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Anextreme ultraviolet spectrometer experiment by University College London for observation of whole-Sun spectrum -line fluxes, and flown on Orbiting Solar Observatory-6, is described. Results for the four lines with absolute calibration, are show n for the first 6 months of flight, from August 1969 to February 1970. The mean fluxes for the 30.4, 53.7, 58.4 and 121.6 nm lines are 8.1 x 10 9 ± 35 % ph cm-2 s-1 , 3.2 x 10 8 + 40% ph cm -2 s-1 , 2 .5 x 10 9 + 40% ph cm -2 s-1 , and 3 x 10 11 ± 50% ph cm -2 s -1 respectively. Relations between these fluxes and the 10.7 cm radio flux and Zurich sunspot number are presented.

Shortly after the study of astronomy by radio techniques began in earnest, a basic problem arose. Three “sources” of radio flux had been delineated: the sun, the cosmic‐noise background, and the discrete sources (radio stars). Were the discrete sources variable, as the sun showed evidence of being, or was the atmosphere modulating fixed‐flux sources? The first answer was that the radio‐star sources exhibited intrinsic fluctuations in intensity, but studies in Australia and England utilizing spaced receivers indicated that the earth's ionosphere and troposphere produced effects similar to the “twinkling” of visible stars. The study of “twinkling” or scintillation was the first of the upper‐atmospheric effects to be investigated in detail.

Thirty four objects appearing in the SharplessCatalogue of HiiRegions with radio flux densities below 0.1 fu* at 1400 MHz, are studied. It is shown that two of them are planetary nebulae, two are reflection nebulae and two weak emission-reflection nebulae. From statistical arguments it is concluded that six may be evolved planetaries while the remaining are faint nearby Hii regions excited by stars of relatively advanced spectral type.

Demonstration of a relationship between the flux densities and red-shifts of quasars suggests that the red-shifts give an indication of their distances.

Two recent articles1,2 have shown that the X-ray flux from M87 is variable over time scales of less than 1 yr. This letter reports detection of variations in the radio flux density of a compact component in the nucleus of M87, over similar time scales.

FOLLOWING the announcement of Gregory et al.1 and Hjellming and Balick2 that the radio source identified with Cyg X-3 had undergone a substantial increase in radio flux output some time between August 31, 1972 and September 2, 1972, we made a search through all data available for dates near this event from the Vela 5B spacecraft to determine if any associated increase in X-ray flux could be detected. Scans of the appropriate region of the sky were made on the four dates shown in Table 1. Cyg X-3 lies close enough on the sky to Cyg X-1 that the two sources were barely resolvable with the angular response of the X-ray detectors on the spacecraft; however, estimates of the strength of Cyg X-3 relative to Cyg X-1 were possible. In all cases, the flux observed from Cyg X-3 in the 3 to 12 keV energy range was consistent with the ratio of 1:3 (flux from Cyg X-3/flux from Cyg X-1) reported in previous observations of these sources (for example, Gursky et al.3).

Various observers (e.g. Slee and Orchiston 1965; Davies et al. 1967; Hughes 1967; Thompson and Colvin 1967; Thompson, Colvin, and Stanley 1967; Kaftan-Kassim 1968) have so far detected nearly 100 planetary nebulae a.t high radiofrequencies (~3 GHz). In this range, the nebulae have been shown to be optically thin, their spectra being almost flat. Wherever possible, the radio flux densities have been compared with hydrogen recombination line observations.

Radio observations of HDE 226868 (Cyg X-l) at 2695 and 8085 MHz made between 1971 February 23 and 1972 October 21 show that (1) the radio flux of this spectroscopic binary went from less than 0.005 f.u. on 1971 March 22 to 0.02 f.u. on 1971 March 31, just as the X-ray flux of Cyg X-l was begnning a significant change in average level; (2) a significant change from a mean level of 0.015 f.u. to 0.018 f.u. occurred at both frequencies betwween 1972 April 25 and 1972 September 3: and (3) radio variability on a time scale of days definitely occurred during October 1972 and may have occurred at other times. (auth)