S U N

Our Sun, somtimes called Sol lies as the very heart of the Solar System. In many early cultures it was worshipped as the supreme god, whose grace is to be given thanks for its glorious rays of warm light and allowing the peoples of the Earth to live and thrive. There were always fears that the Sun was not honoured properly, then the god may become angry and extinguishing its important light - plunging the Earth into perpetual darkness. This idea was perpetuated by solar eclipses threatening to consume the Sun unless the god was appeased in some way. To the Ancient Egyptians under Tutmosese IV this god was Aten. For the Greeks it was the god Apollo, who daily rode his celestial chariot across the sky under the power of four horses.

Sol is in fact a star, similar to the ones that appear in the night-time sky. Obviously, the difference is that the Sun is very much brighter due to its proximity to the Earth. The nearest star is nearly 40 000 times the distance between the Sun and the Earth. Some other stars are similar to the Sun but the vast majority is either hotter or cooler, larger or slightly smaller. In the scheme of things the sun is considered to be an ordinary yellow dwarf star with no particular peculiarities. The smaller mass of the Sun does produce one advantage - the energy will last between eight and ten billion years, unlike the largest stars, which have much shorter lifetimes. The Sun at present is about half way through its evolution.

From its tremendous light, all the planets, the moon, asteroids, comets and the Moon that shine by simple reflection. Solar energy is manufactured constantly and continuously, allowing for the Earth’s stable environment that harbours all life on the Earth. The Sun may also have slight fluctuations in its brightness that have contributed to the Ice Ages that have been known to have occurred many times in the past. The present climate of the Earth may also be affected in the short term by these changes.

The solar sphere occupies is a ball of very hot gases, primarily made from the elements of hydrogen and helium combined with smaller amounts of the other chemical elements. The temperature for the outer surface or photosphere is 5 800K which rises to several tens of million degrees in the core. Matter here exists as plasma, the forth state of matter, where the electrons normally orbiting the nucleus of the atoms have been stripped away by its very high temperatures. In the core, vast quantities of hydrogen dwell. Here several million tonnes per second of hydrogen is being converted to energy in the process known as fusion, or sometimes referred as nucleosynthesis. When hydrogen is fused in this way, it also produces heavier chemical elements. Ie. Hydrogen is converted into helium, helium into carbon, silicon then iron etc. Hence the Sun is not only a power plant but also a elemental chemical factory - manufacturing all the common elements that are found on the Earth and in our bodies.

Once the energies reach the solar surface, it radiates it roughly equally in all directions into space. Earth receives only very tiny fractions of this energy, but despite the distance of about 150 million kilometres, the amount of energy received is so intense that the retina of the eye can be quickly damaged causing irreparably and permanent blindness . Also the UV radiation begins to disrupt external body cells like skin.

STRUCTURE of the SUN

The Solar Surface

The actual visible surface of the sun is not solid but gaseous and is in continuous motion. This seething, boiling caldron is some 200 kilometres thick, and is commonly referred as the photosphere. Such turbulent features give the Sun its mottled appearance - the so-called granulation. All granules are some 200 to 300 kilometres across and last for several minutes before being replaced by newer ones. Often, dark spots appear on the solar disk from time to time on the solar disk as sunspots. Sunspots numbers vary significantly depending on stage in the cycle of the Sun’s activity. They are cooler regions on the Sun, and slowly increase in size over several days to weeks, reach a maximum, then fade away. Some have been observed to last for two or three rotations before disappearing altogether. Sunspots mainly appear either as pairs or groups and are termed active areas. Single sunspots are on the other hand fairly rare.

Other features such as faculae appear as tiny strands of white light, 1" and 2"arc seconds in length. On the solar surface, they can be thought of as hotter areas, opposite to the sunspots, and are about 800K to 1 000K than the surrounding photosphere. They are normally always associated with sunspots, and it is far more usually to see the faculae near to the limb of the Sun.

The Solar Atmosphere

Above the photosphere is the atmosphere of the Sun the chromosphere, and normally cannot be seen except just before and after totality during total solar eclipses. This hot 4 000K region appears against the lunar limb as bright pink colour, with the observed thickness is between ten and twenty thousand kilometres. Its composition being mainly hydrogen. Beyond the chromosphere is the corona, whose true extent is uncertain, but can be seen out anywhere between 3R to 10R in solar radii. The inner corona extends from 0.5R to 1 solar radii, while the outer corona extends from one to three solar radii. Made primarily of hydrogen and helium, the corona exist as a tenuous gas whose temperatures exceeds several million degrees. It emits strongly in both X-ray and ultra-violet light, but the cause of the temperature rise from the chromosphere to the corona is not fully understood. As most of the particles in the corona are highly ionized, the behaviour of the gas is affected by the prominences, flares and the solar magnetic field.

