Improbable Wind (and Other) Propulsion Systems

Can a wind-driven vehicle go straight down wind faster than the wind speed?  Derek Muller’s YouTube channel “Veritasium”, and the image above show Rick Cavallaro’s brilliantly designed “Blackbird” propeller-driven cart.  They say it can be done.  See  and Google, Wikipedia, etc. for more details.  
My intuition suggested otherwise: to ‘sail’ downwind faster than the wind one would need a machine which could first accelerate from stationary up to wind speed – no problem – but then to go faster than the wind, one would have to keep accelerating from that point in time and space where the apparent wind on your craft had dropped to zero.  Sounds impossible!  
UCLA Astronomy and Physics prof. Alex Kusenko, while claiming he has sailing experience, lost a bet of $10,000, as witnessed by Bill Nye and Neil deGrasse Tyson.  Alex claimed it could not be done saying that wind gusts and a higher wind speed at the prop height, rather than as measured at the cart, explained an observed momentarily high cart velocity.  I’m sorry I cannot find any comment on the outcome of the wager from Nye or Tyson. 


Nov 28, 2021.  Deep apologies to all – The following analysis is in great error!  The twist in the drive belt in the Figs. 13 and 16 is reversed and so the conclusions are very wrong.  Revision no. 16 is coming soon.


After much thought I suggest the following analyses might illustrate what is actually happening in a clear manner without resorting to plots of trig functions, etc.

General Physics Principles:

Figure 2

1.  A balloon in a steady wind surely only travels at exactly wind speed and exactly in the wind’s direction.
That great old movie “Around the World in 80 Days” showed a global circumnavigation of approximately 24,000 miles in 80 days (averaging about 12.5 avg. mph).  But did Niven and Cantinflas beat the laws of physics by doing it in (spoiler alert) 79 days, or just over 1% faster than the wind, when crossing the date line was included in their calculations?

Figure 3

2.  A balloon drifting low over a flat desert, in a 10 mph West wind, could lower a wheel-driven electrical generator (G) which could power a tow cart (M) driven by an electric motor.  But due to the second law of thermodynamics (Entropy always increases), and ever-present frictions in the generator and motor, the magnitude of the backwards (Westward direction) drag load of the generator will always be a little greater than the pulling power of the motor towards the East. This would result in our complex balloon actually travelling a little slower than the 10 mph speed of the West wind, showing us that you cannot go downwind faster than the wind, at least when using a balloon, with or without, electrical) propulsion devices. 

3.  Energy is needed to propel a wind driven craft.  Such propulsive force can come from tapping into the kinetic energy available when there is a difference in velocity between the air and the ground (or water).  That velocity difference can come from moving air (wind) over stationary land or water, or from stationary air over a moving body of water (river or ocean stream).  A dramatic example of this by Artemis Racing is shown in:  
where the Amazon River, flowing at 10 mph on a still air day, creates an apparent wind sufficient to drive a foiling catamaran up river (against the current) at 30 mph! 

But I ask: where can one find the potential or kinetic energy difference needed for further acceleration when a craft is travelling straight downwind at 10 mph in a 10 mph wind? 

Sailing Theory 

At age 16 Alen MacW and I canoed the River Shannon and tributaries for a month in a homemade craft, using a bed sheet for a sail when there was wind.  We sadly discovered, as did the square rig sailors of old, that we could not sail upwind at all.  We could sail: 90 degrees across the wind (“beam reaching”); at 45 degrees angle off the wind direction (“broad reaching”); and straight downwind (“running”).  To make any progress in an upwind direction in a canoe or sailboat requires a keel (or centerboard, or a good skeg) and an airfoil section sail.  The Egyptians seemed to have discovered this thousands of years ago with their elegant lateen-rigged feluccas on the River Nile, but they kept the details a secret for a long time. 

The answer to the Blackbird question lies in the application of Bernoulli’s principle

From energy conservation laws: the faster air or liquid moves, then the lower its pressure becomes. For sailing, and flying, you see this principle demonstrated in the use of a curved foil-shape cross-section of a wing, sail, or propeller. 

