Longest Look

Edwin Powell Hubble of Mt. Wilson Observatory has at his disposal a 100-inch reflector, world's largest telescope, and with it he takes longer looks into space than any other man. Before the National Academy of Sciences last spring, Astronomer Hubble put the limit of the visible universe at 300,000,000 light-years from Earth (TIME, May 7).* Later he extended the limit to 400,000,000 lightyears. Last week he reported catching on a high-speed photographic plate the faint impression of a galaxy of stars 500,000,000 light-years away.

Dr. Hubble is renowned for his discovery that the spectrum lines of distant nebulae are displaced toward the red end, indicating enormous speeds of recession away from Earth. The speeds of the most distant cannot be deduced in this manner, since the spectra are too faint to be analyzed. But it has been observed that speeds are closely proportional to distance, increasing about 1,000 miles per second for every 10,000,000 light-years of space. Few months ago Dr. Hubble measured the fastest nebular retreat at 24,000 miles per second. That one was 240,000,000 light-years away. No decipherable spectrum of the outpost nebula reported last week was obtained, but. if it follows the rule, it is receding from Earth at 50,000 miles per second.

*One light-year = approximately six trillion miles.

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