City Creek Nature Notes – Salt Lake City

May 15, 2017

May 13th

Filed under: Astronomy — canopus56 @ 3:32 pm

The Great Journey

Midnight. I return to the canyon under a bright near full Moon to see if moths have returned for this season. A white box lid and a flashlight should attract them. But it too early in the season and none arrive to be photographed. The sky is a blue-slate from the Moon’s rays, and this washes out the stars and their arrangement in constellations. This evening, the washed out sky reveals only a few of the brightest nearby skies, including the tail of the Big Dipper that points southeast to the bright star Arcturus, a mere 37 light years away. It is known as the “Guardian” whose rising in spring was a signal to farmers for thousands of years to being planting. Only bright Jupiter and the brightest star Spica can pierce through the moonlight. When I was in the canyon under a bright Moon in December (Dec. 14th), Orion dominated the sky. The Earth and the Milky Way hurdle towards an unknown fate in the distant future somewhere near Spica. This night sky underscores the fragility of the infinite variety of life, including the Giant crane flies and the Western tanagers, that surrounds me in the canyon. In the silver light, the fragility of all its beauty fills my heart.

* * * *

Throughout much of the last 10 million years of our present Tertiary period, including when mammals came to dominate the Earth, the Earth has been traversing relatively evacuated regions in the Milky Way’s disk. The first of these, which extends over a kiloparsec anti-spinward down the galactic Orion’s Arm for 3,000 kiloparsec (9,800 light-years) is the “Great Dent”. Next, is Gould’s Belt, which the Earth and Sun are currently crossing. Gould’s Belt is a defined by a ring of loose groups of the brightest stars, called OB associations (Grenier 2004). The winter Orion constellation and its star factory, the bright nebulae M42, sits at the out-galaxy end of this 300 by 650 elliptical disk of clouds, nebular star-forming factories, bright open clusters, and older OB star associations (Frisch 2000, Henbest and Couper 1994). The nebular clouds condense into star factories like Orion’s M42 and M8. Newly born bright stars exit the factories in dense gravitationally bound open clusters. With the passage of time they disperse into largely loosely bound OB associations. In a few months in the summer, the opposite inward-galaxy pole of Gould’s Belt, which contains the bright nebulae M8 in the constellation Sagittarius, will be on the southern horizon. In addition to OB star associations, the Gould’s belt disk includes about 40 remnants of novae that exploded during the Belt’s early condensation from an 200 million year old super gas cloud, now called Lindblad’s Ring (Olano 2016, Olano 2001). Those novae evacuated the relatively empty and safe area inside the ring called the Local Bubble. The Earth sits off-center of the Gould’s Belt ellipsis, and the Earth wandered here about ten million years ago, as novae exploded around it. Physicist Ellis and astronomer Schramm suggest that that nearby supernovae could have induced mass extinctions on the Earth that aided in the extinction of the dinosaurs (Ellis and Schramm 1995). The meteorite impact at the end of the Cretaceous is generally accepted as the ending the dinosaur era, but the theory is contradicted. Some dinosaur species survived the impact. Further stress from the supernovae and novae radiation could have provided extra stress that completed the extinction. In 2016 in separate papers based on studies of irradiated metals deposited on ocean bottoms, Breitschwerdt and colleagues, Melott and Wallner and colleagues suggest that the Earth has been bombarded every 2 for 4 million years by intense radiation from supernovae (Breitschwerdt et al 2016, Melott 2016, Wallner et al 2016). This raises the speculation that genetic changes that gave rise to modern humans may have been caused by radiation from Gould’s Belt novae or supernovae as our wandering planet crossed the Belt’s interior.

In addition to this local drama, the Earth, the Milky Way and the surrounding galaxies are all streaming towards the Virgo Supercluster. Almost directly above my head and about thirty degrees celestial north of Spica, the orientation of Earth’s tilted axis and its orbit presents the relatively star-empty skies of the galactic North Pole. Other than Arcturus, there are no bright stars in this direction, and although hidden by moonlight, I am looking up towards the “Realm of the Galaxies”, and this region of sky contains the Virgo super-cluster of galaxies, about 150 million light years away, whose great mass pulls all local galaxies, including the Earth and the canyon, towards it at about 250 kilometers per second (Lyndell-Bell et al 1988). The Virgo Supercluster was originally proposed by French astronomer and galaxy cataloguer Gerard Henri de Vancouleurs while working at Lowell Observatory in Arizona (de Vancouleurs 1953). De Vancouleurs and his astronomer colleague and wife Antoinette spent their lives cataloguing the positions of 23,000 galaxies.

