1. 16-1 (part 2) | A Solar System is Born

2. The Birth of a Star
As the planets are forming, gas and dust near the center of the solar nebula grow dense.
In the center the hydrogen atoms begin to fuse.
Fusion creates energy that pushes outward. The star begins to shine.
A star is born and a new solar system is formed.

3. The Structure of the Sun
Corona: Uppermost part of the atmosphere; millions of miles thick
Chromosphere: orange-red layer of atmosphere; thousands of miles thick
Photosphere: the lower atmosphere and what we see
Core: where nuclear fusion occurs

4. Energy Production in the Sun
The sun has been shining for about 4.6 billion years
Tiny amounts of matter can produce huge amounts of energy

5. Nuclear Fusion
Nuclear fusion is the process by which two or more low-mass nuclei fuse to form another nucleus
When hydrogen nuclei fuse, they form helium and ignition begins

6. Conditions Required for Fusion
Under normal conditions, hydrogen atoms never get close enough to join
In the center of the sun, the temperature and pressure are very high
This forces the atoms to collide, causing hydrogen to fuse

7. Measuring Interplanetary Distances
One way scientists measure distances in space is by using astronomical units (AU)
One AU is the average distance between the Earth and the sun, which is 150,000,000 km

8. Another Way
Another way to measure distances is by using the speed of light
A light-minute is how far light travels in one minute, which is 18,000,000 km
Distance in the solar system can also be measured in light- hours or light-years