Observatory in Space the Hubble Space Telescope

There are other ways to escape the seeing caused by the earth's atmosphere: You can get above and away from the atmosphere. In fact, for observing in some portions of the electromagnetic spectrum, it is absolutely required to get above the earth's atmosphere. That is just what NASA, in conjunction with the European Space Agency, did with the Hubble Space Telescope. High above the earth's atmosphere, the HST regularly achieves its theoretical resolution.

The HST was deployed from the cargo bay of the space shuttle Discovery in 1990. The telescope is equipped with a 94-inch (2.4-meter) reflecting telescope, capable of 10 times the angular resolution of the best Earth-based telescopes and approximately 30 times more sensitive to light, not because it is bigger than telescopes on the earth, but because it is above the earth's atmosphere. Unfortunately, due to a manufacturing flaw, the curvature of the 2.4-meter mirror was off by literally less than a hair (it was too flat by VS<> of the width of a human hair), which changed its focal length. The telescope still focused light, but not where

Astro Byte

At $3 billion, the Hubble Space Telescope is one of the most expensive scientific instruments ever made.

Astro Byte

At $3 billion, the Hubble Space Telescope is one of the most expensive scientific instruments ever made.

it needed to, in the plane of the various detectors. Astronauts aboard the shuttle Endeavour rendezvoused with the HST in space in 1993 and made repairs—primarily installing a system of small corrective mirrors. HST then began to transmit the spectacular images that scientists had hoped for and the world marveled at.

Subsequent repair missions have installed the short-lived but productive infrared camera (NICMOS) and other instrumentation. A final servicing mission is planned for 2003, after which HST will be replaced by the Next Generation Space Telescope (NGST) near 2010.

Close Encounter

As we have said, yet another way to achieve better resolution is to observe at another wavelength. The VLA or Very Large Array was dedicated in 1980, and has been operating continuously since then. It is located near the town of Socorro, New Mexico, and consists of twenty-seven 25-meter antennas that are connected to form an interferometer that acts as a single telescope. In the largest of its variable configurations and at the highest frequency, the VLA has a spatial resolution of about 0.03", or three one hundredths of an arc-second. That resolution is as good as the HST—even though the VLA is an Earth-based telescope. How can this be? We'll talk more about radio astronomy in Chapter 8, "Seeing in the Dark."

The Least You Need to Know

V Light is a form of electromagnetic radiation. Radiation carries energy and conveys information.

V Objects in space produce or reflect the various forms of electromagnetic radiation (including radio, infrared, visible light, ultraviolet, x-rays, and gamma rays); this radiation is what we see with our eyes or detect with special instruments.

V The two basic optical telescope types are the lens-based refractors and the mirror-based reflectors.

V The two main functions of telescopes are to collect light, and resolve nearby objects. Larger telescopes (barring the effects of the earth's atmosphere) are better able to perform both these functions.

V New technologies, such as adaptive optics, allow ground-based telescopes to achieve much sharper images while maintaining the convenience of being on the ground.

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