# The Last Total Solar Eclipse…Ever!

Well…The answer is 700 million years from now, but the details are interesting!

Since the dawn of recorded history, humans have had a love-hate relationship with total solar eclipses. For most of human history, these events were feared and taken as omens of the downfall of empires or the end of the world. Only in the last thousand years or so have people settled down and viewed them as the beautiful and bizarre events that they are. By the 19th Century, scientists and artists traveled the world over to capture them with sketches at the telescope eyepiece. Among the first images taken by primitive cameras were those of total solar eclipses.

Predicting total solar eclipses

Today, the physics and mathematics of these events are known with such detail that they can be predicted to within minutes from 2000 BCE to 3000 CE [1]. They can even be used to track the slowing down of earth’s rotation by comparing the predicted time and place with historical observations [2]. But total solar eclipses require a precise geometric circumstance to exist. Our moon has a diameter of 3,475 km at a perigee distance of 363,300 km, while the sun has a diameter of 1.4 million km at a distance of 150 million km. This means that, although the sun has a diameter that is 403 times the moon, it is 412 times farther away so that the apparent size of the dark lunar disk completely covers the blinding disk of the sun in the sky. Depending on the exact timing of the moon in its orbit, this ratio of 403/412 can be made to be exactly equal to 1.00 so that the disk of the moon exactly covers the sun to give the classic total solar eclipse shown in the picture above. But this precise geometric circumstance is not written in stone. In fact, to get a proper prediction far into the fiuture you need a supercomputer!

Earth orbit evolution

Currently the distance from earth to the sun has an average value of 150 million km, but because Earth’s orbit is an ellipse, it varies from 152 million km in July to 147 million km in January. This leads to the ironic circumstance that in the Northern Hemisphere, the sun is actually farthest away from the sun in the summer and closest in the winter! Only the Southern Hemisphere with its reversed seasons gets it right!

For many decades, researchers have modeled the evolution of the orbit of the Moon and Earth with supercomputers and pretty much nailed down what we can expect to happen for the next few billion years. As it turns out, this is a fiendishly difficult calculation because it depends on an exact knowledge of the interiors of the moon and earth, the location of the continents, and the influences of the other planets. The inner solar system is dynamically unstable and displays a chaotic behavior over times of 100 million years or longer. A consequence of this is that even changing the location of Mercury in its orbit by 1 meter today causes a variety of different outcomes in a billion years including its collision with Venus and ejection from the solar system. Earth, however, seems to exist in a remarkably stable gravitational balance such that its orbit changes only insignificantly from what we see today. [3] It will drift outwards from the sun by a few thousand kilometers due to the sun itself losing mass. The sun converts 4 million tons of mass into radiant energy every second and added up over millions of years, this causes the sun’s gravitational hold on Earth to weaken and its orbit to drift outwards by 1.5 cm/year [4].

The outward drift of Earth in its orbit is entirely negligable so we won’t bother including it. We will assume that the average perihelion and aphelion distances will still remain close to 147 and 152 million km. This means that from Earth the angular diameter of the sun from the surface will vary between 1,964 seconds of arc at perihelion to 1,900 seconds of arc at aphelion, where 3600 seconds of arc equals 1 angular degree.

Lunar orbit evolution.

We know from geologic data that our moon was formed some 4.4 billion years ago and orbited Earth at a distance of only about 30 Earth Radii ( 190,000 km) causing Earth to have a rotation period of about 12 hours in a ‘day’. [5]. Since its formation, it has drifted out to its present distance at a current rate of about 3.8 cm/year based on lunar laser metrology [6]. But this outward drift continues today so that in the future the moon will be even farther from Earth. This means that at some time in the future, the ratio of lunar:solar size and lunar:solar distance will fall below the magic 1.000 needed for a total solar eclipse. The moon will simply be too small in apparent size to perfectly cover the disk of the sun. We can’t predict the exact date when we will see the very, very, very last total solar eclipse from Earths surface, but we can get a pretty good idea what timescales are involved.

