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Webb telescope will see what our eyes can’t

Greetings, stargazers.

The Christmas morning launch of the James Webb Space Telescope, with the “trois, deux, un” countdown in French was fun to watch. Unlike Space Shuttle launches, which ignited the main engines several seconds before zero so they would be at full thrust when the solid rocket boosters fired and liftoff occurred, the Ariane 5 timed the main engines to light at zero and liftoff didn’t happen until several seconds later. The launch was successful, and the telescope is well on its way to its final position at the gravitationally stable L2 Lagrange point.

As of this writing, the Webb telescope just completed the tensioning of the sun shields that will keep the scientific instruments permanently in shadow. This allows them to remain cold enough to effectively detect infrared radiation. Observing the universe in infrared will let the Webb telescope view much more of what is out there than the Hubble telescope can.

When the Hubble telescope was launched, the high-resolution photographs were the most remarkable results for many of us. The Hubble could resolve much finer details than the best ground-based telescopes available at the time. However, in the intervening years, the development of adaptive optics technology and various image processing techniques has allowed many Earth-based telescopes to mitigate many of the detrimental atmospheric effects that the Hubble overcame by simply (but very expensively) getting above the atmosphere.

One atmospheric effect that cannot be overcome on the ground is the absorption of infrared light. The prefix “infra” means beneath. The energy in a photon of infrared light is lower than, or “beneath” that of red light. Our human eyes are not very sensitive to these longer wavelengths, but there is no sharp cutoff to what can and can’t be seen. Our eyes developed the sensitivity in what we call visible light because that is the predominant range of wavelengths emitted by our sun. The Earth’s atmosphere is transparent in these visible wavelengths, but not nearly as transparent in the lower-energy infrared wavelengths.

Even though the sun is considered an “average” dwarf star, it is much bigger, brighter and hotter than most of the objects in the universe. Small red dwarf stars are by far the most numerous type of star, and most other things out there are much cooler and dimmer than the stars we can see in the night sky. If this new telescope hopes to see most of this stuff, then it must look in the wavelengths that are being emitted by these cooler objects, and that means getting above the atmosphere.

Another reason for looking in the infrared has to do with the expansion of the universe. The most distant objects we can see are moving away from us at tremendous speeds, so the light they emit has been shifted toward the red end of the spectrum. Some of the things that might be radiating in visible light will only be visible in the infrared from our perspective.

This month

Orion is prominent in the mid-winter sky. The three stars in the belt, with bright Betelgeuse and Rigel on either side, form one of the more recognizable asterisms. Orion is a good anchor for identifying the surrounding constellations, such as Taurus, Gemini and Canis Major. The three belt stars are on the celestial equator. They rise due east shortly before sunset, follow an arc through the southern sky throughout the night and set due west before dawn.

The Orion Nebula, M42, is the brightest star-forming region visible from Earth. Many of the infant stars seen there radiate predominantly in the infrared. Even if we can’t see the infrared radiation through binoculars, the Orion Nebula is one of the most rewarding binocular targets in the sky.

Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at hakes_c@fortlewis.edu.

Useful links

JAMES WEBB SPACE TELESCOPE: https://webb.nasa.gov/content/news/index.html.

INFRARED: https://en.wikipedia.org/wiki/Infrared.

ASTRONOMY PICTURE OF THE DAY: http://apod.nasa.gov/apod.

OLD FORT LEWIS OBSERVATORY: www.fortlewis.edu/observatory.


FOUR CORNERS STARGAZERS: https://bit.ly/2pKeKKa.