the present volume contains the texts of the invited talks and contributed papers presented at iau colloquium no. 123 on `observations in earth orbit and beyond, which was held at goddard space flight center on 24-27 april 1990. the colloquium featured invited reviews of virtually all current and approved future projects in space astronomy, over the entire electromagnetic spectrum from gamma-ray to radio, of all major space faring nations of the world. the reviewer was typically either the project scientist or principal investigator of a given project. also included are reviews and panel discussions of current and future launch systems, advantages and disadvantages of various orbits and sites in space for astronomical observatories, and major unsolved problems of astronomy. a number of contributed papers were also given at the meeting and are included in the current proceedings. this volume contains an olympian view of the space astronomy program, while serving as a handy reference to researchers who often have difficulties in keeping up with the development in the multidisciplinary field of space astronomy.