Clues about the telescopes

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Eagle Nebula Hubble Space Telescope
Image of Eagle Nebula with WFPC2. Pillars of yellow gas with a green background. Stars in the background are shown in pink. Image Courtesy of NASA/
ESA/STScI/ASU/J.Hester & P.Scowen.

The most important characteristics of a telescope are resolution and operating wavelength. A telescope with better resolution enables astronomers to make images that have finer details. All other things being equal, larger telescopes have better resolution than smaller telescopes. Operating wavelength refers to the type of radiation that a telescope’s mirrors reflect and focus. Optical telescopes manipulate light that has the colors of the rainbow. Radio telescopes collect microwaves—radiation with much longer wavelengths. In the universe, some phenomena produce optical radiation—such as stars and the ionized gas around them, as in the Orion Nebula—and some produce microwave radiation, such as the cold gas that lies in clouds in the deep space between stars.

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Cepheus A star forming region Very Long Baseline Array
Photo taken with the Very Long Base Array of Cepheus A star forming region. The image is comprised mostly of red gases with yellow sources of light. Image courtesy of NRAO/AUI

The Hubble Space Telescope

The Hubble Space Telescope delivers optical images, using a mirror about 2 meters in diameter. It can resolve objects separated by as little as 0.05 seconds of arc on the sky—that is the size Superman standing in New York would report when a Chicagoan holds up a 12-inch ruler.

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Orion Nebula Hubble Space Telescope
Two Hubble images. The left image has mostly green and yellow banks of gas with the Trapezium in the center outlined in pink. The image on the right is primarily purple with the trapezium and aother stars in white. Image Courtesy of NASA and K. Luhman, Harvard-Smithsonian Center for Astrophysics

Very Long Baseline Array (VLBA)

The Very Long Baseline Array (VLBA) is the world’s largest telescope. It consists of 10 radio dish antennas, each 10 stories tall, distributed across North America, Hawaii, and the Caribbean. The VLBA can resolve objects separated by 0.0005 seconds of arc on the sky—that is thinner than the ruler would appear when held end-on. The VLBA performs like a telescope 8000 kilometers across.


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This material is based upon work supported by the National Science Foundation under Grant No. (NSF AST 0507478). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.