19.5 degrees north and south are the latitudes
where the apex points of a star tetrahedra within a sphere
will contact that sphere's surface,
when one apex is positioned at the north or south pole.

On the Sun: sunspot activity and the region of peak temperatures is limited to 19.5 degreees north and south.
On Venus: the presumably active major volcano complexes Alpha and Beta Regio are near 19.5 degrees.

On Earth:
Mauna Loa, Hawaii (19 degrees 28 minutes N, 155 degrees 37 minutes W) The largest shield volcano is at 19.6 degrees north. This is Mauna-Kea volcano on the island of Hawaii.
Mexico City, Mexico (19 degrees 23 minutes N, 99 degrees 10 minutes W) The Pyramid of the Sun at Teotihuacan is at 19.6 degrees north.
Dzibalchen, (Yucatan), Mexico (19 degrees 28 minutes N, 89 degrees 46 minutes W)
Georgetown, Grand Cayman Island (19 degrees 18 minutes N, 81 degrees 26 minutes W)
Mount Emi Koussi, Chad, Africa (19 degrees 47 minutes N, 18 degrees 34 minutes E)
Mount Kalsubai, (near Bombay), India (19 degrees 33 minutes N, 73 degrees 43 minutes E)
Mountain near Xiangkhoang, Laos (19 degrees 17 minutes N, 103 degrees 17 minutes E)
Mountain near Potosi, Bolivia (19 degrees 13 minutes S, 66 degrees 22 minutes W)
Yasur Volcano, Tanna Island, Vanuatu (South Pacific Ocean) (19 degrees 31 minutes S, 169 degrees 25 minutes E)
Mount Samuel, Northwest Territory, Australia (19 degrees 13 minutes S, 134 degrees 8 minutes E)
Gweru, Zimbabwe, Africa (19 degrees 31 minutes S, 29 degrees 49 minutes E)

On Mars: the "vast" Olympus Mons shield cone volcano is at 19.5 degrees.
On Jupiter: the "red spot" which is an obvious vortex is at 19.5 degrees.
On Neptune: in 1986 Voyager II discovered a similar spot at 19.5 degrees north.

Based on Richard Dannelley's book, Sedona: Beyond the Vortex and Bruce Rawles

Why '19.5 degrees' is Significant

19.5 degrees is the angle that's been found by researchers (Richard C. Hoagland, Stanley McDaniel, Erol Torun, Horace W. Crater, etc.) to be repeatedly encoded in the structures of Cydonia. It is viewed as a definite 'signal in the noise' - some kind of a 'message' left there by some intelligence. 19.5 is called t, the 'tetrahedral constant', because of its significance in tetrahedral geometry (a tetrahedron is a pyramid shape composed of four equilateral triangular sides): the apexes of a tetrahedron when placed within a circumscribing sphere, one of the tetrahedron's apexes touching the north pole, the other three apexes touch the surface of the sphere at 19.5 degrees south latitude. Why this number would be important to the builders of the Martian structures is not clear (though Hoagland is theorizing that it has to do with what he calls "hyperdimensional physics").

Nile Time-Map & tetrahedral geometry -- 19.5 degrees
http://prophetic.simplenet.com/elysium/nile-timemap.htm

The emphasis on 19.5 degrees is not confined to the Martian structures. It has been found to be associated with various ancient structures here on earth - Giza pyramids, Avebury (the largest stone circle in the world, near Stonehenge), Pyramids of the Sun and Moon at Teotihuacan, etc. It is also worth noting that the Egyptian hieroglyph for Sirius, the brightest star in the sky which was extremely important to ancient Egyptians, is an equilateral triangle which can be viewed as a 2-dimensional representation of a tetrahedron; and in the Egyptian translation, it means a doorway... a sort of 'stargate'. Curiously, it has also been observed that 19.5 degrees is closely linked, for some reason, with the NASA space missions (for example, Mars Pathfinder landed at 19.5 degrees lat. of Mars on July 4, '97). In fact, not only did Pathfinder landed at 19.5 N, the longitude of the landing site was approximately 33 W - which is the very number of the longitude of the apex of the Great Bend of the Nile (33 E)! Now, this strongly insists on the relevance of the Nile numbers, and someone behind the scenes is well aware of it. As we move on, the number, 19.5, will also be very important in my Nile Time-map theory. Perhaps, as the Nile-Mars connection bridged by '19.5' appears to suggest, Mars was somehow involved during the 'Prometheus / Pandora period.

 
http://imaginativeworlds.com/forum/showthread.php?6788-19-5-Degrees