Figure 4 

Fluids (air, water, etc.) flow faster over the curved top of a foil shape than across the bottom when the flow is laminar, or non-turbulent.  Some think that is so the upper fluid can “catch up” with the slower medium underneath which only had to move a shorter distance across the bottom of the foil.  The faster speed of the fluid on top, perhaps surprisingly, results in it having a lower pressure according to Bernoulli.   See:    and others. 

Including an ‘angle of attack’ of 10 to 20 degrees between the airfoil section and the wind adds the effect of an increase in pressure below the foil to that of the low pressure on top.  In optimum conditions this results in a lift force, red, of greater magnitude than the drag force, blue, shown below. 

Figure 5

A flat surface could be used instead of an airfoil section but it is not nearly as effective – see the flat fan blades on cheap cooling fans: they create noise from turbulence and don’t move the air as efficiently. 

A beautiful and simple demonstration of the Bernoulli reduced pressure lift process is had by delicately suspending a spoon near a stream of laminar flowing (non-aerated) water from a faucet.  Move the spoon towards the stream so that the back of the spoon just contacts the water.  If the water is turbulent it will splash off the spoon and push the spoon away, but when the water flow is smooth and laminar the opposite happens: Bernoulli’s low pressure draws the spoon into the stream.  The spoon’s bowl is strongly ‘sucked’ towards the water, as indicated by the red arrow in the lower photo below.

Figure 6 

This low pressure is what keeps aircraft aloft, allows sail boats to sail upwind, and lets ice yachts travel at high speeds (up to at least 5 times the wind velocity!). 

Sailing Downwind Faster than the Wind 

Using known values from existing high performance craft let us look at the details of an ice yacht, land-cart, or foiling catamaran, blue triangle in the diagram below, speeding along on a NE broad reach at about 25 mph, or two and a half times faster than the wind, in a 10 mph West wind, white arrow.  
The following diagrams use Vectors (arrows) to illustrate, by their length and direction, the magnitudes and orientations of wind speeds, forces, and boat speeds: 

Figure 7

The velocity vectors above show that even though the sail only ‘feels’ an apparent wind of about 19 mph from the NNE, the ice yacht is traveling at a speed of 25 mph. 

The wind force vectors on the sail are shown below.  The red arrow (vector) is the resulting force from the apparent wind acting at right angles to the center of the sail.  It can be resolved into a lateral force (blue) to the SE resisted by sharp skates on the ice, wheels on the sand, or a keel in the water, plus a forward driving force (green) which propels the craft to the NE. 

Figure 8 

The velocity vectors below show that when the craft is travelling to the NE at 25 mph, it is making progress due Easterly, straight downwind, at about 18 mph, or about 8 mph faster than the 10 mph West wind, (and at the same time it is making similar progress Northward at 18 mph). 

Figure 9 

But, of course, if the fixed-sail craft itself tries to sail straight downwind then the sail will stall and the Bernoulli effect will no longer apply.  With a stalled sail it becomes like our earlier balloon and could only travel due Eastward at close to 10 mph at most. 


A Thought Experiment

To address the main question of how to sail straight downwind faster than the wind let us imagine a (triangular shape) land cart, heading due East on the flat desert floor, with a steady 10 mph West wind blowing.  On this cart we have a hypothetical horizontal supporting beam, blue line, with a track mechanism holding an ice yacht sail (same as the one used above) vertically on a sliding track which allows the mast and sail to be moved laterally in a North-South direction relative to the cart axis.  If the sail is moved to the left, on the cart, at a speed equal to the forward speed of the cart then the sail ‘feels’, for a few moments, the exact same wind, force and direction, red, as the ice yacht sail felt, with its fixed sail, when it was travelling to the NE, in the previous case. 

Figure 10 

An observer looking down from a balloon above would see, for a few moments at least, the sail moving in exactly the same direction as the ice yacht’s sail, and therefore generating the same lift and drag vector forces. 

Figure 11

The picture above shows the initial position of the cart (in blue, left) with the sail amidships.  The later position (green), shows the cart a few moments later, moving to the right (Eastward) and with the sail moving left (Northward) on its track, while the sail traverses a NE path over the ground. 

