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Skywatching

Back to the moon

After many years, we are on our way back to the moon. Moreover Canada will be part of it.

There are many reasons to be excited about the prospect. It marks a new beginning for manned exploration of the solar system and one day possibly the universe beyond.

A space station in lunar orbit will be a better jump off place for space missions to Mars and the other planets. One big advantage is that we won't need those huge booster rockets we use to get off the Earth's surface.

A space station in Earth orbit, like the International Space Station, is better, but even if we build our spacecraft in Earth orbit, the components still have to be lifted off the surface of the Earth.

What if we could produce the materials and maybe do some of the construction on the moon, hopefully using locally mined resources.

There is abundant solar energy and there is no atmosphere. This, in addition to the moon's weaker gravity, makes it much easier to get stuff from the moon's surface into lunar orbit.

We can just lob them upward, and when what we lobbed gets to the right height, an onboard engine could accelerate it to orbital velocity, or someone could rendezvous with it and catch it before it falls down again.

You can't do this from the Earth's surface because we will have to lob a lot harder, and launching things from the ground at high speed will probably end up incinerating them due to atmospheric friction.

Current space missions are launched quite slowly and they don't floor the gas pedal until they are above the atmosphere.

Launching from the moon could be done with a big cannon, like the one in Jules Verne's story, From the Earth to the Moon.

However, that would be hard on what is being launched and even harder on any human crew. One popular concept in science fiction that is perfectly workable in fact is to use electromagnetic acceleration.

The load to be sent to orbit will accelerate along the ground like a maglev (magnetic levitation) train, but to much higher speeds. Then the track would curve upward, launching the vehicle into space.

Having a space station in lunar orbit has huge science potential. If the orbit is arranged so that it can always have a line of sight to Earth (critical for communications), it will see both the front and back of the moon.

The back of the moon would be a fantastic place to put a radio telescope or two. Because the Earth never rises above their horizon they will not have to put up with the growing radio cacophony we are making.

A single cellphone would be far brighter than any cosmic radio source. Being screened from the interference coming from Earth would give researchers access to most of the radio spectrum. In addition, we would be able to observe the cosmic emissions that are blocked by our atmosphere and ionosphere, because the Moon has neither.

That's not to say that working and doing research on the Moon will be easy. Equipment will have to handle big lunar daily temperature changes, from far below zero during the night to around the boiling point of water during the day. The biggest challenge for operating equipment on the moon's surface will probably be the dust.

Over billions of years, the moon has accumulated a layer of very fine dust on its surface, like flour or maybe even finer.

As the Apollo astronauts found, it just gets into everything. Being very dry, it easily picks up an electrostatic charge, which makes it stick to anything it touches. However, we have some pretty dusty places on Earth and we have learned how to live and work there.

We can be very creative when there is a strong enough incentive.

  • At 13:58 PST on March 20, the sun will cross the equator heading north, marking the spring equinox. From then on the sun will spend more than 12 hours above the horizon each day.
  • Mars lies in the southwest after dark.
  • Jupiter rises around 2 a.m.
  • Saturn 4 a.m.
  • Venus 5 a.m., in the predawn glow.
  • The moon will be full on the 20th.


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Storms rage on Jupiter

In 1979, the two Voyager spacecraft flew past Jupiter on their way to the outer solar system.

As they shot past, they sent back images of enormous storms. Now we are getting a better look. The Juno spacecraft is orbiting the giant planet and sending back the most amazing images.

Try browsing for "Jupiter polar storms.” One shows one of the planet's poles. There is a huge storm, a polar vortex, encircled by several storms. Other images show more storms, some of them standing against the flow of the atmosphere, and forming turbulent wakes.

Then there is the Great Red Spot, a storm big enough to engulf the Earth, which has been raging for at least 300 years. What drives all this activity, and why is it so organized?

On Earth, the energy for the weather is provided by the sun, and processed by our planet's rotation and circulation of the atmosphere. If we were standing on the equator, that rotation would be carrying us eastward about 1700 km/h.

However, if we were standing at the North or South Pole, we would be moving at zero km/h, just turning round once a day. At the hot equator, air arrives along the ground, warms and rises, and moves poleward.

