الفهرس 
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Abstract
Spectral classification is one of the fundamental branches of astronomy, in the same way as astrometry is. Generally classification is used whenever we need to order a large number of objects, or a variety of phenomena. Classification methods appeared in astronomy in the nineteenth century when a large number of stellar spectra suddenly became available, through two technical developments - the objective prism and the photographic
plate.
The aim of this thesis is to get a new criteria for spectral classification of early type stars
in the ultraviolet region by carrying out spectrophotometric analysis of observational ultraviolet data of stars obtained by the 52/68 Ultraviolet Sky Survey Telescope ( UVSST) aboard the European Space Research Organization ( ESRO) Satellite TDI.
The present thesis consists of three chapters as follows :
The first chapter deals with some fundamentals common to most regimes such as
electromagnetic radiation, energy (Intensity, Flux, Luminosity), Blackbody radiation and
stellar photometry.
Chapter two represents the transitions occurring between the energy levels of the atoms,
from which the line and continuum spectrum obtained, stellar spectrum, spectrum analysis, spectral sequence (0, B, A type stars), ending with a discussion of some methods of
classification in the visible and ultra- violet regions.
Chapter three shows the method of reduction followed in this work to classify some early
type stars. The method of classification depends on the flux in the ultra-violet region, with
the results and discussions.
We have succeeded to establish a new criteria for spectral classification based essentially
on the values of fluxes for some early type stars from which we plot some relations between spectral type and colour index, colour temperature and colour index, spectral type and corrected observed flux ratio , and corrected observed flux ratio and colour temperature.