• There and Back Again

    I awoke yesterday at dawn in a log cabin in Vermont. Fortunately, the wifi was good.

    Each successive test of the SpaceX Superheavy Starship has been a significant improvement over the previous one, and test five was no exception, with both the booster and the ship demonstrating soft pinpoint landings — except this time, the booster falling from the edge of space was caught in mid air by the mechazilla launch tower itself!

    Software controls and coordinates the booster’s position, velocity, and orientation, as well as the chopstick‘s height and opening angle, a single point in an abstract parameter space, to enable the catch. This thrilling and unprecedented engineering achievement was another big step toward perfecting history’s most powerful and reusable launch system.

    Mechazilla captures Superheavy booster
    SpaceX launch tower catches a Superheavy booster returning from the edge of space after propelling a Starship to a pinpoint soft landing in the Indian ocean, 2014 October 13. (SpaceX multiple exposure photo.)

  • Rey’s Theme

    Yesterday, as part of the Polaris Dawn mission, SpaceX engineer Sarah Gillis became the youngest person to walk in space. Today, on a space-qualified violin, she performed Rey’s Theme, composed by John Williams as the musical leitmotif for Rey, the central character in the Star Wars movie The Force Awakens.

    The performance audio and video were transmitted to Earth via SpaceX’s Starlink satellite network and were accompanied by performances of Earth-based musical ensembles. As space travel expands, musicians, artists, and poets will increasingly travel and live beyond Earth.

    Sarah Gillis playing violin in Dragon spacecraft
    Sarah Gillis plays a Star Wars theme aboard the Polaris Dawn SpaceX Dragon spacecraft during orbital night.

    Sarah Gillis playing violin in Dragon spacecraft
    Sarah completes the performance during a daytime pass. (Polaris Dawn experiences a new dawn about every 106 minutes.)

  • Skywalker

    Up before dawn this morning for the Polaris Dawn space walk, the first commercial space walk and the furthest from Earth since the Apollo program over half a century ago. After stalling for so long, human space flight is again advancing.

    Polaris Dawn’s Commander Jared Isaacman, Pilot Scott “Kidd” Poteet, Mission Specialist Sarah Gillis, and Mission Specialist and Medical Officer Anna Menon had already broken the 1966 Gemini XI altitude record for Earth-orbital missions (excluding Apollo cis-lunar missions). This morning, the crew vented the SpaceX Dragon Resilience‘s cabin, exposing all four of them to the vacuum of space, realizing the first four-person spacewalk, and eclipsing the 1992 STS-49 mission, which included history’s only three-person spacewalk.

    At orbital sunset and near orbital apogee, Isaacman then floated outside to the Dragon’s skywalker mobility aid. For about 12 minutes, he tested the new SpaceX extravehicular activity (EVA) space suit in a carefully practiced choreography. Gillis followed next during orbital night and repeated the same tests, becoming the youngest person to perform a spacewalk, younger even than the very first spacewalker, Alexei Leonov. Later today, in yet another milestone, the crew transmitted images via high-bandwidth laser light beams to SpaceX’s Starlink satellite network.

    Excitedly and inspirationally, Gillis and Menon are the first SpaceX engineers to fly in space. They have been intimately involved in human spaceflight development and training and will soon return to Earth to leverage their experience and help accelerate SpaceX’s progress toward making life and consciousness interplanetary.

    Commander Jared Isaacman tests the new SpaceX EVA suit at orbital sunset near apogee.
    Commander Jared Isaacman tests the new SpaceX EVA suit at orbital sunset near apogee. All four astronauts participated in the spacewalk by being exposed to the vacuum of space.

    Polaris Dawn Crew
    From left to right, the Polaris Dawn crew is Sarah Gillis, Kidd Poteet, Jared Isaacman, and Anna Menon. Gillis and Menon are the first SpaceX engineers to fly in space

  • An academic in industry

    Recently, with members of NCSU’s Nonlinear Artificial Intelligence Lab, I completed a 3.5-year project as a subcontractor working on an industrial project. As an academic, this was a novel experience. Unlike most of my research, this work will not result in a journal article or conference presentation, although it might one day contribute to an industrial product.

    Because I signed a Non Disclosure Agreement, I cannot discuss the project details. I can say the work included developing an app in the Swift programming language for the iPhone operating system iOS.