Simple Linear Model

Suppose we just used the current perihelion and aphelion distances and then assumed that the moon is moving away from Earth at a constant rate of 3.8 cm/year. If we calculate the angular sizes of the moon and sun from Earth we get the following figure.

Explanation: The orange line is the angular size of the sun viewed from Earth when Earth is closest to the sun (perihelion) and the yellow line is the same calculation from when Earth is farthest from the sun (aphelion). The black line is the angular diameter of the moon at its farthest distance from Earth (apogee) and the green line is for its closest distance to Earth (perigee). What you see is that the lunar curves cross the solar curves and indicate when these two diameters are equal, allowing a total solar eclipse to be viewed. So long as the solar lines are between the two lunar lines, you will have a total solar eclipse.

What this graph says is that 1044 million years ago, the sun at perihelion matched the moons size at apogee when it had the smallest angular size. After this ‘year’ the moons size at apogee was too small to cover the sun at perihelion and so total solar eclipses at lunar apogee ceased to happen when the solar disk was largest at perihelion. Notice that before 1044 million years the lunar lines were above the solar lines. This means that the disk of the moon was always much greater than the disk of the sun at any time in the lunar orbit. In fact, the lunar disk was so big that not only was the disk of the sun covered by the moon but much of the inner corona too. You would still have total solar eclipses before 1044 million years ago, but they would look dramatically different than the ones we see today.

By the time we get to 710 million years ago, the moon at apogee was also too small to cover the sun at aphelion when the solar disk is smallest. Between 1044 and 710 million years ago, the small apogee moon could still cover the sun when the sun was between aphelion and perihelion, but after 710 million years ago, there would never again be a total solar eclipse of the sun when the moon was at apogee. This was before the emergence of multi-cellular life on Earth during the Cambrian Explosion. Only annular eclipses will be viewed from then on during lunar apogee.

Now the second lunar curve in green is more interesting. It shows the angular size of the perigee moon, and it is pretty clear that today (Time-0) the size of the perigee moon is larger that the sun at both perihelion and aphelion. So we get total solar eclipses no matter if Earth is at perihelion or aphelion. However, by 280 million years from now, the moon will start to become smaller than the solar disk at perihelion and so eclipses will stop being total solar eclipses when the sun is closest to earth and the moon is also closest to earth. After 613 million years from now, you will no longer have total solar eclipses for the perigee moon and the smaller aphelion sun. After 613 million years the lunar disk will never again be big enough to completely cover the solar disk. This is the estimate you are likely to find in many popularizations of this Final Event such as a SpaceMath problem at NASA, and NASAs lunar scientst Dr. Richard von Drak.

A More Accurate Calculation.

The previous linear calculation was based on the moon maintaining its outward 3.8 cm/yr motion for the next 600 million years, but detailed supercomputer calculations of the evolution of the Earth-Moon system give a more accurate result. I used the model published in 2021 by Prof. Houraa Daher and her team at the University of Michigan [7], and specifically used their Figure 5a, which gave the past value for the lunar orbit semi-major axis. I also used the 2020 data from the published work by Dr. Bijay Sharma [8] at the National Institute of Technology in India, specifically Figure 7, which gave the recession speed (cm/yr) with lunar semi-major axis. Ideally, both of these data should be derived from the same calculations but unfortunately this was not possible to obtain at the time of this writing. However, if they are both faithful to the same underlying physics, then the results should be consistent.

The application of these detailed models to the lunar size evolution is shown in the next figure.

The straight, linear extrapolations have now been replaced by more realistic curved predctions. Here we see along the black line that at 700 million years ago, the lunar size at apogee matched the solar disk size at perihelion (1952 arc-seconds) , some 300 million years later than the linear model. By 500 million years ago the apogee lunar disk no longer covered the disk of the sun at aphelion, so from this time forward there were no longer any total solar eclipses when the moon was at its farthest apogee distance. This happened around the time of the Cambrian Explosion.