The net driving force on the land yacht will be somewhat less than that of the ice yacht because of the energy needed to move the sail on the imaginary track.  

Rather than having the complex imaginary supporting track for the mast why not let the sail simply be a blade of a propeller?  As this propeller revolves around its horizontal fore and aft axis the airflow will be very similar to the sails in the two cases above.  By considering a short period of time we can ignore the small change in tilt angle of the sail as it rotates in its new propeller-like configuration.  As the propeller blade rotates through its upper quadrant our overhead viewer would once again see air flowing over an airfoil similar to both the ice yacht and sand cart examples above.   Add a second blade to the prop so while the upper blade is behaving as shown above when in the top quadrant of its rotation, the other blade is in the lower quadrant and supplies a similar Eastward direction driving force, but with an opposite direction (Northward) lateral force. 

As the professor so often says, “I leave it to the student to resolve the details for the prop blades when they are travelling through the side quadrants (3 o’clock and 9 ‘-clock)”.  The answer is simple: when the prop blade (sail shape) is travelling up or down, through the side quadrants, the resultant horizontal forces will similarly drive the craft forward, while the lateral vertical drag component, upward or downward, subtracts from or adds to the craft’s weight on the ground. 

So now we can have a real cart going straight downwind (due East) at 18 mph with a propeller whose sail-shape blades move across the wind in a very similar manner to that of the fixed sail of the ice yacht travelling at 25 mph in a NE direction, in the same 10 mph West wind. Even though at 18 mph Eastward cart speed the apparent wind at the land cart body is 8 mph against it from the East, the propeller blades are still ‘feeling’ an appreciable, and useful, apparent NNE wind. 

The propeller is turned towards the apparent wind by the belt drive connecting the prop shaft and the wheel axle.  The drive force from the propeller provides a forward push to the top of its supporting mast, in the same manner that an airplane’s propeller ‘propels’ an airplane forward.  The forward movement of the cart over the ground drives the wheels which turn the axle and puts tension in the belt to turn the prop. 

An ice yacht, having the least drag resistance (from its skates) to forward motion of the three craft types considered, should have the greatest velocity of the three craft types considered here.  A foiling catamaran, with a similar sail, should be the next fastest given that the drag of the foils through the water would be greater than that of sharp skates on ice.  Our land-cart has low rolling resistance but it does have to supply energy from the rotating wheels to turn the prop against the apparent wind and so could be expected to have the slowest vehicle velocity of the three. 

The magic of the Blackbird rotating propeller is that the blades can ‘feel’ an apparent NNE wind of about 19 mph even though the craft is running straight downwind, Eastward, at 18 mph in our 10 mph West wind.  Note that the ice yacht and foiling cat, with their fixed sails would feel a direct head wind if they turned straight downwind and so they could never find the power needed to sustain their speed. 

But can the Blackbird propeller generate enough forward drive power after overcoming the drag of the drive belt on the wheel axle which has to rotate the propeller against the apparent wind?   Work done is the force multiplied by the distance moved.  For the ice yacht the lateral force is simply resisted by the skates on the, with no ‘distance’ moved on the ice and so no work is done. But in Blackbird work is done equal to the distance the prop is moved against the drag of the wind.  The solution lies in the force vector diagram, Figure 10 above, which shows the driving force, green, is greater than the blue drag force when the vehicle is travelling at 25 mph.  The details of Blackbird operation in the pages below show the drag force, blue, meeting the drive force, green, in the drive belt.  As long as the magnitude of the drive exceeds the magnitude of the drag the craft can continue to accelerate. 

 Can Blackbird function in Zero Apparent Wind? 

The thought experiment above reasonably demonstrates how Blackbird can travel straight downwind faster than the wind, but to get to that velocity, if it is travelling in a straight line, and starting from a standstill, it must first accelerate from zero speed to the velocity of the wind, and then exceed it.  If the wind is 10 mph from the West then when the Blackbird has reached a speed of 10 mph to the East there will be zero apparent wind velocity as measured on the cart.  How could the propeller mechanism create a drive force in zero apparent wind?  A closer examination is needed of the cart and its operation while it accelerates straight downwind, starting at zero velocity. 

