Following a few years of activity related to the observations of Novae in collaboration with Rosino and to the analysis of open clusters under the guidance of Wilhelm Becker, I went at Lick Observatory to work, under the direction of Merle F. Walker, with the Lallemand electrographic camera. In addition to the development of the Laboratory and high vacuum systems I got deeply involved in studies of the galaxies, rotation curves observations with the 120" telescope, analysis of the data and derivation of the physical parameters of the galaxies. In this period Walker and I achieved unique results in the field in addition to improving considerably the observing technique with this state of the art instrumentation. My expertise in this period was addressed to instrumentation and extragalactic astronomy. I had the fortune, during this period, to learn also from George Herbig and to help Ira Bowen (then Director of the Mount Wilson and Palomar Observatories) in setting up the camera he designed for the Lallemand instrument on the Coudé Focus of the 120".
After post doctoring at Lick Observatory I had to carry out military duties in Italy where I became second lieutenant at the Nuclear, Biological and chemical defense laboratories in Italy. During this period I was in charge of a laboratory and I had to set up instrumentation to measure the quality of filters to be used in nuclear shelters.
Following the military service and due to personal reasons, I spent almost a year in Germany at the Observatory of Hoher List, University of Bonn. During that period Dr. Thornton Page offered me to join his group at Wesleyan University and NASA Johnson Space Flight Center, Houston where he was working on a project having as a goal the installation of a telescope on the Moon using one of the Apollo flights. While the plan to build a telescope on the Moon failed because of the high cost and because of the competition with the plan of an orbiting telescope (the project then headed by Lyman Spitzer), during this period I a) further developed expertise in electrographic cameras and Image tubes getting at the JSFC my own laboratory for the Kron camera and b) started in collaboration with Herbert Rood (already expert in clusters of galaxies thanks to his fundamental work on the Coma Cluster of galaxies), at that time astronomer at Wesleyan university, the surveys on clusters of galaxies that generated the research and discovery on the large scale distribution of galaxies.
The research on the large scale distribution of galaxies started in Houston and developed during my appointment at Mc Donald Observatory (University of Texas), where I got involved in instrumentation especially for the 107 inch telescope (Kron Camera, spectrograph and magnetically focused image tubes), and at the University of Oklahoma where I also started to give regular courses of Astronomy.
It is during these years that Rood and I, who were the first to start making redshift surveys of regions of the sky, discovered that the outskirts of clusters (this research was in part triggered by long discussions I had with F. Zwicky) were formed mainly by not virialized galaxies at the same distance of the cluster and that galaxies on a larger scale were distributed in a kind of filamentary structure. Indeed in the early seventies (University of Oklahoma) we fully realized that galaxies were not distributed uniformly in the sky and we discovered as well regions void of galaXies (see my paper in Nature). Indeed it is during that time that we, Rood and I, coined the word VOID (we consulted on the English word with my colleague and friend John Cowan).
Due to limitations I had with observing at KPNO and following my brief permanence in Italy and some contacts I had with Prof. Oort, I started, with the collaboration of Riccardo Giovanelli who knew radio telescopes (in 1975 I asked Dr. Giovanelli to make a study of the largest telescopes in the world in order to optimize the large scale studies and the detection of HI depleted galaxies in clusters), and later also with Martha Haynes, a research on large scale structure and galaxies at the Observatory of Arecibo. Here in addition of further tracking down the structure of the distribution of galaxies on large scales, in particular we did basic work on the region of the Hercules super - cluster (previous studies also in collaboration with Massimo Tarenghi) and on the region of the Perseus Super-cluster (as we called it) we studied and discovered that the spiral galaxies nearest to the cluster center (Coma and A 1367) are deficient of neutral hydrogen because of the effect of ram pressure. These studies of galaxies were at the time one of the major endeavor of the Arecibo Telescope, studies which were later continued and deepen by Haynes and Giovanelli. The study for HI deficient galaxies in A1367 was also triggered by a discussion I had on the phone with Riccardo Giacconi who pointed out that members of his group had just detected X ray emission from galaxies members of this cluster.
In the early eighties, and following the premature death of the dear friend George Abell, I decided to help in carrying out the survey of southern clusters of galaxies, a plan George had since a very long time. To this end I trained a student of mine, Olowin, and collaborated in setting the plan with Corwin. I was the P.I. of the original NSF proposal to carry out the job and however I thought proper not to participate to the publication of the catalogue since practically all the work had been carried out by Corwin and Olowin while the original idea belonged to George Abell.
