3rd May: Sun day

Sun Day - a day for promoting solar energy. Here are 10 things you may not know about the sun:

1. The Sun is the biggest object in the Solar System, in fact it accounts for 99.8% of the total mass. The diameter of the Sun is about 109 times that of Earth and its a mass is about 330,000 times that of Earth.
2. The Sun was formed about 4.57 billion years ago from the collapse of part of a giant molecular cloud that consisted mostly of hydrogen and Helium. That event probably gave birth to many other stars as well as our Sun.
3. About three quarters of the Sun's mass is hydrogen. The rest is mostly helium, with much smaller quantities of heavier elements, including Oxygen, carbon, neon and Iron.
4. The mean distance of the Sun to Earth is approximately 1 astronomical unit (about 150,000,000 km; 93,000,000 mi) - it varies slightly according to the time of year - at this average distance, light takes about 8 minutes and 19 seconds to travel from the Sun to Earth.
5. Although informally designated as a Yellow dwarf, the Sun is white rather than yellow when viewed from space or when sufficiently high in the sky.
6. As the age of stars goes, the Sun is roughly middle aged. It has not changed dramatically for four billion years, and will remain fairly stable for four billion more.
7. When hydrogen fusion in its core has stopped, the Sun will become a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury, Venus, and possibly Earth. But not for another four billion years.
8. The Greeks named the sun Helios; the Romans used the name Sol, which is still in use today and is the root of the word "solar".
9. Sunspots are temporary phenomena on the photosphere of the Sun which look like dark spots. They are not really dark, though - everything is relative. If a sunspot was isolated from the surrounding photosphere it would be brighter than the Moon. Sunspots usually appear as pairs, with each spot having the opposite magnetic polarity of the other. There is an 11 year solar cycle of waxing and waning in the number and size of sunspots. Solar flares and coronal-mass ejections tend to occur at sunspot groups.
10. The first satellites designed to observe the Sun were NASA's Pioneers 5, 6, 7, 8 and 9, launched between 1959 and 1968. They orbited the Sun at a distance similar to that of Earth, and made the first detailed measurements of the solar wind and the solar magnetic field.