Astronomy

Are space telescopes completely out of the earth's atmosphere?

Are space telescopes completely out of the earth's atmosphere?


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Is the Hubble Space Telescope, and every other space telescope for that matter, completely outside the Earths atmosphere?


A handful of space telescopes are located in Langrange point L2, 1.5 million km from Earth. This is much farther away than the Moon, and far outside Earth's atmosphere.

WMAP and Planck, which measure the cosmic microwave background (CMB), are located here because Earth is a hundred times brighter than the CMB in this wavelength region. Herschel observes in the infrared, which is heat radiation, so it was also put in L2 to avoid Earth's heat. Others can be found in the list provided in Keith's answer.

Another advantage of putting a telescope in L2 is that the Earth and Sun are always in the same direction, making it easier to observe most of the sky. The cost of putting it here is probably more than an order of magnitude higher, though.

Whether or not low Earth orbit telescopes like Hubble at 550 km are outside Earth's atmosphere is a bit subjective. The atmosphere doesn't stop at some particular point, instead gradually thinning. These space telescope are definitely far enough away that they are not heated up. Neither does the atmosphere affect their observations (by seeing). They are, however, slowly decelerated and thus need a boost once in a while not to fall down.


This article contains a list of space telescopes. It's likely to be nearly complete.

The extent of the Earth's atmosphere is not very well defined. The altitude at which Hubble orbits (about 550 kilometers above the surface) is above almost all of the atmosphere, but there's still enough residual air to cause some slight drag. It's not higher because it was deployed from the Space Shuttle, which couldn't carry it much higher that its current orbit. It was also useful to be able to fly servicing missions.


Space Telescopes

How can scientists get a clear look at objects in outer space? How can they search for planets that might orbit nearby stars?

Telescopes have been used to study the heavens for over 300 years. But Earth-based telescopes have a serious handicap. The atmosphere surrounding Earth interferes with almost all radiation reaching us from space. For example, radiation in the form of light from distant objects is distorted by the atmosphere, making stars appear to twinkle.

Light is just one form of energy given off by stars. Stars also emit invisible energies, including radio waves, infrared, ultraviolet, gamma, and X rays. Except for light and radio waves, almost all of this energy is screened out by Earth's atmosphere.

Early Space Telescopes

The first space telescopes were designed to observe these screened-out invisible energies. As early as 1947, rockets carried instruments high into Earth's atmosphere to measure ultraviolet and X rays. By the 1970's, telescopes mounted on satellites were observing these and other invisible energies.

In addition to being unaffected by atmospheric distortions of visible light, space telescopes can observe other types of radiation that are blocked by the atmosphere. Instruments attached to the telescopes gather information and transmit it back to Earth.

Early space telescopes included the International Ultraviolet Explorer and the Einstein X-Ray Observatory (named after physicist Albert Einstein), both launched in 1978 and the Infrared Astronomical Satellite, launched in 1983.

Today's Space Telescopes

In the 1980's, the National Aeronautics and Space Administration (NASA) began planning four space telescopes, called the Great Observatories. The first of these, the Hubble Space Telescope, was launched in April 1990. It was followed by the Compton Gamma-Ray Observatory in April 1991, the Chandra X-Ray Observatory in July 1999, and the Space Infrared Telescope Facility in August 2003.

Hubble Space Telescope

The Hubble Space Telescope (HST) is designed to observe visible light and ultraviolet and infrared radiation. It is named after the American astronomer Edwin Hubble (1889-1953). The HST, which is about the length of a large school bus, has a mass of over 11 tons. Its orbit around Earth, at an average altitude of 370 miles (600 kilometers), lasts 95 minutes. Ground stations keep in contact with the Hubble as it orbits, and communications satellites also track it.

The Hubble is a reflecting telescope. Light enters the telescope and strikes a primary mirror. It is then reflected back to a secondary mirror, which redirects the light back through a small hole in the center of the primary mirror. The light is then analyzed by one of the Hubble's scientific instruments.

