Because it is the nearest star, studying it gives us an insight as to the nature and habits of all the other stars in the Universe. However studying it is DANGEROUS, and should only be attempted with the proper equipment.
NEVER LOOK DIRECTLY AT THE SUN WITH THE NAKED EYE OR ANY OPTICAL INSTRUMENT UNLESS FITTED WITH AN APPROVED SOLAR FILTER DESIGNED FOR DIRECT VIEWING.
Stars are spheres of mainly hydrogen gas at a very high temperature and pressure. They shine because of fusion reaction that takes place in the centre of the sphere. The result is an extremely bright dynamic object capable of sustaining life on nearby planets.
Because other stars are so far away they appear to us as pinpoints of light although some are many times the size of our Sun. The fusion reaction causes many different observable phenomenon that can easily be studied from earth with equipment varying from the most basic to more sophisticated.
The easiest phenomenon to observe is sunspots. Huge magnetic turbulences generated in the star occasionally breaks through the photosphere (the visible disk of the star) and leaving a tell-tale dark mark, some larger that the diameter of the Earth. On casual glance it appears to be a hole in the suns surface. In fact the magnetic field reduces the temperature locally and thus doesn’t shine as bright. Sunspots are not a permanent feature and come and go, some lasting a few days, others months. The number of sunspots on the sun varies from zero to many hundreds. Generally the number varies on an 11-year cycle, first increasing then decreasing over the period.
The sunspots can be safely observed by projecting the suns image through binoculars or telescopes onto a white sheet or board (the projection method). Not all telescopes are suitable however and expert advice is required. They can also be observed by directly viewing through AN APPROVED filter. These filters are firmly attached to the Sun ends of the optical device, and viewed directly in the normal way. The Sun can also be viewed directly, that is without optical aid, but again ONLY THROUGH AN APPROVED filter. Do not be tempted to use objects like dark glass or fogged photographic negatives: IT’S NOT WORTH IT. This method of observation is referred to as “white light observations” despite the fact that some filters are coloured.
The observation of sunspots has the advantage that it is conducted in fine weather during the day, not on cold frosty nights!
Because the sun is principally a ball of gas at very high temperature and pressure, it is not surprising that the surface is seething and heaving. The appearance is similar to a saucepan of boiling soup. Although on very clear days when “white light viewing” surface features other than sunspots can be detected, surfaces features are best seen with filters that allow just hydrogen to be observed. They are however rather costly.
An even more sophisticated filter system will allow the observation of large clouds of gas being ejected for the sun. These are called prominences, which flare up when the sun is particularly active. They are very dynamic and spectacular, but the filter is the price of a small telescope. Sometimes these prominences are so violent that they are classed as mass ejections. If they happen to head towards the earth they can cause serious disruption to satellites and even play havoc with power supplies on earth, but they are also the trigger to cause the Northern lights or Aurora.