Prelims Capsule

Prelims Capsule: Space telescopes

Space Telescopes

Why do we need telescopes?

  • To watch the object of faraway we need to have a bigger eye over which we can collect more light coming from an object.
  • With more light we can create a brighter image, we can then magnify the image so that it takes up more space on our retina.
  • That’s where the telescopes come, telescope lens work as a big eye to collect more light coming from an object.
  • The big lens in the telescope (objective lens) collects much more light than an eye can from a distant object and focuses the light to a point (the focal point) inside the telescope.

How does telescope works?

  • A smaller lens (eyepiece lens) takes the bright light from the focal point and magnifies it so that it uses more of retina.
  • A telescope’s ability to collect light depends on the size of the objective lens, which is used to gather and focus light from a narrow region of sky.
  • The eye piece magnifies the light collected by the objective lens, like a magnifying glass magnifies words on a page. But the performance of a telescope depends almost entirely on the size of the objective lens, sometimes called the aperture.
  • Astronomers use a number of telescopes sensitive to different parts of the electromagnetic spectrum to study objects in space.
  • Different detectors are sensitive to different wavelengths of light. In addition, not all light can get through the Earth’s atmosphere,

Types of observatories

Radio observatories

  • Q Radio waves can make it through the Earth’s atmosphere without significant obstacles, hence, we don’t need to put radio telescopes in space.
  • Q However, space-based radio observatories complement Earth-bound radio telescopes in some important ways.A special technique used in radio astronomy is called “interferometry.

Radio astronomers can combine data from two telescopes that are very far apart and create images that have the same resolution as if they had a single telescope as big as the distance between the two telescopes. This means radio telescope arrays can see incredibly small details.

Microwave observatories

  • Q The Earth’s atmosphere blocks much of the light in the microwave band, so astronomers use satellite-based telescopes to observe cosmic microwaves.
  • Q The entire sky is a source of microwaves in every direction, most often referred to as the cosmic microwave background (or CMB for short). These microwaves are the remnant of the Big Bang, a term used to describe the early universe.

Infrared observatories

  • Q While some infrared radiation can make it through Earth’s atmosphere, the longer wavelengths are blocked. But that’s not the biggest challenge – everything that has heat emits infrared light.
  • Q That means that the atmosphere, the telescope, and even the infrared detectors themselves all emit infrared light.
  • Q Another challenge is that Water vapor in the atmosphere absorbs much of the infrared radiation from space so the infrared observatories on Earth are located on high, dry mountains such as Mauna Kea in Hawaii.
  • Q The Herschel Space Observatory was launched in May 2009 and the Spitzer Space Telescope was launched in August 2003.
  • Q Astronomers study the infrared wavelengths to study the early universe and to learn about objects that are too cold to generate visible light including brown dwarf stars and dust clouds.

Visible spectrum observatories

  • Q Visible light can pass right through our atmosphere, which is why astronomy is as old as humanity.
  • Q Ancient humans could look up at the night sky and see the stars above them. Today, there is an army of ground-based telescope facilities for visible astronomy (also called “optical astronomy”). However, there are limits to ground-based optical astronomy.
  • Q As light passes through the atmosphere, it is distorted by the turbulence within the air.
  • Q Astronomers can improve their chances of a good image by putting observatories on mountain-tops.
  • Q Visible-light observatories in space avoid the turbulence of the Earth’s atmosphere.
  • Q In addition, they can observe a somewhat wider portion of the electromagnetic spectrum, in particular ultraviolet light that is absorbed by the Earth’s atmosphere.
  • Q The Hubble Space Telescope observes from an orbit about 559 km above the Earth at wavelengths from near infrared through the visible range and into the ultraviolet.

Ultraviolet observatories

  • Q The Earth’s atmosphere absorbs ultraviolet light, so ultraviolet astronomy must be done using telescopes in space.
  • Q Other than carefully-select materials for filters, a ultraviolet telescope is much like a regular visible light telescope.
  • Q The primary difference being that the ultraviolet telescope must be above Earth’s atmosphere to observe cosmic sources.
  • Q The Hubble Space Telescope and the UltraViolet and Optical Telescope on Swift can both perform a great deal of observing at ultraviolet wavelengths.

X-ray observatories

  • Q X-ray wavelengths are another portion of the electromagnetic spectrum that are blocked by Earth’s atmosphere.
  • Q X-rays also pose a particular challenge because they are so small and energetic that they don’t bounce off mirrors like lower-energy forms of light.
  • Q Focusing X-ray telescope require long focal lengths. In other words, the mirrors where light enters the telescope must be separated from the X-ray detectors by several meters. However, launching such a large observatory is costly and limits the launch vehicles to only the most powerful rockets
  • Q Two X-ray telescopes currently in space are the Chandra X-ray Observatory and the XMM-Newton.