Some of the scientific instruments used on the Hubble over the course of its operation have been repaired, upgraded, or completely replaced during periodic service missions by astronauts aboard space shuttles. Among the instruments used on the Hubble have been a wide field/planetary camera, which photographed large sections of the sky as well as the planets in our solar system and a Space Telescope Imaging Spectrograph (STIS), which analyzed the light from an object in space to determine what elements it was made of, how fast it was traveling, and if it was moving toward or away from the Earth.

The Hubble has given astronomers some of their most detailed pictures ever of various celestial objects. These range from planets in our own solar system to galaxies over 10 billion light-years away.

For example, the Hubble has captured images of giant storms on Mars, collisions of distant galaxies, the birth of young stars, strangely shaped regions of swirling dust and gases, and the evaporation of a gas planet closely orbiting a distant star. And in 1994, Hubble captured remarkable images of comet Shoemaker-Levy as fragments of its nucleus collided with Jupiter.

Compton Gamma-Ray Observatory

The Compton Gamma-Ray Observatory was designed to detect gamma rays--the most powerful, or energetic, form of electromagnetic radiation. This space telescope was named after the American physicist Arthur Compton (1892-1962). Because gamma rays do not penetrate Earth's atmosphere, except at extremely high energies, they cannot be detected by ground-based observatories. Gamma rays can signal events, such as the death of a star, and provide information about black holes, pulsars, and quasars. Quasars make up the most powerful class of objects yet discovered in the universe.

The Compton weighed nearly 17 tons. It orbited Earth at an altitude of about 280 miles (450 kilometers). Three of the Compton's four instruments were each about as large as a subcompact car. The size of the instruments is very important in gamma-ray astronomy. Gamma rays are detected when they interact with matter, so the number of gamma-ray events recorded depends on the size of the detector.

The Compton Observatory made the first comprehensive map of the entire sky. It also discovered the nearby remains of a recent supernova and a new class of high-energy gamma-ray sources called gamma-ray quasars. The Compton completed its mission in 2000 when it re-entered Earth's atmosphere and burned up.

Chandra X-Ray Observatory

The Chandra X-Ray Observatory was named after the Indian astrophysicist Subrahmanyan Chandrasekhar (1910-95). The Chandra is designed to study sources of X rays, including stars, exploding stars called supernovae, and matter falling into black holes.

X rays from celestial objects are focused by mirrors inside the Chandra and directed at special instruments. These instruments include a High Resolution Camera to record the number and strength of the incoming X rays and various spectrometers to analyze the spectrum of the X rays.

Among Chandra's discoveries were a massive black hole swallowing material at the center of the Milky Way Galaxy pulses of X rays emanating from the polar regions of Jupiter and an immense rotating disc of extremely hot gas moving through a distant galaxy. The Chandra also found signs of hidden dark matter, which may make up most of the mass of the universe.

The Space Infrared Telescope Facility

The Space Infrared Telescope Facility (SIRTF) is designed to detect the infrared radiation given off by celestial objects. These objects include those not easily seen in visible light, such as small, dim stars or forming planets hidden by thick clouds of dust and gas.

The SIRTF's scientific instruments include a reflecting telescope, an infrared camera, an infrared spectrograph, and a multiband imaging photometer. Because the SIRTF is sensitive to heat, it is shielded from the sun and the Earth, and a special device called a Cryostat uses liquid helium to reduce the temperature of the equipment to about ¯459°F (¯273°C).

Other Space Telescopes

Other telescopes have been launched into space. Two are operated by the European Space Agency. The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) will make various X-ray observations and create a gamma-ray map of the entire sky. The X-ray Multi-Mirror Mission (XMM-Newton) uses three X-ray telescopes --each with 58 mirrors-- to detect more X-ray sources than any other orbiting observatory. A third, the High Energy Transient Explorer (HETE-2), is jointly operated by the United States, Japan, France, and Italy. It is designed to detect bursts of gamma rays as well as survey X-ray sources.


