Space telescopes observe above most or all of Earth’s atmosphere. This avoids atmospheric blurring and provides access to wavelengths that the atmosphere blocks or absorbs.
Their main advantage is not simply being closer to the stars. It is obtaining cleaner or otherwise inaccessible measurements.
Different wavelengths reveal different physics
Visible light represents only a small part of the electromagnetic spectrum.
- Ultraviolet observations reveal hot stars and energetic gas
- Infrared light can pass through some dust and reveal cooler objects
- X-rays trace extremely hot gas and compact objects
- Gamma rays identify some of the universe’s highest-energy events
No telescope observes everything. Astronomers combine data from multiple instruments to build a more complete explanation.
Looking far away means looking into the past
Light travels at a finite speed. When a telescope detects light from a galaxy billions of light-years away, it records that galaxy as it existed billions of years ago.
The expansion of the universe stretches light from very distant galaxies toward longer, infrared wavelengths. Webb was designed for infrared observations partly for this reason.
This does not make a telescope a literal time machine. It means the arriving light carries information from an earlier period.
Hubble and Webb provide complementary views
Hubble primarily observes visible and ultraviolet light, with limited near-infrared capability. Its long operating history has supported studies of planets, stars, galaxies and cosmic expansion.
Webb observes red and infrared wavelengths. It can examine early galaxies, star-forming regions hidden by dust and some exoplanet atmospheres.
Webb did not simply replace Hubble. Their wavelength coverage and scientific strengths overlap but differ.
Images are also measurements
Astronomical images often combine observations taken through several filters. Colors may represent wavelengths, chemical information or signal intensity rather than what human eyes would see from a spacecraft window.
Spectroscopy provides additional information by separating light into wavelengths. It can reveal composition, temperature, motion and other properties.
Building a history from ancient light
Space telescopes help astronomers test how stars, galaxies and planetary systems formed and changed. Each observation is a surviving signal, and several telescopes may be needed to interpret it correctly.
Sources
- NASA history of Hubble and atmospheric limitations: https://science.nasa.gov/mission/hubble/overview/the-history-of-hubble/
- NASA guide to astronomical wavelengths: https://science.nasa.gov/mission/hubble/science/science-behind-the-discoveries/wavelengths/
- NASA Webb early-universe science: https://science.nasa.gov/mission/webb/early-universe/
- NASA Webb instruments: https://science.nasa.gov/mission/webb/science-overview/science-explainers/webbs-scientific-instruments/