Report from Arecibo: It Just Keeps Getting Better
Feb. 19, 2004
by Seth Shostak - Senior Astronomer
The Arecibo Observatory recently celebrated its fortieth birthday. For me, thats a bit of a jolt in my mind, this telescope is still the new kid on the block. After all, when I first journeyed here as a callow youth with a target list of a few dozen odd-shaped galaxies in my suitcase, the Observatory had barely entered its teen years. Arecibo was, at that time, the worlds largest single-dish antenna. It still is.
Unlike cars or people, major telescopes are built to last, and yet remain cutting edge throughout their lives. They do this by improvements to their detectors and, if necessary and possible, upgrades to their optics.
A good example of this instrumental plastic surgery is the 200 inch Hale Telescope on Palomar Mountain. It was designed in the 1930s and completed in 1948. While no longer the biggest eye around, its doing first-rate science, thanks to the CCD electronic cameras that now fill slots once occupied by glass plates. The original optics and mechanics are still there, and still top drawer.
Ditto for the Hubble Space Telescope. This orbiting ocular first appeared on drawing boards in the 1970s. But anyone who reads the papers knows that every few weeks Hubble delivers yet another spectacular view of the universe nicely appropriate for a double-page spread in a coffee-table book. An astronaut-servicing mission successfully dealt with Hubbles infamously flawed mirror in 1993. The space-suited repairmen inserted small correcting lenses the size of quarters into the optical path, and the performance of this scope has been up to spec ever since. The cameras themselves were upgraded by Shuttle-sent technicians in 2002.
Telescopes are research infrastructure, much like particle accelerators and organic chemistry labs. They are the bridges and highways over which generations of relentlessly improved vehicles ride. Arecibo has been steadily transformed since 1963, when it snagged its first radio photons. For example, in 1974 the original wire mesh that formed the bowl of the antenna coarse, chicken-coop wire was replaced with nearly forty thousand precision aluminum panels. The surface is now so smooth that the average deviation from a perfect sphere is no more than the height (or depth) of an ant.
The Observatory Director at that time, Frank Drake, has remarked that the 1974 surface upgrade "transformed Arecibo from a telescope that could not observe the prime frequencies of radio astronomy, and was therefore of limited value, to an instrument that could not only observe those frequencies, but could do so with more sensitivity than any other antenna. The upgrade also made Arecibo the most powerful radar for planetary studies in the world."
In the 1990s, this good telescope became better when the so-called Gregorian upgrade was completed. This major engineering project involved a reworking of the telescope optics to both increase its effective collecting area and allow for almost instantaneous change of frequency band. According to Drake "The development of the Gregorian system over the period 1980 to 1996 greatly improved the sensitivity of the telescope, as well as making it possible to observe a broad range of radio frequencies with traditional, relatively low-cost signal collectors, or feeds." You may not remember seeing much about the Gregorian upgrade on the nightly news, even though it took many years and $27 million; but thats probably because the installers werent wearing space suits.
Bottom line? Arecibo may be only slightly older than Jack Benny ever was, but its come a long way baby. Originally conceived as a simple radar dish able to bounce radio waves off the ionosphere, it is now a high-precision, powerful instrument for studying asteroids, discovering pulsars, measuring the motions of galaxies, and searching for extraterrestrial intelligence.