Webometric analysis is carried out in order to measure the web structures, content, and visibility / presence. In webometric study, quantitative and qualitative analysis of websites will indicate their impact rate and visibility rate. Webometrics is one of the emerging research fields in Library and Information Science in recent times. The book provides methods of data collection, webometric tools and software used. It describes the analysis carried out on Astronomy and Astrophysics, Observatory and Space Science Libraries Websites in the World. The book covers six areas of Webometrics research, viz., Web Page Content Analysis, Web Link Structure Analysis, Web Impact Factor (WIF), Ranking of Websites, Performance and Accessibility, and Link Network Analysis. The ranking of websites according to WIF, WISER, Google Page Rank and Alexa Traffic Rank are presented. The book describes how the data has been analyzed statistically using various methods such as Regression Analysis, Numerical Analysis, ANOVA Ranking Analysis. Comparative Analysis of all the Ranking identifies the difference in ranking methods. This book will be useful to Library and Information Science Professionals, Librarians, Faculties, Students and Researchers.