June 13, 2008

In Today's One Minute Astronomer...

The Mysterious "Hiss" From The Milky Way (Part 1)

In the early 1930's, Bell Labs wished to use radio "short waves" for transatlantic radio telephone links. A young engineer, Karl Jansky, was assigned the job of finding sources of static that might interfere with radio transmissions. His accidental discovery revolutionized astronomy.

The Basics

• To search for static that might interfere with radio transmission, Jansky built an antenna to detect radio waves at a frequency of 20.5 MHz (a wavelength of 14.5 meters). He mounted the antenna on four Ford Model-T tires to determine the direction of any radio signal he might find. The antenna was jokingly called "Jansky's merry-go-round".

• After recording signals for several months, Jansky found static from nearby and distant thunderstorms.

• But he also found a faint steady radio hiss of unknown origin. The intensity of the hiss rose and fell once a day. At first, he thought the unknown static might be radio waves from the Sun.

A Deeper Look

• After a few months of following the signal, the brightest point moved away from the Sun. The signal repeated not every 24 hours, but every 23 hours and 56 minutes, the same period in which the stars rise and set.

• Jansky eventually figured out the radiation was strongest in the direction of the center of our Milky Way galaxy, in the constellation of Sagittarius. The discovery of radio waves from the center of the galaxy was widely publicized, appearing in the New York Times on May 5, 1933.

• Though he wanted to learn more about the radio waves, Jansky was assigned to another project and did not pursue the subject further.

• Many scientists were fascinated by Jansky's discovery. But no one followed up on it for several years until a modest radio engineer from Chicago became the world's first true radio astronomer. (To Be Continued...)

Good To Know

In honor of Karl Jansky, the unit used by radio astronomers for the strength (or flux density) of radio sources is the Jansky.

Personal View

The unexpected, unexplained measurement ... sometimes it's caused by dust in the electronics, sometimes it's a Nobel-Prize-winning breakthrough. That's what makes life as a working scientist (or as an amateur astronomer) interesting... each day, you're never sure what you'll find, or what will happen. But you have to be alert the nature's unexpected revelations.

--- Highly Recommended ---

Join master science writer Timothy Ferris as he tours the known universe and reveals the technological revolution sweeping amateur astronomy. One of the most elegant and poetic books about stargazing ever written. Learn more...

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