Air density at a height of 128 km,form visual observations of 1972-25g

655 visual observations of 1972-25G, Molniya 1V Rocket, were made when its perigee height was below 130 km, and have been used to determine its orbit at 17 epochs between 5 November 1973 and 24 February 1974 and obtain almost daily values of its rate of decay. These give 52 values of atmospheric density with a relative accuracy of 1 % at a height of 128 km in latitudes 55–65°S. Day-to-day variations correlated with geomagnetic activity of up to 10% are found, plus an irregular semi-annual variation of amplitude 10%. The decrease in inclination has been measured accurately enough to enable the mean atmospheric rotation rate to be determined over the same time-span.