Light spectrum is the many different wavelengths of energy produced by a light source. Light is measured in nanometers, abbreviated to nm. Each nanometer represents a wavelength of light or band of light energy. Visible light is the part of the spectrum from 380nm to 780nm. These light spectrums are important to study because the human eye can only see visible light, which is a small portion of the light spectrum. Therefore, human eye telescopes miss a large portion of the sky and available data.

As NASA states, “spectroscopy can be very useful in helping scientists understand how an object produces light, how fast it is moving, and what elements it is composed of. Spectra can be produced for any energy of light, from low-energy radiowaves to very high-energy gamma rays.”

What Can Scientists Learn From a Spectrum?

Looking at the light spectrum, scientists can help determine which elements are in the stars, the temperature and density of elements in the star, how fast the material is moving, and much more.

Types of Light Spectrum And Astronomy

X-rays

Blocked by the Earth’s atmosphere, X-Rays pose a particular challenge to study because their waves are so small and energetic. These small and energetic waves pass right through mirrors rather than bounce off as do lower-energy forms of light. More about information how X-rays are focused can be found at the X-ray Telescope Introduction page by NASA.

A quick summary of how focusing X-ray telescopes work is that they require long focal lengths. This setup is required because the mirrors where light enters the telescope must be separated from the X-ray detectors by several meters.

Gamma-rays

Just like X-Rays are blocked by the Earth’s atmosphere and are hard to focus, gamma-rays are even harder to focus. This has meant that there have been no focusing gamma-ray telescopes that have been developed. Therefore, instead of focusing telescopes, astronomers rely on alternate ways to determine where in the sky gamma-rays are produced such as utilizing special properties of the detector or by looking for special markers that can directly reveal gamma-rays.

Ultraviolet Light

As a result of atmospheric absorption, ultraviolet astronomy must be done using telescopes in space. Similar in nature to visible light astronomy and telescopes, ultraviolet observatories utilize specific filters to capture the light. Other than the utilization of filters, the other difference is that ultraviolet telescopes must be placed above the Earth’s atmosphere to perform the best science. This means launching specific satellite telescopes.

Visible Light

Visible light can pass right through our atmosphere, which allows an array of ground based telescopes to utilize this methods. Also called “optical astronomy”, these ground based visible light telescopes have issues with atmospheric distortions. To help minimize atmospheric distortions, creating telescopes at higher elevations will help, but even then there will be limits to how these telescopes can perform.

Infrared Light

Not all infrared light makes it through the atmosphere, which makes this challenging. The larger wavelengths get blocked, whereas the smaller wavelengths can make it through the atmosphere. Another challenge faced by studying infrared light is that everything emits infrared light.

To study infrared light, telescopes must be placed at high altitudes in dry climates. This is done in an effort to place the telescopes at an altitude that is higher than much of the atmospheric water vapor. Regardless of how high of an altitude that observatories are placed, the astronomers must still account for the atmosphere in their measurements.

Microwave Light

Just like X-Rays and other sources, the atmosphere of the Earth blocks much of the light in the microwave band. Therefore, astronomers have to utilize satellite-based telescopes to observe cosmic microwaves. What makes microwaves very interesting is that scientists have discovered that the entire sky has many sources of microwaves, which is a remnant of the Big Bang. These microwaves are often referred to as the Cosmic Microwave Background, or CMB for short.

Radio Light

Radio waves can make it through the Earth’s atmosphere without significant obstacles; therefore, on cloudy days, radio telescopes can still be utilized to observe the cosmos. The benefits of putting a radio telescope in orbit is that astronomers can take utilize multiple telescopes that are very far apart and create images with the same resolution of a larger sized telescope. This is called “interferometry.”

References

https://imagine.gsfc.nasa.gov/science/toolbox/spectra1.html

https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html