1. Infrared Telescopes 1

2. The Electromagnetic Spectrum

3. see different phenomena at different wavelengths

4. 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.

5. IR penetrates dust more easily than optical
Infrared

6. Dust glows at the longest IR (and radio) wavelengths
Optical
Near-Infrared
Far-infrared 6

10. Because the most distant galaxies are highly redshifted, IR telescopes are needed to detect them

11. Challenges for IR telescopes
The atmosphere produces many absorption lines at IR wavelengths (called telluric absorption); some wavelength ranges are totally opaque

12. 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

13. 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.).

14. 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. 14

15. 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. 15

16. 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.

17. 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.

18. 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.

19. 2MASS movie of Milky Way

20. 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

21. Spitzer Space Telescope
The Spitzer Space Telescope was full operational from , 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

23. Finding brown dwarfs companions with Spitzer
optical

24. Finding brown dwarfs companions with Spitzer
infrared with Spitzer

25. Finding brown dwarfs companions with Spitzer
optical

26. Finding brown dwarfs companions with Spitzer
infrared with Spitzer

30. 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 m), it produces sharper images. 30

31. 31

32. Herschel’s Orbit 32

33. 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 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) 33

34. Orbit of Wise 34

35. Orbit of Wise
As Earth orbits the Sun, WISE’s orbit also rotates to maintain the spacecraft’s orientation to Earth and Sun. 35

36. Orbit of Wise
Each orbit, a circular strip of the sky is imaged. As the orbit itself rotates, a slightly different strip is imaged. 36

37. 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

38. 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

39. 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