Cool Facts About the Sun

The Sun powers the solar system, providing light, heat and energy for life on the planet.

The Sun is the largest object in the solar system and the most violently active energy source. It influences the life and orbits of every planet circling it. The Sun also does a number of unexpected an unexplained things.

Age and Evolution

The Sun is about 4.5 billion years old, which is only about a third of the age of the universe. Since the beginning of the universe, three stars have occupied this region of space, with the Sun being the third. Stellar systems evolve. Earlier stars were composed almost entirely of hydrogen, with almost no heavier elements, and burned out relatively quickly, imploding under their own gravity to form heavier elements through nuclear fusion. Those stars then exploded, releasing those heavier elements into the solar system. The region of space of the Sun has experienced this implosion-explosion evolution twice, with the result that the Sun and its planets contain significantly higher percentages of heavier elements, though these heavy elements comprise only 2 percent of the total stellar mass.

Fuel

It wasn't until the early 20th century that scientists stopped assuming the composition of the Sun was essentially the same as that of the Earth. Now scientists understand that three quarters of the mass of the Sun is hydrogen while the rest is mostly helium, and only about 2 percent is heavier elements. In its core, the Sun fuses 430 to 600 million tons of hydrogen each second, and this fusion produces the incredible energy fueling the sun.

Size

Though smaller than the majority of stars in the universe, the Sun is still so large that about 1,000,000 Earths would fit inside it. The sun has an atmosphere, and the outermost layer of this atmosphere, called the "heliosphere," extends beyond the orbit of Pluto. The Sun accounts for 99.86 percent of the total mass of the solar system.

Brightness

For a long time, scientists assumed that the relatively small size of the Sun meant that the Sun was also dimmer than most of the stars in the Milky Way galaxy. It is now understood that, though small, the Sun is brighter than about 85 percent of the stars in the Milky Way.

Unexplained Anomalies

Astronomers don't understand why, but as of 2010, the sun is getting progressively dimmer, sun spot activity is at an all-time low, magnetic activity has decreased markedly, and the speed and energy of the solar wind has dropped by a few percentage points.

References

• NASA: Imagine the Universe