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Skywatching

Hunters of planets

Our ancestors did a lot of sky watching. They did not understand much of what they were seeing, but they were good observers.

They used the sky as a clock and calendar. Today, apart from the weather, we live largely independent of the sky.

Those early astronomers noticed the Sun, Moon and stars move from east to west, and that the stars form unchanging patterns, constellations, which got named mostly after characters, animals and objects in myth and legend.

However, there were some star-like objects that moved against the stars. Unlike the stars, they shone steadily, like lamps, and because of their changing positions, they were called wandering stars, or planets.

Those ancient observers also noted that the Sun, Moon and planets always wandered within a defined strip of sky, which we now call the ecliptic.

This path passes through 13 constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus, Sagittarius, Capricornus, Aquarius and Pisces.

These are the constellations of the Zodiac. Having 13 signs of the zodiac was not popular, so Ophiuchus was quietly dropped. We see all these bodies moving along one strip in the sky because all the planets orbit the Sun in the same plane, like marbles rolling around a plate.

This is useful in that to find planets we just search along the ecliptic.

Our ancestors spotted five wandering stars, which came to be named, Mercury, Venus, Mars, Jupiter and Saturn.

These planets are bright and easy to spot with the unaided eye; in fact, Venus and Jupiter can be so bright they are impossible to miss.

Further discoveries had to wait for the development of the telescope.

There is a rather strange thing called the Titius-Bode Law, in which a totally arbitrary (as far as we know) formula that predicts, remarkably accurately, the distances from the Sun at which planets can be found.

The formula gave distances at which planets might be found beyond Saturn, and in 1781, William Herschel started looking. On May 13, he discovered the planet Uranus. From here on, calculation and position measurement became the main tools in finding new planets.

Planets orbit the Sun because they attract each other gravitationally. It is easy to predict the positions of a single planet orbiting the Sun.

However, when there are multiple planets, they tug at each other, making tiny distortions in each other's orbits. This provides a powerful method for finding unknown planets.

We calculate the positions of known planets taking into account the perturbations by the other known planets. If we find a discrepancy, we can calculate how big a body is needed to explain that discrepancy, and also where to look for it.

From differences between the predicted and observed positions of Uranus, John Couch Adams and Urbain Le Verrier independently predicted the position of the new planet. Adams passed the prediction to the U.K. Astronomer Royal, George Airy, who conducted an unsuccessful search.

Le Verrier persuaded Johann Gottfried Galle to look for the new planet, and on Sept. 23, 1846, Galle found it. The new planet was named Neptune, after the God of the Sea, because of its deep, blue colour.

Perturbations in Neptune's orbit led to the prediction of yet another planet, along with a rough idea as to where to look.

On Feb. 18, 1930, Clyde Tombaugh found it. The new world was named Pluto. However, its mass was too small to explain those perturbations.

We now know that Pluto is just one of a very large number of similar bodies orbiting in the outer Solar System, all contributing to the distortion of Neptune's orbit.

We cannot say if there are any more planets out there.

  • Mars is low in the southwest after dark.
  • Jupiter and Saturn lie low in the southeast before dawn.
  • The Moon will reach First Quarter on the 19th.


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Blood Moon super, eclipsed

The Moon will be "blood,” "super" and eclipsed on May 26.

Unfortunately, the main phase of the eclipse will be starting around 2:45 a.m. PDT, when the dark edge of the Earth's shadow starts to move across the Moon's face.

At the time, the Moon will be low in the southwest and close to setting. How far into the eclipse we will see depends on the southwest horizon.

To see the rest of this eclipse we would need to be on a tropical island out in the Pacific Ocean.

However, just in case you find yourself on one of them, here is the eclipse timetable.

The Moon will start to enter the Earth's inner shadow at 2:45 a.m., and will be fully in shadow by 4:12 a.m. It will start to exit at 4:26 a.m. and all will be over by 5:53 a.m.

All times are in PDT. The terms Super Moon and Blood Moon are being applied to this eclipse. What do these terms mean?

The Moon's orbit around the Earth is not circular, so its distance from us varies a bit, between 356.500 kilometres at its closest to about 406,700 km at its furthest. That is, a variation of around 13%.

Since things look larger when they are closer, we see the size of the Moon in the sky change by that percentage. This size variation is most visible when the Moon is full, that is, when the Earth lies roughly between the Sun and Moon so we see the Moon lit from behind us.

