The Sun On-line Lesson

On-line Lessons: The Sun  What is the Sun ?

On-line Lessons: The Sun Another planet ? A star ? Or a galaxy ?

On-line Lessons: The Sun Well, the Sun is a Star and it is the largest object in our Solar System : Sun + 9 planets (see “The Nine Planets” in the Links) Sun

On-line Lessons: The Sun A list of the mass distribution within our Solar System : Sun: 99.85% of all the matter in the Solar System Planets: 0.135% condensed out of the same disk of material that formed the Sun Comets: 0.01% ? Satellites: % Minor Planets: % ? Meteoroids: % ? Interplanetary Medium: % ?

On-line Lessons: The Sun The Sun's outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F). This layer has a mottled appearance due to the turbulent eruptions of energy at the surface. (see “Views of Solar System” in the Links)

On-line Lessons: The Sun  What is the age of the Sun ? Well, the Sun has been active for 4.6 billion years and has enough fuel to go on for another five billion years or so.  What will happen then ? The Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a Red Giant, it will suddenly collapse into a White Dwarf -- the final end product of a star like ours. It may take a trillion years to cool off completely.

On-line Lessons: The Sun  How heavy is the Sun ? The Sun is 332,830 times heavier than the Earth !!!  What does this mean in kilos ? The mass of the Sun is 1,98 x This is a really huge number !!!!!!!!!

On-line Lessons: The Sun  Is the Sun the only such object around ? Not really, it is one of about 100 billion similar objects in the Milky Way (see “The Virtual Amateur Astronomer, VI section”, in the Links)

On-line Lessons: The Sun  The Earth rotates around its axis and the Sun. Does the Sun rotate, too ?  The Sun like the planets rotates around its axis in an anti-clockwise direction when viewed looking down from above its North Pole. For an observer at Earth the rotation is from left to right, i.e., features move from the Eastern limb towards the Western. (see “Windows to the Universe” in the Links)

On-line Lessons: The Sun  How can we observe the Sun’s Rotation ?  On the surface of the Sun there are dark spots, some as large as 50,000 miles in diameter, moving across the surface, contracting and expanding as they go. These strange and powerful phenomena are known as sunspots.

On-line Lessons: The Sun  The Sunspots above all other features give us the opportunity to study the Sun’s Rotation

On-line Lessons: The Sun  The spots are carried along with the rotation of the Sun and therefore by measuring their motion it is possible to measure the rotation period of the Sun. (see “On-Line lessons” in the EUDOXOS website)

On-line Lessons: The Sun  At this point we need to notice that while the Earth rotates around the Sun at the same time the Sun rotates around its axis, so the period we observe from Earth is slightly larger than the true period, which we would observe if we were viewing the Sun from a distant star.  In addition, the Sun is not a solid body like the Earth, and unlike the Earth it’s made up of hot gas, and therefore it exhibits differential rotation. That means that the rotation period can vary with latitude and depth.In the photosphere, it varies from 25 days on the equator to more than 30 days at 60 degrees latitude.