    Towards an engaging and intuitive Graphical User Interface, I created virtual 3D buttons that cast virtual shadows, depending on the iPhone‘s physical orientation, due to a virtual light source directly above the phone. When touched, the buttons appear to depress (and click or vibrate the phone, depending on the user’s preferences). The hole in the cog-wheel button really works — if you touch the hole, the button will not depress — because a virtual hole in a virtual cog wheel is real!

    Animation of virtual 3D buttons casting virtual shadows as a real iPhone physically pitches and rolls. A virtual light source is always directly above the phone. (You may need to click to start the animation.)
  • Does a charge in gravity radiate?

    Caltech, Saturday night, grad student pizza. The conversation turns to a famous general relativity puzzle: does an electric charge at rest in a gravitational field radiate? According to Einstein’s equivalence principle, a static homogeneous gravitational field is indistinguishable from constant acceleration in empty space, and as is well known, accelerating charges radiate. Does that mean electrons in the table radiate as we eat? Sam says Kip says the electromagnetic field lines bend. We don’t resolve the paradox, and after dinner we return to our grad school homework.

    Here, I outline a partial solution to the problem based on the work of Fritz Rohrlich. It’s a long calculation, which I checked using Mathematica. Round parentheses (\ ) group terms, square brackets [\ ] enclose function arguments, and boxes \square enclose matrix elements.

    Outline

    • Model static homogeneous gravity G with Rohrlich spacetime metric.
    • Transform to free-fall coordinates F where G is in hyperbolic motion
    • Find hyperbolic geodesics of constant proper acceleration g, as in Fig. 1..
    • Find electromagnetic field of charge q at rest in G as observed by F.
    • Transform to find electromagnetic field as observed by G.

    Charge worldliness in the gravity and free fall frames.
    Figure 1: Charge q (blue) at rest in static homogeneous gravitational field (left) and in hyperbolic motion in a freely falling reference frame (right). Gridlines are null (light) lines, which suggest a coordinate singularity at z_G = 1/g, and dashed lines are hyperbola asymptotes. Black lines outline future light cones.

    Model Gravity

    If g is the non-relativistic gravitational field magnitude, relativistic units implies constant light speed c = 1 with time scale T = c/g_E \approx 1~\text{year}, and length scale L = c^2/g_E \approx 1~\text{light-year}. Restricting spatial motion to the vertical z direction implies cylindrical symmetry, so use cylindrical spacetime coordinates

    x^\mu = \boxed{\begin{array}{c} x^0 \\ x^1 \\ x^2 \\ x^3 \\\end{array}} = \boxed{\begin{array}{c} ct \\ \rho \\ \phi \\ z \\\end{array}} = \boxed{\begin{array}{c} t \\ \rho \\ \phi \\ z \\\end{array}} = \boxed{\begin{array}{c} t \\ \vec x \\ \end{array}}.

    The line element

    \text d\tau^2 = \sum_{\mu=0}^3 \sum_{\nu=0}^3 g_{\mu\nu} \text dx^\mu \text dx^\nu = g_{\mu\nu} \text dx^\mu \text dx^\nu

    gives the proper time d\tau between nearby events. Model a free-fall spacetime using the Minkowski metric tensor with matrix representation

    g^F_{\mu\nu} = \boxed{\begin{array}{cccc} 1 & 0 & 0 & 0 \\ 0 & -1 & 0 & 0\\0 & 0 & -\rho^2 & 0 \\0 & 0 & 0 & -1 \\ \end{array}} = \eta_{\mu\nu},

    and line element

    \text d\tau^2 = \text dt^2-\text d\rho^2-\rho^2\text d\phi^2-\text dz^2 = \text dt^2-\text d\vec x^2,

    where

    \frac{1}{\gamma^2} = \left( \frac{\text d\tau}{\text dt} \right)^2 = 1-\left( \frac{\text d\vec x}{\text dt} \right)^2.

    Simply model gravity using the Rohrlich metric tensor with matrix representation

    g^G_{\mu\nu} = \boxed{\begin{array}{cccc} u[z_G]^2 & 0 & 0 & 0 \\ 0 & -1 & 0 & 0 \\0 & 0 & -\rho^2 & 0 \\0 & 0 & 0 & -u'[z_G]^2/g^2 \\ \end{array}} = \boxed{g^{\mu\nu}_G}^{-1},

    where

    u[z] = \text{sech}\left[\sqrt{(1-g z)^2-1}\right] = 1 + g z + O[z^2].

