Hi folks First off I have only just figured out that v is used as bloody frequency in loads of astrophysics equations. Not fun. I've got monochromatic flux as: Fv = dE / dt·dA·dv now I'm happy with this. But now the lecture notes I'm looking at describes monochromatic luminosity as "the energy emitted by the source in unit time, per unit wavelength" but then gives the equation as: Lv = dE / dt·dv so surely it should be ""the energy emitted by the source in unit time, per unit frequency" BUT monochromatic means the energy at a given wavelength doesn't it, however there is no wavelength in the equation. Could somebody please clearly state the definition and equation, saying what each letter in the equation represents, of monochromatic/bolometric flux/luminosity as I'm really getting stressed over it and can't revise anything else until I've got my head wrapped round it.