The Milky Way and the Virgo Supercluster themselves are all being drawn at about 570 kilometers per second towards an unseen mass about 500 million light-years away that the astronomers originally called “the Great Attractor”. The Great Attractor is at a point in the sky obscured by the Earth’s mass (as seen from the canyon) in the southern hemisphere in the constellation Norma, and we know of the Attractor’s existence only from its effects on surrounding galaxies. Those effects are found from the position and relative direction of travel of galaxies, and direction of travel is a galaxy’s Doppler redshift. Having survived its traverse into a hazardous, but now relative safe, resting place in the Milky Way within Gould’s Belt, the Earth and the canyon speed towards the Great Attractor. In 1987, Tully and Fisher at the University of Hawaii completed their graphic atlas of nearby galaxies out to 40 million parsecs (Tully and Fisher 1987). In 1988, Lynden-Bell at Cambridge, Faber at Lick Observatory and colleagues by analyzing the red shifts of galaxies identified a larger mass, supposed as located in region of the constellations Hydra and Centaurus, toward which both Milky and Virgo Supercluster are drawn (Lyndell-Bell et al 1988). Since 1988, surveys of the estimated 100 billion galaxies in the observable universe have continued, and in 2015, red shifts for about 1.2 million galaxies are known. With this increased knowledge in 2014, Tully, Courtois, Hoffman and Pomarede prepared an improved analysis of the direction flow of galaxies within one billion light-years and this better revealed the structure of what they now call the Laniakea supercluster some 500 million light-years distant. The Laniake supercluster is a filament of galaxies that stretches from the constellations Hercules through Virgo and down to the constellation Norma (Tully, Courtois, Hoffman and Pomarede 2014a, Tully, Courtois, Hoffman and Pomarede 2014b (Video)). The Virgo supercluster is a local spur that connects to that larger filament, the Laniakea supercluster. Laniake is a compound word from Hawaiian: lani for sky, heaven and kea for wide or broad.

Changes in the Earth’s fate and night sky will come sooner then our encounter with the Great Attractor. The Earth travels in a sinusoidal path, moving above and below the mean galactic plane about every 33 million years (Bash 1986). It is now pointed above and traveling away from the mean galactic plane and towards a point below the constellation Hercules. In the rotating frame of the Milky Way, the Earth travels galactic spinward about 1,000 parsecs every 10 million years (Bash 1986). In about 1,500,000 million years, the wandering Earth will exit the Local Bubble and re-enter a region of dense dark nebular clouds that separates the Gould’s Belt and the wall of Lindbald’s Ring from the next bubble evacuated by novae, called the Cygnus Loop, and then pass by the North American nebula, called NGC 7000 by astronomers, on its way in the direction of the bright star Deneb in the constellation Cygnus. In another 55 million years, the Earth will enter the next galactic arm out, the Perseus Arm (Bash 1986), but its path cannot be predicted with certainty, since how the Sun will gravitationally interact with large molecular clouds along its route is not known. On a clear summer night far from the city, the dark nebular clouds that separate Lindblad’s Ring from the Cygnus Loop’s interior can be seen obscuring constellation Cygnus and stretching between Deneb and the nearby bright double star Albireo.

* * * *

On May 13th, 2014, a man with mental health issues was convicted of attempting to set an arsonist fire in Memory Grove (Salt Lake Tribune). On May 13th, 2004, the 10th annual Memory Grove cleanup was set (Salt Lake Tribune). (In 2017, the annual cleanup remains a well-attended spring event). On May 13th, 2003, Wildlife Firefighter Trainee Dirk Huber recalls fighting fires in City Creek Canyon during the 2002 season (Salt Lake Tribune). On May 13th, 1914, the City Commission adopted an ordinance for the creation of a scenic boulevard to be called Wasatch Boulevard (Salt Lake Telegram). The boulevard was planned to run up City Creek Canyon, then to 11th Avenue, then to along 11th Avenue to Popperton, then south on Thirteenth East to 1200 South, then westward back to Main Street past farms along 1200 South, and finish by going back up Main to downtown. A budget of $5,000 was provided to widen the City Creek Canyon road using prison labor to support automobiles for the first seven and one-half miles. On May 13th, 1913, City Creek water was tested and found to have a high purity (Salt Lake Tribune). On May 13th, 1913, the City Commission rejected the Waterworks Superintendent Korn’s proposal to construct a highway up City Creek Canyon and into Morgan County (Salt Lake Tribune). On May 13, 1906, racing bicyclists were training in City Creek for an upcoming 18 miles event (Salt Lake Tribune).


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