    The Rohrlich spacetime is static (independent of time t), homogeneous (independent of horizontal coordinates x = \rho\cos\phi, y=\rho\sin\phi), and depends only on height z and parameter g.

    Free fall

    Newtonian free fall \vec x[t] satisfies \text d^2\vec x / \text dt^2 = \vec 0. More generally, geodesic motion x^\alpha[\tau] satisfies

    \frac{\text d^2 x^\alpha}{\text d \tau^2} = -\Gamma^\alpha_{\mu\nu} \frac{\text dx^\mu}{\text d \tau}\frac{\text d x^\nu}{\text d \tau},

    with implied sums over the repeated indices, where the connection coefficients

    \Gamma^\alpha_{\beta\gamma} = \frac{1}{2}g^{\alpha\delta}\left(\frac{\partial g_{\delta\beta}}{\partial x^\gamma} + \frac{\partial g_{\gamma\delta}}{\partial x^\beta} – \frac{\partial g_{\beta\gamma}}{\partial x^\delta} \right)

    encode the rates of basis vector component changes with coordinate changes. Here, the solutions

    \boxed{\begin{array}{c} t_G \\ \rho_G \\ \phi_G \\ z_G \end{array}} = \boxed{\begin{array}{c} \text{arctanh}[g\tau]/g \\ 0 \\ 0 \\ (1-\sqrt{1+\text{arctanh}[g\tau]^2})/g \end{array}}

    imply hyperbolic motion

    (z_G-1/g)^2-t_G^2 = 1/g^2,

    where

    z_G = \frac{1-\sqrt{1+g^2 t_G^2}}{g} = -\frac{1}{2} g t_G^2 + O[t_G^4],

    as designed.

    Transform to free fall frame

    By the equivalence principle, a freely falling test particle defines a locally flat or inertial system. Equating the free and gravity line elements

    \begin{aligned}\text d\tau^2 &= \text dt_F^2-\text d\rho_F^2-\rho_F^2 \text d\phi_F^2-\text dz_F^2 \\ &= u[z_G]^2 \text dt_G^2-\text d\rho_G^2-\rho_G^2 \text d\phi_G^2-\frac{u^\prime[z_G]^2}{g^2} \text dz_G^2,\end{aligned}

    implies the transformation

    x^\mu_F = \boxed{\begin{array}{c} t_F \\ \rho_F \\ \phi_F \\ z_F \end{array}} = \boxed{\begin{array}{c} \sinh[g t_G] u[z_G]/g \\ \rho_G \\ \phi_G \\ \cosh[g t_G] u[z_G] / g \end{array}}

    with Jacobian

    \underset{F\leftarrow G}{J^\mu_\nu} = \frac{\partial x^\mu_F}{\partial x^\nu_G} = \boxed{\begin{array}{cccc} \cosh[gt_G]u[z_G] & 0 & 0 & \sinh[gt_G]u^\prime[z_G]/g \\ 0 & 1 & 0 & 0\\0 & 0 & 1 & 0 \\ \sinh[gt_G]u[z_G] & 0 & 0 &\cosh[gt_G]u^\prime[z_G]/g \end{array}}

    Thus, the charge q at rest in G at x_G = y_G = z_G = 0 moves in F along the hyperbola

    z_F^2\ -\ t_F^2 = u[z_G]^2/ g^2 = u[0]^2/ g^2 = 1 / g^2,

    where

    z_F = \frac{\sqrt{1+g^2 t_F^2}}{g} = \frac{1}{g}+\frac{1}{2} g t_F^2 + O[t_F^4].

    Generally, the spacetime acceleration A^\mu = d^2 x^\mu / d^2\tau^2 implies the Lorentz-invariant

    \sqrt{-A^\mu A_\mu} = \sqrt{-g_{\mu\nu}A^\mu A^\nu} = \frac{\ddot{z}}{(1-\dot{z}^2)^{3/2}} = \gamma^3 \ddot z,

    for \ddot z >0, where the over-dots indicate differentiation with respect to time t. Here, the proper acceleration of q fixed in G

    \ddot z_G = \gamma_G^3 \ddot z_G^{} = \gamma_F^3 \ddot z_F = \frac{\ddot{z}_F}{(1-\dot{z}_F^2)^{3/2}} = g

    is constant, as expected. (Furthermore, 1 < \gamma_F implies \ddot z_F < g, and \ddot z_F \rightarrow 0 as \dot z_F \rightarrow c, so F never observes q superluminal.)

