sky is severely hampered, and background galaxies, such as Dwingeloo 1, were only discovered recently through observations in radio and infrared. The general shape of the ultraviolet through near-infrared (0.125 to 3.5 μm) extinction curve (plotting extinction in magnitude against wavelength, often inverted) looking from our vantage point at other objects in the Milky Way, is fairly well characterized by the stand-alone parameter of relative visibility (of such visible light) R(V) (which is different along different lines of sight), but there are known deviations from this characterization. Extending the extinction law into the mid-infrared wavelength range is difficult due to the lack of suitable targets and various contributions by absorption features. R(V) compares aggregate and particular extinctions. It is . Restated, it is the total extinction, A(V) divided by the selective total extinction (A(B)−A(V)) of those two wavelengths (bands). A(B) and A(V) are the total extinction at the B and V filter bands. Another measure used in the literature is the absolute extinction A(λ)/A(V) at wavelength λ, comparing the total extinction at that wavelength to that at the V band. R(V) is known to be correlated with the average size of the dust grains causing the extinction. For our own galaxy, the Milky Way, the typical value for R(V) is 3.1, but is found to vary considerably across different lines of sight. As a result, when computing cosmic distances it can be advantageous to move to star data from the near-infrared (of which the filter or passband Ks is quite standard) where the variations and amount of extinction are significantly less, and similar ratios as to R(Ks): 0.49±0.02 and 0.528±0.015 were found respectively by independent groups. Those two more modern findings differ substantially relative to the commonly referenced historical value ≈0.7. The relationship between the total extinction, A(V) (measured in magnitudes), and the column density of neutral hydrogen atoms column, NH (usually measured in cm−2), shows how the gas and dust in the interstellar medium are related. From studies using ultraviolet spectroscopy of reddened stars and X-ray scattering halos in the Milky Way, Predehl and Schmitt found the relationship between NH and A(V) to be approximately: (see also:). Astronomers have determined the three-dimensional distribution of extinction in the "solar circle" (our region of our galaxy), using visible and near-infrared stellar observations and a model of distribution of stars. The dust causing extinction mainly lies along the spiral arms, as observed