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En IR

Defining the Infrared Region in Astronomy

Spectral regionWavelength range
(μm)
Temperature range
(oK)
What can be observed
Near IR(0.7-1.0) -- 5.0740 -- (3000-5200)Cool red stars; red giants; high-redshift explosions; galaxies; early universe. Dust is transparent.
Mid IR5.0 -- (25-40)(92.5-140) -- 740Planets; comets; small planets; protoplanetary disks; dust warmed by starlight
Far IR(25-40) -- (200-350)(10.6-18.5) -- (92.5-140)Central regions of galaxies; very cold molecular clouds; emission from the cold dust

Definition of Infrared Based on the Detector Response

Near IR0.7 - 1.0 μmfrom the response of the eye to silicon
Short-wave IR1.0 - 3.0 μmfrom silicon to mid-wave-IR atmospheric window
Indium gallium arsenide (InGaAs) covers up to 1.8 μm;
less sensitive lead salts cover this region
Mid-wave IR3.0 - 5.0 μmdefined by the atmospheric window
covered by InSb, HgCdTe, and partially by PbSe
Long-wave IR8.0 - 12.0 μm
7.0-14.0 μm
atmospheric window
covered by HgCdTe and microbolometers
Very-long-wave IR12.0 - 30.0 μmcovered by doped silicon

Infrared Reflectance of Metal Coatings

Atmospheric Transmittance and Reflectivity


Photon Flux in the Known Bands

Bandλc (μm)Flux @m=0 (Jy)ReferenceTransmissivity
U0.361810(1) 
B0.444260(1) 
g0.523730(2) 
V0.553640(1) 
R0.643080(1) 
r0.674490(2) 
I0.792550(1) 
i0.794760(2) 
z0.914810(2) 
Infrared Bands   
J1.1-1.41600(3)High
H1.5-1.81080(3)High
K2.0-2.4670(3)High
L3.0-4.0  3.0-3.5: Normal
3.5-4.0: High
M4.6-5.0  Low
N7.5-14.5  8.0-9.0: Normal
10.0-12.0: Normal
Rest: Low
Q17-25  Very low
Z28-40  Very low

(1) Bessel (1979)
(2) Schneider, Gunn, & Hoessel (1983)
(3) Campins, Reike, & Lebovsky (1985)