The universe is extremely large and consists of all time, space, energy, and matter It contains hundreds of billions of galaxies These galaxies exist together in super clusters Galaxies contain hundreds of billions of stars like our Sun Space is so large, distances are measured in light years We are looking back in time when we observe galaxies through telescopes The Universe

Gravity causes objects in space to be grouped together in different ways The Earth is apart of a solar system, which contains our Sun, all the planets, asteroids, and comets The solar system is part of the Milky Way Galaxy, which contains hundreds of billions of stars, like our Sun The Universe contains hundreds of billions of galaxies The universe is expanding, galaxies are moving away from each other…Doppler effect The Universe

Types of Galaxies Our solar system lies within the Milky Way Galaxy A Galaxy is hundreds of billions of stars held together by gravity Milky way is a spiral galaxy, a disc with arms and a huge glowing center Milky way is 100,000 LY across 3 types of galaxies: spiral, elliptical, and irregular…most are spiral or elliptical Spiral: have arms of stars, gas, and dust that is in a spiral pattern Elliptical: shaped like spheres or ovals. Most stars are old, no gas or dust Irregular: Faint galaxies without a definite shape, smaller & few stars Most galaxies have super massive black holes at their center Quasars centers of galaxies are very bright & look like stars Types of Galaxies

The Sun The Sun is a star, the only one in our solar system Produces energy from hydrogen gas from fusion…gas is dense, especially @ core Contains 99.9% of the mass of the solar system Although the Sun is a gas, it does have structure & layers

Becomes cooler and less dense as you move from the center Core: very dense gas, 15 million oC, Fusion occurs Radiative Zone: thick layer, dense, no fusion Convection Zone: energy moves by convection Photosphere: a.k.a Sun’s surface, what you see, light is emitted from here Chromosphere: Think middle layers, gives off pinkish light, hotter than photosphere Corona: outermost, hotter than photosphere, only see during eclipse Sunspots: cooler than other areas, appear dark Solar Flares: Prominence ejects hot gas Layers of the Sun

Classifying Stars Brightness depends on distance from Earth To measure distance, astronomers use parallax, which is its shift in position when viewed from different locations Color: diff. in color is a difference in temp.

Star Life Cycle Stars begin their life as nebula Main Sequence is the stage when stars are turning hydrogen into helium When H runs out it becomes a giant star and fuses He into C Giant stars shed layers and become a white dwarf = dead core of giant star High mass stars (8x our Sun) spend less time in MS stage…become Supergiants form elements up to iron, then collapse to produce supernovas Cores of supergiant stars may become neutron stars or black holes Star Life Cycle

Star Life Cycle