Problem with diffraction equations (diffraction and astrophysics)

1. The problem statement, all variables and given/known data
Hey everyone. Just as a preface so you all know, I’m in England studying AQA Physics A.
I’m currently studying the optional astrophysics module.
I have a problem – in all the textbooks and revision guides I have, there is a topic on diffraction of light through a grating (Unit 2 topic), and there’s a topic in my Collins Unit 5 textbook on resolving power of telescopes (Unit 5 optional topic astrophysics).

First of all, in the Unit 2 diffraction topic, it states that for light being diffracted, the equation for finding the maxima is given by sinθ = nλ/d (where n = a whole number (integer)).

However, in the Unit 5 astrophysics resolving power of telescopes topic, it states that for light being diffracted (and forming an Airy disc), the equation for finding the minima is given by sinθ = nλ/d (where n = a whole number (integer)).

I’m really confused here, because both are examples of light diffraction and I have no idea whatsoever why the same equation has been used to describe the locations of maxima and minima. It just doesn’t make sense.

Help pls?

edit: I should note that in the equation, d = mirror diameter (telescopes) or distance from grating to screen (gratings).

http://ift.tt/1ja0SvJ

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