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About the Sun satellite
THE Solar and Helio- spheric Observatory (SOHO) satellite completed its ten years in space earlier this month. SOHO has been generating valuable information and constantly furnishing data to the relevant authorities for the past one decade.
The main purpose of SOHO’s launch was to observe the Sun more closely. This project was jointly planned and initiated by NASA (National Aeronautics and Space Administration) of the US and the European Space Agency (ESA).
Although SOHO was launched in early December 1995, it began operating in May 1996. The programme was initially designed for a two-year duration, but after its initial success the authorities decided to extend it until 2003. In 2002, the mission was further extended and now it is to continue its operations until March of 2007.
SOHO is a sophisticated composition of twelve instruments jointly developed by the American and European scientists. To enable its prompt and successful launch, a number of teams of engineers and scientists from many countries joined hands. They also provided support during its operations and in analysing the data sent by it.
The SOHO spacecraft was developed in Europe. A team mainly headed by Matra Marconi Space (MMS) was given the job of designing the craft. MMS is Europe’s largest producer of spacecraft. It is a joint venture company with professionals from France and the UK. Both European and American scientists assisted in furnishing the requisite instruments.
The spacecraft comprises two main components. The lower portion is called service module and the upper part is called payload module.
The service module is a box-shaped structure, made up of aluminum panels attached to a corrugated aluminum cylinder by four shear webs. The data handling, communications, altitude and orbit control, and power subsystems are linked using the four lateral panels. The box’s upper floor includes the propulsion subsystem, tank and thruster masts. The high-gain antenna is coupled into the rear part of the central cylinder.
The payload module includes all the scientific instruments that the system possesses. This module furnishes an optical work surface for the experiments and is made up of four upper lateral panels and a top panel linked to a central cylinder by a number of shear webs. The bottom division includes three lower lateral panels, each connected to the central cylindrical tube by a number of shear webs and floors.
Instruments
The SOHO spacecraft has twelve built-in instruments each of which is capable of conducting independent observations of the Sun or its parts. Following are the various functions of the instruments:
— The Coronial Diagnostic Spectrometer (CDS) provides measurement of density, temperature and flows in the corona.
— The Charge, Element, Isotope Analysis (CELIAS) studies the ion composition of the solar wind. Solar wind is a stream of ionized particles ejected at a high speed from the surface of the Sun. It is a mixture of certain materials found in the solar plasma. It consists of ionized hydrogen, eight per cent component of helium and small amounts of heavy ions.
— The Comprehensive Suprathermal and Energetic Particle Analyser (COSTEP) analyses the ion and electron composition of the solar wind.
— The Extreme ultraviolet Imaging Telescope (EIT) analyses the low coronial structure and relevant activity.
— The Energetic and Relativistic Nuclei and electron Experiment (ERNE) measures high-energy particles which originate from the Sun and the Milky Way. It serves as a complementary apparatus to COSTEP.
— The Global Oscillations at Low Frequencies (GOLF) measures velocity oscillations of the entire solar disk to explore the core of the Sun.
— The Large Angle Spectrometer Coronagraph (LASCO) studies the structure and evolution of the solar atmosphere (corona).
— The Michelson Doppler Imager (MDI) records each minute, the vertical motion (tides) of the Sun’s surface at a million different points.
— The Solar Ultraviolet Measurement of Emitted Radiation (SUMER) accounts for the plasma flow, temperature and density in the corona. This is the only remote sensing contraption which does not look at the Sun, but observes the rest of the sky and determines how the solar wind is distributed. As such, it can be rated as SOHO’s solar wind ‘mapper’.
— The Variability of Solar Irradiance (VIRGO) computes changes and solar constant both of the entire solar disk and at low resolution, again exploring the core of the Sun.
— The Ultraviolet Coronagraph and Spectrometer (UVCS) measures density and temperature in the solar atmosphere or corona.
Most of SOHO’s activities are solar-related, which include the structure and dynamics of the solar interior, the causes for the existence of the solar corona and for its extremely high temperature (1,000,000°C). Solar corona is the upper or the extended outer atmosphere of the Sun.
The temperature of the corona is in millions of degrees. Consequently it is 10 billion times less dense as compared to the atmosphere of the Earth at sea level.
Results
This mission helped a great deal in furnishing important images of the Sun’s ‘convection zone’, which is also regarded as its turbulent outer shell. It also collected images of the sunspots below the surface.
It was SOHO that enabled the scientists to have the most comprehensive and defined measurements in connection with temperature structure, the rotation and gas flow of the solar interior. The human capacity to forecast space weather was revolutionized, as a result.
SOHO is also playing a leading role in the early warning system for space weather by serving timely notices on the disturbances directed towards the Earth. Today, it is also possible to monitor features like the total solar irradiance (the ‘solar constant’), and variations in the ultraviolet flux, which are important to comprehend the impact of solar variability on the Earth’s climate.
SOHO also helped in discovering plasma. With regard to physics and chemistry, plasma is also known as ionized gases. It is the state of the matter when it is more energetic, as some or all of the electrons of the outer atomic orbit become isolated from the atom. This results in an amassment of ions and electrons, which are no longer bound to each other.
SOHO also enabled scientists to measure the acceleration of the solar wind, besides pinpointing the source regions and the mechanism of acceleration of the wind in the magnetically ‘open’ regions at the Sun’s poles. Phenomena such as coronal waves and solar tornadoes were also discovered by it.
The writer <cocographer@ yahoo.com> is a senior instructor at a technical college
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