Astronomy: The James Webb Space Telescope and Infrared Astronomy Worksheet

Question 1

The James Webb Space Telescope observes mostly infrared light rather than visible light. Explain two reasons infrared observations are useful for studying space.

Accepted Answer

Infrared observations are useful because infrared light can pass through dust clouds better than visible light, allowing astronomers to see hidden stars and forming planetary systems. Infrared light also helps astronomers study very distant galaxies because their light has been redshifted from visible or ultraviolet wavelengths into the infrared.

Question 2

JWST has a large segmented primary mirror about 6.5 meters across. Explain why a larger telescope mirror improves astronomical observations.

Accepted Answer

A larger mirror collects more light, which makes faint objects easier to detect. It also improves angular resolution, allowing the telescope to distinguish smaller details in distant objects.

Question 3

Infrared wavelengths are generally longer than visible wavelengths. If a photon has a longer wavelength, how does its energy compare to a shorter-wavelength photon? Explain using the relationship between energy and wavelength.

Accepted Answer

A longer-wavelength photon has lower energy than a shorter-wavelength photon. This is because photon energy is inversely related to wavelength, so as wavelength increases, energy decreases.

Question 4

A galaxy emitted ultraviolet light when the universe was young, but JWST detects that light today in the infrared. Explain what happened to the light as it traveled through space.

Accepted Answer

As the universe expanded, the wavelength of the galaxy's light was stretched. This process is called cosmological redshift, and it can shift ultraviolet or visible light into infrared wavelengths by the time it reaches Earth.

Question 5

JWST orbits near the Sun-Earth L2 point instead of orbiting close to Earth like the Hubble Space Telescope. Give one advantage of placing JWST near L2.

Accepted Answer

Near L2, JWST can keep the Sun, Earth, and Moon on the same side of the telescope. This allows its sunshield to block heat and light from all three sources, helping the telescope stay cold enough for infrared observations.

Question 6

Explain why JWST needs a large sunshield and very cold operating temperatures to observe infrared light.

Accepted Answer

Warm objects emit infrared radiation, including the telescope itself. JWST must stay very cold so that its own heat does not overwhelm the faint infrared signals coming from distant astronomical objects.

Question 7

A star-forming region contains thick clouds of gas and dust. Visible-light images show mostly dark patches, but infrared images reveal many young stars. Explain why the two images look different.

Accepted Answer

Dust blocks and scatters visible light, so many young stars are hidden in visible-light images. Infrared light can travel through dust more easily, so infrared images can reveal stars forming inside the cloud.

Question 8

JWST can study exoplanet atmospheres using transit spectroscopy. During a transit, a planet passes in front of its star. Explain how astronomers can learn about gases in the planet's atmosphere from the starlight.

Accepted Answer

When the planet passes in front of its star, some starlight filters through the planet's atmosphere. Different gases absorb specific wavelengths of light, so astronomers can study the spectrum to identify gases such as water vapor, carbon dioxide, or methane.

Question 9

A spectrum from a distant object shows a strong hydrogen feature at 1.6 micrometers, but the same feature is normally measured at 0.4 micrometers in the object's rest frame. Calculate the redshift z using z = observed wavelength divided by rest wavelength minus 1.

Accepted Answer

The redshift is z = 1.6 divided by 0.4 minus 1, which equals 4 minus 1. The object's redshift is z = 3.

Question 10

Compare JWST and Hubble in terms of the main wavelengths they observe and the kinds of objects or processes they are especially good at studying.

Accepted Answer

Hubble mainly observes visible and ultraviolet light, so it is especially useful for sharp visible images of stars, galaxies, and nebulae. JWST mainly observes infrared light, so it is especially useful for studying dusty regions, cool objects, exoplanet atmospheres, and very distant redshifted galaxies.

Question 11

JWST's instruments include cameras and spectrographs. Describe the difference between an image and a spectrum, and explain why both are valuable in astronomy.

Accepted Answer

An image shows where light is coming from and reveals the shape, structure, and location of objects. A spectrum spreads light by wavelength, which reveals information such as composition, temperature, motion, and redshift. Both are valuable because they answer different scientific questions.

Question 12

Some objects in space, such as brown dwarfs and newly forming planets, are relatively cool compared with stars like the Sun. Explain why infrared astronomy is well suited for studying these objects.

Accepted Answer

Cool objects emit much of their radiation at infrared wavelengths rather than visible wavelengths. Infrared telescopes like JWST can detect this heat radiation, making it possible to study objects that are too dim to observe well in visible light.

Astronomy: The James Webb Space Telescope and Infrared Astronomy

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