Electromagnetic Spectrum Observateries

October 2, 2019
Earth Telescope light

Astronomers use a number of telescopes sensitive to different parts of the electromagnetic spectrum to study objects in space. Even though all light is fundamentally the same thing, the way that astronomers observe light depends on the portion of the spectrum they wish to study.

Radio observatories

Radio waves pass through Earth's atmosphere without any problem and we can observe even on cloudy days so, we don't need to put radio telescopes in space. A special technique used in radio astronomy is called "interferometry." Radio astronomers 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 very small details. One example is the Very Large Baseline Array (VLBA), which consists of 10 radio observatories that reach from Hawaii to Puerto Rico, nearly a third of the way around the world.

Microwave observatories

When it comes to microwaves, earth's atmosphere blocks much of the light so astronomers have to use satellite-based telescopes to observe cosmic microwaves. And if we talk about sky, entire sky is a source of microwaves in every direction- the cosmic microwave background (or CMB for short). These microwaves are leftover radiation of Big Bang. The first precise measurements of the temperature of the microwave background across the entire sky was done by the Cosmic Background Explorer (COBE) satellite from 1989 to 1993. After that Wilkinson Microwave Anisotropy Probe (WMAP) refined the COBE measurements, operating from 2001 to 2010.

Infrared observatories

In case of Infrared rays, Some radiation can make it through Earth's atmosphere but the longer wavelengths are blocked and another challenge is everything that has heat emits infrared light That means that the atmosphere, the telescope, and even the infrared detectors themselves all emit infrared light. So astronomer have thought few solution for these two major problem. First one is ground-based infrared telescopes reside at high altitudes in dry climates so less infrared radiation (which is observe by water vapor near ground) observe. Second is both ground-based and space/airborne observatories designed to limit the spurious infrared radiation from reaching the detector and and the detectors are cooled to limit their infrared emissions. In 2003, NASA launched the Spitzer Space Telescope in heliocentric orbit where it did not have warm environment so it makes observation easy. Another major infrared facility is the Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA carries a large telescope inside a 747 aircraft flying at an altitude sufficient to get it well above most of the Earth's infrared absorbing atmosphere. The James Webb Space Telescope is a large, space-based observatory, that is optimized for infrared wavelengths.

Visible spectrum observatories

In case of visible light , we all know it can pass right through our atmosphere and I believe that is one of the reason we humans are learning and observing about astronomy from ancient times.. Today, there is an army of ground-based telescope facilities for visible astronomy called optical astronomy one of the most power full way for almost all human to observe night sky (even without any telescope). 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, but sometimes it is still difficult to observe very faint objects and that is why we have space base observatory like Hubble. Again Hubble isn’t the only one in space , Kepler observatory. Kepler is using visible light to survey a portion of the Milky Way galaxy to discover planetary systems. The Swift satellite also carries an UltraViolet and Optical Telescope (the UVOT) to perform observations of gamma-ray bursts

Ultraviolet observatories

If we talk about Ultraviolet waves , unfortunately it is observer by our thick atmosphere (although it is good thing for us human because it protect us but imagine what if our body has tolerance of observing this waves, and earth’s atmosphere won’t block it , our backyard have these telescope Fascinating isn’t it !!!) so ultraviolet astronomy must be done using telescopes in space. a ultraviolet telescope is much like a regular visible light telescope except in terms of filters. The GALEX observatory was the most recent dedicated ultraviolet observatory, launched in 2003 and shut down operations in 2013, Its has observe the history of star formation in our Universe in ultraviolet wavelengths, and it observed over a half-billion galaxies going back to when our Universe was just about 3 billion years old. The Hubble Space Telescope and the UltraViolet and Optical Telescope on Swift can both perform a great deal of observing at ultraviolet wavelengths, but they only cover a portion of the spectrum that GALEX observes.

X-ray observatories

In case of X-rays , again , this part of electromagnetic spectrum that are blocked by Earth's atmosphere. There is another problem with this radiation , because they are so small and energetic that they don't bounce off mirrors like lower-energy forms of light. Instead, they pass right through. 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. But launching such a large observatory is costly and limits the launch vehicles. Although astronomer has find their way around, In 2012, the Nuclear Spectroscopic Telescope Array (or NuSTAR for short), solved this problem by designing an observatory with a deployable mast. In other words, NuSTAR was designed with its mirror module and detector module on a mast, or boom, that could be extended once it was in orbit. By doing that, NuSTAR could be launched on a low-cost rocket.

Gamma-ray observatories

In case of this , Gamma rays not only 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 find a gamma ray in universe, This can be properties of the detector or using special "masks" that cast gamma-ray shadows on the detector. Telescope “ Swift Satellite “ , launched in 2004 has gamma-ray detector that can observe half the sky at a time, and if it detects a gamma-ray burst, the satellite can quickly point its X-ray and optical telescopes in the direction of the burst. Moreover The Fermi Space Telescope was launched in 2008 and is designed to study energetic phenomena from a variety of cosmic sources, including pulsars, black holes, active galaxies, diffuse gamma-ray emission and gamma-ray bursts 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. The HESS array has been in operation for over 10 years. The array began with four telescopes arranged in a square, and recently added the HESS II telescope to its ranks.