| The Fly's Eye group has studied two of the most important topics of extremely high energy cosmic ray (EHECR) physics--the spectrum and composition. The results from study of these two topics show evidence of two components in EHECRs. One is a heavy source, mainly iron nuclei, which dominates at energies lower than 3EeV. The other is a light source, mainly protons, which dominates at energies higher than 3EeV. This study uses several anisotropy analyses to study the arrival directions of EHECRs.;The analyses consist of the six sky lobes, the harmonic analysis, the galactic plane enhancement factor, the galactic latitude gradient, the galactic plane clustering, and the supergalactic plane clustering. A consistent trend exists in all analyses except harmonics analysis and supergalactic plane clustering; the largest anisotropy is at 0.4-1.0EeV and then decreases as energy increases. This trend can be explained by an overestimation of events near the galactic plane and an underestimation of events near the poles. This trend shows that a small degree of anisotropy exists at energies below 3.2EeV and might be a clue to the galactic origion of these cosmic rays. We also found a clustering of events near the supergalactic plane. Although this finding is a confirmation of other reports, the relation of this clustering and the supergalactic structure is not yet clear.;We start with a review of cosmic ray physics and the Fly's Eye detector. The system resolutions and the difference between the real detector and the Monte-Carlo are examined. Some systematic errors and differences are found. The data structure and isotropic backgrounds are then discussed. Some improvements are made to avoid large error or to increase statistics. Two types of backgrounds, scrambled events and live time, are discussed and compared. For the first time, event rate is introduced in the live time background. The two backgrounds are consistent with each other in the large scale. |