Gamma ray observatories

  • Q Not only are gamma-rays blocked by Earth’s atmosphere, but they are even harder than X-rays to focus. In fact, so far, there have been no focusing gamma-ray telescopes.
  • Q Instead, astronomers rely on alternate ways to determine where in the sky gamma-rays are produced. This can be properties of the detector or using special “masks” that cast gamma-ray shadows on the detector.
  • Q It might be surprising to know that astronomers can use ground-based astronomy to detect the highest energy gamma-rays. For these gamma-rays, the telescopes don’t detect the gamma-rays directly. Instead, they use the atmosphere itself as a detector.
  • Q Studying gamma-rays helps astronomers learn more about many things including active galactic nuclei, blazars, gamma-ray bursts, pulsars and solar flares.

Some major observatories

Chandra X-ray Observatory

  • Q Chandra is the world’s most powerful X-ray telescope. Chandra, named for Indian-American physicist Subrahmanyan Chandrasekhar.
  • Q It examines the X-rays emitted by some of the universe’s strangest objects, including quasars, immense clouds of gas and dust and particles sucked into black holes.
  • Q X-rays are produced when matter is heated to millions of degrees.The hottest and most energetic areas are shown in purple
  • Q ChandraX-ray Observatory observed light from exploded stars, million-degree gas, and material colliding around black holes and neutron stars.

Spitzer Space Telescope

  • Q The red colors show infrared light, as seen by the Spitzer Space Telescope. These areas show the heat emitted by star forming dusty lanes in the galaxy.
  • Q Spitzer telescope gathers the infrared radiation emanating from cosmic objects, including faraway galaxies, black holes and even comets in our own solar system.
  • Q Spitzer was the first telescope to see light from an exoplanet.

Hubble Space Telescope

  • Q Hubble, the observatory, was the first major optical telescope to be placed in space
  • Q The yellow component is visible light, observed by the Hubble Space Telescope.
  • Q Most of this light comes from stars, and they trace the same spiral structure as the dust lanes revealed in infrared.
  • Q Hubble has shed light on the scale of the universe, the life cycle of stars, black holes, and the formation of the first galaxies.
  • Q Hubble takes sharp pictures of objects in the sky such as planets, stars and galaxies. Hubble has made more than one million observations.
  • Q Hubble has helped scientists understand how planets and galaxies form. An image called “Hubble Ultra Deep Field” shows the farthest galaxies ever seen.
  • Q Hubble has detected black holes, which suck in everything around them, including light.
  • Q The telescope has played a key role in the discovery of dark energy, a mysterious force that causes the universe to expand faster and faster as time goes on.
  • Q And it has revealed details of gamma-ray bursts — powerful explosions of energy that occur when massive stars collapse.

Herschel space observatory

  • Q Herschel will be the largest, most powerful infrared telescope, looking at the far-infrared to sub-millimeter wavelengths of light generated by some of the coldest objects in space.
  • Q Herschel is designed to look for water, both in nearby comets and faraway dust clouds, and will also peer into the womb of star formation.
  • Q Like its predecessor Spitzer, Herschel will also take a peek at a few exoplanets.

Planck Observatory

  • Q Herschel’s launch partner, the Planck Observatory, will be concentrating on the microwave light of the universe. Planck will be looking at the remnants of the first light to shine freely in the universe.
  • Q Planck will also probe the mysteries of dark matter and dark energy and map the magnetic field of the Milky Way in 3-D.

Kepler Mission

  • Q Kepler is NASA’s new planet-hunting telescope that will be specifically searching for other Earth-like planets in the galaxy.
  • Q Kepler will be looking for characteristic variations in the light from a pre-selected target group of 100,000 stars. Dips in the light from the stars can indicate a planet passing in front of the star.

Fermi Gamma-ray Space Telescope

  • Q Gamma rays can reveal some of the most energetic and mysterious events in the universe, including dark matter, black holes and spinning pulsars.
  • Q Not longer after arriving in orbit, it took an all-sky map that shows gamma rays from numerous sources, including our own sun.

ARIES telescope

  • Q ARIES telescope is a joint collaboration between Indian, Russian, and Belgian scientists.
  • Q The telescope is located at Devasthal, Nainital at a height of 2,500 metres
  • Q The high end technology incorporated in the telescope enables it to be operated with the help of remote control from anywhere in the world
  • Q The telescope will be used in the study and exploration of planets, starts, magnetic field and astronomical debris
  • Q The scientists will also help in research of the structures of stars and magnetic field structures of stars.


India’s first dedicated Astronomy satellite, AstroSat, completed its first year of successful operation on Sept 28, 2016.

NASA’s Hubble Telescope provides data on the visible range while the Chandra observatory is limited to X-rays. In contrast, Astrosat would be a multi-wavelength space telescope

ASTROSAT covers all ranges of wavelengths unlike any other space telescope

To avoid repairing process as faced by HUBBLE, ASTROSAT has been launched with the life-time of five years only.

Scientific Objectives of ASTROSAT:

  • To understand high energy process in binary star systems containing neutrons star and black holes.
  • To estimate the magnetic field of neutron stars.
  • To study the star birth regions and high energy processes in star systems lying beyond our galaxy.
  • To detect new briefly bright X-ray sources in the sky.
  • To perform a limited deep field survey of the universe in the ultraviolet region.


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