I just watched live the first **kinetic-impact** **asteroid-redirection** test as **NASA’s** Double Asteroid Redirection Test spacecraft collided with the asteroid-moon **Dimorphos** of the asteroid **Didymos**. Below is the last image **DART** transmitted, truncated by the impact itself!

The goal is to **measurably** change the speed of Dimorphos as it orbits Didymos to test asteroid **planetary defense**. Ground-based telescopes cannot resolve the system, which is only a few hundred meters across. (To DART Dimorphos looked like a spheroidal rubble pile). However, the system undergoes **mutual eclipses** as seen from Earth and its brightness dips periodically when one asteroid blocks the other. The head-on collision should have slowed Dimorphos, lowering its orbit and reducing its **orbital period** by several minutes, which should be noticeable over the next few weeks. Confounding variables include momentum exchanged with **ejecta** and the consequent gravity change due to their **reshaping**.

(In 2005, NASA’s **Deep Impact **space probe released an impactor into **comet Tempel 1** not to redirect it but to excavate the interior for remote analysis, like taking a core sample from a tree.)

To distinguish Hubble and Webb images, look for their **signature diffraction spikes**: Due to their **primary mirror** shapes and **secondary mirror** support strut configurations, bright stars in Hubble and Web space telescopes images display distinctive 4 and 6 + 2 = 8 diffraction spikes.

In GRAVITY, “gravity” refers to both the **Newtonian** force that causes the astronauts and their spacecraft to endlessly free-fall around Earth and to the grave nature of their situation, a brilliant and stunning drama of adversity, courage, persistence, and triumph.

It’s especially exciting because it’s the **Feature article** in the Focus Issue, From Chemical Oscillations to Applications of Nonlinear Dynamics: Dedicated to Richard J. Field on the Occasion of his 80th Birthday.

After many months of email exchanges and virtual meetings, I met Bob Mazo for the first time in person this January (see blog entry ‘50 years later‘). Together with Dick Field, the sole living scientist of the Field-Kőrös-Noyes (FKN) mechanism, developed in the early 1970s we revisited the exciting start of a new field in physical chemistry. The FKN mechanism was the first complete reaction scheme to describe the behavior of the Belousov-Zhabotinsky (BZ) reaction, a nonlinear chemical reaction-diffusion system (more here). Shortly after, they developed a mathematical three-variable model to describe the BZ reaction’s nonlinear behavior – the Oregonator model. The name was a response to the Brusselator model, developed by Ilya Prigogine in Brussels in the 1950s and 1960s. For his work on non-equilibrium thermodynamics and dissipative structures, Ilya Prigogine was awarded the Nobel Prize in Chemistry in 1977.

**Fun fact: The total author age is 225, the average author age is 75!** This will be difficult to beat.

Michelle and I began studying the architecture of **daylighting** terrestrial buildings for energy efficiency as part of her senior thesis, but due to our mutual interests, we gravitated to **extraterrestrial** possibilities. After my return from a yearlong sabbatical, Ariel eagerly continued the work for her senior thesis. Despite a **pandemic** keeping us a planet apart and meeting via **video conference** at simultaneously very early and very late hours, we completed the project, one of the most beautiful in my 33 years at **Wooster**. During one of our early morning, late evening sessions, we mathematically derived the solar reversals condition for the important special case of zero **obliquity** or tilt.

In the first figure below, exoplanet **spin-orbit ratio** \rho increases rightward, **orbital eccentricity** e increases upward, and **time** t increases outward. Red rods represent planetary observers, and coils represent apparent position and angle of their suns for 8 orbits. Yellow and cyan indicate apparent clockwise and counterclockwise motion, which signify reversals in coils with both colors. Our own solar system’s **Mercury** (Me) is just inside the reversal region. Red-white-blue background colors represent the product of the differences of the planet’s spin angular speed and its extreme orbital angular speeds at **apoapsis** and **periapsis**; red means no apparent solar reversals, blue means reversals, and the saturation indicates the reversal magnitude.

On Mercury, **one (solar) day lasts two years,** and once a year an equatorial observer witnesses a brief solar reversal, as in the second figure below, surely a special day for any future inhabitants. For a civilization inhabiting such a planet, we expect “reversal day” to be culturally significant.

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The** Event Horizon Telescope** team combined signals from radio telescopes that span Earth to reconstruct the image using** Very Long Baseline Interferometry**. Famously, not even light can escape a black hole, but EHT can see the glow of compressed and ionized gas or **plasma** in its orbiting **accretion disk** and the “shadow” of its **event horizon**. A conventional false-color black-orange-white palette makes visible the averaged radio-wave data.

The giant **Taylor Bowl** slide rule used to be used to teach the slide rule but today is the **trophy** for the annual Taylor Hall bowling tournament between the **Physics** and **Math Clubs**.

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\log \frac{x}{y} = \log x - \log y.Slide rules feature logarithmic scales that slide past each other. For **straight** slide rules, logarithms of the numbers are proportional to their distances along them. To multiply 2\times 3 = 6, as below, slide the upper (blue) scale from 1 to 2 along the lower (red) scale, add the distance from 1 to 3 along the upper (blue) scale, and read the product from the lower (red) scale.

For **circular** slide rules, logarithms of the numbers are proportional to their distances around them. To multiply 3\times 7 = 21, as below, rotate the outer (blue) scale from 1 to 3 around the inner (red) scale, add the distance from 1 to 7 around the outer (blue) scale, and read the product from the inner (red) scale. Circular slide rules eliminate **off-scale** calculations because they naturally **wrap around**, with each wrap multiplying (or dividing) the numbers by 10.

The test image below shows a long exposure of a faint star. The radial lines are **diffraction spikes**. Confine light in one direction and it spreads in the perpendicular direction. Here, the six large spikes are from Webb’s 18 hexagonal mirror-segment edges and the one horizontal spike is from the vertical **strut** supporting **the secondary mirror, **which is visible in the Webb **selfie**. (The remaining two secondary mirror struts are parallel to mirror edges and their diffraction patterns combine with the mirror edge patterns.)

Due to Webb’s unprecedented **resolution** and **sensitivity**, many **galaxies** are also visible in this alignment image, whetting the appetite of Earth-bound astronomers!