Infrared astronomy: a. The Wide-field Infrared Survey Explorer (WISE) surveyed the entire sky in four infrared wavelength bands between January 2010 and February 2011 . Why do astronomers want to see the whole sky in the infrared? Go to the WISE website (http://wise.ssl.berkeley.edu/ news.html). An all-sky map and catalog was released in March 2012 (see Figure 15.5 ). What types of objects were detected with this mission? Have many new brown dwarfs been detected? b. The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5 -meter telescope on a modified Boeing 747 aircraft. Go to the SOFIA website (http://sofia.usra.edu) Why would astronomers put an infrared telescope on an airplane? What has been detected with this telescope?

The Wide-field Infrared Survey Explorer (WISE) was a groundbreaking mission designed to survey the entire sky in four infrared wavelength bands. To understand why astronomers are interested in infrared surveys, it's crucial to note that many celestial objects emit infrared light but are invisible in other wavelengths. By surveying the entire sky in infrared, WISE aimed to create a comprehensive map, helping to detect and catalog various infrared-emitting objects. This includes everything from distant galaxies and star-forming regions to comets and asteroids within our solar system. A significant accomplishment of WISE was the detection of numerous brown dwarfs, which are too cool and dim to be detected easily in visible light but show up more clearly in the infrared spectrum.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a unique 2.5-meter telescope mounted on a modified Boeing 747 aircraft. Observing from such altitudes, SOFIA bypasses the majority of the Earth's water vapor, which otherwise absorbs infrared radiation, thereby allowing clearer and more detailed infrared observations. This airborne observatory has significantly advanced our understanding of the universe. With SOFIA, astronomers have been able to study star formation in distant galaxies, analyze the composition of interstellar matter, and detect complex organic molecules. These findings are crucial for piecing together the life cycles of stars and the evolution of galaxies.

Infrared astronomy utilizes different wavelength bands to study various cosmic phenomena. Each band corresponds to a specific range of wavelengths within the infrared spectrum. The four bands observed by WISE range from 3.4 to 22 microns. Understanding these wavelength bands is vital because different objects emit infrared radiation at different wavelengths. For instance:

• Shorter wavelengths (near-infrared) often capture images of cooler stars and brown dwarfs.
• Medium wavelengths give insights into warm dust and star-forming regions.
• Longer wavelengths (far-infrared) can detect cooler objects like interstellar dust.

By using multiple bands, astronomers can construct a more comprehensive picture of the infrared universe.

Brown dwarfs are substellar objects that lie between the largest planets and the smallest stars in terms of mass. They are particularly intriguing because they do not sustain stable hydrogen fusion like main-sequence stars, making them faint and difficult to detect in visible light. However, brown dwarfs emit relatively strong infrared radiation, making infrared astronomy crucial for their discovery. Missions like WISE have been instrumental in detecting new brown dwarfs, expanding our understanding of these elusive objects. The infrared capabilities of WISE revealed many previously unknown brown dwarfs, providing critical data on their distribution, formation, and characteristics.

Interstellar dust is made up of small particles present in the space between stars. These particles absorb visible light, often obscuring the view of the objects behind them. However, interstellar dust itself emits infrared radiation. By observing in the infrared spectrum, astronomers can not only detect these dust clouds but also study the objects hidden behind them. This capability is particularly valuable for understanding star formation as new stars are often born in dense clouds of gas and dust. With infrared astronomy, we can peer into these 'stellar nurseries' and study the processes occurring within them.

One of the powerful aspects of infrared light is its ability to penetrate gas and dust clouds that block visible light. This property allows astronomers to observe regions of space that are otherwise hidden. For example:

• Star-forming regions and planetary systems shrouded in dust can be studied in detail.
• Core regions of galaxies, often obscured by dust, can be observed directly.
• Colder objects, which are faint in visible light, show up prominently in infrared.

This penetrating capability of infrared light opens up a wealth of information, enhancing our understanding of a variety of cosmic phenomena and objects.