The Great Observatories

Young Astronomers Blog, Volume 28, Number 5.

Light is all around us. When we look at the world, we can see incredible colors. However, visible light is only a very small part of the electromagnetic spectrum. Light is a particle and a wave. Light waves can be measured in terms of its wavelength and frequency. Visible light has a wavelength from around 380 nm to 750 nm. We perceive different wavelengths as different colors; red, orange, yellow, green, blue, indigo and violet. You can remember these seven primary colors with the mnemonic ROY G BIV.

The electromagnetic spectrum extends far below and far above the visible spectrum. Longer wavelength (lower frequency) light is found as radio waves, microwaves and infrared light. Shorter wavelength (higher frequency) light is ultraviolet light, x rays and gamma rays. The Earth’s atmosphere is transparent to only specific wavelengths of light. Visible light, radio waves and some infrared waves make it through, but much of the electromagnetic spectrum is blocked by our atmosphere.

To see the full spectrum, astronomers need to reach above the atmosphere with telescopes in Earth orbit and beyond. To address this, NASA launched the four Great Observatories; telescopes designed to view different portions of the electromagnetic spectrum. The four telescopes are:

• Spitzer Space (infrared) Telescope (2003-2020)
• Hubble Space Telescope (1993-present)
• Chandra X-Ray Observatory (1999-present)
• Compton Gamma Ray Observatory (1991-2000)

Of course, the Hubble Space Telescope is the observatory we are most familiar with. It was launched from a space shuttle in 1990 but had to be repaired in 1993. It still sits 380 miles above the Earth giving us tremendous views of the universe.

Launched on August 25, 2003 and after 16 years in service, the Spitzer space telescope was retired on January 30, 2020. It was an infrared telescope which allowed astronomers to view a portion of the universe that was blocked from visible light. Among its discoveries was the TRAPPIST-1 system of exoplanets.

The James Webb Space Telescope (JWST) is the next “great observatory” on its way. It will follow Spitzer as an infrared telescope providing an expanded view through the dust of the galaxy. Images will be computer enhanced to show as visible photos and, as a 2 ½ times larger telescope than Hubble, we expect to be amazed. Webb will also follow the Kepler and TESS missions to provide follow up observations of previously discovered exoplanets. Due to technical limitations, the JWST will not view the inner solar system, but will observe solar system objects farther out from the Earth. The initial plan was to launch the Telescope in 2018. However, it has been delayed several times. The current plan is for a July 2021 launch from French Guiana on an Ariane 5 rocket. Once in space, Webb will be located at the stable second Sun-Earth Lagrange point, which is around one million miles from the Earth.

Selected Sources and Further Reading

“The Electromagnetic Spectrum.” NASA Imagine the Universe. (accessed February 3, 2020). https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html

“Tour of the Electromagnetic Spectrum.” NASA Science, Share The Science. (accessed January 31, 2020). https://science.nasa.gov/ems/

Dianne, J.. “What Are the Properties of the Visible Light Spectrum?” sciencing.com, https://sciencing.com/properties-visible-light-spectrum-8101926.html. 8 February 2020.

“NASA’s Great Observatories.” NASA Education, Student Features. (accessed February 3, 2020). https://www.nasa.gov/audience/forstudents/postsecondary/features/F_NASA_Great_Observatories_PS.html

“NASA’s Spitzer Space Telescope Ends Mission of Astronomical Discovery.” NASA press release 20-010. January 30, 2020. https://www.nasa.gov/press-release/nasa-s-spitzer-space-telescope-ends-mission-of-astronomical-discovery

“Frequently Asked Question Lite.” NASA James Webb Space Telescope. (accessed February 3, 2020). https://jwst.nasa.gov/content/about/faqs/faqLite.html