Step by Step Detail from Zero to Twice Wind Speed Straight Downwind in a Prop Driven Land Cart 

The cart’s propeller blades are continuously pitch-adjusted, by the sailor, to an angle of attack of about 20 degrees to their apparent wind to optimize the Bernoulli lift effect.  

  1. The sketch below shows a 10 mph West wind with about 1 mph Eastward cart speed.  An apparent West North West wind, light blue arrow, is felt by the rotating prop. The resulting wind force, red, on a single blade of the prop (black cross section) drives the prop around, and drives the cart forward. The wind force shown can be divided into two component parts, or vectors, (green and blue) in two different directions, at 90° to each other.

                        Figure 12

Figure 13

The green arrow shows the drag force component of the wind on the prop pushing it against the bearings in a hub at the top of its support mast (not shown). This green arrow force is countered by an equal and opposite direction force at ground level against the drive wheels, making them rotate. The blue arrow shows the lift force on the prop, in this case driving it ccw (when viewed from behind) around its axis.  That force pulls the aft side of the drive belt up adding to the forward driving torque on the axle 

 With the cart at slow speed the wind turns the prop and propels the cart downwind, like a balloon, whether there is a drive belt or not, up to a speed approaching that of the wind, but no further. 

2.  At about 5 mph cart velocity the propeller blades are turning  with a velocity of say 5 mph at the middle point of each blade as they are driven by the wind and the belt from the wheel axle, assuming a 1 to 1 drive ratio.  The apparent wind felt by the blade in the upper quadrant will be coming from NW. The prop pitch angle is adjusted to keep laminar flow over the blade as the cart velocity increases. 

At 5 mph speed the cart is still being accelerated.
Figure 14 

3.  When we reach the very interesting speed of 10 mph the land cart’s propeller generates more thrust. The center of each blade is travelling in a vertical North-South plane at the same 10 mph speed.  This gives an apparent wind on the blade from the North of about 10 mph while it is passing through the top quadrant of its circular path, even though the apparent wind velocity on the cart body is zero!  Note that the blue drag force vector is now colored blue because it has reversed direction and is working, through the belt action, against the green drive force (now colored green).
 Figure 15

Figure 16

It is worth examining this step in more detail as the conundrum centers here where the apparent wind on the craft body is zero and a reason for its continuing acceleration must be found. 

To drive the cart there must be an available source of energy. This can be found when there is a velocity difference potential between two locations.  While there is no velocity difference available between the 10 mph wind and the cart body moving at 10 mph, there is a spot at the middle of the propeller blade (moving around the prop axis at about 10 mph) where there is a velocity difference of about ph between the resultant apparent N wind and the blade, see Figure 15.  Tapping into this potential creates lift, and drag, on the propeller.  As long as the lift force is greater than the drag there will be a net drive force available to push the craft forward and accelerate it. 

4.  At 15 mph craft speed to the East, the nose of the land cart feels an apparent wind of 5 mph from the East.  This starts to create drag resistance.  

 Figure 17 

But each blade of the rotating propeller feels a stronger wind, say about 16 mph (from the NNE for the blade passing through the top quadrant) and supplies a greater forward thrust (green) than the drag (blue) so the craft can continue its acceleration. 

5.  At say 25 mph cart velocity, the apparent wind on the prop moves more towards the East, the wind drag (blue arrow) of the propeller increases until it matches that of the forward thrust of the propeller (green arrow) and the craft no longer accelerates. 

 6.  If the wind strength were to increase above 10 mph then then the West wind vector would lengthen. This would cause the apparent NW wind on the prop to move more towards NNW. With the prop pitch re-adjusted a new drive force greater than the drag could result in new acceleration.

 Figure 18

  Other Thoughts 

Could there be a way to exploit the power generated by the wheel driven propeller in zero wind seeing that this was almost done when the apparent wind on the cart was zero in the 10 mph example above? 

