Astronomy

What Causes Halo Around The Sun

blue sun

The proposed telescope would be timely as it comes in the wake of astonishing new discoveries being reported in recent times. One of the recent findings is that the entire Sun vibrates from acoustical waves like a bell! The sound waves are in too low frequencies for us to hear. Astronomers call it helioseismology. There is, however, no such thing as seismic activity on the Sun. They are what are called pressure waves, generated by the turbulence in the convection zone near the solar surface. The waves are transmitted to the outer photosphere. The waves are transmitted to the outer photosphere. The waves rise and fall and rise again every five minutes or so.

Two types of waves are found in the Sun. one type is called pressure waves (p mode), which are trapped in the Sun’s outer layers near the surface. Only a very few penetrate a little into the core of the Sun. On the other hand, the other type of waves, called gravity waves (G mode) are found in the core, where energy-producing fusion reactions occur as well as in the radiative zone. Observers study the oscillations produced on the solar surface by these waves.

Over the last 15 years, a new approach has marked the direct measurement of the internal structure and dynamics of the Sun. Though the propagating sound waves in the Sun were discovered in 1959, only recently were the millions of sound waves measured to explore the invisible internal structure and dynamics of the Sun. the five-minute oscillations are now studied worldwide.

Astronomers at Stanford University have recorded acoustical pressure waves by tracking the movements on the surface of Sunspots. The waves bounce from one side to the other in about two hours. The scientists have, in an innovative approach compress 40 days of vibrations into a few seconds! Since the waves travel under the Sun, they indicate its interior structure. A project called global oscillations at low frequencies observes the whole Sun oscillating by detecting velocity changes all the way to the core.

The Udaipur Solar Observatory is one of the six centres that participates in the worldwide Global Oscillations Network Group.

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SOHO’s Images

The oscillations are observed from space as well, besides a network of ground-based telescopes.

SOHO’s oscillations imagery observes a million points on the Sun’s visible surface once every minute! It can detect subtle short-range oscillations due to sound waves penetrating only a short distance into the Sun. SOHO has been looking at the Earth without a single blink! Some 3,200 scientists have been working on the data returned by SOHO. One common feature stands out: the solar crust is made mostly of iron. SOHO has revealed consistent surface features, seen from image to image rotating in the same direction at the same speed, notwithstanding periodic erosions on the surface.

The Sun sparkles like a diamond in the images sent by SOHO. Its Extreme Ultraviolet imaging telescopes show “speckles” of various kinds, energetic upheavals that may cause the heating of the outer atmosphere to more than two million degrees C. Visible plumes in ultraviolet resemble ropes that stretch out far into space from the Sun’s poles.

Variations in the Sun’s brightness from minute to minute, associated with oscillations, are also seen. The motion at the visible surface that can be detected may well be related to the measurement of magnetic fields. These studies may explain why dark Sunspots occur and why they become more numerous every 11 years.

A ten-year study using one SOHO’s detectors called Global Oscillations at Low Frequency (GOLF) found the pressure waves evenly space. GOLF is a spectrometer which measures the velocity displacements of the solar photosphere. Astronomers suggest a faster rotation rate in the core than in the rest of the radiative zone.

The light emitted by the Sun’s surface undergoes a Doppler shift. The tiny variations in the surface velocity reveal a change of colour from red to purple and blue and back to red again. The periods of the waves depend on the propagation speeds and the depth of their resonant cavities.

The changes show that the outer convection zone and the inner radiative zone rotate as different speeds to generate the main magnetic field. It is also possible to detect Sunspots on the far side of the Sun from the Earth.

The American satellite, Voyager-1, and its twin, Voyager-2 (launched in 1977) have entered the helio-sheath, the zone where the Sun’s influence wanes, as the supersonic wind of solar particles is abruptly slowed by the presence of the interstellar medium. The spacecraft will soon sail into the interstellar medium. They have become the most distance human-made objects in outer space.

During its epic journey, voyager-1 flew past the outer planets – Jupiter, Uranus, Saturn and Neptune, besides dozens of moons. The spacecraft endured radiation and the solar wind –the constant stream of charged particles—blowing past the Earth’s protective magnetic bubble at a million kilometers an hour. The satellites have become famous for their continuous working, 24 hours, seven days a week over three decades.

During Voyagers’ three decades of travel, satellite astronomy matured into a new frontier area of research revealing for the first time many cosmic wonders. In fact, the very fist US satellite, Explorer-1, discovered the Van Allen radiation belts that surround the Earth. They were named after the distinguished scientist, James Van Allen, who designed the probe. Dr. Van Allen, who died in 2006 at the age of 91, was also actively involved in many exploratory satellites including Pioneer-10 and 11.

These two spacecraft are also nearing the edge of the solar system. But they have already thrown up a big puzzle. Since the 1980s, they have slowed down more quickly than expected. Taking a cute from their unusual behavior, scientists found that some other NASA and European spacecraft somewhat dragging in their orbits. One intriguing question being posed is whether the anomalies in the trajectories are due to as yet unexplained dark matter presumably prevalent in space.

As the Voyagers enter into ‘unknown’ regions, the data deluge will virtually drown the knowledge centers of the world. A future Archimedes is likely to jump out of the flood of data, which are being stored on a mind-boggling scale. It is now possible to store 108 data in a millimeter square and it is expected this rate would go up to 1015. The huge increase in data storage would be possible with the use of nanotechnology in fabricating electronic chips with their circuits etched at intervals of 45 nanometres. (A nanometre is a billionth of a metre.) New sensors based on nano electronics would be able to trace and store the findings of the satellites for future generations as well. That would be a challenge to be addressed perhaps in an IHY initiative.

By 2010, five more solar observing satellites are expected to join SOHO. They are expected to advance the International Living with a Star (ILWS) Programme dedicated to the long-term study of Sun and its effects on the Earth.

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