    Electromagnetic fields in free fall frame

    Generally, for a charge q in arbitrary motion x^\mu_q[\tau], the Coulomb potential \varphi = q / r generalizes to the Liénard-Wiechert potential

    \mathcal{A}^\mu = q\frac{U^\mu}{R^\nu U_\nu} \bigg|_{t_r} = q\frac{U^\mu}{g_{\alpha\beta}R^\alpha U^\beta} \bigg|_{t_r},

    where the spacetime velocity U^\mu = dx^\mu_q / d\tau, the spacetime displacement R^\mu = x^\mu-x^\mu_q, and because electromagnetic “news” travels at light speed, the right side is evaluated at the earlier, retarded time t_r defined implicitly by

    t-t_r = \big| \vec x-\vec x_q[t_r] \big| / c.

    Let the cylindrical coordinates of the field point at time t be \{\rho, \phi, z\}, and define

    \begin{aligned}\delta^2 &= -t^2 + \rho^2 + z^2 + g^{-2}, \\ \Delta^2 &= +t^2 + \rho^2-z^2 + g^{-2}, \\ d^2 &= +t^2-\rho^2-z^2 + g^{-2}, \\ \xi &= \sqrt{4 g^{-2} \rho^2 +d^2}.\end{aligned}

    Here, for the charge’s hyperbolic motion in the free-fall frame, explicitly solving for the retarded time is possible, and

    t_F-t_r = \sqrt{\rho_F^2 +(z_F-\sqrt{g^{-2}+t_r^2}\,)^2}

    implies

    t_r = \frac{t_F\delta_F^2-z_F\xi_F}{2(z_F^2-t_F^2)}.

    Evaluating the Liénard-Wiechert potential at this time gives

    U^\mu_F = \frac{g}{2(z_F^2-t_F^2)}\boxed{\begin{array}{c} z_F \delta_F^2-t_F\xi_F \\ 0 \\ 0 \\ t_F \delta_F^2-z_F \xi_F \end{array}}

    and

    R^\mu_F = \frac{1}{2(z_F^2-t_F^2)}\boxed{\begin{array}{c} z_F \xi_F-t_F\Delta_F^2 \\ 2\rho_F(z_F^2-t_F^2) \\ 0 \\ t_F \xi_F-z_F \Delta_F^2 \end{array}}

    and finally

    \mathcal{A}^\mu_F = \frac{q}{\xi_F(z_F^2-t_F^2)}\boxed{\begin{array}{c} z_F \delta_F^2-t_F\xi_F \\ 0 \\ 0 \\ t_F \delta_F^2-z_F \xi_F^2 \end{array}}.

    Differentiating the electromagnetic field tensor

    \boxed{\begin{array}{cccc}0 & +\mathcal{E}_\rho & +\mathcal{E}_\phi & +\mathcal{E}_z \\-\mathcal{E}_\rho & 0 & -\mathcal{B}_z & +\mathcal{B}_\phi \\-\mathcal{E}_\phi & +\mathcal{B}_z & 0 & -\mathcal{B}_\rho \\-\mathcal{E}_z & -\mathcal{B}_\phi & +\mathcal{B}_\rho & 0 \end{array}}_F = \mathcal{F}_F^{\mu\nu} = \frac{\partial \mathcal{A}_F^\nu}{\partial x_F^\mu}-\frac{\partial \mathcal{A}_F^\mu}{\partial x_F^\nu},

    generates the electric and magnetic field vectors

    \begin{aligned}\vec\mathcal{E}_F &= \frac{4 g^{-2} q}{\xi_F^3} \boxed{\begin{array}{c}2\rho_F z_F \\0\\-\Delta_F^2 \end{array}}, \\ \vec\mathcal{B}_F &= \frac{4 g^{-2} q}{\xi_F^3} \boxed{\begin{array}{c}0 \\2\rho_F t_F\\0 \end{array}}, \end{aligned}

    for z_F> t_F, as in Fig. 2. The directional energy flux density or Poynting vector

    \vec\mathcal{S}_F = \vec\mathcal{E}_F \times \vec\mathcal{B}_F = \frac{32 g^{-4} q^2 t_F \rho_F}{\xi_F^6} \boxed{\begin{array}{c}\Delta_F^2 \\0 \\ 2\rho_F z_F \end{array}}.

    Electric and magnetic field in the free fall frame.
    Figure 2: Electric and (nonzero) magnetic fields in the free fall frame F for a charge q at rest in G and accelerating upward in F. Parameters are q=1, g = 0.2, and t_F=0.1.