When we have a full Moon when the Moon is at its closest to us we have a Super Moon.

Actually, a change in apparent diameter of a few percent is not really noticeable without measuring devices. However, when the Moon is low in the sky, we see another, much more obvious effect.

The Moon looks huge near the horizon and as it gets higher in the sky it looks smaller and smaller. This actually has nothing at all to do with the Moon. It is a trick our brains are playing in interpreting what we see.

To confirm this, look at the Moon through a drinking straw when it is near the horizon. You might be surprised to find that through an average drinking straw you will see the entire lunar disc plus a good chunk of sky around it.

Note how much of the field of view is filled by the Moon. A more precise method would be to make a tube out of paper, rolling it tightly enough for the view through it to show the whole Moon and nothing more.

Look at the Moon when it is close to the horizon and repeat the observation when the Moon is high in the sky. The lunar disc will look the same size. The Moon will be low in the sky during this eclipse.

If the Earth had no atmosphere, during a lunar eclipse it would simply block out the sunlight falling on the Moon, so that it would just vanish from the sky.

However, the fact we do have an atmosphere changes everything.

  • First, the atmosphere bends or refracts the sunlight into the shadow zone, illuminating the Moon.
  • Second, dust and other materials in our atmosphere subtract the blues and greens from the sunlight, leaving the reds and yellows.

This is the reason sunsets can be so spectacular. So the sunlight refracted by our atmosphere onto the eclipsed Moon is mainly red. The eclipsed Moon looks red — a Blood Moon.

If we were standing on the Moon, looking at the Earth, we would see a dark disc surrounded by a thin, bright ring of sunset red.

Lunar eclipses are scientifically useful. With no atmosphere and a very dry surface, the lunar surface starts to cool off very rapidly when the Sun's heat is blocked out.

This means we can use lunar eclipses to study lunar soils. Using infrared and radio telescopes we can measure the temperatures at various depths below the surface layer and how they change during the eclipse.

From this we can deduce soil properties, density, water content (if any) and many other things. Measurements like this were helpful in planning the first manned trips to our cosmic neighbour.

  • Mars is quite high in the west after dark.
  • Jupiter and Saturn lie low in the southeast before dawn.
  • The Moon be New on the 11th and will reach First Quarter on the 19th.


Flaring red dwarf stars

The nearest known star to us after the Sun is a red dwarf star called Proxima Centauri.

It is 4.25 light years away, which means its light takes 4.25 years to reach us. This star has about an eighth of the Sun's mass, is about a seventh of the Sun's diameter, and its energy output compared with our star is microscopic.

Its fuel consumption is so low that it should be able to keep shining happily for tens of billions of years. This suggests that Proxima Centauri, along with the countless other red dwarf stars scattered around the universe, could be ideal hosts for inhabited planets.

They can provide a stable environment over a long enough time for life to appear and evolve. It turns out that Proxima Centauri has a potentially inhabitable planet, but on the downside, this star, along with many other red dwarfs, produces large flares.

Stars are big spheres of hot, churning plasma, atoms so hot they have lost some of their electrons. This means plasma is a good conductor of electricity. Fluorescent lights contain a little bit of plasma.

Stars are also threaded by complex systems of strong magnetic fields. The continuous churning leads to the magnetic fields getting crowded, twisted and/or stretched.

These distortions lead to a colossal amount of energy being stored. In most cases this energy gets slowly dissipated again. However, sometimes the tangle of plasma and magnetic fields is too complicated or severe to just relax.

In this situation, the stresses build up until something snaps, and all the stored energy, which in the case of the Sun could add to millions of hydrogen bombs, is released in seconds.

The result is blasts of X-rays, even gamma rays in some cases, beams of high-energy particles, and often a large chunk of material is shot off into space at thousands of kilometres a second. These are called coronal mass ejections, or solar storms.

Flares don't threaten living things on the ground, but can pose a risk to those at high altitudes or in space. On other hand, flares can severely degrade or even destroy the complex power, transportation and communications infrastructure our lives depend on.

It does help that we live about 150 million kilometres away from the Sun. However, imagine living 20 times closer, to a star that produces even bigger flares.

For any star there is a Goldilocks Zone, the distance from the star where a planet would be at the right temperature for liquid water to exist on its surface.

