecutive full moons is 29.5306 days, and a year, the time the Earth takes to go around the Sun, is 365.25635 days.

This is why we have to have leap years, leap seconds and other adjustments to keep the date in step with the seasons. There are therefore 12.3687 lunar phase cycles in a year. 

Just as 13 fence posts in a line have 12 gaps between them, the time interval covered by 13 full moons is 354.3672 days. Therefore, if the first full moon of the year turns up early enough in the year, there will time for a 13th full moon before the year ends.

This can lead to a confusing situation. If the first full moon of the year occurs at 1 a.m. on Jan. 1 Eastern Standard Time, then that year will be a Blue Moon year for inhabitants of Ontario and points east.

However, in B.C. that moment will happen at 10 p.m. Pacific Standard Time on Dec. 31 the preceding year, so that year would have been a Blue Moon year for those in British Columbia.

This sort of confusion is why in science we use just one time zone. By international agreement it is Universal Time, the standard time at the Old Greenwich Observatory, in the U.K., located on the zero degrees of longitude meridian.

Compared with the size of the Earth, the moon is unusually large. This has often led to astronomers referring to the Earth-Moon combination as a double planet.

For example, Mars has two moons: Phobos and Deimos, both of which are tiny. One day, when we are standing on the surface of the red planet, looking up, we will see those moons as small, star-like objects.

The fact that the moon looms so large in our skies, and its phases are so obvious, led to it becoming the basis of our calendar, which is where the word month (moonth) comes from.

The problem of managing a lunar calendar based on 12.3687 lunar months for each orbit of the Earth around the Sun has led to abandonment of the moon as a calendar basis over much of the world.

However, the moon's presence in our daily and cultural life is more intimate than just something associated with the date. It has been associated with religious events for thousands of years.

Easter is celebrated on the first Sunday after the first full moon falling on or after the spring equinox.

In addition, think of the amount of classical, jazz and popular music where the moon is featured, or its widespread presence in poetry and art.

This helps explain why, on those stormy nights in those old, spooky movies, the moon is always there.

  • After dark, Saturn and Jupiter lie low in the south
  • Mars is rising in the east.
  • Venus rises in the early hours.
  • Mercury lies low in the dawn glow.
  • The moon reaches Last Quarter on the 8th. 


How old is that star?

We're a funny species.

On one side we try to set up standard ways of referring to things, so that people around the world, working in other disciplines, stand a chance of understanding what is being discussed.

However, there is also this other impulse to develop a jargon that we understand in our group, but outsiders do not. A good example is calculus. To dentists, this is something nasty on your teeth, but to physicists and mathematicians, it is a calculating tool we cannot do without.

A second example is what is regarded as a metal. Physicists, chemists and engineers agree on what is a metal and what is not. Iron, copper, zinc and gold are metals; sulphur, carbon and oxygen are not.

Astronomers have, however, a different idea. They refer to hydrogen and helium as non-metals, but all the other elements, including sulphur, carbon and oxygen are referred to as metals.

There is a clear reason for considering hydrogen and helium as different from the other elements, although the terminology could be a bit less confusing.

Hydrogen and helium are the most common elements in the universe, and are unique in that all the hydrogen and most of the helium were produced right back at the beginning of the universe.

All the other elements were formed as a by-product of energy production in stars. Let's refer to hydrogen and helium as primary elements and the others as secondary ones.

The first stars to form in the universe, around 100 million years after the Big Bang, formed from hydrogen and helium because at the time there was nothing else available.

Hydrogen is a star's primary energy source. Then, when making the energy those stars needed to shine, they produced more helium as a waste product, along with sulphur, carbon, oxygen and the other elements.

Some are made during routine energy production, and the rest when large stars explode at the ends of their lives. The explosion distributes all those secondary, waste elements out into space, where they mix with the gas and dust clouds waiting to form new stars.

One interesting and useful fact about stars is that the energy production takes place in their cores, and the waste products stay there. What we see at the surface is the material from which the stars formed, unchanged.

This means we can identify old stars, because we see no or very weak signatures of secondary elements in their surface layers, or younger stars, because they formed from material containing secondary elements from early generations of stars. Our Sun is a young star, since its surface contains secondary elements.

There is a complication. The length of a star's life depends on its mass. Stars with large masses get through their lives in about ten million years or so, going out with a huge explosion.

Our Sun is a low-mass star, and will last about 10 billion years. A star with a tenth of our Sun's mass will last far longer. This means most of the stars formed in the youth of the universe and still shining are low-mass stars, such as red dwarfs. Young stars might be low mass, or high-mass ones that have not yet reached the blowing up stage.

The short lives of high-mass stars have worked out in our favour. These stars are the biggest producers of secondary elements, and thanks to there having been many generations of them since the beginning of the universe, there are large amounts of secondary elements out there, available to make planets, complex molecules, and of course us.

  • After dark, Saturn and brilliant Jupiter lie close together low in the south
  • Mars, even brighter, rises in the east.
  • Venus, brighter still, rises in the early hours. It is well worth getting out the telescope.
  • The Moon will be full on the 31st. 

A near miss - in 1908?

The old, black-and-white pictures show men up to their knees in mud and water, making measurements with theodolites and other instruments, with their heads surrounded by a fog of mosquitoes.

These pictures were taken in 1921, in Siberia, when scientists were trying to have a closer look at what happened there in 1908.

On the morning of June 30, 1908, at Tunguska, Siberia there was a huge explosion. Trees were flattened for tens of kilometres, and glasses rattled on shelves in Paris. Due to political instabilities, the First World War and then the Revolution, it was not until 1921 that scientists made it to that remote location to investigate what happened.

