Maarg Manthan · Topic 12.22

Astrosat, Astrosat-Chandra-Hubble Joint Detection of Cosmic Explosions

Science & Technology › Space Technology and ISRO · Topic 12.22

Astrosat is India's first dedicated multi-wavelength space observatory, launched by PSLV-C30 on 28 September 2015 into a near equatorial low Earth orbit of about 650 kilometres with an inclination of 6 degrees. It observes the sky at the same time in visible, ultraviolet and X-ray light using five main instruments: the Ultra Violet Imaging Telescope, the Soft X-ray Telescope, the Large Area X-ray Proportional Counters, the Cadmium Zinc Telluride Imager and the Scanning Sky Monitor. Because cosmic explosions such as gamma-ray bursts, supernovae and mergers of neutron stars shine at many wavelengths, Astrosat is used together with other telescopes in space and on the ground, such as the Chandra X-ray Observatory and the Hubble Space Telescope, for joint studies.

5 min read · UPSC Prelims · Science & Technology · Space Technology and ISRO

At a Glance

Launched 28 September 2015, PSLV-C30
Orbit About 650 km, 6 degrees inclination
Bands Visible, UV, X-ray
Instruments Five
Partners Chandra, Hubble and others
Exam link UPSC Prelims, Science & Technology: Space Technology and ISRO

Where Does It Fit?

This topic follows MAST and Resourcesat-2A. It returns to astronomy from space and builds on the account of space observatories in the macro on astrophysics, where Chandra and Hubble were introduced. Previous topic: Multi Application Solar Telescope and Resourcesat-2A. Next topic: Air-Breathing Propulsion System.

What Are the Instruments and Aims of Astrosat?

Instrument	Role
Ultra Violet Imaging Telescope (UVIT)	Twin telescopes imaging in near ultraviolet, far ultraviolet and visible bands. Gives sharper ultraviolet pictures than many earlier telescopes
Soft X-ray Telescope (SXT)	Images and measures X-rays in the soft band
Large Area X-ray Proportional Counter (LAXPC)	Three counters for high time resolution X-ray observations of binaries and black holes
Cadmium Zinc Telluride Imager (CZTI)	Hard X-ray imager that also detects gamma-ray bursts and acts as a polarimeter
Scanning Sky Monitor (SSM)	Scans the sky for sudden changes in X-ray sources
Charged Particle Monitor	Protects instruments by monitoring particles
Organisations	Developed by ISRO with the Tata Institute of Fundamental Research, Indian Institute of Astrophysics, Inter-University Centre for Astronomy and Astrophysics, Raman Research Institute and foreign partners from Canada and the United Kingdom

How Does Joint Observation of Cosmic Explosions Work?

Cosmic explosions: gamma-ray bursts, supernovae, flares from black holes and neutron star mergers release energy across the spectrum
Why many telescopes: X-rays come from very hot gas, ultraviolet from young hot stars and visible light from cooler gas, so each wavelength shows different physics
Chandra: NASA’s X-ray observatory gives very sharp X-ray images, as in Space Observatories and Telescopes (Hubble, Chandra X-Ray Observatory, Thirty Metre Telescope, Spitzer Space Telescope)
Hubble: gives ultraviolet and visible images to locate the host galaxy of an explosion
Astrosat’s role: detects the burst or tracks its X-ray and ultraviolet changes with time, with its broad band coverage
Rapid alerts: CZTI and SSM can notice transients and alert other telescopes
Polarisation: CZTI measures polarisation of gamma-ray burst light, which tells about the magnetic structure of the explosion
Gravitational waves link: explosions from merging neutron stars produce both waves and light, linked with Gravitational Waves

What Else Should You Remember?

Orbit choice: the low inclination orbit keeps the satellite away from the high radiation regions near the poles for most of the time
First results: Astrosat observed pulsars, black hole binaries such as Cygnus X-1 and distant galaxies
Deep ultraviolet galaxy: UVIT detected extreme ultraviolet light from a galaxy about 9.3 billion light years away, reported in 2021, a result with international teams
Open access: data are made available to scientists from India and other countries
Astrosat 2: a follow up mission has been proposed
Other Indian missions: Aditya-L1 for the Sun and XPoSat for X-ray polarisation launched on 1 January 2024
XPoSat: India’s first polarimetry mission, to study X-ray polarisation of sources such as black holes and neutron stars
Ground telescopes: Giant Metrewave Radio Telescope near Pune, Indian Astronomical Observatory at Hanle in Ladakh and the Devasthal telescopes
International cooperation: India’s astronomers work with NASA, ESA and others, and joint observations raise the value of Astrosat
Transients: short lived events that need quick follow up
Wavelength bands: X-rays and gamma rays are blocked by the atmosphere, so space telescopes are needed, as in ionosphere Space…">Electromagnetic Wave Behaviour
Caution: specific discoveries with each telescope should be checked in official ISRO and scientific reports before quoting
Black hole binaries: Astrosat tracks matter falling into black holes in X-ray binaries, and the fast changes tell about the region close to the hole
Data policy: after a proposal period for Indian scientists, Astrosat data are made public through the Indian Space Science Data Centre, which widens research use

Why Does It Matter for the Exam?