For dimmer stars that zone lies close to the star, and is quite narrow. So the chance of a planet orbiting a dim, red dwarf star lying in the zone is smaller than it would be for a brighter star. However, red dwarf stars are the commonest stars in the universe, so there must be lots of them out there with planets lying in the zone.

Red dwarf stars produce much larger flares than do more massive stars like the Sun, which is why we can detect them from so far away.

The result for a planet in the Goldilocks Zone for Proxima Centauri or other red dwarf stars is that even a solar flare of the size produced by the Sun would hit the planet hundreds of times harder than we get hit.

Imagine a flare tens of times larger than what our Sun produces. The environmental impacts would be huge, let alone the disruption of any technological infrastructure.

It is likely that whether there is liquid water, the radiation and wild environmental instabilities would stop life getting going on any of these worlds.

However, not all red dwarf stars we observe are producing these huge flares. This could mean some of these stars could have inhabited worlds. That is unless this flaring behaviour is something all these stars go through at some points in their lives.

Of course, our arguments are based on life as we know it. There could be other forms of life.

  • Mars is still high in the southwest after dark.
  • Jupiter and Saturn lie low in the southeast before dawn.
  • The Moon be New on the 11th.


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First flight on Mars

Until we discover otherwise, the first ever known powered flight on Mars has just happened.

The helicopter that went to Mars with the latest rover just had a test flight, going about three metres into the air, hovering and then landing safely. Having an aircraft on Mars is going to have a huge impact on our exploration of the planet.

This is not the equivalent of flying a drone here on Earth. There are two huge, additional challenges.

Mars' atmosphere is much thinner than what our drones fly in on Earth.

With radio signals taking many minutes to get from Mars to Earth and just as long to go the other way, there is no way we can remotely control the vehicle.

Although here on Earth jet aircraft can reach the edge of space, helicopters are confined to low altitudes. It is possible to coax the most advanced helicopters to heights of around eight kilometres, but the highest they can hover is about three kilometres.

The atmospheric pressure on the surface of Mars is about the same as we find here on Earth at an altitude of around 25 kilometres. Our earthly helicopters would not get off the ground on Mars.

The problem is getting enough lift. This is the force that gets an aircraft off the ground and keeps it in the air.

The amount of lift depends on the density of the air, the area of the wing surface and how fast that wing surface is moving. Can we not just "flap our wings" faster? Unfortunately that won't work.

When the ends of the blades of the propeller get close to the speed of sound, they stop producing lift. So the only real solution is to go for as much wing area as possible, so that the propeller blades don't have to move as fast.

The other thing we can do is cut the weight of the aircraft to a bare minimum, and this includes the weight of our larger propeller blades. Luckily there are advanced construction materials available that provide strength while being lightweight.

Thanks to great efforts by NASA, that helicopter weighs in at less than two kilograms, is ready to go. The cameras and other electronics on the helicopter are small and very lightweight.

The first spacecraft that landed on Mars were immobile. They just observed their surroundings, so the fact that signals took many minutes to get between Earth and Mars was not a huge problem. Things changed when the rovers landed on the Red Planet.

The solution to the time-delay problems involved first, driving slowly, which was necessary on rough, unpredictable terrain; the main thing was to make the vehicles smart.

They would have to make all the decisions necessary for driving safely, relying on operators on Earth to merely point out what to drive to.

Robot helicopters bring up a whole range of new issues. They fly faster, so they have to "think" faster. It is true there are few things to hit while flying, but Mars can be a windy place, so conditions can be turbulent.

With nobody around to put things right when something happens at take-off or landing, the aircraft has to be smart enough to identify all the hazards a human pilot has to, and to respond to them.

For example there are frequent "dust devils" on Mars: small tornadoes of whirling dust that extend well up into the atmosphere. It would not be good to fly a fragile, small, light aircraft into one of them.

These first flights can be planned to avoid or minimize these threats, but eventually vehicles carrying out long, autonomous exploratory flights will have to be smart enough to avoid such hazards.

This flying Martian explorer is the first of its kind, but certainly won't be the last. The ability to explore Mars by flying around, studying the atmosphere and maybe landing for a closer look at places of particular interest will revolutionize our knowledge of our neighbour world, and make it all much safer for those first human explorers.

  • Mars is still high in the southwest after dark.
  • Jupiter and Saturn lie low in the southeast before dawn.
  • The Moon will reach Last Quarter on the 3rd.


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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