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The diagram (Fig. 1) qualitatively exhibits how several important observations will have to be undertaken. Here, I would like to, at least, raise the question or discuss the problem referring; to “Man in Space”.

I would like to trace the evolution of the major problems or questions since the 1950’s by showing several diagrams (Fig. 1a-e) based on my own recollections. As for the coordinates of the diagrams, the latitude towards North indicates the magnitude of surprise and that towards the South indicated is the deepening of our knowledge. Of course such a visual approach is incomplete and is full of personal prejudices, and many important subjects and considerations may be missing.

Two-dimensional maps of the Crab Nebula have been synthesized in 22–64 keV range through the modulation collimator experiment. The effective angular resolution is about 15″. The result indicates that the Crab morphology is strictly controlled by the pulsar.

Prof. Watase will be remembered among Japan’s scientific community as a great leader in cosmic ray physics. He was one of the leaders who revitalized activities in Japan’s physics, which was deeply damaged by the war, and helped to build it up to the present level.

Observational results on X-ray bursts obtained by the Japanese X-ray satellite are reviewed in conjunction with the general context of the neutron star model of the burst. Evidence indicates the existence of physically different kinds among type-I bursts which are widely believed to be from a thermonuclear flash occurring on the surface of a neutron star. There are cases which can not be accounted for by a simple nuclear flash model: The flash in a confined region of the surface and a change of the emitting area during the burst are suggested. Two type-I bursts were observed in succession within a short interval which was not of sufficient duration to accumulate the nuclear fuel for a flash. Coordinated optical/X-ray observations of bursts were performed. Optical bursts are tentatively interpreted in terms of the reprocessing of X-rays are at the accretion disk. The results will provide the basis for a discussion of the physical structure of the system. The evolution of the activity of type-II bursts from the rapid burster was observed from its onset for about two weeks and a novel mode of burst activity was discovered.

On the basis of my experience in the X-ray astronomy, and on some typical highlights of multi-wavelength observations, I emphasize the importance of collaboration between space astronomy and ground-based astronomy.

The present status of observations of the diffuse cosmic X-rays is discussed. The energy spectrum in the energy range 1–100 keV has been well established. The flux around 0.25 keV appears to be rather high. The basis of the classical argument that the integration of normal galaxies in the universe is not sufficient to explain the diffuse X-ray flux is re-examined. Recent observations around 0.25 keV are discussed and results are compiled.

We performed a couple of balloon experiments to measure the size and the location of Cyg-X-1 using the techniques of the modulation collimator [1]. The angular periods of the modulation collimator were 26′ and 10′ for the respective flights corre­sponding to the approximate angular resolutions of the size determination and location, 3′ and l′ respectively. Preliminary results of the experiment with 3′ resolution are reported here.*