Are space telescopes completely out of the earth's atmosphere? - Astronomy

The advantage of using a telescope in space is that you don't have to look through the Earth's atmosphere. For very detailed observations the atmosphere is pretty murky and horrible so it's a real advantage to get above that. You've probably seen HST pictures, and they really are much more detailed than you can get from the ground.

The disadvantages are mainly to do with the hassle of operating in space. It's much more expensive, so you can't have such a large telescope. If things go wrong it's much harder to repair them. You can't update the instruments so often so they quickly become out of date. Also with the modern technique of Adaptive Optics (basically correcting for the turbulence of the atmosphere as you observe), ground based telescopes are catching up with the HST.

By the way, the above is for optical telescopes which I assume is what you mean. For other wavelenghts there is no choice as our atmosphere can block them completely (eg. Far infra-red and X-rays and Gamma-rays). Telescopes for these have to be in space. For most radio wavelengths the atmosphere is very little problem, so instruments like Arecibo and the VLA are not limited by the atmosphere at all.

This page was last updated July 18, 2015.

About the Author

Karen Masters

Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.


Types of Telescopes

Optical Telescopes

People have been making and using lenses for magnification for thousands of years. However, the first true telescopes were made in Europe in the late 16th century. These telescopes used a combination of two lenses to make distant objects appear both nearer and larger. The term telescopewas coined by the Italian scientist and mathematician Galileo Galilei (1564–1642). Galileo built his first telescope in 1608 and subsequently made many improvements to telescope design.

Telescopes that rely on the refraction, or bending, of light by lenses are called refracting telescopes, or simply refractors. The earliest telescopes, including Galileo’s, were all refractors. Many of the small telescopes used by amateur astronomers today are refractors. Refractors are particularly good for viewing details within our solar system, such as the surface of Earth’s moon or the rings around Saturn (Figure below).

The largest refracting telescope in the world is at the University of Chicago’s Yerkes Observatory in Wisconsin and was built in 1897. Its largest lens has a diameter of 102 cm.

Around 1670, another famous scientist and mathematician — Sir Isaac Newton (1643–1727) — built a different kind of telescope. Newton used curved mirrors to focus light and so created the first reflecting telescopes, or reflectors (Figure below). The mirrors in a reflecting telescope are much lighter than the heavy glass lenses in a refractor. This is significant, because:

  • To support the thick glass lenses a refractor must be strong and heavy.
  • Mirrors are easier to make precisely than it is to make glass lenses.
  • Because they do not need to be as heavy to support the same size lens, reflectors can be made larger than refractors.

Larger telescopes can collect more light and so they can study dimmer or more distant objects. The largest optical telescopes in the world today are reflectors.

(a) Reflecting telescopes used by amateur astronomers today are similar to the one designed by Isaac Newton in the 17th century. (b) The South African Large Telescope (SALT) is one of the largest reflecting telescopes on Earth. SALT’s primary mirror consists of 91 smaller hexagonal mirrors, each with sides 1 m long. (c) Many amateur astronomers today use catadioptric telescopes.

Catadioptric telescopes have a combination of mirrors and lenses to focus light. Catadioptric telescopes have large mirrors to collect a lot of light, but short tubes for portability.

KQED: Amateur Astronomers

Amateur astronomers enjoy observing and studying stars and other celestial objects. Both professional and amateur astronomers use telescopes. A telescope is an instrument that makes faraway objects look closer. Learn more at: http://science.kqed.org/quest/video/amateur-astronomers/.

Radio Telescopes

Notice it says above that the largest optical telescopes in the world are reflectors. Optical telescopes collect visible light. Even larger telescopes are built to collect light at longer wavelengths — radio waves. What do you think these telescopes are called? Radio telescopes look a lot like satellite dishes because both are designed to do the same thing — to collect and focus radio waves or microwaves (the shortest wavelength waves) from space.