During a total solar eclipse is the only time when the corona can be seen to the naked-eye. It is also observable using a special instrument called the coronascope, where the solar disk is obscured. To the naked eye it is pearly white and as bright as the Full Moon. The optical telescopic view reveals tiny broken strands of light in filamentary structures.

The Solar Interior

Knowledge of the Sun’s interior is poor, though recent observations of the seismic activity or helioseismology, much akin to using seismology to find about the Earth’s interior, has shown better understanding of its structure. It is believed that below the photosphere lies the convection zone, the region that transports the hot materials from the Sun’s interior to the surface. We know of this kind of mixing occur because the elements manufactured in the core can be seen on the surface. Further down, perhaps third to half a solar radius, is the radiative zone. Here the generated energy is passed into the upper atmosphere is very similar to bar radiators used to heating the surrounding air at home. At the very centre is the solar core. The core, the powerhouse of the Sun, is estimated to be about the size of Jupiter and is composed of very hot plasma, whose temperature is present estimated between three and five million degrees. Energy is created here, and under tremendously high pressures, atoms are literally squeezed together to make the heavier elements. Light once produce in the core may take about one million years to eventually radiate from the surface and be seen on Earth.

The strong electrical flows within the solar interior are thought to be mechanism that produces the observed strong magnetic fields. These fields can also split into localised areas that produce either flares and prominences. They are commonly associated with sunspots. 

Solar Activity and Sunspots

The sun is not a passive body, as during high solar activity, streams of atomic particles and radiations are produced, which are closely associated with increased prominence activity. Prominences are extremely violent events and appear like tongue of red gas leaping away from the photosphere and are commonly associated with the plage areas.

During total solar eclipses they appear like reddish-pink “loops” around the solar disk. A special solar filter, called Hydrogen-alpha filter, can be used to look at these prominences and flares at any time during the day. Many prominences may last several hours with the more violent ones extending millions of kilometres into interplanetary space. These can strongly interact with the Earth’s upper atmosphere, damaging circuitry in spacecraft and cause serious radiation problems for astronauts.

Flares appear to emanate from the active regions of the photosphere. These suddenly brighten up and last from a few seconds to several minutes. Some of these events are violent and can be very intense in radio, X-Rays and ultra-violet light. Charged particles are also emitted from these events that can diminish the strength of the protective ionosphere, and in some instances the most powerful of blasts may cause fade-outs, power and communication blackouts. These then absorb the radio waves that are normally reflected by the ionosphere. The types of charged particles included, proton, neutrons and helium nuclei. The velocity of the charged particles, called the solar-wind, is thought to be about six hundred kilometres per second, or just 0.2% of the speed of light.

White Flares rarely appear on the Sun. They are the brightest of the red-flares and can produce thousands of times more energy than normal flares. White flares can be seen during observations of the Sun and last several minutes.

Observations of flares can be for the observer of an interesting pastime as the changes that do occur do so in minutes.

Observations of the Sun

Sunspots can easily be seen even with small telescopes, and more often than not, really do not require large apertures at all. Sunspots can also be observed from day to day to reveal the changes as they undergo growth and decay. Observations of sunspots, can be used to estimate the solar activity - useful understanding the long-term effects seen on the Sun and in many other scientific subjects, like the weather or radio broadcasting.

!! W A R N I N G !!

Using any telescope, the Sun should ONLY be observed by projecting the image on to a white screen or card. (Even this should be for short periods)
Direct viewing of the Sun, by either eye or any other optical equipment, is VERY DANGEROUS without proper protection. Otherwise, BLINDNESS WILL RESULT, and even glancing will blind you in less than a ten-thousandth of a second.
If your telescope has something called a sun filter - You should NEVER use. If this filter cracks while you are observing, blindness is the only outcome.

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Disclaimer

The user applying this data for any purpose forgoes any liability against the author. None of the information should be used for regarding either legal or medical purposes. Although the data is accurate as possible some errors might be present. The onus of its use is place solely with the user.

Last Update : 21st May 2005

Southern Astronomical Delights © (2005)

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