James Webb Space Telescope's view of the universe

Seeing into space

The James Webb Space Telescope (JWST) continues to make the front pages in astronomy news.

One of the latest images is of the planet Uranus, the seventh planet out from the Sun. Despite the distance this world is from us, the images show the planet's system of fine rings and storm activity in its atmosphere.

The JWST was not designed for these operations. The prime objective was to study the extremely distant evidence of what was happening during the youth of the universe.

When did the first stars and galaxies form? What were they like? What was going on inside them? It just so happens that the JWST is a potent tool for optical astronomy and is usable in many cutting edge areas of astronomy.

Why is this? If you have ever made astronomical observations from the ground you will know the answer. Atmospheric turbulence makes stars twinkle and makes telescope images blur and dance around. Sometimes the atmosphere steadies and for a little while the "seeing" can be excellent. However, all too soon the blurring and dancing come back. Then, of course, some nights are cloudy.

On top of all this, during the day the sky glows blue and we cannot observe anything other than the Sun, the Moon and the brightest planets.

Finally, although the wavelength range of electromagnetic waves we call visible light gets to the ground, other wavelengths, such as ultraviolet and infrared radiation, are partially or totally absorbed.

To some extent we can mitigate some of these problems by putting our telescopes on top of mountains. However, the only real solution is to put our instruments in space, beyond our turbulent atmosphere.

Our first major telescope in space was the Hubble Space Telescope (HST). Now we also have the James Webb Space Telescope. The HST is designed to observe visible light. The JSWT observes infrared wavelengths. The two instruments are intended to be complementary.

The main reason the JWST was designed to operate in the infrared wavelength range was to observe the most distant and oldest reaches of our expanding universe. The more distant the reaches of the cosmos we observe, the faster they are receding from us.

This shifts the light coming from those parts of the universe to longer wavelengths, making it look redder. We call this "red shift". The bigger the distance, the bigger the red shift.

This means that visible light from the most distant galaxies will be red shifted to infrared wavelengths, which the JWST can observe. However, operating at infrared wavelengths brings other benefits: things we can't do with visible light.

If you have ever driven in mist or fog, particularly at night, you may have found that glasses with amber or orange lenses make it much easier to see what is going on. The reason for this is a process called Rayleigh scattering. Light scatters to and fro off the tiny droplets of water making up the fog, causing glare and hiding detail.

This scattering is very strongly dependent on the wavelength of the light. The shorter the wavelength (bluer) the worse the scattering. Filtering out the highly scattered blue and concentrating on the much less-scattered red wavelengths makes driving so much easier.

Space is filled with fine dust and gas clouds. Rayleigh scattering is going on there too. This is the reason that what the HST, operating at visible light wavelengths, shows as thick or opaque clouds are partially or totally clear at the infrared wavelengths used by the JWST. This makes it possible to observe the birth of new stars and planetary systems, and all sorts of other interesting things going on in the depths of those clouds.

Thanks to the JWST we are seeing things we have never seen before. The lineup of scientists eager to use that instrument is very, very long.


• Venus shines brightly low in the west after sunset, with Mars above it.

• Saturn lies low in the east before dawn.

• The Moon will be new on April 19.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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