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 August 2018 is an X-ray image of the Tycho Supernova Remnant in the 0.8-2.0 nanometres (0.6-1.6 keV) range, made by the Soft X-ray Telescope on board AstroSat. The supernova remnant is roughly 8 arcminutes big (3.7 times smaller than the full moon in the sky) and the emission is brighter near the edge of the expanding supernova remnant.

Pic Credit: Kulinder Pal Singh (IISER Mohali) and the entire SXT Instrument and POC teams at TIFR, University of Leicester, and IUCAA

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“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.

X-raying a Supernova Remnant

This month, for the first time, we bring you an X-ray image from AstroSat. We feature the image of the Tycho Supernova remnant or SN 1572, imaged by the Soft X-ray Telescope (SXT). Located in the constellation Cassiopeia, at a distance of about 10000 light years, SN 1572 is a historic object. It is one of the 8 supernova explosions that were seen with the naked eye. This new star appeared in the sky during early November in 1572, and was observed by many astronomers across Europe and China. It is named after Tycho Brahe since he was the one who studied it in great detail till it faded away in 1574. He published his observations in his work 'Concerning the Star, new and never before seen in the life or memory of anyone', which included a star chart too. At its peak, it rivalled Venus at its brightest, confounded astronomers at that time, and changed their perspective of an unchanging sky.

We now know, from historic data, that this was a Type 1a supernova explosion. Sometimes, a normal star and a white dwarf (which is a very compact object that is the end stage of stars like our Sun) orbit each other. Material from the normal star is pulled on to the white dwarf due to gravity, making it heavier. When the mass of the white dwarf exceeds the famous Chandrasekhar Limit, it explodes, leading to a Type 1a supernova, like our SN 1572. What we see today is what is left of this explosion. The debris is expanding outwards like a sphere, with an edge which is the shock front. This supernova remnant, discovered first in radio wavelengths, and then in optical and X-rays and infrared, is a beautiful object indeed.

X-rays can penetrate metal easily. Hence, the cleverly designed Soft X-ray Telescope uses 320 concentric gold coated mirrors and a very cold CCD to form images in the X-ray. The image of the Tycho Supernova remnant shown here is made from photons with wavelengths between 0.8 to 2.0 nanometres (0.6-1.6 keV). Most of this emission, coming from the limb of the expanding shell, is due to emission from Iron atoms where electrons jump from higher levels to the 2nd level.

The paper can be downloaded here.


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.


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