    Electromagnetic fields in gravity frame

    The electromagnetic field transformed to the gravity frame is

    \boxed{\begin{array}{cccc}0 & +\mathcal{E}_\rho & +\mathcal{E}_\phi & +\mathcal{E}_z \\-\mathcal{E}_\rho & 0 & -\mathcal{B}_z & +\mathcal{B}_\phi \\-\mathcal{E}_\phi & +\mathcal{B}_z & 0 & -\mathcal{B}_\rho \\-\mathcal{E}_z & -\mathcal{B}_\phi & +\mathcal{B}_\rho & 0 \end{array}}_G = \mathcal{F}_G^{\mu\nu} = J^{\mu}_\alpha J^{\nu}_\beta \mathcal{F}_F^{\alpha\beta},

    with implied sums over repeated indices. Hence,

    \begin{aligned}\vec\mathcal{E}_G &= \frac{4 g^{-2}q}{\xi_G^3} \frac{\text{sech}\chi_G}{\chi_G} \boxed{\begin{array}{c}2\rho_G (z_G \cosh[g t_G]-t_G\sinh[g t_G])\chi_G \\ 0 \\ -\Delta_G^2 (1-g z_G)\text{sech}\chi_G \tanh\chi_G \end{array}}, \\ \vec\mathcal{B}_G &= \boxed{\begin{array}{c}0 \\ 0 \\ 0 \end{array}}, \end{aligned}

    where \chi = \sqrt{(1-g z)^2-1}, as in Fig. 3. As a check,

    \lim_{g\rightarrow 0} \vec\mathcal{E}_G = \frac{q}{(z_G^2 + \rho_G^2)^{3/2}} \boxed{\begin{array}{c}\rho_G \\ 0 \\ z_G \end{array}} = \frac{q}{z_G^2 + \rho_G^2} \frac{\rho_G \hat\rho + z_G \hat z}{\sqrt{z_G^2 + \rho_G^2}} = \frac{q}{r_G^2} \hat r_G,

    as expected. The Poynting vector

    \vec\mathcal{S}_G = \vec\mathcal{E}_G \times \vec\mathcal{B}_G = \boxed{\begin{array}{c} 0 \\ 0 \\ 0 \end{array}}.

    Electric and magnetic field in the gravity frame.
    Figure 3: Electric and (zero) magnetic fields in the gravity frame G for a charge q=1 at rest in G with g = 0.2.

    Summary

    Kip was right; the field lines bend (downward). But also, radiation is not a frame-invariant concept.

  • Sabbatical trip to Europe – Part 3 (Otto Rössler)

    After the conference in Switzerland, I stopped in Tübingen, Germany to visit Otto Rössler. Nearly everyone who learned about nonlinear systems knows the nowadays named Rössler attractor and his work in chaos theory in the 1970s.
    For the last four years we were in contact for my science history project and this year, I finally visited him. We had a great day and I received MANY documents from conferences 40-50 years ago. He saved ‘everything’ in countless binders, sorted by years, and kept them in ceiling-heigh bookshelfs at his home.

    In the 1970s, Otto Rössler designed a famous 3D flow that mimics the folding and bending of taffy in a taffy machine, which is now named the Rössler attractor. Described by the 3 coupled differential equations

    \begin{aligned}\dot x &= -y – z, \\ \dot y &= x + a y,\\ \dot z &= b – c z + x z,\end{aligned}

    with just one nonlinear term, the x z in the third equation. The Rössler velocity field results from the interaction of two crossed vortices, one near the origin and the other far away pointing at the “fold” in the Rössler band. The parameter space \{a,b,c\} is large, but the system undergoes a period-doubling route to chaos in \{0<a<2, b=2, c=4\}, as in the animation below, which culminates in a period-3 window.

    Post-transient {x ,y, z} solutions to the Rössler system for 0.1 < a < 0.411, b = 2, c = 4, exhibiting a period-doubling route to chaos culminating in a 3-cycle window. (You may need to “click” on the figure to see the animation.)

    The animation was created by John Lindner.

  • Sabbatical trip to Europe – Part 2 (Switzerland)

    The second stop of my Europe trip was Switzerland. In Zürich, I visited places where Boris Belousov (the discoverer of the Belousov-Zhabotinsky reaction I am using in my lab) lived and studied during his time in exile (1910-1915). But the theme of that part of my science history project keeps validating “Searching for a ghost”.

