The main purpose of this thesis is to study and analyze the solar radiation data in iraq, and to review the relationships developed by researchers in different countries and different locations in the world.They are used to predict the monthly average hourly and daily for direct, normal diffuse and global solar radiation in horizontal and tilted surfaces in W/m2 and W-day/m2 .at 25 stations in Iraq. Some of these equations depend on meteorological parameters such as: sunshine duration .air mass, altitude and elevation of sun. Monthly average hourly distribution of solar radiations on horizontal surface for all month of the years form 1991-1993 was studied at Baghdad city using solar radiations data supplied by the Solar Energy Research (S.E.R.C.) in Baghdad. The results showed a maximum yearly average monthly average hourly of global radiation of (950) W/m2 during June at noon; diffuse radiation of (250) W/m2 during May, between 10:00 a.m. and 14:00 p.m. : net solar radiation of (600) W/m2 during July at noon : ultraviolet of (32) W/m2: during June and July between 11:00 a.m. and 13:00 p.m. and infrared radiation of (130)W/m2 during July and August between 16:00 and 17:00 p.m.. Generally ; the global, net and ultraviolet solar radiations were higher during the year 1993 than in the year 1992. Seven modified. Angstrom linear equations were used to estimate predicted values of global, diffuse and direct solar radiations for the years (1971-1980) for 25 stations in Iraq. In this model, the values of (a and b) for I he seven equations and a ,B and y were calculated. The results were plotted, and analyzed on the geographical map of Iraq, so that the isoradiation lines can be utilized to estimate the solar radiation values in any part of the country and at any time of the year. From North to South, daily mean annual variations of global, diffuse and. direct radiations of (5000-5200, 1400-1700 and 3000-3400) W-day/m2 respectively were found. The same model was applied on Bahgdad city for the years (1992-1993). The daily mean annual global diffuse and direct radiations were (4810, 1450 and 3380) W.day/m2 respectively A Trigonometric equations were developed to estimate the monthly average hourly lor direct normal radiation and direct, diffuse and global solar radiations on horizontal and tilted surtace in Baghdad. The maximum monthly average hourly direct radiation was found lo be higher on (300 tilted surface (824) W/m2 than on horizontal surface (613) W/m2 during June at noon. Similarly, the global radiation was higher on the tilted than on horizontal surface (1028 and 968)W/m2 during May. respectively. Th3 MgO powder is prepared by thermal decomposition of hydromagnesite of Mg5(CO3)4.(OH)2.4H2O and magnesium hydroxide Mg(OH)2 powders in the temperature range 400-1000°C. The peak full width at the ha!f maximum measured and corrected according to three different equations Deals with the shape of the diffraction peak. The crystallite size is then determined by using Scherror's equation. The crystallite size is found to increase linearly with temperature. Adding a binder (P.V.A) to the initial reactants assist the hydromagnesite to decomposed at lower temperature . The effect of adding Calcium carbonate to the hydromagnesite in air and in vacuum on the crystallite size of MgO is studied and it is found that the crystalline size of MgO obtained is smaller than crystallite size of MgO which is obtained without adding Calcium Carbonate which means that the CaCO3 act to inhibit the growth of MgO. Yet, Smaller crystallite size of MgO are observed when the decomposition of the mixtures of hydromagnesite and Calcium carbonate occurred in vacuum. Minimum crystallite size for Magnesium Oxide obtained after total converion of the initial reactants was 112.5 A° when CaCO3 is added and the decomposition take place in vacuum. First harmonic analysis (Fourier series) of global and diffuse solar radiations in 25 stations in Iraq lor the years (1971-1980) was applied. For global radiation the maximum to minimum values on explained per cent and total variance were [98.17-94.01 and 43.39-14.24 (W/m2)2] while for diffuse radiation ihe values were [53.83-14.34 and 2.22-1.03 (W/m2)2 respectively. In addition, phase angles and the dates of maximum intensities were estimated for those stations for both global and diffuse radiations. First harmonic analysis was also developed to predicted monthly aven-ge daily global and diffuse radiations on horizontal surface in Baghdad for the years 1992 and 1993. Maximum values were during June of the years 1992 and 1993 for both the global and diffuse radiations (709 and 701) W/m2 and (203 and 177) W/m2 respectively. In addition, phase angles and amplitudes for global and diiiuse radiations were calculated up to the first harmonic. The model of modified Angstrom linear equations gives a generalized view (annual average daily) of the global, diffuse and direct radiations on horizontal surface in clear and cloud sky conditions. In comparison, the model of trigonometric equations provides a more detailed view (monthly average hourly) of the direct normal radiation and global, direct and diffuse on both horizontal and tilled surfaces in clear sky conditions only. However, ihe latter requires an input of geometrical parameters only (altitude and latitude) while the first needs measured data of diffuse and global radiation and the sunshine duration.