1. Telephones and Radio Astronomy - the Beginning We should be grateful to the telephone companies for bringing many things into our life, and Radio Astronomy is one of those things. At first that may sound strange - what the telephones have to do with exploration of the Universe with radio waves? In 1931 antennas used for transoceanic radio-telephone circuits were picking up thunderstorm static that was decreasing the signal-to-noise ratio for the circuits. Karl G. Jansky, a radio engineer at the Bell Telephone Laboratories, was assigned to study that problem. The idea was to find a predominant direction from which that interference was coming, and to build an antenna that would not be sensitive to signals coming from that direction. To study that problem Jansky built an antenna, about 30 meters long by 4 meters high, mounted on wheels running on a circular horizontal track. In this arrangement the antenna, connected to a receiver equipped with a pen-on-paper recorder with a long time constant, was rotated horizontally, making one revolution in 20 minutes and continuously recording the intensity of radio radiation received from all directions. As a result of these experiments, Jansky was very quickly able to identify three kinds of static: - from local thunderstorms, - from distant thunderstorms, coming mainly from the South, and - "a steady hiss type static of unknown origin". The last type of static was the most intriguing since, as Jansky stated in his first paper, "The direction of arrival of this static changes gradually throughout the day going almost completely around the compass in twenty-four hours". This is how Radio Astronomy was born, in January 1932.
	2. Discovery of Radio Radiation from our Galaxy The Earth is rotating in space once in 23 hours and 56 minutes (sidereal day). At the same time the Earth is moving on its orbit around the Sun. As a result, the observer on Earth can see the Sun in the sky every day from a different place in space. In consequence, one rotation in space is not enough for the observer on Earth to see the Sun at the same place in the sky the next day - we need to wait additional 4 minutes for the Sun to appear roughly at the same spot in the sky where it was yesterday (this makes full 24 hours, the solar day). During the time the Earth travels one full orbit around the Sun, the Sun crosses the local meridian of an observer 365 times. At the same time, because of the same motion of the Earth around the Sun, our planet has to rotate 366 times. We have then 366 rotations of the Earth in 365 days. The position of the Sun in the sky (with respect to distant stars) changes every day - the Sun moves along a line called Ecliptic to the East, traveling full 360 degrees in 365 days. Detection of a source of radio waves that appears at the same direction every 24 hours would suggest that the source is somehow related to the Sun. That was the initial conclusion that Jansky published in his paper in 1932. Jansky's observations continued for several more months and it became apparent that static that he was investigating was appearing every day, but not when the Sun was at the same direction in the sky. Gradually the correlation between the presence of the static and the Sun was less and less clear. Instead, it became apparent that static was correlated with a certain part of the sky rather than the Sun. Jansky estimated the position of that part of the sky - it coincided quite well with the direction to the center of our Galaxy.
	To be continued soon...