Interstellar Extinction (Galactic Smog)
=======================================

... is a fractal.  Very patchy and nonlinear.

The local "average" is about A(V) ~ 1 mag/kpc.

Usually expressed as a ratio of total to selective
extinction, in magnitudes:

A(  )/E(B-V) = f (  ; R)

Where the parameter R = A(V)/E(B-V) varies from
here to yonder, but a good average value is 3.2.

Useful interpolation formulae and data:

- Seaton, M.J. 1979, M.N.R.A.S. 187, 73p.

- Rieke, G.R., and Lebofsky, M.J. 1985, Ap.J. 288, 618.

- Cardelli, J.A., Clayton, G.C., and Mathis, J.S.
  1988, Ap.J. (Lett.) 329, L33.

Useful maps:

- Burstein, D., and Heiles, C. 1982, A.J. 87, 1165.