1. The problem statement, all variables and given/known data Calculate the wavelength of the Lyman-α line (the transition from the 1st excited state to the ground state) for (a) hydrogen atoms and (b) positronium e+e-, and explain the origin of their difference. In the light emitted from a star, a pattern of emission lines is found with every second line coinciding with a line of the Lyman series of hydrogen. Identify which ion causes this pattern and identify the observed transitions [assume the star is stationary with respect to the Earth]. 2. Relevant equations 3. The attempt at a solution (a) the positronium is simply a particle of reduced mass μ = m1m2/(m1+m2) orbiting a central particle of m1+m2. μ = m/2. Is the ion a positronium? Since the E1 is proportional to m, and that positronium has half the mass of hydrogen..