Astrosat Picture of the Month

Sharing the excitement of India's first dedicated space observatory, every month!

Image of the Month

The AstroSat Picture of the Month for December 2018 presents the Ultra Violet Imaging Telescope itself. A schematic of the design of the UVIT is shown on the top left, and a photograph of the two UVIT telescopes is in the top right. An image of the fully assembled UVIT, containing both telescopes sitting snugly together, wrapped in insulating foil, waiting to be integrated into AstroSat, is shown at the bottom. The Indian Institute of Astrophysics, the Inter-University Centre for Astronomy and Astrophysics, and the Canadian Space Agency developed the UVIT.

Picture credit: ISRO, UVIT Team

ISRO logo




“AstroSat Picture of the Month” is an initiative of the Public Outreach and Education Committee of the Astronomical Society of India and the AstroSat Training and Outreach Team.

UVIT – the bright star in the galaxy of UV telescopes in the sky

Over the past few months, we have brought you many images taken by the Ultra Violet Imaging Telescope (UVIT) on the AstroSat. Don't you think it is time you met the famous UVIT itself? UVIT is a pair of telescopes that has a unique place in the ensemble of ultraviolet telescopes. Let us tell you why.

Though the optics of an ultraviolet telescope is similar to the commonly found optical telescopes, the shorter wavelength of UV demands certain special modifications. UVIT is made of a pair of very similar telescopes, each of which has a 37.5 cm diameter mirror, specially coated to make it highly reflective in the UV. In one of them, the light is split into two beams of different wavelengths, one of which goes into a detector for visible light, and the other into a detector for the Near UltraViolet (NUV, 200-300 nm). The other telescope is solely for the Far UltraViolet (FUV, 130-180 nm). Astronomers can also isolate just a narrow range of wavelengths within the NUV and FUV light by choosing specific filters before the light hits the detector. There is a diffraction grating as well, that can disperse the UV light into a spectrum.

The detectors are places where things get more interesting. The NUV and FUV detectors are photon counting devices and can respond to each individual UV photon. These are capable of measuring the time of arrival of every single photon to an accuracy of 2 milliseconds! The signal from these photons are then amplified before they fall on the 0.25 megapixel CCD cameras. This design makes the UVIT very sensitive, and objects very bright in the UV can also permanently damage the detectors. Because of this, the UVIT is only operated when the Earth hides AstroSat from the Sun. In addition, UV light reflected from the Earth is quite strong and hence the UVIT is never pointed towards us. There are a number of additional built-in safeguards that protect this instrument from any ultraviolet glare that may strike it.

How does the UVIT, with its special design, compare with other UV telescopes in space? Its field of view is about 0.5 degree (i.e., the size of the Moon). This is 80 times larger than that of the Hubble Space Telescope, and about half as much as that of the Galaxy Evolution Explorer (GALEX) of NASA. Although the UVIT's resolution of 1.4-1.7 arcseconds is poorer than the HST, it is much better than the 5 arcseconds resolution of GALEX. Hence, UVIT's uniqueness lies in its ability to image a large field of view combined with its superior resolution. This makes it a remarkable telescope to study large galaxies and galaxy clusters in fine detail, as well as look into the crowded centres of star clusters in our own Galaxy. Since the energy of UV photons is more than that of visible light photons, UVIT has been used extensively to study hot stars, both young and old, as well as final stages of these stars, allowing astronomers to peek into the ultraviolet sky as never before.

Click here for the entire APOM archive


AstroSat, India's first dedicated multi-wavelength space observatory, was launched by ISRO on 28 September, 2015. It has five instruments on board – the Ultra Violet Imaging Telescope, the Soft X-ray Telescope, the Large Area X-ray Proportional Counter, the Cadmium-Zinc-Telluride Imager and the Scanning Sky Monitor.

Get answers to your common queries about ASTROSAT in English, in हिंदी, and in मराठी.


  1. Pale Blue Dot (EARTH): Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam.

    The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds.

    Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.

    The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.

    It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known.


Leave a Reply

Your email address will not be published. Required fields are marked *