29 Jun 2018

The Magic of GPS

By Simon Shapiro

Science fiction author Arthur C Clarke famously said "Any sufficiently advanced technology is indistinguishable from magic." Usually when you discover how a magic trick works, it stops being magic; it becomes much less impressive. But when you discover how GPS works, it becomes even more impressive. So how does it work?

The Satellites

The first step is to put a bunch of satellites into a geostationary orbit. Which means: the satellite orbits above the equator, moving at the same speed as the surface of the earth. One complete rotation every 24 hours. This means that wherever you are on the surface of the earth, the satellite appears to be in the same spot in the sky. 

The magic in doing this is to match the satellite speed and the height of the orbit. To stay in  a lower orbit a satellite has to move faster; a higher orbit needs a slower speed. Satellites have to be right over the equator 35,786 km high and travel at a speed of 3.07 km/second to be geostationary

Satellites need to be far enough apart not to interfere with each others' radio signals and not to bump into each other. So there's only room for a limited number of satellites in the geostationary orbit. The International Telecommunication Union assigns slots for geostationary orbit and settles disputes between countries about slots. It seems magical that there's enough cooperation in the world to do that!

It's hard enough to put a satellite into space at exactly the right height and speed. But the difficulty doesn't end there. Satellites drift out of position due to solar wind and the gravitational pull from the sun, moon and planets. (Low orbit satellites are also affected by atmospheric drag, which is negligible for high-orbit geostationary guys). So the satellite operators have to monitor the position and use tiny rocket engines on the satellite to correct the position periodically. These corrections are known as stationkeeping.

So Where Are We?

To determine its location the GPS receiver measures its distance from at least three, but usually four different satellites. Doing that needs more advanced technology magic. Each satellite broadcasts data on radio waves. Some of the data it sends is about its exact location. Some of it is a unique sequence of digits together with the exact time it started sending the sequence. The GPS receiver receives the signal after a delay of about one tenth of a second - the time it takes for light to travel from the satellite to the receiver. Knowing this time of travel (T) and the speed of light (S = 300,000 km/second) makes it easy to calculate the distance (D = S x T).

But there's a catch to measuring that fraction of a second's lag in the signal. If the clock in the satellite isn't perfectly synchronized with the clock in the receiver, the distance calculations will be wrong. An error of one nanosecond (one billionth of a second) will make the calculated distance wrong by 30 cm (1 foot). Satellites are equipped with $50,000 atomic clocks that are accurate to 2 nanoseconds (2 billionths of a second) each year. But that's unaffordable for a receiver like a cell phone. The solution is a very clever trick. The receiver gets a cheap quartz clock that's accurate to only 100 nanoseconds a day.  The trick is to get frequent clock corrections as a by-product of calculating its location. How? 

Let's look at the process in two dimensions. If the clocks on the satellites and the receiver are all correct, the distances (d1, d2 and d3) will be correct and the receiver can calculate its position as the single point where the three circles intersect.  

If the receiving clock is running slow the time lag will be measured as longer than it really is. The calculated distance will be too long, and the three circles will overlap, instead of intersecting at a point. 

And if the receiving clock is running fast, the circles won't touch at all. 

So the magic trick is to shrink or expand the measured circles by the same proportion until they intersect at a point, which is where the receiver is. Then the receiver calculates how much its clock must be running fast or slow, and corrects the clock. Just like magic.

In real-world 3D, distance from a satellite provides a sphere, not a circle. So the calculations are more complicated, but the principle is the same.

One final magic trick

The idea of using geostationary satellites to create a global communication network came not from a scientist, but a science fiction author. In 1945 this author wrote an article for Wireless World  magazine, titled "Extra-Terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?". In the article he discussed technical details of the required orbits, what power and frequencies would be needed. All this was twelve years before the launch of Sputnik, the first artificial satellite. Who was the author? Of course - the author we first pulled out of the deck: Arthur C. Clarke.

16 Jun 2018

The House That Termites Built

Eastgate Centre in Harrare, Zimbabwe 

Eastgate Centre
is a large shopping mall and office center. It stands in the heart of the business district in Harare, the most populous city in Zimbabwe, Africa.

It's a very big building, occupying half a city block. The interior is elegant and modern, with small boutiques on the ground floor and a large interior space with cool fountains, hanging catwalks and steel pillars straight out of a science fiction movie.

Interior atrium of Eastgate Harrare. 

The shopping center is made of two nine-story office towers, which are connected by a glass atrium that lets in the light and keeps out the rain. On the surface, it might look like any other modern mall in the world, but Eastgate has a secret. This is very special building.

Eastgate uses very little artificial air conditioning, compared to other structures in the tropics. The city of Harrare has a high elevation and a temperate climate, with daily temperatures out   

Would you believe it was designed by termites?

Mick Pearce, an architect from Zimbabwe.