The largest single telescope in the world is at the Arecibo Observatory in Puerto Rico (Figure below). This telescope is located in a naturally occurring sinkhole that formed when water flowing underground dissolved the limestone rock. If this telescope were not supported by the ground, it would collapse under its own weight. Since the telescope is set into the ground it cannot be aimed to different parts of the sky and so can only observe the part of the sky that happens to be overhead at a given time.

The radio telescope at the Arecibo Observatory has a diameter of 305 m.

A group of radio telescopes can be linked together with a computer so that they are all observing the same object (Figure below). The computer combines the data, making the group function like one single telescope.

For more on radio telescopes and radio astronomy in general, go to http://www.nrao.edu/whatisra/index.shtml.

The Very Large Array in New Mexico has 27 radio dishes, each 25 m in diameter. When all the dishes are pointed at the same object, they are like a single telescope with a diameter of 22.3 mi.

KQED: SETI: The New Search for ET

Scientists have upped their search for extraterrestrial intelligence with the Allen Telescope Array, a string of 350 radio telescopes, located 300 miles north of San Francisco. Find out why SETI scientists now say we might be hearing from ET sooner than you think. Learn more at:http://science.kqed.org/quest/video/seti-the-new-search-for-et/.

KQED: Interview with Astronomer Jill Tartar

SETI listens for signs of other civilization’s technology. Dr. Jill Tartar explains the program: What it’s looking for what the problems are what the potential benefits are. Learn more at: http://www.youtube.com/watch?v=QwEm3WHvNHI.

Space Telescopes

Telescopes on Earth all have one significant limitation: the electromagnetic radiation they gather must pass through Earth’s atmosphere. The atmosphere blocks some radiation in the infrared part of the spectrum and almost all radiation in the ultraviolet and higher frequency ranges. Furthermore, motion in the atmosphere distorts light. That distortion is why stars twinkle in the night sky. To minimize these problems, many observatories are built on high mountains, where there is less atmosphere above the telescope. Even better, space telescopes avoid such problems completely because they orbit outside Earth’s atmosphere in space. Space telescopes can carry instruments to observe objects emitting various types of electromagnetic radiation such as visible, infrared or ultraviolet light gamma rays or x-rays. X-ray telescopes, such as the Chandra X-ray Observatory, use X-ray optics to observe remote objects in the X-ray spectrum.

The Hubble Space Telescope (HST), shown in (Figure below), is perhaps the best known space telescope. The Hubble was put into orbit by the Space Shuttle Atlantis in 1990. Once it was in orbit, scientists discovered that there was a flaw in the shape of the mirror. A servicing mission to the Hubble by the Space Shuttle Endeavor in 1994 corrected the problem. Since that time, the Hubble has provided huge amounts of data that have helped to answer many of the biggest questions in astronomy.

Find out more by visiting the Hubble Space Telescope website at http://hubblesite.org.

(a) The Hubble Space Telescope orbits Earth at an altitude of 589 km (366 mi). It collects data in visible, infrared, and ultraviolet wavelengths. (b) This starburst cluster is one of the many fantastic images taken by the HST over the past two decades.

The National Aeronautics and Space Administration (NASA) has placed three other major space telescopes in orbit, comprising what NASA calls the ‘Great Observatories’. Each of these telescopes specializes in a different part of the electromagnetic spectrum (Figure below). NASA is planning for another telescope, the James Webb Space Telescope, to serve as a replacement for the aging Hubble. The James Webb is scheduled to launch in 2018.

NASA’s four space-based Great Observatories were designed to view the universe in different ranges of the electromagnetic spectrum. A. Hubble Space Telescope: visible, infrared and ultraviolet light B. Compton Gamma Ray Observatory (inactive): gamma ray C. Spitzer Space Telescope: infrared D. Chandra X-ray Observatory: X-ray.


Can the Hubble Space Telescope be fixed?

