Even small telescopes give good views of external galaxies, many of which look like pinwheels spinning in space. But when astronomers try to look at the "home" galaxy of which the solar system is a part, all they see is a scattering of stars and the hazy streak of the Milky Way. No spiral is apparent, and the dense nucleus so conspicuous in other galaxies is hidden behind dust clouds that fog the Milky Way.
Last week Jan H. Oort of Leyden University Observatory told how Dutch astronomers have been probing the nucleus of the home galaxy with the powerful new tool of radio astronomy. The commonest element in the universe is hydrogen, which exists both in the stars and among them. When it is diffuse, it sends out radio waves 21 centimeters long that permit radio astronomers to spot clouds of hydrogen drifting among the stars. Their speed can be measured by a slight shortening (for approach) or lengthening (for recession) in the length of the radio waves that come from them.
Hydrogen near the nucleus of the Milky Way galaxy is hard to observe, but by refining their dish-shaped radio telescope at Kootwijk, the Dutch astronomers picked up its radiation. They found, as they had expected, that the nucleus is revolving faster than the rim of the galaxy near the solar system. They also found another and surprising fact. Hydrogen abounds in the nucleus, but it is not arranged in the familiar pattern of stars and clouds with near-empty space between them. Instead, it seems to be a "continuous medium" in a state of violent turbulence, with streams of hydrogen twisting and eddying at enormous speed. At one point, the astronomers detected radio evidence of a small spiral arm uncoiling from the dense heart of the nucleus.
A more conventional effort to map the Milky Way galaxy has just been completed at Lick Observatory, Calif. Dr. C. D. Shane announced last week that he and his observer. C. A. Wirtanen, have just finished a picture of the northern hemisphere sky. The job took seven years and required 1,246 plates, each 17 inches square and exposed for two hours. If all the plates were assembled on a single surface (not likely to be done), the picture would be about 50 feet square.
Most of the objects on the plates are stars that belong to the Milky Way galaxy, but beyond them are external galaxies which are so far away that they may be considered motionless. As the Milky Way galaxy revolves majestically, its stars seem to stream past the background of distant galaxies. The stars themselves seem to move at varying speeds because of their varying distances and their own individual motions within the galaxy.
When a similar picture is taken 50 years hence, as is planned, comparison of the two pictures will give a good idea of how the galaxy's stars are arranged in streaming spiral arms, and how the whole galaxy is spinning like a pinwheel in space.