According to our current understanding of the world, the sun is our central star and one of 100 billion fixed stars in our galaxy which we call the Milky Way.  
The diameter of the sun is about 1.392.000 km, more than three times the distance between the Earth and the Moon. Theoretically our planet earth would fit 1.3 million times over into the sun. As the sun mainly consists of hydrogen and helium, its mass only makes up 333000 times that of our home planet.        
During fusion when hydrogen is burned to helium, the sun consumes four million tons of its own mass per second. According to Einstein` s formula (E =m c²) the sun transforms this directly into energy; due to this process the temperature at the core of the sun presently reaches about 15 million °C and on the surface still 5500 °C. It will provide energy for the next 5 billion years, but the power of the sun will increase, the creatures on earth will die out and the oceans will evaporate a long time before the end of that period.                       
On average the activity of the sun changes in an 11-year-cycle, which can easily be seen by the number of sunspots. This cycle was discovered by the Chinese more than thousand years before Galilei. With the help of the sunspots, which reached another culminating frequency in the year 2000, people have discovered how the sun rotates around its own axis. In relation to the fixed stars this takes 25.4 days. In this time the earth continues revolving around the sun and from our point of view one turn takes 27.3 days. The movement on the sun's surface was first discovered by Christopher Carrington (1826- 1875) and he also recognized that it does not rotate like a static sphere, but one rotation at its poles (which are tilted towards the ecliptic poles) takes 6 days longer than at the equator. Eruptions accompany the spots` activity. The eruptions are called prominences, they are gas currents guided by magnetic fields, which often reach higher than 100000 km (ca. the distance between earth and moon).  
In Austria, in Carinthia on Kanzelhöhe there is a sun observatory and the satellite SOHO rotates in the earth's orbit, permanently observing the sun` s activity.   The sun` s mass provides the cohesion of the nine planets and their moons, thousands of planetoids and millions of asteroids, which move around the sun in different and mostly elliptical circles.   From the Earth you can` t see those parts of the night sky which are next to the sun, because the sun lights them up. Due to the movement of our home planet, the sun seems to move through the sky. During a year it crosses 12 zodiac signs or 13 constellations.   The sun's orbit is called ecliptic. The position of the sun is in the zodiac sign which is lit up by the sun and therefore not visible. It is located to the east of the sunrise and to the west of the sunset. Only in the case of an eclipse of the sun can you see its real position, because then you might be able to see bright stars.   The sun seems to move from west to east annually and from east to west daily, because of the earth's rotation around its axis. During one day the sun moves nearly 1° (about two times the diameter of the sun's small disc) in the sky to the east, because of the earth's orbital movement. It needs one year to return to the same zodiac position.   Because of the tilt of the equator to the ecliptic of about 23.5°, one part of the year the sun shines more on the northern hemisphere and the other part of the year on the southern hemisphere. That is why we have different seasons (different length of days and the sun varies in height at midday).  

In the ancient Greek mythology Helios is the sun-god, who drives the sun carriage. The Romans call the sun-god Sol. In the Christian mythology Jesus takes their place. A typical depiction from ancient times shows Helios on his carriage pulled by four steeds. The Roman poets Ovid and Nonnos describe the sun's daily course and its way through the zodiac wonderfully with the legend of Phaeton` s fall: Phaeton, Helios` son, had asked his father to allow him to drive the sun carriage for one day across the sky. Helios warned Phaeton, described the way in detail and told him how to handle the steeds. But the steeds ran wild and Zeus/ Jupiter threw a thunderbolt to stop Phaeton causing any more damage than he had already done. Phaeton fell out of the carriage, his body burning, into the river Eridanos.

In all cultures the zodiac sign before the sunrise on special days was an important sign in the calendar. Among these days, the first day of spring has a special significance. The so-called spring zodiac sign has changed, because of the precessional movement of the earth, nearly every two thousand years and has determined ages and cultures. 3800 B.C. this spring zodiac sign was Taurus, whereas the sun itself stood in Gemini. The spring star sign Taurus was the root of many cults and cultures (for example: Minoic culture, Apis, gold calf). Around 1500 B.C. the zodiac sign Aries took the place of Taurus, the sun itself stood in Taurus. Aries became the symbol of many different cults, e. g. Amun or the Argonauts. At the turn of the era 2000 years ago, the zodiac sign Pisces became the spring zodiac sign ; and from this the Christian cult of ICHTHYS (abbr. IHS) took its origin. The next spring zodiac sign will be Aquarius. No one is certain when this era will start, it is still "written in the stars": The zodiac sign which is already visible on the sunrise of the spring equinox is Aquarius. Again, the sunrise on this day heralds  a new era.
Sunday has its name from our central star.

Picture: Sol as one of the seven planets with the sun carriage