Mick Pearce, an architect from Zimbabwe, was the designer of Eastgate Harrare. His style of architecture is based on a science called biomimicry. In science and engineering, biomimicry happens when humans copy the forms and the processes they find in nature: the word literally means "imitating life".
The great architects of the insect world, the mound-building termites

The natural forms that Pearce studied to build Eastgate Harrare were created by some of the greatest architects on our planet: the mound-building termites. 

Mound-building termites come in many different varieties and are found throughout Africa, southern Asia and Australia. They are named for the towering mounds they build out of hardened clay. These mounds can be over five meters tall (25 feet)  and twelve meters in diameter (40 feet), and incorporate many tons of earth. They can be very impressive on the outside...but on the inside, they are even more amazing.

An African termite mound

Termites are hardy insects with a social structure that allows them to cooperate to achieve great things. Their mounds are not just tall and massive but very elegantly built to provide a controlled environment inside, with very restricted temperatures and humidity.

The reason that termites need such a regulated environment is that their lives depend on farming. Underneath the mounds, they grow an elaborate fungus garden, which provides them with nourishment. Although the termites are fairly tough, the fungus garden can be delicate, and needs a regulated temperature and humidity--like the greenhouses that we use to grow fruits and vegetables.

Interior drawing of a termite mound - the fungus garden is in the middle!

In order to provide a stable environment for their farms, the termites have to build a home with a very well-regulated temperature and humidity. The temperature and moisture must never fall below or rises above the conditions that the fungus needs to thrive.

The termites have to achieve this stability in some of the hottest and driest climates on Earth. In Africa and Australia, daily temperatures can soar to 42 degrees Celsius (over 107 Fahrenheit) or drop to below freezing at night. And unlike humans, termites cannot rely on technology to provide them with air conditioning or artificial heat!

Nevertheless, the temperature and humidity inside a termite mound rarely varies more than a few degrees year round. Their fungus gardens continue to grow, and their colonies continue to thrive.

Know your air flow: termite mound versus office building

How Do They Do It?

Both Mike Pearce and the termites begin the building process by knowing their environment. The human architect makes a point of studying the "micro climate" of his future build site, the place where the structure will someday stand.

Pearce gathers information about the daily and nightly temperatures, the rainfall, the path of the sun and the flow of wind and air currents. Termites do the same! Their mounds are often placed to avoid the worst of the direct sun. They use the thickness of the walls to resist heat, and cleverly build channels and chimneys to direct the flow of air through their mounds.

This keeps the chambers where the termites live very comfy! The tropical heat stays in the parts of the mound where they don't spend as much time. The mound has so many clever chambers and channels that it serves as a giant lung, breathing in fresh cool air into the lower levels, and venting hot dry air out the chimneys.

Eastgate Air Flow - how the chimneys work

The walls and chimneys of Eastgate Harrare follow this model. The building uses passive cooling and keeps the indoor temperature stable year round. Eastgate uses almost no air conditioning. The building uses 35% less energy than other buildings in the city, and the lower energy bills makes the rents in its offices less expensive too. It also means that during power outages, the building can often remain open and useful while other buildings must shut their doors!

By not adding a full central air conditioning system, Mike Pearce also saved 10% of the cost of the building, 3.5 out of 35 million dollars.

Mister Pearce learned a lot while building the Eastgate Center. Some of his other projects have been even more successful. One of his buildings in Melbourne uses 70-80% less energy use than other buildings in the city!

A House That Termites Built is much less expensive, and saves millions of dollars in energy bills over time. But perhaps most importantly, it makes a more sustainable future for all of us.


The Eastgate Harrare building is a very interesting place for those who want to build Smart Spaces, human structures which are more energy efficient and environmentally friendly. To learn more about Eastgate Harrare and biomimicry, check these links.

MICK PEARCE - This is the personal website of the architect, Mick Pearce. It has great videos, Powerpoint presentations and essays for students about his work around the world, and about his fascination with termite mounds or "terminaries".

BIOMIMETIC ARCHITECTURE: Green Building in Zimbabwe Modeled after Termite Mounds -
This is an image gallery of the Eastgate Harrare building and the termite structures on which it was based.

Termites, their social organization and their knack for architecture are also really fascinating subjects. To find out more about them, check these links:

TERMITES ARE TEACHING ARCHITECTS TO DESIGN SUPER-EFFICIENT SKYSCRAPERS - This is a quick article in Wired Magazine, but it has quotes from both biologists and architects who study termite mounds and apply their architecture to human buildings to save energy.

WHY TERMITES BUILD SUCH ENORMOUS SKYSCRAPERS - This is an article from BBC Earth, and goes deeper into termite behavior and technology. You also get to read about real termite scientists at work, and how the termites fight back against their intrusions!

COLLECTIVE MIND IN THE MOUND - An article from National Geographic featuring great photos and science about mound-building termites.


Arinn Dembo is a professional science fiction writer and software developer working in Vancouver, BC. She has degrees in Anthropology and Classical and Near Eastern Archaeology, and volunteers as a science educator at Vancouver's The Learnary, where she teaches an ongoing series of workshops called Gothic Science.