It has been before. Immediately after its 1990 launch it was discovered that its mirror had an aberration causing images to be blurry, so it was visited in orbit by astronauts aboard NASA’s Space Shuttle Endeavour in 1993. They installed corrective optics. More servicing missions took place in 1997, 1999, 2002 and 2009 to upgrade various components, notably adding the telescope’s Wide Field Camera 3.

However, servicing missions ceased with the retirement of the Space Shuttles in 2011. It’s not clear what orbital vehicle could now be used to visit and fix the Hubble Space Telescope.

However, many fixes can be performed remotely. A few years ago the space telescope experienced a gyroscope failure and on March 8, 2021 it went into safe mode due to an onboard software error that was soon fixed.

This photograph of NASA’s Hubble Space Telescope was taken on the fifth servicing mission to the . [+] observatory in 2009.


Contents

Wilhelm Beer and Johann Heinrich Mädler in 1837 discussed the advantages of an observatory on the Moon. [2] In 1946, American theoretical astrophysicist Lyman Spitzer proposed a telescope in space. [3] Spitzer's proposal called for a large telescope that would not be hindered by Earth's atmosphere. After lobbying in the 1960s and 70s for such a system to be built, Spitzer's vision ultimately materialized into the Hubble Space Telescope, which was launched on April 24, 1990 by the Space Shuttle Discovery (STS-31). [4] [5]

The first operational space telescopes were the American Orbiting Astronomical Observatory, OAO-2 launched in 1968, and the Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971.

Performing astronomy from ground-based observatories on Earth is limited by the filtering and distortion of electromagnetic radiation (scintillation or twinkling) due to the atmosphere. [2] A telescope orbiting Earth outside the atmosphere is subject neither to twinkling nor to light pollution from artificial light sources on Earth. As a result, the angular resolution of space telescopes is often much higher than a ground-based telescope with a similar aperture. Many larger terrestrial telescopes, however, reduce atmospheric effects with adaptive optics.

Space-based astronomy is more important for frequency ranges which are outside the optical window and the radio window, the only two wavelength ranges of the electromagnetic spectrum that are not severely attenuated by the atmosphere. For example, X-ray astronomy is nearly impossible when done from Earth, and has reached its current importance in astronomy only due to orbiting X-ray telescopes such as the Chandra observatory and the XMM-Newton observatory. Infrared and ultraviolet are also largely blocked.

Space telescopes are much more expensive to build than ground-based telescopes. Due to their location, space telescopes are also extremely difficult to maintain. The Hubble Space Telescope was serviced by the Space Shuttle, but most space telescopes cannot be serviced at all.

Satellites have been launched and operated by NASA, ISRO, ESA, CNSA, JAXA and the Soviet space program later succeeded by Roscosmos of Russia. As of 2018, many space observatories have already completed their missions, while others continue operating on extended time. However, the future availability of space telescopes and observatories depends on timely and sufficient funding. While future space observatories are planned by NASA, JAXA and the CNSA, scientists fear that there would be gaps in coverage that would not be covered immediately by future projects and this would affect research in fundamental science. [6]


The disadvantages of space telescopes

Mirrors of the James Webb Telescope, which has suffered multiple delays in its development.

On the other side of the coin, there are also some disadvantages to putting a telescope in orbit. If putting one up there was an easy task, there would be no reason for us to keep building big observatories down here. Let’s take a look at some of the most negative aspects of space scopes.

This is the big one really. Building a 44 feet telescope with perfectly aligned mirrors, ultraviolet sensors and a bunch of cameras that can withstand the hostile environment of space is expensive. And that is just the beginning. You still have to put over 11 tons in a rocket and launch it into space. After that, you have to send regular maintenance missions if something goes wrong.

The cost of putting the Hubble Telescope in space was $4.7 billion. In 2010 an estimate of the cumulative costs including maintenance had the total cost of the Hubble at around $10 billion.

Difficult repairs

If a critical instrument in the telescope breaks or malfunctions for any reason, replacing it is no easy task. You have to send trained astronauts up there to repair it and hope you actually know what the problem is. If you misdiagnose it on Earth and the problem is completely different, you would be wasting an entire mission.

