Telescope Reviews: Re: Ground Truth for the Bortle Scale

Some sites, like Mike's description of Joshua Tree above, have such radically different darkness conditions in different quadrants that they're difficult to categorize. One spot I regularly use, Sunset Beach NC (a narrow inhabited barrier island on the NC/SC border) is a prime example of extreme sharp differences. It's shoreline faces just slightly east of due south, and is blessed toward its west end by a several-hundred foot wide swath of dunes and low scrub forest between the front row of houses and the beach, with unlit wooden boardwalks every block for public beach access from the street out to the strand - pefect to set up a grab n'go refractor on the boardwalk, protected from the ocean by the final (relatively high) line of dunes before the tidal strand.
TO THE WEST: Unfortunately, in a due west to northwest direction, the "redneck riviera" metropolis of Myrtle Beach throws up a hopelessly washed out dome of light up to forty-five degrees up into the sky. Unless it's a planet in this part of the sky, fuggetaboutit.
TO THE SOUTH: Wow, what a difference! There's NOTHING between you and St, Thomas, Virgin Islands nearly a thousand miles south-southeast over open ocean, and it's very dark, with the Milky Way being brightly visible from Sagittarius up through Cygnus. Many nights when wind is light, the ocean tends to create very stable seeing conditions to boot. Even thirty-five degrees rotation southward from the due west Myrtle Beach light-dome makes a vast difference in the observability of DSOs. These favorable conditions extend all the way to about twenty degrees south of due east...
TO THE EAST AND NORTH: when smaller local domes from the fishing pier and neighboring Ocean Isle begin to progressively intrude, extending nearly thirty degrees upward due east, but don't wash out the sky to nearly the extent that Myrtle Beach does to the west. To the northeast, the town of Shallotte throws up a dome nearly forty-five degrees in extent, and to the north, retirement and golf course developments on the mainland make the sky to the north below about 45 degrees more like typical suburban conditions anywhere.
OVERHEAD: However, straight overhead and down to about 45 degrees in any direction, the sky is dark enough to see somewhere between mag 5 and mag 6 stars easily, depending on moisture content and transparency. The Milky Way is easily visible, even from my the roof deck of my house back a quarter-mile from the ocean (where there are streetlights along the streets), though it is somewhat more washed-out viewing it from here than from out on the strand.

This is by no means a true "dark site" - just one that's good enough to still be quite enjoyable, especially out toward the ocean. But how in the world could you accurately pin down what this site is on the Bortle scale? If you were interested in objects in the Ophicus/Sagittarius/Scorpius region - fantastic. Also very good for the Virgo region of galaxies, cause they pass high overhead to the south. Also good even for galaxies in Ursa Major/Coma V. etc., when positioned high enough overhead to be out of the light domes. But terrible when that region rotates downward and westward. Downright disappointing for astronomy to the northeast and directly west below 45 degrees.

--------------------
Chris M., aka "First Sight"
Orion XT12i Dob with Moonlite CR-2 focuser
WO Megrez 90 refractor on UniStar Light mount
Nikon 10x50 Binoculars

Post Extras