Infrared Telescopes
The Electromagnetic Spectrum
see different phenomena at different wavelengths
1800: Discovery of IR Light
Herschel used a prism to
separate sunlight into colors.
He used a thermometer to
determine the temperature in
each color. Two were placed
off to the side as controls.
The highest temperature was
found beyond red light where
no light was seen.
IR penetrates dust more easily than optical
Optical
Infrared
Dust glows at the longest IR (and radio) wavelengths
Optical
Near-Infrared
Far-infrared
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Because the most distant galaxies are highly
redshifted, IR telescopes are needed to detect them
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Challenges for IR telescopes
The atmosphere produces many absorption lines at IR wavelengths
(called telluric absorption); some wavelength ranges are totally opaque
Challenges for IR telescopes
The telescope and atmosphere glow brightly at IR wavelengths, which
hampers detection of faint IR photons from space. It’s like trying to
observe stars at optical wavelengths during the day!
on the ground
in space
Designing an Infrared Telescope
The same basic design and
materials are used for collecting
both optical and IR light. As a
result, telescopes often can observe
in both wavelength regimes.
However, telescopes are usually
optimized for specific wavelengths
through the details of their design
(mirror coatings, camera detectors,
etc.).
Designing an Infrared Telescope
To reduce the absorption of starlight by the atmosphere (mostly water
vapor) and thermal emission from the atmosphere, place a telescope
on a high mountain, on an airplane, or in space.
Designing an Infrared Telescope
To reduce the thermal emission by the telescope and instrument,
make them as cold as possible. For shorter IR wavelengths, it is
sufficient to cool the instrument with liquid nitrogen (77 K); the
telescope can be at room temperature. But for longer IR wavelengths,
both the telescope and instrument need to be close to absolute zero,
so they are placed in space.
Mauna Kea
IR telescopes became possible in the 1960's with the advances in IR
detectors. At an elevation of 13,796 ft., the summit of Mauna Kea on
the island of Hawaii is above much of the absorbing water vapor in
the atmosphere. It was one of the first sites for IR telescopes.
IRAS
In 1983, the Infrared Astronomical Satellite
(IRAS) scanned most of the sky at far-IR
wavelengths. IRAS doubled the number of
cataloged astronomical sources by detecting
about 500,000 IR sources. IRAS discoveries
included a disk of dust grains around the star
Vega, six new comets, and ultra-luminous IR
galaxies, as well as wisps of warm dust called
IR cirrus.
2MASS
Between 1997 and 2001, the Two Micron All-Sky Survey (2MASS)
imaged the entire sky at near-IR wavelengths using two telescopes in
Arizona and Chile. 2MASS has been valuable for many topics in
astronomy, including the structure of the Milky Way and the
discovery of brown dwarfs.
2MASS movie of Milky Way
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Hubble Space Telescope
Although it focuses primarily on optical wavelengths, Hubble does
operate at near-IR wavelengths as well. As in the optical, Hubble
provides very sharp images at IR wavelengths because it is above the
atmosphere.
2MASS
Hubble
Spitzer Space Telescope
The Spitzer Space Telescope was full operational from 2003-2009,
and continues to function in a more limited capacity. It operates from
near- to far-IR wavelengths and is the last of NASA's "great
observatories”. Like Hubble, Spitzer observes specific targets rather
than the entire sky.
Spitzer
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Finding brown dwarfs companions with Spitzer
optical
Finding brown dwarfs companions with Spitzer
infrared with Spitzer
Finding brown dwarfs companions with Spitzer
optical
Finding brown dwarfs companions with Spitzer
infrared with Spitzer
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Herschel Space Observatory
Herschel was launched in 2009 by the European Space Agency for a 3
year mission. It operates at far-IR wavelengths. Because it has a larger
mirror than Spitzer (3.5 m vs. 0.85 m), it produces sharper images.
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Herschel’s Orbit
Wide-field Infrared Survey Explorer (WISE)
WISE was launched by NASA in late 2009 and completed a mid-IR
imaging survey of the entire sky in July 2010. The survey is a new
version of IRAS with much sharper and more sensitive images. WISE
will be used to search for objects that are cold, dusty, or highly
redshifted. IRAS
WISE (predicted)
Orbit of Wise
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Orbit of Wise
As Earth orbits the Sun, WISE’s orbit also rotates to maintain the
spacecraft’s orientation to Earth and Sun.
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Orbit of Wise
Each orbit, a circular strip of the sky is imaged. As the orbit itself
rotates, a slightly different strip is imaged.
Which of these 3 space telescopes would be best for detecting light
from a brown dwarf? (Brown dwarfs are very cold objects, sort of
like planets free-floating in space.)
Compton
C) Spitzer
A) Chandra
B) Hubble
Which of these 3 space telescopes would be best for detecting light
from very hot gas spiraling into a black hole?
Compton
C) Spitzer
A) Chandra
B) Hubble
Which of these 3 space telescopes would be best for obtaining a
sharp image of Mars to study its surface features?
Compton
C) Spitzer
A) Chandra
B) Hubble