The Hubble has undergone at least five major servicing mission in which its mirrors, gyroscopes, solar panels, cameras, and other instruments have been replaced. But this is expensive and very work-intensive. At some point during its early years, NASA even considered just abandoning the project after they discovered one of the mirrors was not polished correctly and was sending blurry images. In fact, at that time, the Hubble was considered a failure and waste of money. It wasn’t until the first service mission in 1993 that it started working as intended.


Are space telescopes completely out of the earth's atmosphere? - Astronomy

The air also absorbs and scatters electromagnetic radiation by an amount that varies with the wavelength. Redder (longer wavelength) light is scattered less by atmosphere molecules and dust than bluer (shorter wavelength) light. This effect is known as reddening. This effect explains why the Sun appears orange or red when it is close to the horizon. The other colors of sunlight are scattered out of your line of sight so that only the orange and red colors make it through the atmosphere to your eyes. This effect also explains why the sky is blue. Since blue light is scattered more, you will see more blue light scattered back to your eyes when you look in a direction away from the Sun.

All wavelengths of light are scattered or absorbed by some amount. This effect is called extinction. Some wavelength bands suffer more extinction than others. Some of the infrared band can be observed from mountains above 2750 meters elevation, because the telescopes are above most of the water vapor in the air that absorbs much of the infrared energy from space. Carbon dioxide also absorbs a lesser amount of the infrared energy. Gamma-rays and X-rays are absorbed by oxygen and nitrogen molecules very high above the surface, so none of this very short wavelength radiation makes it to within 100 kilometers of the surface. The ultraviolet light is absorbed by the oxygen and ozone molecules at altitudes of about 60 kilometers. The longest wavelengths of the radio band are blocked by electrons at altitudes around 200 kilometers.

The atmosphere also scatters light coming from the ground to wash out a lot of the fainter stars and planets in what is called light pollution. As more people move to the cities and the cities get larger, an increasing percentage of people are missing out on the beauty of a star-filled night sky. The increasing light pollution is also threatening the amount and quality of research that can be done at many of the major astronomical observatories. The image below shows how much of the world is now cut off from the night sky. Select the image to bring up a larger version from NASA's Earth Observatory website. Visit the International Dark-Sky Association website for more about light pollution and ways to bring back the night sky.

Select the image to go to the Chandra X-ray Observatory Center

Select the image to go to the XMM-Newton site

Telescopes used to observe in the high-energy end of the electromagnetic spectrum, like the Chandra X-ray Observatory and XMM-Newton above and NuSTAR at the high-energy end of X-rays, must be put above the atmosphere and require special arrangements of their reflecting surfaces. The extreme ultraviolet and X-rays cannot be focused using an ordinary mirror because the high-energy photons would bury themselves into the mirror. But if they hit the reflecting surface at a very shallow angle, they will bounce off. Using a series of concentric cone-shaped metal plates, high energy ultraviolet and X-ray photons can be focused to make an image.

Swift (above) has a gamma-ray burst detector (BAT) plus a X-ray telescope (XRT) and an ultra-violet/optical telescope (UVOT) to study the gamma-ray bursts in other wavelength bands. NuSTAR (below) is the first orbiting telescope to focus light in the high energy X-ray (6 - 79 keV) region.

Fermi Gamma-ray Space Telescope

Spitzer Space Telescope trails far behind the warm Earth and its sun shield (on the left side) blocks the warm sunlight.

WISE against a view of the Milky Way as seen in the mid-infrared wavelengths.

Atmospheric lines

Gases in the Earth's atmosphere can introduce extra absorption lines into the spectra of celestial objects. The atmospheric spectral lines must be removed from the spectroscopy data, otherwise astronomers will find a hot star with molecular nitrogen, oxygen and water lines! Such lines are only produced by gases much cooler than that in stars.


