Answer and Explanation:
Dispersion is the splitting of white light into a band of seven colors that constitutes the white light where after splitting each light corresponds to specific wavelength, where violet has the shortest wavelength and red has the longest.
As a result of dispersion, the images formed of the planets and stars so formed appears to blurred because the red and the violet component of white light come to meet from different locations or points.
This problem was avoided by using the telescope in such a way that the spectrograph slit lies perpendicular to the horizon.