Towing the cart Eastward at any speed, in a zero wind velocity, and then releasing it, at first sounds similar to the above situation of 10 mph cart velocity Eastward in a 10 mph wind from the West.  But plotting the vectors quickly shows the apparent wind on the prop now comes from the NE.  With a 20° angle of attack the forward drive vector to the East, green arrow, is much smaller than the lateral drag force Southward, blue arrow, and so when they pull the drive belt in opposing directions, the craft will quickly come to a halt.
Figure 19 

 It would be interesting to see what speeds Blackbird could attain as it started to turn towards the wind.  I have since read that Cavallero did alter Blackbird a little – he widened the axle for stability against the torque of the propeller- and reportedly travelled straight upwind at twice the wind speed.   


  Other Unlikely Propulsion Methods:

 1. Straight downwind sailing, faster than a very low wind velocity, can be done on flat water, by experienced racing windsurfers who vigorously ‘pump’ the sail back and forth.  But this is adding energy (human) from an exterior source and cannot be accepted in our case. 

2.  I remember clearly, about 45 years ago, looking with my young son at our first skateboard on the smooth varnished floor of the Algonquin Island clubhouse and wondering if there was any way it could be propelled without putting one’s foot to the ground.  I erroneously concluded that was impossible, but not long later others showed us how to do it with a “tic-tac” motion, pumping the board forward by twisting it back and forth, while simultaneously popping the front wheels forth and back. 

3.   Perhaps the hardest is to levitate oneself by standing in a bucket and pulling up on the handle (which principle may come to mind when you first hear of the Blackbird story).  But even that improbably could work, at least momentarily, by performing an energetic series of hops.  Or have I just invented a ‘Pogo Bucket’?

4.  In my year (1965) of wandering through India I did watch out for the infamous rope trick and actually met these great characters who appeared as though they might be keepers of the secret:
 Sadly I never did see the rope trick performed. 

 5. I close with my disappointment in the late but brilliant magician Doug Henning who long ago told us from the stage of Ryerson Theater in Toronto, on his return from visiting the Maharishi Mahesh Yogi in Switzerland, that he would soon be genuinely levitating.  He failed to truly do that. Photos similar to the one above were created by the Yogi’s followers bouncing on trampoline-like devices.  Doug tragically died too young of a liver problem which he falsely believed (according to Wikipedia) could be cured by his faith in the Maharishi’s “Transcendental Meditation” methods.




Sea-Bee  (OH-10)
V15  2021/11/05 

Flying Feats

Look closely at the winged creatures around us and you’ll see many have extraordinarily athletic abilities, some of which we are trying very hard to copy with the latest mechanical drones.  Did you see the amazing formation flying, amid the regular fireworks, of lights carried by perhaps more than a hundred drones at President-Elect Biden’s victory speech on Nov 7?


Last season’s Eagle nest, nearly ½ mile away to the North on Audubon Island, is gone.  It was good for at least two years and two sets of young birds, but now it is nowhere to be seen.  We last saw it on May 1st when the leaves opened and hid it, with the two young ones who were almost ready to fly, from our view:

The tree is bare now in November and with the summer leaves fallen we can see that the nest has gone without a trace.

To our great good luck the parents seem to have decided to give Garden Island, just 150 yards away, another try. An effort there 2 or 3 years ago failed miserably.
This time, in just one month, they’ve built a nest up from nothing.  Seems that one (the male?) collects a branch in less than 5 mins and brings it back. The other (the female?) then repositions it, while he’s gone looking for another stick.  (Everyone know that men can’t properly load a dishwasher!).

