PROBLEM OF ORIGIN OF SUN'S PLANETS STILL BAFFLES SCIENTISTS
IRREGULARITIES IN ROTATION OF EARTH ARE DESCRIBED
The following excerpts are taken from a lecture given recently at the College of the City of New York by Professor Harlowe Shapley, director of the Harvard Astronomical Observatory. The subject of the lecture is "Concerning Planets and their Fate."
No withstanding our immense accumulation of observations and theory, some of the most baffling mysteries of all astronomy are associated with the planets and satellites of the sun's family. No theory of the origin of the planets is wholly satisfactory, though the current tidal evolution hypothesis, which has developed from the planitesimal hypothesis, accounts for the major features of the system.
The interpretation of the origin of the asteroids, those thousands of tiny bodies that circulate around the sun in orbits between those of Jupiter and Mars, leaves much to be desired. Are they fragments of one or more small planets broken up by collision, or are they the wreckage of a planet that came too near to the gigantic Jupiter? Persistent observation and the development of mathematical theories should in time solve this mystery.
Whence the Comets?
The origin of the several thousand comets that are members of the solar system is equally baffling. The origin of the moons of Mars, and some of the other peculiar satellites, is only guessed at; and perhaps most disturbing of all is the difficulty in accounting for the observed speeds of rotation and revolution of the planets and the sun.
To account for the observed rotation of the sun, Dr. Joffreys of England has recently proposed the theory that the planets were formed not through the tidal disruption of the sun by the near approach of another star, but by the actual glancing collision of our sun with another star. The shearing forces of such a collision could account for the rapid rotation.
Stars Rarely Meet
The near approach of two stars is an exceedingly rare phenomenon. It is calculated to occur in our galactic system not oftener than once in a thousand million years. The actual collision of two stars would be a much more uncommon occurrence. Even so, however, since the astronomer measures time in terms of ten millions of millions of years, it is probable that many planetary systems exist throughout our galaxy and the innumerable other galaxies that are strewn throughout space.
Earth's Rotation Irregular
A planetary mystery much nearer home is the problem of the irregularities of the rotation of the earth--a phenomenon discovered through studies of the motion of the moon. For some years we have been familiar with the fact that the earth's rotation is slowing down, that the day is lengthening, and that the moon is receeding; we have learned that after an interval of some fifty thousand million years the month and the day will be the same length again, as they were at the time the earth-moon system was formed. That equality of month and day in the future will be forty seven of our days in length; at the time of the origin of the moon from the earth it was less than five of our present hours in length.
Miss Cannon Classifies
Within the last few years the spectra of more than 75,000 faint stars have been classified in the star clouds of the Milky Way by Miss Cannon and her assistants at the Harvard Observatory. She has classified altogether more than 300,000 stars, and the resulting catalogue is one of the fundamental collections of data for astronomers.
Recent and as yet unpublished studies of a star cloud in Aquila show that practically all the stars are of the same type as the sun--a very unusual circumstance, since Milky Way stars elsewhere have mainly been of the hotter classes. It is unknown whether this anomalous result, which involves tens of thousands of stars, means that we have here a star cloud of dwarfs like the sun, or if it means that we are dealing with a peculiar assemblage of yellowish giant stars at a special stage in the evolution of a stellar system.