At the poles the air cools and sinks, and moves equatorward. This means air is constantly moving into places where it is faster than, or closer than the Earth's rotation.

The collisions between masses of air moving at different speeds drive most of our weather. The situation is rendered more chaotic by the presence of large oceans and continental landmasses.

Things are different on Jupiter. Firstly, Jupiter is around 1,400 times the volume of the Earth, but has only
318 times the Earth's mass, which means Jupiter is mostly gas, although there might be a rocky body somewhere in the middle. The atmosphere is very deep and has no underlying land or ocean to interfere.

Secondly, the Earth has a diameter of 12,756 km and rotates once every 24 hours, which translates to a rotation speed of 1,700 km/h at the equator.

Jupiter has a diameter of 143,000 km and takes less than 10 hours to complete each rotation. So the top of the atmosphere over the equator is moving at almost 43,000 km/h.

As in the case of the Earth, the atmosphere over the poles is moving at 0 km/h. This speed difference means that north-south motion of the atmosphere is more difficult, and the weather systems settle into east-west bands. Even a small telescope will show them.

The speed differences in and between these bands drive lots of small storms - small by Jupiter's standards. Some of them are bigger than the Earth. This band structure of the atmosphere helps form that regular ring of storms around the polar vortex.

One thing that is particularly intriguing about weather on this giant world is that storms can stay fixed as the rest of the atmosphere flows past. The Great Red Spot is a particularly good example. It has not moved much since it was discovered.

Some suggested this is because it is driven by a huge volcano erupting under it. However, there is no volcano, just thousands or tens of thousands of kilometres of atmosphere.

There is a very interesting illustration in James Gleick's book Chaos. It shows a rotating pan of coloured oils. After it had been run enough to settle down, bands of colour developed, as on Jupiter, and an eddy formed.

The colours must have been picked with this in mind, because that eddy is coloured red in the picture. Once it formed, it stayed, rotating between adjacent bands. This suggests that the Great Red Spot is not just a local feature, it is related to Jupiter's global weather system. How is that?

  • Mars lies in the southwest after dark.
  • Jupiter lies low in the south in the predawn sky
  • Saturn to Jupiter’s left
  • Venus shining low in the dawn glow.
  • The moon will reach first quarter on the 14th.


Women stars of astronomy

Beatrix Potter was interested in the natural sciences and wanted to be a botanist.

However, in 19th Century England, it was nearly impossible for women to break into science, so she became a famous writer of Children's books.

There were some women who overcame the obstacles of that time and became renowned scientists, such as Marie Curie.

However, not all institutions were hostile to women, so some had the opportunity to make an indelible mark on modern astronomy.

In 19th-Century astronomy, women mainly worked as computers and data analysts. Back then, the word "computer" meant someone who spent their time doing calculations, by hand.

Today, although computers still do all those calculations, the word now means something completely different.

Until quite recently, astronomical images were recorded on glass, photographic plates. They were insensitive by modern standards, and required exposures of many hours to record usable images.

fter processing, these plates were passed to the usually female data analysts, who carefully extracted the desired information, and meticulously searched the plates for other things that had been caught by accident, such as previously unknown comets, asteroids and exploding stars.

Back then observations were made mainly in two ways. The telescope could be used as a giant camera, recording images of the sky on the glass photographic plates. Alternatively, a diffraction grating would be put before the plate, often over the front of the telescope.

This would split the light from each star into its constituent colours, just as we see when we pass light through a glass prism, or simply look at a rainbow. On these plates, each star image is smeared out into its constituent colours.

From these the data analysts would establish the temperature of the star and its composition. By comparing any given star with its neighbours, its brightness could be measured.

Over time the women analyzing these plates came to understand photographic plates and their limitations, and became highly skilled at extracting information from them.

To do this they had to learn some astronomical science, and over time, their work taught them a whole lot more, leading them to ask their own science questions and becoming researchers in their own right.

In most places this evolution received little encouragement or was even deterred, but at other places, such as the Harvard College Observatory, things were different.

The result was women making important and fundamental contributions to astronomy, some of which are still at the core of astrophysics.

For example, Henrietta Leavitt discovered a special class of variable stars, called Cepheids, after the first one to be discovered, Delta Cephei. These stars cycle periodically in brightness, and the time taken to cycle tells us how bright that star is.