    None of the buildings mentioned in publications still exist. And searching for original document is two archived did not provide any new information. Therefore, two impressions from Zürich: the beautiful Zürich train station and the street sign of the street Belousov supposedly lived in.

    From Zürich, I traveled to Les Diablerets in the southwest of Switzerland to attend the Gordon Research Conference on Oscillations and Dynamic Instabilities in Chemical Systems. This is a beautiful location at 1200 m to interact with scientists from all over the world and to spend the free afternoons. One afternoon, I ‘ran’ up the switchback road to the Col de la Croix and took several hiking trails back to the village – to be back in time for a poster session.

    After the conference, I walked towards the Lake Geneva to take the ‘train’ at the last possible ‘train station’ before the track winds into the next valley. It was a beautiful hike to relax the brain.

  • Sabbatical trip to Europe – Part 1 (Lviv, Ukraine)

    Since about 2018, I was interested in the work of Julian Hirniak, who published an article on periodic chemical systems in 1908 (and a follow-up in 1911), before Alfred Lotka’s famous theoretical 1910 paper and William Bray’s experimental work in 1921.
    The article had been published in a journal of the Shevchenko Society in Lviv (Austria-Hungarian empire at that time) in, as I read everywhere, in Ruthenian language. All those years, I could not get a scan of the article, or the journal, not even from the Shevchenko Society archive in New York City.
    In January, I contacted a physicist at the Ukrainian National Academy of Science, who recently published about the Shevchenko Society and asked him about Julian Hirniak and the journal. He immediately responded and shortly after, he sent me pictures of the article in question. He translated that article into English, I translated Hirniak’s German 1911 article into English and, together with another co-author, we submitted a manuscript in June.
    When I mentioned that I will be in Europe this summer, he invited me to visit him in Lviv, Ukraine. It became the first trip during my nearly 6-week time in Europe.

    Impression of Lviv, located close to the Polish border in Western Ukraine: surreal!
    Despite the war in the Eastern/Southern part of the country, life is going on. Electricity outages are compensated by power generators outside every shop/restaurant. On Saturday evening, we saw Mozart’s Don Giovanni in Lviv’s Opera Theater.

    We also visited the archive of the Shevchenko society – on a Saturday morning. The director Kostiantyn Kurylyshyn (Head of the Department at the Vasyl Stefanyk National Scientific Library of Ukraine in Lviv) invited us because he is, as he said, nevertheless there and could show us around. Finally, I visited the place, build in 1912, where ‘every’ Ukrainian publication can be found. This is similar to the Library of Congress in Washington DC. And I could finally see the original 1908 publication – and take my own picture.

  • The Longest Flight

    As a kid pouring over the Guinness Book of World Records, I was astonished by the record longest flight, which lasted not just a few hours – as I would have guessed – but more than two months! Today, nearly 65 years later, that amazing achievement remains one of aviation’s most enduring records.

    For over 64 days in 1958-1959 (!), Robert Timm and John Cook flew a modified Cessna 172 above and around Las Vegas. Modifications included an extra fuel tank, a mattress, a small steel sink, and a camping toilet. The duo took turns piloting, and they refueled and resupplied every 12 hours by flying low and slow above a speeding truck.

    Robert Timm (right) and John Cook (left).
    Robert Timm (right) and John Cook (left) flying their modified Cessna 172 near Las Vegas, Nevada, 1958-1959. (Howard W. Cannon Aviation Museum)

    Refueling.
    Twice a day Timm and Cook refueled and resupplied from a fast truck. (Howard W. Cannon Aviation Museum)

  • Where Are the Stars?

    When viewing space photography, such as Apollo or International Space Station photos, people often ask, “Where are the stars?” Typically such photos properly expose the bright lunar or space station surfaces and consequently underexpose the dim background stars, rendering space as featureless black.

    Current ISS astronaut Matthew Dominick has been experimenting with photography, and his photo below, of a docked SpaceX Dragon taken from a docked Boeing Starliner, just after orbital sunset and just as Earth’s moon rises, does show stars from our Milky Way galaxy, with the spacecraft dimly illuminated by moonlight. Note the face in the Dragon window.

    Dragon spacecraft with Milky Way stars illuminated faintly by moonlight, 2024 June 29. A 1s, f1.4, ISO 5000, 28mm photo by NASA astronaut Matthew Dominick. Click for a larger version.


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