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 January 2019 shows the 97 minute long orbit of AstroSat around the Earth. This orbit is roughly equatorial (top right), inclined at around 6 degrees to it (top left). This results in each orbit being slightly displaced from the previous one (bottom).

Picture credit: Leo Jackson John, Operation Director - AstroSat, ISTRAC, ISRO

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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.

Following the path of our cosmic eye in the sky

When seeing images from AstroSat, have you ever wondered where exactly is the satellite, how does it move, and how do astronomers get their hands on the data? This month's APOM is here to answer those questions for you.

AstroSat was launched by ISRO on 28 September 2015 from Sriharikota, on board the PSLV-C30 into its current orbit. This is a low-earth equatorial orbit, at a height of 650 km above the Earth. This orbit is not exactly over the equator, but is inclined at an angle of about 6 degree to it. In the top left image, the green line marks the equator and the yellow line marks the orbit of AstroSat. The top right image is a view from over the north pole. But why was this orbit chosen?

Our Earth has a magnetic field, which behaves overall like a bar magnet, with its poles a few degrees away from the poles defined by our rotation. These magnetic fields trap charged particles within them, which form the Van Allen belts. These belts are much closer to the Earth over the southern Atlantic Ocean. An equatorial orbit reduces the effect of this South Atlantic Anomaly on AstroSat which carries very sensitive instruments. Making the inclination exactly zero requires more resources and hence a 6 degree inclination was chosen.

AstroSat takes about 97 minutes to orbit the Earth once. Hence, it will not pass directly overhead at the same point in successive orbits. Each orbit, therefore, will be slightly shifted with respect to the previous one. You can track the movement of AstroSat live on this page. The individual orbits shown in red in the bottom image represent orbits that are one week apart, clearly showing this drift. Data is beamed down from an antenna on the satellite once every orbit, when it passes near India. This is received by ISRO's antenna in Byalalu near Bengaluru (marked as BLR). All orbits of AstroSat fall within the visibility of this antenna, which is marked by a circle centred at Byalalu. ISRO can also use an antenna in Indonesia, marked BIK, to monitor the satellite when needed. All the command, control and tracking of AstroSat is done by ISTRAC in Bengaluru.

As of 30 January 2019, AstroSat has completed 18000 orbits around the Earth, acting as our high energy eye, uncovering the nature of neutron stars, black holes, hot stars, and many strange celestial objects. May it continue to do so for many more orbits!

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.


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