Saturday, April 24, 2010

Hubble is 20 Years Old!

I've been married for almost as long as the Hubble Space Telescope has been in orbit.

But talk about schedule creep. After delays in construction on a project conceived in 1969 as the "Large Space Telescope", and approved in 1977, the Hubble space telescope was finally completed by the mid 1980's, and scheduled for launch in October 1986. But then the Challenger disaster happened in January 1986 and the shuttle fleet was grounded in the aftermath of Challenger's loss. Over four years after the accident, space shuttle Discovery finally took the Hubble Space Telescope into orbit on April 24, 1990 -- twenty years ago today.

Mission STS-31 was the tenth launch of the shuttle Discovery. On board were Mission Commander Loren Shriver (replacing John Young, the originally assigned commander), Pilot Charles Bolden, and Mission Specialists Bruce McCandless, Steven Hawley, and Kathryn Sullivan. Hubble was deployed in a 380 statute mile (612 km) orbit, a record orbital altitude for shuttle missions, in order that the HST could be released near its operational altitude well above the atmosphere. The height ensured that there would be no atmospheric interference for its optics, and minimal atmospheric resistance to affect its orbit.

Shortly after the telescope was launched and saw first light in orbit, it became clear that there was a serious problem with the main mirror. Manufactured by Perkin-Elmer Corporation, the mirror had a flaw called "spherical aberration" that caused all images to be fuzzy. This problem was fixed on the first servicing mission in 1994 with a device called COSTAR -- Corrective Optics Space Telescope Axial Replacement -- which remained in place until the fourth servicing mission in 2009, by which time all Hubble instruments had built-in corrective optics. [Note: There were four servicing missions, but five actual servicing mission shuttle flights, since servicing mission 3 was performed over the course of two flights.]

During the telescope's lifetime, perhaps one of the most important images obtained by Hubble was the so-called "Deep Field" composite.

This material was presented to the 187th meeting of the American Astronomical Society in San Antonio, Texas on January 15, 1996.

Several hundred never before seen galaxies are visible in this "deepest-ever" view of the universe. Besides the classical spiral and elliptical shaped galaxies, there is a bewildering variety of other galaxy shapes and colors that are important clues to understanding the evolution of the universe. Some of the galaxies may have formed less that one billion years after the Big Bang.

Representing a narrow "keyhole" view all the way to the visible horizon of the universe, the HDF image covers a speck of sky 1/30th the diameter of the full Moon (about 25% of the entire HDF is shown in the image above). This is so narrow, just a few foreground stars in our Milky Way galaxy are visible and are vastly outnumbered by the menagerie of far more distant galaxies, some nearly as faint as 30th magnitude, or nearly four billion times fainter than the limits of human vision. (The relatively bright object with diffraction spikes just left of center may be a 20th magnitude star.) Though the field is a very small sample of sky area it is considered representative of the typical distribution of galaxies in space because the universe, statistically, looks the same in all directions.

The image was assembled from many separate exposures (342 frames total were taken, 276 were fully processed and used for this picture in 1996) with the Wide Field and Planetary Camera 2 (WFPC2), for ten consecutive days between December 18 to 28, 1995. This picture is from one of three wide-field CCD (Charged Coupled Device) detectors on the WFPC2. This "true-color" view was assembled from separate images were taken in blue, red, and infrared light. By combining these separate images into a single color picture, astronomers will be able to infer — at least statistically — the distance, age, and composition of galaxies in the field. Bluer objects contain young stars and/or are relatively close, while redder objects contain older stellar populations and/or farther away.

In 2007, while doing routine mapping of the distribution of dark matter within the galaxy cluster Cl 0024+17 (ZwCl 0024+1652), located 5 billion light-years from Earth, astronomers got an unexpected first-hand view of how dark matter behaves during a titanic collision between two galaxy clusters. The interaction created a ripple of dark matter, which is somewhat similar to a ripple formed in a pond when a rock hits the water. The ring's discovery is among the strongest evidence yet that dark matter exists.

Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

Astronomers have long suspected the existence of dark matter -- a hypothesized invisible substance -- as being the source of the additional gravity that is needed to hold together galaxies and galaxy clusters. Such objects would fly apart if they relied only on the gravity from their visible stars. Although astronomers don't know what dark matter is made of, they believe that it is a type of elementary particle that pervades the universe. Over the next decade, results from the Large Hadron Collider will provide more insight into this question.

A ring-like structure is evident in a composite image of the cluster made from Hubble observations. The ring can be seen in the blue map of the cluster’s dark matter distribution, which is superimposed on an image of the cluster. This is the first time that dark matter was detected, having a unique structure different from the gas and galaxies in the cluster.The ring measures 2.6 million light-years across.

The last photo below was taken after the fourth and final servicing mission in 2009, which repaired and upgraded Hubble so that it is expected to be functional until at least 2013, and likely much later. Although NASA originally intended to return the telescope to Earth for display in the Smithsonian, Hubble will actually outlast the remaining service lifetime of the shuttle fleet, now expected to end in September of this year.

So happy 20th birthday, Hubble! We hope you can provide us with many more years of incredible imagery out to the edge of the Universe.

BoingBoing has a review of a stunning new book -- Hubble: A Journey Through Space and Time by Edward J. Weiler, published by Abrams in collaboration with NASA. Much better pictures there.

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