Chapter 1: Stars and Galaxies

1. Chapter 1: Stars and Galaxies • When you look up at the sky on a clear night, you see billions of stars in the sky. Each star is actually a sun! A sun is hot sphere of glowing gas.

2. Our sun is a single-star system, however most of the stars in the sky are double-star systems in which 2 stars revolve around each other. These are called binary stars.

3. Constellations are groups of stars that were once believed to be imaginary people or animals. • Examples: Big Dipper, Orion, Hercules

4. A nova is when a sun suddenly increases in brightness due to a nuclear explosion. Nova’s release gas, heat, and light into space. • A huge cloud of dust and gas where new stars are formed is called a nebula.

5. A huge collection of stars is collectively known as a galaxy. Our galaxy is named the Milky Way.

6. The Big-Bang Theory states that our universe began as one large mass that exploded and gave rise to our modern-day planets. • According to this theory, all the matter and energy in the universe was once concentrated into a single place. About 15-20 billion years ago, an explosion sent matter and energy in all directions.

7. Astronomers estimate that there are more than 200 billion stars in the universe! • Stars differ in: size, mass, color, temperature, and brightness

8. SIZES OF STARS... • 1. Giant stars: 10-100 times the size of our sun • 2. Supergiant stars: 1000 times the size • 3. White dwarf: smaller than Earth • 4. Neutron star: the smallest star

9. The elements Hydrogen (H) and Helium (He) make up 96-99% of a star’s mass.

10. BRIGHTNESS OF STARS... • Apparent Magnitude refers to the brightness of a star as it appears on Earth. • Absolute Magnitude refers to the actual amount of light that a star gives off.

11. THE SUN... • Our sun is 150 million kilometers from the Earth. It is an average-sized star, about 4.6 billion years old. • The sun’s volume is 1 million times the size of Earth!

13. LAYERS OF THE SUN... • Corona: outermost layer of the sun’s atmosphere, 1.7 million degrees Celsius! (white halo) • Chromosphere: beneath Corona, average temp. of 27,800 C (middle layer of the Sun’s atmosphere) • Photosphere: referred to as the sun’s surface, temp. of 6000 C • Core: innermost part, up to 15 million degrees C, site of nuclearfusion (H + H  He)

14. Solar Flare: a “storm” on the sun, temperature increases, large amounts of energy are released. • Sunspots: dark spots that are seen on the sun’s surface, cooler than the rest of the sun.

15. SUPERNOVA... • When the nuclear fusion reaction is finished, the sun explodes in a tremendous release of energy called a Supernova. When this happens, temperatures of 1 billion degrees C are released!

16. BLACK HOLES... • After a star burns out, or supernovas, a core where the star used to be remains. This is called a black hole. Here, gravity produced pulls matter and energy inward and eventually is swallowed.