Meanwhile, the green line for the perigee moon shows that it has a disk size greater then the size of the large perihelion sun (1952 arcseconds) disk until 300 million years from today. At this time, the lunar diameter varies from 1718 arcseconds (black line) to 1952 arcseconds (green line) so we can still have total solar eclipses so long as the moon is close to its perigee when the sun passes through one of the lunar ‘nodes’ during the equinoxes. At about 700 million years from now the large perigee moon with a diameter of 1952 arcseconds covers the sun at perihelion, but after this time, its diameter continues to decrease until from this time forward all we ever see are annular eclipses. So this critical ‘date’ is about 80 million years later than the linear model.

By 700 million years from now, the moon will continue to drift away from Earth, but at a slower rate of 3.0 cm/year. Its distance from Earth will have grown from 60.2 Re (384,400 km) to 63.8 Re (407,155 km). The moon will then take 28.4 days to orbit Earth having gained about 26.4 hours since today. This means that the time between one full moon and the next will be 30.7 days instead of the current 29.5 days. Meanwhile, the Earth’s rotation has changed from its current 23h 56m to about 26h 25m as the lunar tides continue to do their work. What this means is that an Earth Year at 700 million years from today will only about 330 days long!

Will there be anyone there to care? Probably not.

Our sun continues to evolve and grow in luminosity so by then it will be about 10% more luminous than it is today.  This means the average global temperature will be 117o F and not the 57o F we enjoy today. By this time, the level of carbon dioxide will have fallen below the level needed to sustain C3 carbon fixation photosynthesis used by trees.  Some plants use the C4 carbon fixation method to persist at carbon dioxide concentrations as low as ten parts per million. However, the long-term trend is for surface plant life to die off altogether. The extinction of plants  will be the demise of almost all animal life since plants are the base of much of the animal food chain on Earth. Climate models suggest that by about this time Earth will be hot enough to cause the slow evaporation of the oceans into the atmosphere. This will be the start of what is called the “moist greenhouse” phase, resulting in a runaway evaporation of the oceans and Earth becoming Venus.  Meanwhile, the current continents will have merged and separated and merged again into yet another supercontinent with its own lethal contribution to global heating and weather [9].

So basically by about 700 million years from now, Earth will be a humid, desert world with no complex living organisms to appreciate total solar eclipses except perhaps extremophile bacteria…and cockroaches?

Have a nice day!

[1] Five Millennium Catalog of Solar eclipses https://eclipse.gsfc.nasa.gov/SEcat5/catkey.html

[2] Ancient eclipses Reveal How Earths Rotation has Changed https://www.space.com/ancient-eclipse-records-earth-rotation-history

[3] Highly Stable Evolution of Earths Future Orbit Despite Chaotic Behaavior of Solar System https://iopscience.iop.org/article/10.1088/0004-637X/811/1/9

[4] https://www.forbes.com/sites/startswithabang/2020/04/09/earth-is-spiraling-away-from-the-sun-for-now-but-will-eventually-crash-into-it/?sh=863220238580

[5] Long-Term Earth-Moon Evolution With High-Level Orbit and Ocean Tide Models https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006875 figure 6

[6] The moon has been drifting away from Earth for 4.5 billion years. A stunning animation shows how far it has gone. https://www.businessinsider.com/video-moon-drifts-away-earth-4-billion-years-2019-9

[7] Long‐Term Earth‐Moon Evolution With High‐Level Orbit and Ocean Tide Models, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9285098/

[8] The Past, Present and the Futuristic Earth-Moon Orbital-Global Dynamics – and its habitability – https://www.proquest.com/openview/c945a68d9b4a2354aaea7cf859b776ba/1?pq-origsite=gscholar&cbl=4882998

[9] What if You Traveled One Billion Years into the Future? https://whatifshow.com/what-if-you-traveled-one-billion-years-into-the-future/

# Math Anxiety: Origins and Cures

Someone asks you to perform a simple arithmetic calculation, or perhaps you encounter these while doing your income tax. As a consumer you might want to compare the cost of two products with different sales prices. Or perhaps the tags give  you the same product by two different manufactures who tell you the unit cost, but the products are  in either 12-count or 18-count packages. The odds are very good that along with millions of other adults you will have some trepidation in ‘doing the math’. That’s because math anxiety (MA) is endemic not only among US adults but around the world. It crosses ethnic groups, cultures and continents. According to a recent study of MA[1] 93% of all adults in the US suffer from some level of this condition; internationally and across many cultures, this incidence can be over 40%.  It is reinforced by parents, the news media, and even by teachers using outdated pedagogy– all with devastating consequences, long-term. Like ADHD, you can find yourself somewhere on the Math Anxiety Spectrum. Your location might even change as you advance from childhood to adulthood.

The evolution of our brains over millions of years has prepared it to do many kinds of math but often at an unconscious level. We, along with thousands of other species, have an innate ability to compare quantities and figure which is larger. Some species can even count including chimpanzees, crows, bees and frogs[2]. Our brains come hard-wired at birth to understand addition and subtraction. There are actual brain neurons in the parahippocampal cortex that are only active during addition while others are only active during subtraction[3].They also respond when the instruction is written down symbolically as a word or a symbol (five and three  or 5+3).

The number of brain regions involved in mathematics performance reads like a catalog of nearly half of the cerebral cortex itself. This means that many of these math-activated regions are also used for other purposes in the brain. This is a common feature of brain architecture in that regions are recycled to form other neuronal networks depending on the task at hand.

• Dorsolateral prefrontal cortex
• Left inferior parietal lobe
• Left precentral gyrus
• Left superior parietal lobe
• Left supramarginal gyrus
• Left middle temporal gyrus
• Insula
• Middle cingulate cortex
• Middle frontal gyrus
• Superior temporal gyrus
• Inferior frontal gyrus
• Thalamus
• Bilateral intraparietal region
• Dorsal prefrontal region
• Inferior temporal region

As a brain matures, these regions respond to external experiences but are always influenced by innate survival instincts provided by the limbic system composed of the thalamus and the amygdala. When no previous  negative experiences trigger a limbic response for fight-or-flight, all is well.  Even by the age of 7, children still have an enthusiastic and playful attitude towards math. This attitude unfortunately starts to wane in direct proportion to the number of negative performance tests they experience, which is why MA arises.

A common view shared by many MA students is that, unless I can do math quickly, I must not be very good at it. This is also a pervasive attitude among adults who, despite performing well in grade-school math may still not see themselves ‘good’ at math. Math skills are unlike reading skills because there has evolved over time a massive social permissiveness to being a poor math performer that simply  isn’t found in other academic topics.

Thanks to advances in brain research and mapping, we have a ring-side seat into what brain regions and neuronal circuitries are responsible, not only for handling mathematical problem-solving of increased sophistication, but how this process maps into generating anxiety. There is even a specific brain protein called MAOA that correlates with MA and can be used to spy on your emotional state as you are confronted with different problems.

Math comprehension and execution, like our language centers (Broca and Wernicke Regions) are activated primarily in two main regions: The parietal lobe is involved with calculating and processing numbers; The frontal lobe is involved in recalling numerical knowledge and working memory[3].

The sub-region called the dorsolateral prefrontal cortex is most curious because it is also activated as we regulate our emotions. For example, most children learn how to tone-down their glee at winning a game when they see their friends are mortified at  having lost. In math this region seems to be activated when the individual is keeping track of more than one concept at a time[2]. This region, which in math helps us keep relevant  problem-solving information ‘fresh’ in our working memory,  is also shared by circuits that allow us to suppress selfish behavior, foster commitment in relationships, and inferring the intentions of others, which is called a Theory of Mind. Researchers have proposed that math training not only makes us better at math, but also strengthens our ability to moderate our feelings and our social interactions because of the brains proclivity in  sharing brain regions for other purposes.

The Amygdala Hijack

Brain imaging studies[3] show that individuals with MA, not unexpectedly, activate circuits associated with negative emotional processing (amygdala, prefrontal cortex), the experience of pain (insula), but also areas involved with inhibiting irrelevant information, and conflict processing. The emotional control network is activated even before mathematical performance occurs. MA does its dirty work by literally robbing the individual of resources in its working memory so that they no longer have access to recalling how similar problems were previously solved. In fact, actual physical changes to the brains of MA students were found in the amygdala, the anterior corpus callosum, the right inferior frontal sulcus and the pericallosal sulcus. In particular the right amygdala volume is smaller and more reactive in students with MA[4]. Chronic hyperactivity of the amygdala in response to stress results in cellular atrophy and a decreased ability to regulate negative emotions. This effect continues into adulthood, so repeated negative math experiences in childhood alters the way that adults handle MA in a way that is both cumulative and apparently not easily mitigated in adulthood because it involves physical changes (atrophy) to specific brain regions.

One of the most troubling features of exercising a math skill is that the regions used are also connected via neuronal synapses to  the prefrontal cortex and to the amygdala. The PFC is a vital executive brain region used for synthesizing data symbolically, keeping information present in a ‘working memory’ and forecasting what happens next. This means that getting better at math allows your PFC to be trained to make better decisions about the future. But here is the BIG PROBLEM. The amygdala also watches over this process and stamps it with an emotional context. Under conditions were the stress hormone cortisol is elevated, the amygdala sees your current condition as a fight-or-flight situation and ‘hijacks’ your brain. [5]This immediately shuts down your PFC and flavors your conscious thinking with the survival instinct of wanting to flee the situation. Forget about logic and planning – it’s time to run! Of course this is not possible when working on a difficult math problem, plus the hijack has now robbed you of clear executive thinking, planning and working memory, which only increases the cortisol.

Defeating MA

This cycle of increasing stress can be defeated by first recognizing it is happening   (sweaty palms, rapid heartbeat), using deep slow breathing, and especially clearing your mind of intrusive thoughts. It only takes 90 seconds to defeat this progression. But sometimes, putting yourself in a state where MA cannot get a toe-hold is ‘simply’ a matter of not triggering the Amygdala Hijack in the first place. Here are some recommendations for teachers from researchers who have studied this triggering process.

• Incorporate math into real-world concepts that students understand.
• Focus on the fun elements of math like pattern making and a curiosity about numbers, not on rote memorization and theory.
• Have them see how numbers and data literacy surround them in life from supermarket shopping to predicting future trends.
• Avoid negative self-talk. Train yourself to have a positive attitude.
• Consider math as a foreign language that takes practice.
• Never scold a student for being wrong or having failed to perform a ‘simple’ math task.
• Never tell your child ‘I was never good at math either’. This tells the child they can succeed in life without knowing math, which is demonstrably false in the 21st century.
• Find ways to provide alternate student assessments rather than timed tests. This is a major source of stress and a key factor in MA.
• Investigate ‘mixed-ability’ groupings to avoid placing MA student together, which only reinforces and normalizes  MA through peer-pressure.
• Make math fun with lots of positive reinforcement. This reduces stress and heart rates and mitigates MA.
• Have parents read math-related bedtime stories.
• Encourage understanding not rote memorization. STEM professionals are those who think slowly, creatively and deeply..not necessarily quickly.
• Display ‘anchor charts’ with examples of work, previous problems or formulas as visual clues to recall previous material.
• Draw or write down facts or relevant equations before working on a math problem
• Have students describe the problem to a partner to help articulate their thinking
• Start the class with a ‘diffuser’ such as sharing a joke, or asking ‘who can tell me something we did in class yesterday?”
• Focus on how a student got their answer and not on it whether it is right or wrong. If incorrect the student may realize this as they explain the process they used.
• Allow students to post pictures or written explanations of their methods of solving a problem.
• Pay attention to the words you use. Instead of ‘this is easy’ say ‘this is like the problem we did yesterday”.
• Always project a positive, confident attitude to support modeling MA-free behavior and attitudes.

