Astrophysics (Index)About

collecting area

(collection area)
(cross-sectional area over which a telescope receives EMR)

A telescope's collecting area is the area of the cross section of incoming EMR. For a small refracting telescope, this is generally the area of the aperture or the primary lens, i.e., the aperture's radius squared times π. For a reflector telescope, any part blocking the primary mirror e.g., a secondary mirror, or an instrument (if prime focus) would have to be subtracted to yield the collecting area. With a segmented mirror, there may be spaces between the segments that would be subtracted. The collecting area is related to how dim an astronomical object can be detected whereas the aperture is related to the angular resolution.

For arrays, the effective aperture may be larger (through aperture synthesis), providing better angular resolution if the individual units are spread out, but the collecting area remains the same whether they are close to each other or far apart. Some arrays are primarily aimed at better angular resolution, whereas others are aimed at sensitivity. The Square Kilometre Array is a planned array aimed at achieving a very large collecting area.


The term collecting area is used in the analogous sense for instruments and detectors that would not be termed telescopes and/or sense something other than EMR.


(telescopes,instruments)
Further reading:
http://burro.case.edu/Academics/Astr201/Chap06.pdf
http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit4/telescopes.html
https://web.njit.edu/~gary/728/Lecture4.html
https://www.teachastronomy.com/textbook/Detecting-Radiation-from-Space/Collecting-Area-and-Resolution/

Referenced by pages:
aperture masking interferometry (AMI)
Cherenkov Telescope Array (CTA)
Colossus Telescope
Dragonfly Telephoto Array
etendue (AΩ)
European Pulsar Timing Array (EPTA)
FAST
IXPE
Low-frequency Array (LOFAR)
Murchison Widefield Array (MWA)
Nançay Radio Telescope (NRT)
Next Generation Very Large Array (ngVLA)
Pierre Auger Observatory (PAO)
POEMMA
RATAN-600
spectral flux density (S)
Square Kilometre Array (SKA)

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