The widely held theory was that something had come in from space at high speed, entered the atmosphere and exploded, causing the blast wave that flattened the trees. Something big enough to do that should have left fragments that reached the ground. In absolutely horrible conditions, these dedicated individuals were there to survey the site and find some of those bits.

Paradoxically, they found evidence of a huge explosion, but found no crater and no cosmic debris at all. That is how the situation remains. The most widely held theory at the moment is that the object that caused the blast was made of ice.

Then, most of it would have vaporized in the atmosphere and anything left would have melted long ago, providing more habitat for breeding mosquitoes. There is still no explanation that everyone is happy with, but some new research has come up with an idea that seems to fit the bill, an ominous one.

Some Russian scientists have been researching the event. They calculated what would have happened if a lump of ice came into the atmosphere at around 20 kilometres a second: a typical velocity for such objects.

Their conclusion was that unless it was coming straight down, it would have been vaporized long before it got low enough to cause an explosion that produced damage at ground level.

The few witness statements from the time of the event indicate an oblique path through the atmosphere. They therefore suggested something else, a lump of iron 200 metres across, which did not hit the ground at all; it simply shot through our atmosphere at high speed and went back into space.

Something that big could absorb all the heat produced by a few seconds in the Earth's atmosphere, and something that massive would not slow down much. Its path would be an almost straight line that happened to just miss the Earth, so it passed by through the lower atmosphere. 

A speed of 20 km/s is about 50 times the speed of sound — hypersonic. At such speeds, the air does not have time to get out of the way. It is trapped in front of blunt objects, compressed and heated to around 10,000 degrees. Huge shock waves would be produced, which, if the body passed close enough to the ground, could have done the observed damage.

If this object had hit the ground, it would have blown a crater three kilometres across. The environmental consequences would have been huge.

With no plate tectonics to erase them, the Moon is covered with craters, some many kilometres across, a record of impacts over billions of years. The Earth has been hit too, and on the oldest rocks that have not yet been recycled, such as those of the Canadian Shield we find old, large craters.

The jury might still be out on what actually took place over Tunguska in 1908.

However, over the Earth's 4.5 billion-year history, we have been hit many times, and it will happen again. This is why there are projects dedicated to searching for asteroids and other bodies with impact potential.

  • After dark, Saturn and brilliant Jupiter lie close together low in the south
  • Mars rising in the east.
  • Venus, even brighter, rises in the early hours. It is worth getting out the telescope. The Moon will reach First Quarter on the 23rd. 


Close encounter with Mars

"No one would have believed, at the end of the 19th Century, that human affairs were being watched by ..... intellects vast, and cool and unsympathetic, regarding this Earth with envious eyes, and who slowly and surely drew their plans against us...."

This is how H.G. Wells began his book War of the Worlds. The intellects in question were those of the Martians, sitting on their drying, cooling world and thinking a move to somewhere wetter and warmer would be in order.

In Wells' story, the invasion happened when Earth and Mars were passing close to one another. These close encounters are the best times to observe the Red Planet, and we are having one of those encounters now.

These evenings we see Mars in our skies overnight. It is bright, red, and shining steadily, like a lamp, not twinkling.

Earth is the third planet out from the Sun, and Mars is the fourth. Since planets closer to their stars have to move faster in their orbits, and in addition have further to travel than planets further out, the Earth overtakes Mars on the inside track every 26 months.

Since at that moment Mars, Earth and the Sun are in line, with Mars on the opposite side of the Earth from the Sun, we say that Mars is in opposition. Since Mars' orbit is a bit elliptical, and Earth's is too, but less so, some oppositions are closer than others.

If Mars is at the point in its orbit closest to the Sun, and Earth at its most distant point, the two planets can be really close. The encounter in 2008 brought the two planets to around 57 million kilometres of one another, which is almost as close as it gets.

This time round the closest we will get, in mid-October, will be about 61.5 million kilometres. Considering that some oppositions might have the planets passing at a distance of over 100 million kilometres, our current opportunity to observe Mars is worth taking seriously.

We won't have another encounter as good as this until 2035.

Mars can be a tantalizing object to observe. At the moment even a small telescope will show Mars as a reddish-orange disc, a desert planet.

The main impediment to getting a really good view of the planet is turbulence in our atmosphere, making the planet look like a coin at the bottom of a stream. Fortunately, during this encounter, Mars gets quite high in the sky, which reduces the effect of the turbulence.

Those hazy, anti-cyclonic days, where the stars don't twinkle much are the best. However, the key is patience. Amidst the flashing and rippling, there are occasional moments of steadiness that allow us to see the planet in much more detail.

The challenges in getting really good views of the planet are the probable cause of one of the great misunderstandings about Mars, one that persisted until as recently as the 1960s. This was a consequence of staring too hard, for too long, under poor observing conditions.

In 1877, Italian astronomer Giovanni Schiaparelli reported seeing irregular lines on Mars: naturally occurring channels.  Of course, he used the Italian word for channels, canali.

English speaking astronomers mistranslated this word as canals, artificial waterways, made by Martians for water management on their drying planet. American astronomer Percival Lowell built an observatory at Flagstaff, Arizona, just to map the Martian canals. He worked hard, stared hard and worked long hours, and mapped the canals.

It was probably Lowell who launched our obsession with Martian invasions and other stories about Mars.

Of course, the great irony is that in the end, we invaded Mars.  We have sent more spacecraft there than to any other planet. One day there will be intelligent beings on Mars — probably us.

  • After dark, Saturn and brilliant Jupiter lie low in the south
  • Mars is rising in the east at the same time.
  • Venus, even brighter, rises in the early hours.
  • If you have a telescope, all these planets are worth a look.
  • The Moon will be New on the 16th. 

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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