Question

Which of these forms of radiation passes most easily through the disk of the Milky Way? (a) red light (b) blue light (c) infrared light.

Short answer

(c) infrared light passes most easily through the Milky Way's disk.

Step-by-step solution

Identify Types of Radiation

The types of radiation mentioned in the exercise are red light, blue light, and infrared light. Each has different wavelengths and properties that impact how they interact with matter, such as the interstellar dust in the Milky Way disk.

Consider Wavelengths of Radiation

Red light has a longer wavelength than blue light, and infrared light has the longest of the three. Wavelength significantly affects how radiation interacts with dust and gas in space.

Evaluate Interaction with Dust

Interstellar dust scatters and absorbs light more effectively at shorter wavelengths. Therefore, blue light is most affected by dust, red light less so, and infrared light the least affected due to its larger wavelength, which allows it to pass through dust more easily.

Infer Impact on Passing through the Milky Way

Since infrared light is the least affected by dust due to its long wavelength, it can pass through the Milky Way's disk more easily than red or blue light.

Key concepts

Infrared Radiation

Infrared radiation is a type of electromagnetic radiation with wavelengths longer than those of visible light. While visible light covers a small range, infrared extends from about 700 nanometers (just beyond visible red light) to 1 millimeter. This means infrared radiation encompasses a wide spectrum. Because its wavelengths are longer than those of visible light, infrared can penetrate dust and gas that scatter or absorb shorter wavelengths. This penetration capability makes it highly useful in astronomy. When observing the universe, infrared allows us to glimpse areas obscured by dense clouds of dust and gas. Scientists use infrared telescopes to detect stars forming in nebulas or to explore the core of our galaxy, the Milky Way, regions typically hidden in other wavelengths. Moreover, infrared is not just significant in space but also for its heat-emitting properties used in everyday technologies, like remote controls and thermal imaging.

Interstellar Dust

Interstellar dust is made up of tiny solid particles found between the stars in galaxies. These particles are usually composed of carbon, silicon, oxygen, and other elements, typically from the remnants of stars.

• These particles can range from very small, less than a micrometer, to slightly larger grains.
• Interstellar dust plays a crucial role in the life cycle of stars, as it helps to cool down hot gases and provides a base for molecules to form.

Despite its small size, interstellar dust can have a significant impact on light traveling through space. It scatters shorter wavelengths, like blue and ultraviolet light, more than longer wavelengths, like red and infrared light. This scattering is why distant stars can appear redder—a phenomenon known as "interstellar reddening." Dust absorption and scattering are key in determining what we can observe in our galaxy, affecting everything from starlight to the signals received by telescopes.

Wavelengths of Light

Wavelengths of light refer to the distance between successive crests of a wave. In the electromagnetic spectrum, this concept can vary widely, affecting how different types of light interact with matter.

• Shorter wavelengths include gamma rays, X-rays, and ultraviolet light, which are generally more energetic and can be harmful to living organisms.
• Visible light comprises a small portion of the spectrum, spanning from violet at about 400 nanometers to red at around 700 nanometers.
• Beyond visible light, there are longer wavelengths like infrared, microwave, and radio waves. These have less energetic photons but can travel through various media with minimal scattering.

When light travels through the Milky Way, its interaction with interstellar dust depends significantly on its wavelength. Shorter wavelengths, like blue light, scatter more, getting absorbed and deflected by dust particles. In contrast, longer wavelengths, like infrared, can navigate through the dust with greater ease, resulting in clearer astronomical observations.