Chapter 1 Stars and Galaxies l When you

Chapter 1: Stars and Galaxies l 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.

l 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.

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

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

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

l The Big-Bang Theory states that our universe began as one large mass that exploded and gave rise to our modern-day planets. l 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.

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

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

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

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

THE SUN. . . l Our sun is 150 million kilometers from the Earth. It is an averagesized star, about 4. 6 billion years old. l The sun’s volume is 1 million times the size of Earth!

LAYERS OF THE SUN. . . l. Corona: outermost layer of the sun’s atmosphere, 1. 7 million degrees Celsius! (white halo) l. Chromosphere: beneath Corona, average temp. of 27, 800 C (middle layer of the Sun’s atmosphere) l. Photosphere: referred to as the sun’s surface, temp. of 6000 C l. Core: innermost part, up to 15 million degrees C, site of nuclear fusion (H + H He)

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

SUPERNOVA. . . l 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!

BLACK HOLES. . . l 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.