This article on 4 great observatories is a guest article by Ariana Vlad, senior at the International Computers High School of Bucharest, Romania, where she focuses on studying Physics and Mathematics.

Astronomical Observations

Astronomers usually have to rely on observations made from Earth to analyze the structure, the temperature, the evolution, and the motion of a celestial object. For electromagnetic radiation from millions and billions of light-years away to reach an astronomical observatory, it has to scatter, to be absorbed, and to be deflected by Earth’s atmosphere. This leads to an incomplete received spectrum, therefore incomplete data for scientists to work with.

The limitations of a singular receptor – that can only detect wavelengths within a limited spectrum – add to this first inconvenience. Astronomers solve these problems – at least partially – by using multiple observatories to gather data from only one celestial object or one specific area of the universe. The greatest complex of observatories created for this purpose is known as NASA’s 4 Great Observatories: the Hubble Space Telescope, the Compton Gamma Ray Observatory, the Chandra X-Ray Observatory, and the Spitzer Space Telescope. All the 4 great observatories have their own goals and all decode the universe in different wavelengths.

The Hubble Space Telescope

4 great observatories - Hubble
The Hubble Space Telescope Was The First Of The Four Great Observatories (Image: NASA)

The first and most renowned of the four great observatories is the Hubble Space Telescope. Named after the discoverer of the universal expansion, Edwin Hubble, this telescope is most famous because of the mesmerizing images it took of some of the most peculiar celestial objects, such pictures being credited in over thousands of scientific papers. 

Although its detection in the visual specter is responsible for the said images, the telescope can also detect ultraviolet and near infra-red radiation. All these characteristics determined the device to become vital to our understanding of the birth and death of stars, of our galaxy evolution, and most importantly, of the black holes.

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The incredible Mystic Mountain inside the Carina Nebula, image taken by the Hubble Telescope (Image: ESA/Hubble)

But as all things need to be replaced some day, even the Hubble will be replaced by its successor, the James Webb Space Telescope. This new telescope will be way bigger and powerful than the Hubble and will study the deep space and answer the mysteries that Hubble could not.

Also watch: How powerful is the James Webb Space Telescope

The Compton Gamma Ray Observatory

Named after the famous Arthur Compton, the observatory is, just as his namesake, a pioneer in gamma-ray studies. Launched in 1991, its primary purpose was the monitoring and data collecting for the most violent physical phenomena in the Universe. The observatory is so performant that it can detect radiation with very high energy (from 30 keV to 30 GeV) that results from such processes.

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Of the four great observatories, Compton decodes the universe in gamma spectrum

One of its most special characteristics is its size (with components as big as a subcompact car) and the total weight of 17 tons, which can be explained by noting that gamma rays can only be detected when interacting with matter. Therefore, the greater the devices, the greater the probability that a photon will scatter on atoms. 

The Chandra X-Ray Observatory

Named after the Indian astronomer Subrahmanyan Chandrasekhar, this observatory is unmatched when it comes to X-ray detections. Thanks to a system of very smooth and precise mirrors, this 21 years old apparatus is able to record images 25 times sharper than its predecessors. Its focusing power is analogous to an average person being able to read the newspaper at a distance of almost half a kilometer.

Also read: The world’s first time machine

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This composite image of the Antennae galaxies contains X-rays from Chandra (blue), optical data from Hubble (gold and brown), and infrared data from Spitzer (red). (Image: NASA)

This improved sensibility – so high that it can detect high-energy particles right before they fall into a black hole – is what made the Chandra Observatory the most important device for the study of black holes, supernovas, and dark matter, all of which will strengthen our understanding of the birth and evolution of the universe. 

The Spitzer Space Telescope

The last of the 4 great observatories is the Spitzer Telescope which covers the thermal infrared radiation. Named after Lyman Spitzer and launched only in 2003, the telescope completes the electromagnetic spectrum by detecting radiation that can easily penetrate the gas clouds in space but is blocked by Earth’s dense atmosphere. Therefore, it gives information that can’t be collected by optical telescopes placed on the ground.

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The Spitzer Space Telescope, the last of the NASA’s four great observatories (Image: NASA)

Scientists are able to recognize different molecules by their infrared signatures, and so they can analyze the data this telescope gathers. This is particularly useful in the case of newly formed galaxies and planetary systems that are surrounded by visible light blocking gas clouds or for smaller stars that are too dim to be observed. 

Also read: 10 most expensive space missions in the history

Although all the 4 great observatories can be used independently, a better understanding of a phenomenon is achieved when two or more are paired together. Every object looks different when viewed in X-ray, visible light, or infrared, but by correlating data from all the images these detectors can give, scientists can form their one, more complete image of what actually happens out there, in space. These 4 great observatories are one of the the most important machines in astronomy.

Note: We are starting a 30 article long Basics of Astrophysics series from April 10. To receive the articles right in your inbox, do subscribe our newsletter.

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