15 Jun 2018

Happy Book Birthday!

Post by Helaine Becker

Happy book birthday! June 19th, 2018!

Five years in the works! I'm so excited that Counting on Katherine: How Katherine Johnson Saved Apollo 13, is now available everywhere!

You can see the trailer here.

9 Jun 2018

Snow?!? You've got to be kidding!

Over the past week, parts of Atlantic Canada have experienced one of the features ("It's not a bug, it's a feature!") of a Canadian spring -- June snow. In sympathy with the afflicted parts of the country, including those in the North where the winter's snow still lingers, we present this brief poem by Sci/Why contributor Margriet Ruurs - CE

Whether to Like the Weather or Not

Calm wind, clear sky, nice.
Shifting wind, scattered-cloud sky
Stratus clouds drifting by.
Cold front, sleet and ice.

Slightly drifting, shifting snow.
Freezing rain, snow and squall
I don’t like this at all.
Quick inside! Winter, go!

Photo by Margriet Ruurs

Cumulus clouds climbing high,
Cirrus clouds scatter
Back to sunny, warmer weather
And bright blue summer sky.

1 Jun 2018

Mushrooming in Chile: Canada South

by Jan Thornhill

I’ve just returned from a fabulous mushrooming trip to Chile. Before I left, I joked that I was going to “Canada south” – my simple way of explaining that I would be visiting a temperate country when it would be cold and wet – the best time to collect fungi. Of course I didn’t mean it literally; I didn’t expect Chile to actually be Canada south. But in a lot of ways, 
particularly outside of urban areas, it was. Which was not only disconcerting, but discombobulating.

I've been trying to find a word to describe the strange brain/mind phenomenon that kept happening to me. I'd be looking at a woods before we went in, (there were 26 of us fungi fans), and suddenly I'd be transported for a moment right back to Canada. It wasn't déjà vu, or even déjà vu's little sister déjà visite, the feeling while in a new place that you've not only been in that place before, you know the place. It wasn't that at all. 

The French have a word for another phenomenon, dépaysement, which is used to describe the feeling of not being in one’s own country when travelling, of being out of place, of being uncountrified. As far as I'm concerned, that feeling is the whole point of visiting foreign lands – glorying in the differences between the new and the familiar. But in non-urban parts of Chile, sheltered in the woods and countryside from the culture and language, I kept having the opposite experience – that, in a dreamlike way, 
I was actually in Canada, and not 10,000 kilometres away. Anti-dépaysement.

In those moments of being in Canada cerebrally while at the same time being almost as far away from home as possible, the fun was in the double-takes, when I was suddenly taken aback by one or more details that just weren't right, or that were radically different – and my sudden remembering that I wasn't home would instantly teleport me back into Chile again. It was one of the weirdest and most entertaining things I've ever experienced. I loved it.

Here are some photos I took that might give you an idea of why this kept happening to me.

Near Punta Arenas 

This picture could easily have been taken on a 
Mycological Society of Toronto fall foray...

...except the ground was covered in the TINY 
leaves of Nothofagus – the southern beech...

 ...and some of those trees sported really weird 
mushrooms, like these edible Cytaria.

Torres del Paine National Park north of Punta Arenas

Is that the Rockies? Are those 
animals in the distance deer?

Nope. That's the southern Andes, and the animals 
are guanacos, a type of llama. 

We also saw the very un-Canadian 
Nandu, or Darwin's Rhea.

Banff? The Yukon? 

White foam collecting on the shore?

 Nope. An Andean salt lake. Big salt.

 And flamingos!

Near Puerto Montt

A lovely Canadian fall scene...except 
the trees aren't quite right...

...and some of the nearby flowers are just plain weird...

...and exotic fungi (Aleurodiscus vitellinus
grow in the trees...

...and the tree trunks are submerged 
in knee-deep lava ash...

 ...lava ash so deep it had to be plowed off the highway.

Near Curarrehue in Central Chile

 A typical Canadian fall scene...

...but turn to the left and that's a volcano...

...and turn a bit more and you're back in 
Canada again, except that's a flock 
of parrots landing in a tree.

El Parque Nacional Conguillío in central Chile

Northern Ontario? Quebec?

Not when you pull out and see the lava plain...

...and when you turn the other way you see 
the astonishing amount of lava and lava ash from 
a 2009 eruption of Mount Llaima...

...and only a couple of kilometres down the road you enter 
the other-worldly Araucaria or Monkey Puzzle Tree Forest...

...ancient conifers that are truly weird, and completely 
un-Canadian, though some grow in Vancouver. 

 And, of course, when the clouds finally
move out of the way, there's a giant volcano... 

..and in the scant soil, an orange truffle that no one
in our group had ever seen before...

...that might be an undescribed species.

And of course there was the southern night sky, 
crowded with stars that looked different than 
what I'm used to in the northern hemisphere,  
but the bigness is the same wherever you go.