Genetic Predispositions

Here’s some bad news. MA might be genetically inheritable. The epigenetic genome controls how genes are expressed. It represents an additional way that traits and tendencies can be passed on. It is well known that traumas to parents can be passed to children, especially starvation and malnutrition. If the starving mother is pregnant, the epigenome she gives to her fetus can cause childhood difficulties in expressing proteins needed for proper digestion. Epigenetics also seems to explain how stress-related disorders can be inherited. According to a review article by TruDiagnostic published in 2020[6], the amount of cortisol in the brain can be regulated by the inherited epigenetic genome and predispose a child to stress-related behavior. It is not impossible that the same transfer of tendencies might happen that predispose the child to MA.  MA seems to result from an interaction of genetic vulnerability with negative experiences learning math. Only an unkind word from a teacher, parent or social group would be enough to set MA in motion, full-blown.

Researchers have also found that a molecular genetic marker called the monoamine oxidase A gene (MAOA) when not expressed at high enough levels correlates with increased MA especially in girls who are known from other studies to be especially susceptible to MA[7]. However, Zhe Wang at Ohio State finds that genetic factors may only account for about 40% of the individual differences in math performance based on a study of 216 twins “If you have these genetic risk factors for math anxiety and then you have negative experiences in math class, it may make learning that much harder.”[8]

MA causes millions of children, especially girls, to not consider STEM careers. This can relegate them to lower-paying jobs that are less quantitative in skill-set. With manual cash registers, some arithmetic acumen was always required even in low-paying sales jobs. Today, change is made with computerized terminals so low-paying jobs require virtually no math and are free of MA triggers.  However, the consequences of not continuing  math education in adolescence can be potentially disastrous not only reducing their career options but in the actual development of their brains.

A recent study of adolescents in the UK shows that a lack of math education affects adolescent brain development. In the UK, students can elect to end their math education at age 16.  The chemical called gamma-Aminobutyric acid (GABA) is present in the middle front gyrus (MFG), which is a region involved in reasoning and cognitive learning. GABA levels are a predictor of changes in mathematical reasoning as much as 19 months later.  What was found among the older adolescents was that GABA showed a marked reduction[9]. Because this chemical is also involved in brain plasticity and the ability to learn new skills and thinking, this reduction at this critical stage in brain development can have far-reaching impacts into adulthood.

Don’t worry…Be happy

But the good news is the brain is not a static thing. It is very ‘plastic’ when it comes to learning and dealing with new experiences. With patience and a more-supportive classroom environment, students can be shown how to make other associations between math and emotions, but this time ones that mitigate MA.

References

[1] Brain areas associated with numbers and math, 2018, doi.org/10.1016/j.dcn.2017.08.002

[2] Mental math and the fine-tuning of emotions. Sandra Ackerman, 2017, Dana Foundation Blog, dana.org/article/mental-math-and-the-fine-tuning-of-emotions/

[3] Dorsolateral Prefrontal Cortex, 2013, Simmon Moss,  and Wikipedia [ref 8]

[4] Neurostructural correlate of math anxiety in the brains of children. Karin Kucian et al,   Translational Psychiatry, 2018; 8:273. Doi: 10.1038/s41398-018-0320-6. And www.ncbi.nlm.gov/pmc/articles/PMC6288142/

[5] The stress-learning connection: Manage an Amygdala Hijack in three steps. The Brain Health Magazine, 2022, thebrainhealthmagzine.com/hormones/the-stress-learning-connection-manage-an-amygdala-hijack-in-three-steps/

[6] Epigenetics and Anxiety – The relationship between genes and stress-related disorders, 2020, blog.trudiagnostic.com/epigenetics-and-anxiety/

[7] MAOA-LPR polymorphism and math anxiety: A marker of genetic susceptibility to social influences in girls, 2022, Annals of the New York Academy of Sciences 1516(1), DOI:10.1111/nyas.14814.

[8] Who’s afraid of math? Genetics plays a role but researchers say environment still key, 2014, geneticliteracyproject.org/2014/03/19/genetics-plays-a-role-in-math-anxiety/

[9] www.sciencedaily.com/releases/2021/06/210607161149.htm and DOI:10.1073/pnas.2013155118