The eagle prefers branches directly from a tree. (A few years ago I temptingly laid out a dozen good branches on the river bank and none were taken by any nest builders.)  Occasionally the bird clasps a tree branch which won’t break off and he is left dangling precariously, upside-down.  I was lucky enough to have the camera (iPhone) running when he came to the walnut tree right outside.  Look carefully and you’ll see the eagle first snaps off a twig.  Could it have been testing the wood to see if it was brittle enough to break easily?  If so, then the answer was ‘yes’ – he jumped onto and grasped the branch which broke under his 10 to 14 lb. weight, dropped, spread his wings and flew back to the nest.
The new nest is holding up well even though there was a 37 mph wind this week:


Other very fine fliers are the Big Brown Bats.  Twice this summer they crept into the house through a very small hole under the balcony screen door.  Alice and Pinot quickly tell us we have an early morning visitor:

I close all doors but one, leaving a rectangular loop for their flight: down the corridor, through the bedroom, and into the other end of the corridor.  At one end of corridor the balcony door is open, but at that point they are turning on their circuit.  No combination of indoor and outdoor lights on and off will induce them to turn the other way and leave.

Alice watches it fly round and round, never bumping into me or the walls, until we are all exhausted and a bat finally lands on a wall.

At that point you can easily pick them up in a towel and take them out before Pinot closes in.  I know: I should wear gloves and a bee suit, but it is 3:00 am.  The good news is I can see no sign of the ‘white nose syndrome’ which is badly hurting so many bat species.


A beautiful late summer sight is the vertical flight of a bunch (sometimes hundreds) of miniscule gnats who swarm on a warm evening, presumably in a wild mating dance?  Also hard to photograph, but watch carefully and you’ll see individuals rising and falling.  Even a gust of wind only temporarily disturbs the flying formation.  How do they navigate?  Pheromones may be attracting them back to the spot, even though wind must surely carry away any scent.  How do they navigate in 3D?  I never see them bump into each other.


One day on the Portage River we found a 2D version of the 3D gnat swarm.  These magnificent water striding bugs were having their pre-start maneuvers to a regatta like no other.  Turning and swerving, hardly making a dent on mirror smooth water, they somehow gain traction for accelerating and braking without penetrating the surface tension skin of the river.  I switched the movie to slow-motion but can hardly see a ripple in the water from their feet.  What is their rhyme or reason?  Perhaps they’re just having fun?



Thoughts from Totality or Seeing the Only Star We Can Truly ‘See’

The Solar Eclipse of 21 August 2017

Starting at 5:00 a.m. we drove South: 415 miles in 8 hours. Two days before Google Maps had said it could have been done in 6 ½ hrs. (without the Eclipse traffic).  We used Google Maps to tell us how bad the traffic jams were, and to watch the developing Infra-Red and visible satellite view of the sky so we could attempt to avoid clouds at our destination.

– there was disturbed weather (colored areas on the map above) to the West of our path but we found a lovely little public park in Bowling Green KY, just 6 miles inside the totality path and just short of the Tennessee border (a white X marks the spot in the map above). They were having a very friendly eclipse party there and happily had room for us on the grass and under the trees.  That was fortunate because the highway police were making great efforts to prevent people from stopping on the hard shoulders of the interstates.

The eclipsing moon was just starting its path across the sun when we arrived under clear blue skies.  As during the annular eclipse I’d seen decades ago in Toledo, I once again felt slightly uneasy as an ever increasing greyness of the sunlight became more apparent.  It was like someone very slowly sliding a dimmer switch to our prime source of light (and life), but with a steadily increasing speed.  The change in light quality is very different from that in our daily sunsets.  The typical evening setting sun has a warmth to its reducing light.  During the eclipse there was a coldness to the illumination as it dimmed – I tried rubbing my eyes to fix it.

The easiest watching tool was my bird spotting scope on a tripod.  A science school teacher from Illinois took over focusing and tracking the moving image on a white screen, while I worked on mirrors and cameras:

My straw hat made more pinhole images on my collar and on the telescope screen when I looked down on it:

The ‘pinhole mirror’ was a 3 inch (75 mm) square sample of one quarter inch (6 mm) thick front surface mirror: 80% reflection Pilkington Mirropane™. It has incredible float glass optical flatness.  Taping over half the sample provided a bright reflection light to allow easy steering of the mirror, while the exposed 1/16 inch (1.5 mm) top left corner of the taped half, provided a ‘pinhole mirror’ image alongside – all it needed was a screen.

