nass news 2022 apr phobos eclipse by perseveranceOn April 2, 2022 the Perseverance Martian rover's Mastcam-Z camera looked sunward and took a video of the eclipse of the sun by the "potato-shaped" moon Phobos. 

According the NASA Mars Exploration Program site, "It’s the most zoomed-in, highest-frame-rate observation of a Phobos solar eclipse ever taken from the Martian surface."  NASA reports that "Several Mars rovers have observed Phobos crossing in front of the Sun over the past 18 years. Spirit and Opportunity made the first observations in 2004; Curiosity in 2019 was the first to record video of the event. Each time these eclipses are observed, they allow scientists to measure subtle shifts in Phobos’ orbit over time. The moon’s tidal forces pull on the deep interior crust and mantle of the Red Planet; studying how much Phobos shifts over time reveals something about how resistant the crust and mantle are, and thus what kinds of materials they’re made of."

Watch the video: 

The Land Institute is a not for profit organization based in Salina, Kansas, having a goal to create an agriculture system that mimics natural systems in order to produce ample food and reduce or eliminate the negative impacts of industrial agriculture.  A mile north of the Institue is their Marty Bender Nature Area where Owen Brown has created an art project "Units of Measurement".  According to Jason Beets of the Salina Journal, his project "consists of three sets of sun dials created from praire-colored angled flag poles to symbolically represent the passage of time."

The idea is to meditate on the passage of time.  The first set of three poles, called "In the Beginning" is 1,190 feet east of another set of poles called "The Passage of a Second".  According to the artiist, this is the distance that the earthrotates in one second.  A third site, called "From the Future" is located 723 feet north of "In the Beginning" is placed such that at "... dawn of the summer solstice, the shadows of the sundials at “From the Future” will touch [point to] the sundials at “The Passage of a Second.” Owen said, "I want this installation to make us more aware of where we are, who we are, and how we are ... in relation to the earth, to what we grow, and to what nurtures us."

Interesting art but very poor science.  For each cluster of three flag poles, only the one point to North can work as a sundial.  And the pole needs to be at an angle from the ground equal to the latitude of 38.855° N.  From the photo, the angle is closer to 60°.  Fortunately there are no hour lines on the ground to show the incorrect time of the shadow.

Updated Content: 28 Feb 2022

We've recomputed "The Passage of a Second" using Earth Centered Earth Fixed (ECEF) coordinates for the latitude of 38.855° N and an altitude of 1,227 ft attributed to Salinas, KS.  The result is an earth radius of 4.973775 x 10^6 meters giving a circumference of 31,251.15km.  But to count exactly one revolution of the earth (in inertial space) we need to use the sidereal day of 86164.1 sec rather than the mean solar day of 86400 sec. And just as Owen Brown has separated "In the Beginning" and "The Passage of a Second", the distance is 1190 feet.  The angle from east of "From the Future" 723 feet north of "In the Beginning" as seen from "The Passage of a Second" is 31.28° or 121.28° from south.  The first rays of the sun appear on the eastern horizon when the center of the sun is actually 0.833° below the horizon.  The sun's apparent position is due in part to atmospheric refraction.  Taking this effect into account, sunrise on the summer solstice will occur at an azimuth from south of 121.3°, the alignment used by Owen Brown.

Indeed the sunlight is coming from the future on the solstice, travelling the Pathagorean distance of 1,392.4 feet in (424.4m) between Future and Passage requires 1.4 microsecond. Owen Brown's simple constructs with precision placement is something to be contimplated.

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The heart of the Cosmic Room is an unusual vertical meridian sundial created by sunlight passing through a slot on the roof above.  In winter the solar meridian transit is labeled  with a column of blue tiles and at the spring equinox the tiles change to orange.  The sign "Analemma 12:45" indicates civil time on the spring equinox when the sun is on the local meridian.  With the sun overhead, the beam of light follows the vertical set of tiles downward until it reaches the boundary between orange and blue tiles - the equinox has arrived.  Ruben Nohitol has been photographing this event for the last 16 years, every year since 2002.  From a ceiling hole Ruben marks the image of the sun at 12:45 on the floor with a small green circle.  He does this on dates throughout the year(s), not only creating a nice analemma, but does it with such precision that he is able to notice the slight shifts in solar equinox position through the leap year cycle of four years.

More impressive is the due west sunset on the equinox.   A beam of light streams though a hole in the western wall of his hacienda, across the living room,  through a square hole between rooms, across the Cosmic Room grazing past the vertical sundial and its tiles, and lands as a bright solar disk at the far end of the Cosmic Room on a vertical wood screen mounted on an exit doorway.   To add to the drama of the setting equinox sun, Ruben placed a model of the pyramid of El Cerrito on a shelf in the Cosmic Room blocking some of the sun's rays. The result is a shadow of the the pyramid against the solar disk, giving the illusion of thesun setting over the great pyramid.  You can see his vertical meridian and more at and the sundial in operation at See his patience to photograph the real setting sun over the pyramid of El Cerrito in Queretaro, Mexico at

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[photo courtesy of Ruben Nohuitol]

Ruben Nohuitol of Queretaro, Mexico has a unique solarium or “cosmic room” to observe the rays of the sun throughout the year.  He has patiently constructed a wonderful time-lapse video following the sun every day at 12:45 pm.   His construction has a vertical meridiana beam of light descending and then ascending the wall as time passes throughout the year. A second sky-light gnomon creates a classical analemma on the floor.