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What is a Telescope's Sensitivity?

The sensitivity of a telescope indicates the minimum detectable brightness of an object. In other words, sensitivity puts a lower limit on the signal strength that a telescope can clearly pick up. High sensitivity permits detection of dim objects. With low sensitivity, only bright objects can be discerned.

Many celestial objects shine quite brightly in the radio spectrum. However, the amounts of radio energy detected from them are normally very small. The total amount of electromagnetic energy collected by all radiotelescopes since their invention decades ago would not even melt a snowflake! No wonder radiotelescopes have to be extremely sensitive to incoming radio waves.

Then there are some objects that are intrinsically dim; they simply emit very small amounts of light or other electromagnetic radiation. Other objects only appear to be very dim because of their great distance from Earth -- all the more reason for a telescope to possess the maximum possible sensitivity.

Increasing the BIMA Array's Sensitivity

The amount of electromagnetic radiation a telescope collects is proportional to the surface area of its lens, mirror, or dish, often referred to as the collecting area. The surface area of an array is simply the sum of the areas of all the dishes in the array. As more dishes are added to the BIMA array, it will be able to collect greater amounts of millimeter radiation. The array's sensitivity will increase correspondingly.

Specifically, the sensitivity of the BIMA array is proportional to the square root of the total number of possible baselines, which increases rapidly with each dish added to the array. For instance, raising the number of dishes from six to ten will increase the number of baselines from 15 to 45, which in turn improves the sensitivity by about 70 percent.

For more technical details, visit the BIMA Consortium's server at the University of Maryland. See the information under "Map Sensitivity."

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NCSA. Last modified 11/12/95.