The smaller the pinhole – the sharper the image, but also the fainter.  The further back the mirror is from a white projection screen – the larger the image, but the harder it is to hold the mirror steady.
(Next time I should put the mirror on a pan/tilt head on a tripod, and incorporate an operating iris diaphragm, if I can find one).

Both images attracted lots of attention as the light inexorably dimmed.

Meanwhile John Muggenborg in Brooklyn (see Muggphoto on Instagram) had amazing results with his similar front surface mirror, just under one inch square.  He had the great idea of fixing the mirror 200 feet (50 meters) away and shifting his screen to track the moving image.  His screen was a beautifully effective open box, dark on 4 sides and white at the back:

Susan spotted Venus brightly shining even though the sun was only about 90% covered at the time (near the top right corner in the photo below):

And in the lobby of his Vancouver apartment, Keith projected an image from his small front surface mirror sample, with a hole in a piece of paper over it to reduce the aperture, onto a screen to delight the residents and guests.

Then with an alarming suddenness, and no sound from the sky (apart from people’s cries in the park), the sun went out!

The Corona was too dim to see through the very dark eclipse glasses, and yet it felt too bright to try my binoculars to search for corona details.  Rushing with camera and iPhone camera in manual overdrive to try to get an appropriate exposure at full 20 x zoom using new add-on lenses, while dripping sweat on the equipment, I did get the following with full zoom on a Canon G-10.

The corona was too bright to see details.  It looks much better in digitally enhanced images as in the APOD site:

In the excitement I forgot to look through polaroid filters but doubt they would have shown anything.

One minute, 10 seconds later into the darkness, a diamond ring burst into view with a startling brilliance – it was the way kids might think that diamonds should appear if all the advertisements were true – the ‘stone’ in the ring was bright as an arc welders spot.  You could not look at it even if you tried.

My iPhone could only get:

I don’t seem to have burnt out any receptors in the iPhone but it must have been close!

Then 90 minutes of slow and steady return to the sky we once knew.


So we clearly saw that the overhead sun, and the moon, are truly circular and most probably spherical.  Our sun is the only star we can truly ‘see’, meaning whose shape we can ‘discern’ or ‘discriminate’.  All the other stars in the sky are so far away that their images, even through the best telescope, do not even cover ONE pixel in a camera.

The popular images of star fields seem to show big, medium and small size stars, but those images are ‘false news’.

The big, bright white circles are simply relatively close stars (more than 30,000,000,000,000 miles (5 light years) away).  The reason we see them ‘big’ in the camera is that their light is so incredibly bright that even though it is only shining on part of one pixel receptor, it reflects off it and overexposes many pixels around it.  (And, of course, the horizontal and vertical ‘spikes’ coming off the brighter stars are telescope reflections/refraction side effects and don’t really exist!)

So we cannot say for sure, from observation at least, that stars (other than our sun) are not square ﬦ , triangular Δ, or even star shaped   ҉ . . But now we have seen our overhead sun to be circular ⃝    and from some elementary astrophysics we can now safely assume that most stars really are spherical!


Spare a thought for the exoplanet hunters. They use this eclipsing method we just saw, along with others, to find planets around distant stars.  But the geometry never allows for ‘totality’ to be seen from distant earth, so those astronomers must work with only a very faint effect of partial eclipsing.

Perhaps my biggest surprise was that before the occulting moon had fully moved out of alignment with the sun, the very friendly eclipse watchers in the park packed up and drifted off – like leaving a great movie before the credits have even played.

We waited for the credits to roll, or the bloopers to play (none did), ate the strangest BLT ever for dinner and then joined the crowd for the drive home.

Well, if the traffic was heavy as people converged over 2 days on the 100 mile or so band of totality across the country, when the show was over, they ALL went home at once.  Google Maps traffic showed a wonderful screen of a network of red lines (choked roads) heading North and South away from the East-West path of totality.  Sadly we were too emotional to think of taking a screen-shot but Leslie and Glen, watching their syzgy just a little South of us in Tennessee did get one of the ‘eclipcalyptic’ traffic (Thank you):The drive home took 9 hours, but we’ve already started making plans to watch the next one!