Facts: launch date, orbit, instruments
Concept: multi-wavelength astronomy
Related missions: XPoSat and Aditya-L1
Current affairs link: new Astrosat results and XPoSat
Common errors: placing Astrosat in polar orbit or confusing it with Chandrayaan

As an analytical point, no single telescope can show a whole cosmic explosion. Astrosat gives India a seat in the global network of observatories, which multiplies its scientific return.

Why Is This Topic Important?

Facts Launch and orbit
Instruments Five payloads
Network Joint study

What Came Next?

The next topic covers air-breathing propulsion systems such as the scramjet. Next topic: Air-Breathing Propulsion System.

Key People and Terms

Gamma-ray burst Intense flash from distant explosion
Transient Short lived event
UVIT Ultraviolet imaging telescope
CZTI Hard X-ray imager
Polarimetry Measuring light’s polarisation
Multi-wavelength Many bands together

Exam Corner

Points to Remember

Astrosat launched: 28 September 2015.
Launcher: PSLV-C30.
Orbit inclination: 6 degrees.
Five main instruments.
XPoSat: 1 January 2024.

Do Not Confuse With

Astrosat and XPoSat Multi-wavelength observatory versus X-ray polarimetry mission
Astrosat and Aditya-L1 Deep sky versus Sun
Chandra and Hubble X-ray versus ultraviolet and visible

Memory Hook

Five eyes on the sky in ultraviolet and X-ray, a six degree low orbit, and teamwork with Chandra and Hubble.

Mains Angle

Questions ask for facts and the multi-wavelength idea. These points help.

Importance Broad band coverage
Cooperation Joint studies
Next XPoSat

A Question You May Face

An original practice question, not a past paper question.

“Discuss the significance of Astrosat for Indian astronomy and the value of multi-wavelength cooperation with space telescopes like Chandra and Hubble.”

How to Answer

Facts Astrosat details.
Instruments Five payloads.
Cooperation Joint events.
Way XPoSat.

GS Relevance

Prelims: launch date, instruments, orbit, collaborative observations. GS Paper 3: science and technology, space astronomy.

Frequently Asked Questions

What is Astrosat?

Astrosat is India's first dedicated multi-wavelength space observatory, launched by PSLV-C30 on 28 September 2015. It observes the sky at visible, ultraviolet and X-ray wavelengths at the same time using five main instruments, and studies black holes, neutron stars, galaxies and cosmic explosions such as gamma-ray bursts.

What are the instruments on Astrosat?

Astrosat carries the Ultra Violet Imaging Telescope, the Soft X-ray Telescope, the Large Area X-ray Proportional Counters, the Cadmium Zinc Telluride Imager and the Scanning Sky Monitor. Together they cover ultraviolet, soft and hard X-rays, and monitor the sky for sudden changes in bright X-ray sources.

Why does Astrosat work with Chandra and Hubble?

Cosmic explosions release energy at many wavelengths, and each telescope sees only part of it. Astrosat covers ultraviolet and X-rays, Chandra gives very sharp X-ray images and Hubble gives ultraviolet and visible images, so joint observations give a fuller picture of the physics and the host galaxy of an event.

What orbit does Astrosat use?

Astrosat is in a near equatorial low Earth orbit at about 650 kilometres with an inclination of 6 degrees. This orbit keeps the satellite away from the intense radiation regions near the poles for most of the time, which protects the detectors and gives long uninterrupted observations.

What is XPoSat?

XPoSat, the X-ray Polarimeter Satellite, is India's first mission to study the polarisation of X-rays from bright sources such as black holes and neutron stars. It was launched by a PSLV on 1 January 2024 and complements Astrosat by revealing the geometry and magnetic fields of these extreme objects.

PYQ Practice — Statement Analysis

1 Astrosat was launched in September 2015 by PSLV-C30.

True

India's first multi-wavelength observatory.

2 Astrosat orbits in a polar orbit.

False

It is in a low inclination orbit.

3 The Cadmium Zinc Telluride Imager is one of the instruments of Astrosat.