High-Energy Observatories

Ultraviolet, X-ray, and direct gamma-ray (high-energy electromagnetic wave) observations can be made only from space. Such observations first became possible in 1946, with V2 rockets captured from Germany after World War II. The US Naval Research Laboratory put instruments on these rockets for a series of pioneering flights, used initially to detect ultraviolet radiation from the Sun. Since then, many other rockets have been launched to make X-ray and ultraviolet observations of the Sun, and later of other celestial objects.

Figure 4. Chandra X-Ray Satellite: Chandra, the world’s most powerful X-ray telescope, was developed by NASA and launched in July 1999. (credit: modification of work by NASA)

Beginning in the 1960s, a steady stream of high-energy observatories has been launched into orbit to reveal and explore the universe at short wavelengths. Among recent X-ray telescopes is the Chandra X-ray Observatory, which was launched in 1999 (Figure 4). It is producing X-ray images with unprecedented resolution and sensitivity. Designing instruments that can collect and focus energetic radiation like X-rays and gamma rays is an enormous technological challenge. The 2002 Nobel Prize in physics was awarded to Riccardo Giacconi, a pioneer in the field of building and launching sophisticated X-ray instruments. In 2008, NASA launched the Fermi Gamma-ray Space Telescope, designed to measure cosmic gamma rays at energies greater than any previous telescope, and thus able to collect radiation from some of the most energetic events in the universe.

One major challenge is to design “mirrors” to reflect such penetrating radiation as X-rays and gamma rays, which normally pass straight through matter. However, although the technical details of design are more complicated, the three basic components of an observing system, as we explained earlier in this chapter, are the same at all wavelengths: a telescope to gather up the radiation, filters or instruments to sort the radiation according to wavelength, and some method of detecting and making a permanent record of the observations. Table 1 lists some of the most important active space observatories that humanity has launched.

Gamma-ray detections can also be made from Earth’s surface by using the atmosphere as the primary detector. When a gamma ray hits our atmosphere, it accelerates charged particles (mostly electrons) in the atmosphere. Those energetic particles hit other particles in the atmosphere and give off their own radiation. The effect is a cascade of light and energy that can be detected on the ground. The VERITAS array in Arizona and the H.E.S.S. array in Namibia are two such ground-based gamma-ray observatories.

Table 1. Recent Observatories in Space
Observatory Date Operation Began Bands of the Spectrum Notes Website
Hubble Space Telescope (HST) 1990 visible, UV, IR 2.4-m mirror images and spectra www.hubblesite.org
Chandra X-Ray Observatory 1999 X-rays X-ray images and spectra www.chandra.si.edu
XMM-Newton 1999 X-rays X-ray spectroscopy www.cosmos.esa.int/web/xmm-newton
International Gamma-Ray Astrophysics Laboratory (INTEGRAL) 2002 X- and gamma-rays higher resolution gamma-ray images sci.esa.int/integral
Spitzer Space Telescope 2003 IR 0.85-m telescope www.spitzer.caltech.edu
Fermi Gamma-ray Space Telescope 2008 gamma-rays first high-energy gamma-ray observations fermi.gsfc.nasa.gov
Kepler 2009 visible-light planet finder kepler.nasa.gov
Wide-field Infrared Survey Explorer (WISE) 2009 IR whole-sky map, asteroid searches www.nasa.gov/mission_pages/WISE/main
Gaia 2013 visible-light Precise map of the Milky Way sci.esa.int/gaia

Infrared observations are made with telescopes aboard aircraft and in space, as well as from ground-based facilities on dry mountain peaks. Ultraviolet, X-ray, and gamma-ray observations must be made from above the atmosphere. Many orbiting observatories have been flown to observe in these bands of the spectrum in the last few decades. The largest-aperture telescope in space is the Hubble Space telescope (HST), the most significant infrared telescope is Spitzer, and Chandra and Fermi are the premier X-ray and gamma-ray observatories, respectively.


Watch the video: e-ASTR - 30 Χρόνια Διαστημικό Τηλεσκόπιο Hubble (June 2022).