The mathematical form, the symmetry of the spiral structure, and the projection of the galactic disc on the image rnof the spiral galaxy M31 have been directly studied. It is found that M31 has two symmetric arms, i.e. the pitch rnangles of the two arms are nearly equal; these are 7.7° and 8.0°, respectively. Using the method proposed in this rnletter, the inclination angle of the galactic disc ofM31 is also obtained, which is 77.5° and is in good agreement rnwith previously published results.
展开▼