It is during this period, however, that following a collaboration with the European Southern Observatory that started in 1976, I formulated the decision, also because of the various discussions I had with some Italian colleagues, to go back to Italy. After a sabbatical period at ESO I accepted the position in Milano where I was asked to organize the astronomical research and above all to rebuild and reorganize the Observatory of Brera (Merate and Milano sites) that was not producing state of the art research, had no activity in extragalactic astronomy and which had completely decayed. At the same time my experience in instrumentation, telescopes and cosmology could be used to help in bursting Italian astronomy.
Brera became a very well known observatory in the following years and we developed optical astronomy and above all we were able to develop technology in the X-ray. To have an observing facility we started to collaborate with Mexico, helping with the instrumentation in exchange of telescope time, and triggered, when I was part of the Italian Astronomical Research Council, the call for proposal to build what later became the National Italian Telescope at the Canaries Islands (TNG). I also started, in collaboration with younger colleagues (Vettolani especially) the ESP survey and later, mainly in collaboration with Peter Shaver and Hans Boehringer, we generated the REFLEX survey.
My goal when I accepted the position at Brera was to make out of it one of the best research Institute in Italy an make it rather competitive abroad. While the collaboration with Mexico was very important and the solution of an immediate observational and instrumental need (we got routinely telescope time at the 2 meter telescope, adjusted the telescope and started an advanced instrumental program) the main tasks for Brera were: a) create a research activity and collaborative atmosphere, b) initiate a strong instrumental program developing expertise existing in Milano (X ray) and start as soon as possible the further development in optical instrumentation, c) foster the development of National facilities. At the same time the plan was to develop at ESO large observational programs in order to have data and make the youngest grow scientifically. In ESO I had also a very active permanence as an Italian member of the OPC (TAC) where the major contribution was probably in generating, in collaboration with other members and following some instructions given by Giacconi, the panel system with an evaluation procedure similar to that in use at the HST.
Milano and Brera participated to most of the largest activities initiated in Italy and triggered many of these at a National level including a deep and strong interaction with ESO where I continued a strong collaboration. on the other hand many of the plans we had did not succeed. Among these the project of data analysis Institute aimed to the advanced development of software and Archives to compete in science and the making of a X ray satellite with a wide field of view to make a deep survey of the sky in the soft X rays. The first designed under the guidance and following some ideas by Burg et al. and the second following also ideas, analysis and science goals of scientists with vision.
The WFXT (Wide Field X ray Telescope - of which was the P.I. heading an International collaboration for the phase A study) development supported in part by the Italian Space Agency has been nevertheless the leading and supporting goal that allowed us to push the replica Mirror technology and gain experience. The technology that was improved considerably and with increasing know-how thanks to the contribution of the Germany Industry that controlled Medialario during the manufacturing of the XMM Mirrors.
We participated to the Russian satellite program developing and producing in collaboration with the UK the JETX Telescope. However due to the evolution of the Russian events this project had to be stopped. Fortunately we were able to use the JETX spare mirrors for the US MIDEX mission Swift and this became one of the major endeavors of our group that started an excellent collaboration with US and UK involving in it various Italian researchers as well.
Swift and the GRB research triggered also the idea of the robotic Telescope that is now working on the La Silla peak in Chile. While I generated this project and got the funding from the Ministry of education, the coordination of the building and of the telescope itself has been due to Zerbi who coordinated the project and the instrumentations and to an enthusiastic and professionally competent team.
To better support these projects, but also because of an Italian science politics and environment that I could not support, I decided to detach myself from the direction of the Observatory and for any other duty at the National level. The council of the Observatory nominated me "Astronomer Emeritus".
On the Teaching side as Professor at the University of Milano I was able to develop extragalactic astronomy (there was no extragalactic astronomy or cosmology at the Observatory of Brera) and get students interested in it. In the University effort I got in the early phases a large contribution by the then Director of the CNR in Milano Dr. Enrico Tanzi. As a whole astronomy developed in Milano quite nicely forming in the various centers expertise that is worldwide recognized. We did not reach however the high level goal I believe we could reach.
In the 2004, and in relation due the Swift Project, I became adjunct Professor at Penn State University at State College, Pennsylvania, USA.