Center-to-limb variation for the Fe I 6303.5 Å line. Top and middle panel: spectral profile and bisectors from the disk center (purple) toward the solar limb (decreasing gray scale), with FTS atlas comparison (yellow). Intensities were normalized to the spectral continuum. Air wavelengths (in Å) were translated into Doppler velocities (in m s⁻¹ ). Bottom panel: line core velocities plotted against the heliocentric position μ, with colored symbols indicating the solar axis. The average trend is drawn in black as a thick, solid line.