So we can look at a distant galaxy, find a Cepheid or two, measure their cycle time and how bright they look, and from this calculate how far away that galaxy is. She gave us a ruler to measure the universe.

One of the big efforts went into coming up with a system for classifying stars. After Williamena Fleming and Antonia Maury collected and tabulated a huge number, of observations, Annie Jump Cannon assembled them into the system we still use today.

Then, Cecilia Payne showed that this system was simply arranging stars in the order of descending temperature.

These women, together with others, made significant contributions to astronomy and are recognized for them.

One last thing: Beatrix Potter was interested in all natural sciences other than astronomy. Maybe that was her big mistake.

  • Mars lies in the southwest after dark.
  • Jupiter lies low in the south in the predawn sky,
  • Saturn is to its left
  • Venus is shining brightly, low in the dawn glow.
  • The moon will be New on the 6th.


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Over the moon

One of the images sent back by the Chinese Longjiang-2 spacecraft shows the far side of the moon, a monochrome, heavily cratered disc, and in the distance the Earth, a blue marble with white clouds.

It is hard for the two objects to look so different since they have so much in common. Even though the moon is one of the easiest objects to observe, it is one of the most puzzling.

First, it is big. It has a diameter of 3,475 km, compared with the Earth's 12,756. The moon's diameter is over a quarter of the Earth's.

There are larger moons in the solar system, such as the four largest moons of Jupiter, or Titan, the largest moon of Saturn.

However, Jupiter and Saturn are huge planets, and their largest moons are less than four per cent the diameter of the planets they orbit. This has led to the Earth-moon system being often referred to as a "double planet."

How this arrangement came about is still an open question.

The solar system formed around 4.5 billion years ago from the collapse of a cloud of dust and gas. It formed a rotating, shrinking disc, with a big lump forming in the middle, which became the sun.

In the surrounding disc, smaller discs formed with the planets building up in their centres, and their moons from what was left over in their birth discs. This approach always leads — as far as we know — to a big lump with lots of small lumps orbiting it.

This mechanism nicely explains the moon systems of the other planets, and of course the Solar System itself, but not the Earth-Moon double planet.

The moon should be far smaller than it is.

The idea getting a lot of attention at the moment is that a planet was well in the process of forming when another planet smashed into it at many kilometres a second. The two bodies were pulverized, forming a spinning cloud of dust and fragments, which eventually collapsed to produce two bodies, the Earth and moon.

This could also explain why the plane of the moon's orbit around the Earth is at angle to the plane in which the Earth and other planets orbit the sun.

The Earth and moon probably started out with basically the same mixture of ingredients. However, whereas both the Earth and moon started out as hot, molten rock balls, the Earth had enough mass to gravitationally hang onto its atmosphere and the water vapour in it.

The moon, being less massive and with weaker gravity, could not, and its atmosphere was lost into space. So today it is an almost airless, dry rock ball that bakes during the lunar day and freezes at night.

When the inside of the moon was still soft, the slightly stronger pull of the Earth's gravity on the side facing Earth than the pull on the lunar far side pulled the moon out of shape, making it slightly egg-shaped with the long axis pointed at the Earth.

This continuous shape change as the Moon rotated turned the energy of the moon's rotation into heat, slowing that rotation until eventually the moon became locked, with the same side of the moon facing the Earth all the time, like two whirling dancers holding hands and facing each other.

There is another lunar puzzle. Our side of the moon consists of old, cratered areas and huge plains formed from huge lava flows. These are darker than the surrounding terrain and form the well-known face of the "Man in the moon.”

The side facing away from the Earth has much smaller lava plains and is mostly craters. We do not yet have a good theory as to why the two sides of the moon are so different. It is intriguing to think that today, as we probe the depths of space and time, there is still much we do not know about the moon.

  • Mercury, the closest planet to the sun, is low in the west after sunset.
  • Mars lies in the southwest after dark.
  • Jupiter lies low in the south in the predawn sky
  • Saturn is to its left of Jupiter .
  • Venus is shining brightly in the dawn glow.
  • The moon will reach last quarter 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]nrc.gc.ca



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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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