Hour Horary Quadrant

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Published: 04 December 2011

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Washington's Sundial in the Spotlight

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Published: 15 October 2011

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George Washington's Sundial is in the Spotlight: Sometime during 1765-1781 Washington placed a 12 inch brass horizontal sundial at the heart of his Mount Vernon plantation. The sundial sits atop a white painted octagon wood pedestal in the center of the front lawn of his mansion.  It stands as a visual reminder of the importance of time to all who passed it.  A replica of the original dial now reminds tourists of the time, but the original is in the museum.  Go to http://www.georgewashingtonwired.org/ and read more about Mount Vernon and visit NASS_Registry_Dial167 where you can find details of Washington’s dial.

Oldest Sundial in the Western Hemisphere

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Published: 01 July 2011

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Where would you look for the oldest dials in the Western Hemisphere?  One is attributed to the Pilgrims in Salem in 1620.  Earlier slate dials were used by Newfoundland fisherman.  But La Fortaleza, in San Juan, the oldest Executive Mansion in the New World may lay claim to the oldest sundial.

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Sundial Rededication

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Published: 24 May 2011

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A sundial that was originally purchased by the 1910 class of Springfield (Ohio) High School and which adorned the original high school grounds for decades was recently refurbished and rededicated at the new Springfield High School.

Even though the dial adorned the school grounds for much of the 20th century, it eventually found its way into storage, where it remained until it was recently uncovered. 

Read more: Sundial Rededication

Rare Sundial Sold

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Published: 17 March 2011

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[photo credit: Christie's ]

A rare stone, polyhedral sundial discovered in England, and thought to date from the Scottish renaissance, sold April 7, 2011 for £16,250 (\(26,500) at Christie's South Kensington, London. 

The sundial discovered in 1974, and thought to date from the Scottish renaissance, went on the auction block this April as part of Christie's Travel, Science and Natural History sale in London.  The dial is made of stone and technically described as a polyhedral dial, with several independent sundials arranged on different facets of the stone.  Pre-auction estimates placed a value somewhere between £7000 and £10,000 (\)11,400 and $16,300) but sold for nearly three times the initial estimate.

Read more: Rare Sundial Sold

Today - Chicagohenge

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Published: 22 September 2022

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The date is Sep. 22, 2022, the date of the fall equinox.  Although this is supposed to be the day of equal day and night, we know it's not exactly correct.  We measure daytime from sunrise to sunset, measured as the first and last light from the sun peaking over the horizon.  When we include sunrise and sunset plus atmospheric refration, at mid latitudes daylight wins by about 10 minutes (not even counting twilight).

Chicagohenge photo by Tim Hara

But something magical happens as the sun sets due west on the equinox in Chicago. The sunset direction matches the direction of the Chicago grid of East-West streets.  The effect is known as Chicagohenge.

From the Adler Planetarium website (https://www.adlerplanetarium.org/blog/chicagohenge/): "Chicagohenge occurs twice a year and happens when the Sun directly lines up with Chicago’s east-west facing streets ... To fully understand Chicagohenge, you have to be aware of the two main factors that cause it: Chicago’s grid plan and equinoxes...The present-day Chicago grid system can be attributed to the Public Land Survey System -- a surveying method created in 1785 that was used to divide land for selling and settling. But this style of city design has been around since the dawn of civilization and can be found in the ruins of ancient Rome, Greece, and others [sometimes creating solar alignments in these cities such as Manhattan Henge] ... Fun fact: Chicago’s streets line up almost perfectly with the cardinal east and west directions on a compass. This in turn, sets up the perfect stage for Chicagohenge to take place."

The Planetarium Blog continues. "Since the Earth’s axis is tilted, sunlight is not always distributed equally. At any given point, one-half of the Earth is tilted towards the Sun more than the other. As the Earth orbits around the Sun, the part that was tilting away from the Sun begins to be the part that is facing towards the Sun. This is why we have seasons! ... There are two equinoxes each year, one that marks the start of spring (Spring Equinox) and one that marks the end of summer (Autumn Equinox). Thanks to Chicago’s perfectly lined grid system, the bi-annual equinoxes mark a time when the Sun rises and sets directly in line with Chicago’s east and west streets, causing Chicagohenge! ... Finding a place to spot Chicagohenge is a no-brainer! Simply find one of Chicago’s east-west facing streets, plop a seat, and enjoy the view."

Eclipse of Sun by Phobos Seen by Perseverance Rover

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Published: 22 April 2022

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On 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: https://mars.nasa.gov/news/9172/nasas-perseverance-rover-captures-video-of-solar-eclipse-on-mars/ 

Art Project: "Unit of Measurement"

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Published: 09 November 2018

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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.

Read more at: http://www.salina.com/news/20181027/land-institute-art-project-reflects-on-time-nature