Thursday, April 17, 2008

The Sun

Life on Earth is absolutely dependent on the Sun. If it suddenly shut down, it would take eight minutes for our world to be plunged into total darkness.
Its energy comes from nuclear fusion taking place deep in its core. Heat and pressure at the center force hydrogen atoms together to make heavier helium. This process releases unimaginable amounts of energy, similar to the explosion of a hydrogen bomb.This energy travels slowly through the Sun's surface (its journey takes over 200,000 years). Here, it escapes into space as heat and light, making life possible here on Earth.

The Sun makes up more than 99.9% of the mass of our Solar System, 332,946 times the mass of our planet. It orbits the Milky Way Galaxy, with the planets trailing, at 240 km per second, a trip that takes 225 million years.

The photosphere is the visible layer of the Sun, the part where the light we see is emitted. The chromosphere  is the outer layer of the surface, above the photosphere and below the corona. It has a deep red glow.
The corona is a blazing region of hydrogen that extends millions of miles into space. It is visible on Earth only during a solar eclipse, when it appears as a halo around the Sun. The corona's temperature of 2,000,000oC greatly exceeds that of the photosphere and chromosphere, although these two layers are under it, closer to the Sun's super-heated core.

The core contains only 7 percent of the Sun's volume, but half of the mass. The very center of the core has a temperature of 15,500,000oC.

The Sun's behavior is somewhat erratic, determined by its electromagnetic activity. Its magnetic field is formed by the movement of electrically charged particles: a mixture of positively charged nuclei and free electrons that have been separated by the intense heat and pressure of the core. Activity rises and falls over the course of a cycle that lasts 11 years. It is these shifting magnetic fields that cause electrical storms in the Sun's outer atmosphere. 

A sunspot looks like a dark patch on the surface, the photosphere. Sunspots happen when the Sun's magnetic field suppresses light and heat from the area it surrounds. The middle of a sunspot, called the umbra, looks black because it is a thousand degrees cooler than the neighboring photosphere, which is about 5,500oC.
Sunspots vary in size, color, and duration. The smallest are just a few hundred miles across. The largest span up to 60,000 miles, several times the diameter of Earth, and last for several months.

The Sun's atmosphere also throws off blasts of plasma in eruptions called coronal mass ejections. These can extend millions of miles above the surface, and can appear to be as large as the Sun itself. These are the largest explosions in the known universe.
Occasionally, solar flares erupt, spewing vast amounts of material high above the photosphere, with so much force that they travel at nearly the speed of light.

For my previous posts on astronomy, click here.

There's a great book with lots of breathtaking pictures called Astronomy: A Visual Guide, by Mark A. Garlick. Check it out.

No comments: