Identify Greek letters used in formulas
The first one is alpha (α); the second one is delta (δ). You can study the shapes of the letters here:

https://en.wikipedia.org/wiki/Greek_alphabet

Here's what they mean (information from a comment to your question):


  Orientation models use three Euler angles to describe body
  orientation. The first two angles are the right ascension and
  declination of the north pole of a body as a function of time. The
  third angle is the prime meridian location (represented by "W"), which
  is expressed as a rotation about the north pole, and is also a
  function of time.