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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

  • Radio waves can make it through the Earth’s atmosphere without significant obstacles, hence, we don’t need to put radio telescopes in space.
  • 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

  • The Earth’s atmosphere blocks much of the light in the microwave band, so astronomers use satellite-based telescopes to observe cosmic microwaves.
  • 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

  • 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.
  • That means that the atmosphere, the telescope, and even the infrared detectors themselves all emit infrared light.
  • 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.
  • The Herschel Space Observatory was launched in May 2009 and the Spitzer Space Telescope was launched in August 2003.
  • 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

  • Visible light can pass right through our atmosphere, which is why astronomy is as old as humanity.
  • 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.
  • As light passes through the atmosphere, it is distorted by the turbulence within the air.
  • Astronomers can improve their chances of a good image by putting observatories on mountain-tops.
  • Visible-light observatories in space avoid the turbulence of the Earth’s atmosphere.
  • 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.
  • 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

  • The Earth’s atmosphere absorbs ultraviolet light, so ultraviolet astronomy must be done using telescopes in space.
  • Other than carefully-select materials for filters, a ultraviolet telescope is much like a regular visible light telescope.
  • The primary difference being that the ultraviolet telescope must be above Earth’s atmosphere to observe cosmic sources.
  • 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

  • X-ray wavelengths are another portion of the electromagnetic spectrum that are blocked by Earth’s atmosphere.
  • 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.
  • 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
  • Two X-ray telescopes currently in space are the Chandra X-ray Observatory and the XMM-Newton.

Gamma ray observatories

  • 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.
  • 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.
  • 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.
  • Studying gamma-rays helps astronomers learn more about many things including active galactic nuclei, blazars, gamma-ray bursts, pulsars and solar flares.
February 2024